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= October13 =
= December 24 =
== Chicken'sancestorsvs.ours ==
== Unknown species of insect ==
Am I correct in inferring that ] this guy is an ]? I was off-put by the green head at first, but the antennae seem to match. ''']]''' 03:00, 24 December 2024 (UTC)
I have heard it claimed that at some point in prehistory, the chicken's ancestors ate our ancestors. Is that actually true? ] ] 17:20, 13 October 2024 (UTC)
:My ancestors weren't eaten by prehistoric chickens 🏃♀️🏃♂️🐤 - well at least not until after they'd had eggs/babies :-) ] (]) 17:38, 13 October 2024 (UTC)
It's likely true. Chickens are ], which are surviving ] dinosaurs, which originated around 230 million years ago and (it is thought) were originally mostly carnivorous or omnivorous. ], the clade including bird ancestors, became distinct from other Theropods perhaps around 160 million years ago. We are ] mammals, whose ancestors the ] evolved some time between 200 and 150 million years ago, were mostly small, and were undoubtably predated by many dinosaurs, including some Avialae. {The poster formerly known as 87.81.230.195} ] (]) 20:41, 13 October 2024 (UTC)
:<s>It looks like one of the invasive ]s that happens to like my blackberries in the summer.</s> ] (]) 13:11, 24 December 2024 (UTC)
::Astonishingly, this question is an existing Google search term: . The top result, from ], a reputable scientific journal, says:
::{{xt|The most recent common ancestor for humans and chickens is thought to have been some kind of primitive reptile that lived more than 310 million years ago.}}
::] (]) 11:49, 14 October 2024 (UTC)
:::But unless it was cannibalistic, this common ancestor is not an example of an ancestor of the birds ''eating'' an ancestor of the primates. --] 17:22, 14 October 2024 (UTC)
::::Ah yes, misread the question (again). ] (]) 08:54, 15 October 2024 (UTC)
:::::I misread ''ate'' as ''are'', too. ] (]) 21:05, 17 October 2024 (UTC)
:The split between the clades ] (which includes chickens) and ] (which includes us) took place about 312 million years ago.<sup></sup> There was ample opportunity for the carnivorous ]s in the ancestral line of today's chickens, which appeared 231 million years ago, to snack on contemporaneous siblings of some of our ancestors. --] 17:56, 14 October 2024 (UTC)
::It's even conceivable that an actual ancestor of chickens (not just a random member of an ancestral population) ate an actual ancestor of humans. --] (]) (]) 15:12, 17 October 2024 (UTC)
::I would say not necessarily a Japanese beetle, but almost certainly one of the other ] beetles, though with 35,000 species that doesn't help a lot. Looking at the infobox illustration in that article, 16. & 17., "]" looks very similar, but evidently we either don't have an article or (if our ] article is a complete list) it's been renamed. {The poster formerly known as 87.81.230.195} ] (]) 14:18, 24 December 2024 (UTC)
= October 14 =
:::Yes, it's not the Japanese beetle for this beetle appears to lack its white-dotted fringe although its condition is deteriorated. Its shape is also more or less more slender; and not as round. ] (]) 15:02, 24 December 2024 (UTC)
== Does the Minkowski space (or the Min. metric) add, any '''empirically verifiable information''', to Einstein's original Special Relativity theory? ==
JustasEinstein'sSpecialRelativitytheoryaddedsomeempiricallyverifiableinformation,to what scientists had known about physics. ] (]) 08:01, 14October 2024 (UTC)
:Perhaps it is the ] ]. Shown . ] (]) 16:09, 24 December 2024 (UTC)
::That looks like easily the best match I've seen so far, and likely correct. {The poster formerly known as 87.81.230.195} ] (]) 17:09, 24 December 2024 (UTC)
:No it doesn't. It is a name for the mathematical structure of the space described in Special Relativity. If you take it away you just make things cumbersome and can't talk properly to physicists. It would be like taking complex numbers away from electronics - it would make formulae bigger and annoy people. ] (]) 09:06, 14 October 2024 (UTC)
::That's what I think as well, but surprisingly, your first sentence is not mentioned (nor hinted) in our article ], although it's '''a very important point''' that should have been pointed out, IMO. ] (]) 09:47, 14 October 2024 (UTC)
:The earliest empirical confirmations of <s>special</s> relativity announced by Einstein in 1905 included ]'s photographic record of the ]. I expect that Eddington was aware of Minkowski's lecture that presented his ] in 1908. ] (]) 09:17, 14 October 2024 (UTC)
::AFAIK, this solar eclipse has nothing to do with '''special''' relativity. ] (]) 09:43, 14 October 2024 (UTC) <small>Thank you for that correction. ] (]) 15:20, 17 October 2024 (UTC)</small>
:::The very first sentence of ] says "In physics, Minkowski space (or Minkowski spacetime) is the main mathematical description of spacetime in the absence of gravitation", and later in the lead "Minkowski space is closely associated with Einstein's theories of special relativity and general relativity and is the most common mathematical structure by which special relativity is formalized". It says it is used in formalizing special relativity, it does not say it is a theory or anything like that. That's straight in your face! No extra 'hinting' is needed! ] (]) 11:10, 14 October 2024 (UTC)
::::{{tq|In physics, Minkowski space (or Minkowski spacetime) is the main mathematical description of spacetime in the absence of gravitation.}} Yes, but I can't see any relation between this fact and my question in the title.
::::{{tq|Minkowski space is closely associated with Einstein's theories of special relativity.}} Of course, just as the electric force - actually expressed by Coulomb's law, is closely associated with the magnetic force - actually expressed by the Lorentz force law. Yet, the Lorentz force law, does add some empirically verifiable information to Coulomb's law. For the same reason, the sentence you've quoted from our article ], doesn't rule out the possibility that the Minkowski space adds some empirically verifiable information to Einstein's theory of special relativity.
::::{{tq|Minkowski space...is the most common mathematical structure by which special relativity is formalized}}. Of course. That's because the Minkowski space is an integral part of Special relativity. However, my question in the title didn't ask whether the Minkowski space added new information to "'''Special relativity'''", but rather whether the Minkowski space added new information to "'''Einstein's original''' Special Relativity theory".
::::That's why I'm still asking, if you think the article should have pointed out the very important fact (IMO), that the '''Minkowski''' space added no new information to "'''Einstein's original''' Special Relativity theory. ] (]) 11:54, 14 October 2024 (UTC)
:::::No I see no good reason for thinking the article should say irrelevant things like that. Find a reliable source if you want to add it. ] (]) 13:20, 14 October 2024 (UTC)
::::::Isn't your first sentence (in your first response) based on a reliable source? If it is, then what does your last sentence (in your last response) mean? ] (]) 13:24, 14 October 2024 (UTC)
:::::::No what I said is not based on a reliable source. This discussion is not an article. ] (]) 13:46, 14 October 2024 (UTC)
::::::::I'm quite surprised. You are calling - the relation between the Minkowski space and Einstein's theory of Special relativity - {{tq|"irrelevant things"}}, but you admit that your own opinion (about this relation) - that the Minkowski space adds no empirically verifiable information to Einstein's original Special Relativity theory - {{tq|"is not based on a reliable source"}}.
::::::::Anyway, we will probably remain in disagreement, about whether this relation is "irrelevant" (as you claim) or "very important" (as I claim). I wonder what other users think about this controversy between us. ] (]) 15:26, 14 October 2024 (UTC)
:There are experimentally verifiable geographic facts, such as that Europa and Asia are part of a connected landmass that is not connected to the Americas. There are many ways to create flat two-dimensional maps of the surface Earth, such as the ] and the ]. The maps are alternative ways of describing the same geographic reality; obviously, they cannot produce <u>new</u> verifiable geographic facts. Likewise, Minkowski space is an alternative way of mathematically describing the same physical reality; it cannot produce <u>new</u> verifiable physical facts. --] 17:18, 14 October 2024 (UTC)
::Yes, that's what I think as well, as I have already responded to the user above you, but then I asked them a follow-up question, as you can see above. ] (]) 07:08, 15 October 2024 (UTC)
:::I'm not sure what the follow-up question is. In my opinion, it would be curious, to say the least, to see some statement in Misplaced Pages to the effect that the Molweide projection did not add any empirically verifiable information to geography. It is not different for Minkowski space and physics. --] 15:26, 16 October 2024 (UTC)
:Mathematics is a symbolic system used for describing and organizing information. Like ]s. Minkowski space is a mathematical construction, used for...describing and organizing information. This question is in essence like asking, "Did the German language (the original language Einstein wrote his big scientific papers in ]) add any empirically verifiable information to sp. relativity?" It's a ]. I guess the simple answer is, "No, why would it? Does the number 17 add any?" ] (]) 04:14, 20 October 2024 (UTC)
::Yes, all agree that mathematics is a symbolic system used for describing and organizing information. Of course the Minkowski space is a mathematical construction, '''intended''' to describe and organize the information in Einstein's Special relativity. The only question is, if the Minkowski space only does what it's intended to do, or - not on purpose - does more. For example, If I try to describe and organize the '''finite''' sequence: (1,2,4,8,16,32), I may use the mathermatcal construction <math>a_{n+1}=2a_n</math>. But this mathematical construction does more than what it's intended to do, because it also predicts that 32 is followed by 64... I guess that's why your last sentence begins with "I guess". But my original question is about what the facts really are. ] (]) 05:40, 20 October 2024 (UTC)
If the OP's question ever find a "Yes" reply, its explanation would likely benefit the articles ] and ]. At present neither article mentions Minkowski. ] (]) 15:20, 17 October 2024 (UTC)
= December 25 =
:There is the possibility to switch the sign in ]. Then the Minkowski space would have properties of ]s. '''That''' would add additional properties. ] (]) 13:27, 20 October 2024 (UTC)
::Now you can ask why the sign is chosen that way it is. The possible answer is to avoid the consequences. Another answer is that a coin never falls on both sides. You can choose which answer you like most. Even by tossing a coin. ] (]) 13:34, 20 October 2024 (UTC)
::{{tq|'''That''' would add additional properties.}} '''Empirically verifiable''' ones? ] (]) 15:52, 20 October 2024 (UTC)
== Mass of oscillating neutrino ==
== Violation of the conservation of energy by virtual particles, vs violation of the formula E=mc^2 ==
From the ] it follows that a particle that is not subject to external forces must have constancy of mass.
Virtual particles, appearing out of the cacuum, are known to be a (theoretical) instance violating the conservation of energy.
:
Is there also any instance (even a theoretical one only), violating the formula <math>E_0=m_0c^2</math> (while <math>E_0</math> denotes a given body's rest energy and <math>m_0</math> denotes the body's rest mass)? ] (]) 12:56, 14 October 2024 (UTC)
:Theory says they don't. However they can for instance have negative kinetic energy which balances the equation. ] (]) 13:25, 14 October 2024 (UTC)
::What do you mean by "they"? Do you mean virtual particles?
:::
::Additionally, what do you mean by "don't"? Do you mean they don't ? Or don't ?</math>
If I am right, this means that the mass of the neutrino cannot change during the ], although its flavoring may. Is this written down somewhere? Thank you. ] (]) 19:24, 25 December 2024 (UTC)
:Any (flavored) neutrino that is really observed is a superposition of two or three mass eigenstates. This is actually the cause of ]. So, the answer to your question is complicated. ]_] 19:40, 25 December 2024 (UTC)
:::Yes they refers to a virtual particle, but really since one never comes across an actual isolated virtual particle one should be considering the whole configuration, see ]. ] (]) 13:42, 14 October 2024 (UTC)
:Important note: particle physicists today generally only ever use "mass" to mean "]" and never anything else: . Like the term says, invariant mass is well, invariant, it never changes ever, no matter what "external forces" may or may not be involved. Being proper particle-icans and following the standard practice in the field, then, the three neutrino masses are constant values. ..."Wait, three?" Yeah sure, turns out ]. As mentioned, due to Quantum Weirdness we aren't able to get these different states "alone by themselves" to measure each by itself, so we only know the differences of the squares of the masses. Yeah welcome to quantum mechanics.
::::Thank you. ] (]) 15:28, 14 October 2024 (UTC)
:]: "Quantum mechanics describes nature as absurd from the point of view of common sense. And yet it fully agrees with experiment. So I hope you can accept nature as She is {{snd}} absurd." --] (]) 06:06, 26 December 2024 (UTC)
:I don't think they're violating conservation of energy. Yes, they "exist" and would have mass. At the same time they're entangled to have a zero sum of mass. That means, if you observe one of the particles into existence, the other particle automatically achieves negative mass equivalent to the observed particle. Such a "negative" particle is for all intents and purposes like an anti particle,but with one exception. If it encounters it's partner (entangled or not) it doesn't annihilate, it merely nihilates. That is like annihilation but without releasing energy. ] (]) 02:30, 15 October 2024 (UTC)
::The equation <math>E^2 = (p c)^2 + \left(m_0 c^2\right)^2</math> uses invariant mass {{math|''m''<sub>0</sub>}} which is constant if {{math|''E''}} and {{math|''p''}} are constant. The traveling neutrino has a varying mass mixture of different flavors with different masses. If a mixture of different masses changes, you would expect the resulting mass to change with it. But somehow this does not happen as the neutrino mass mixture changes. These mixture changes cannot be any changes. The changes must be such that the resulting mass of the traveling neutrino remains constant. My question is whether this is described somewhere. ] (]) 11:16, 26 December 2024 (UTC)
:::I freely confess I'm uncertain exactly what's being "asked for" or "gotten at" here. Have you looked at the ] article? From it: {{tpq|That is, the three neutrino states that interact with the charged leptons in ]s are each a different ] of the three (propagating) neutrino states of definite mass. Neutrinos are emitted and absorbed in weak processes in flavor ]s '''but travel as mass eigenstates.'''}}
:::What is it that we're "doing" with the ] here? For the neutrino, we don't have a single value of "mass" to plug in for <math>m_0</math>, because we can't "see" the individual mass eigenstates, only some ] of them. What you want for describing neutrino interactions is ], which is special relativity + QM. (Remember, relativity is a "classical" theory, which presumes everything always has single well-defined values of everything. Which isn't true in quantum-world.) --] (]) 18:41, 26 December 2024 (UTC)
::::Not all potential evolutions of a linear combination of unequal values produce constant results. Constancy can only be guaranteed by a constraint on the evolutions. Does the fact that this constraint is satisfied in the case of neutrino oscillation follow from the ], or does this formulation allow evolutions of the mass mixture for which the combination is not constant? If the unequal values are unknown, I have no idea of how such a constraint might be formulated. I think the OP is asking whether this constraint is described somewhere. --] 00:51, 27 December 2024 (UTC)
= October 15 =
= December 27 =
== Audio Engineer vs. Music Engineer ==
== Low-intensity exercise ==
Are these two things interchangeable? Or is there a meaningful difference? ] (]) 01:44, 15 October 2024 (UTC)
If you exercise at a low intensity for an extended period of time, does the ] still occur if you do it for long enough? Or does it only occur above a certain threshold intensity of exercise? ] (]) 20:13, 27 December 2024 (UTC)
:Hows about you try it and report back? :) ←] <sup>'']''</sup> ]→ 21:31, 27 December 2024 (UTC)
::I wanted to try it just today, but I had to exchange the under-desk ] I got for Christmas for a different model with more inclined treadles because with the one I got, my knees would hit the desk at the top of every cycle. Anyway, I was hoping someone else tried it first (preferably as part of a formal scientific study) so I would know if I could control whether I got a runner's high from exercise or not? ] (]) 03:09, 28 December 2024 (UTC)
Also, sorry for adding to my own question, but here's a related one: is it known whether the length of a person's ] (which is inversely correlated with its sensitivity) influences whether said person gets a runner's high from exercise (and especially from low-intensity exercise)? ] (]) 03:14, 28 December 2024 (UTC)
== ] vs ] ==
:Neither are engineers, but we let them bask in reflected glory. ] (]) 04:18, 15 October 2024 (UTC)
::Seriously tho both audio engineer and music engineer are sharing the same Wikidata item and i need to figure out if i should split them ] (]) 05:13, 15 October 2024 (UTC)
:Is a music engineer the same as a music producer? thinks audio and music engineers are different, although it implausibly claims that the primary skill for an audio engineer is video, and I don't know why music engineers need to know ]. ] ] 05:27, 15 October 2024 (UTC)
:Engineering in the recording industry can be very well defined. There are engineers who focus solely on drum kits and nothing else. There are engineers who focus solely on microphone gear and placement and nothing else. If you ask them for their title, they might say they are a sound engineer or recording engineer or audio engineer or music engineer. The title isn't important. The skill being implemented during the production of a recording is what is important. My short experience (installing Sony hardware in one studio) involved working with engineers in front of and behind the glass. The ones in front of the glass set up mics, cables, etc... The ones behind the glass worked on the audio levels, mixes, and such. They worked together, but did not do each other's jobs. Then, when finished, more engineers came in and worked on optimizing the mix for CD compression (this was pre-MP3 days). So, in summary, the title means whatever they want it to mean because the title is not directly related to the job performed. ] (]) 13:09, 15 October 2024 (UTC)
::The behind glass people can also be called "sound desk operators", if you want a less vain designation. ] (]) 05:12, 16 October 2024 (UTC)
:::I’ve been practising audio engineering at my college. When I’m in the studio, I would call myself a recording engineer or mixing engineer. ] (]) 16:56, 16 October 2024 (UTC)
Hi,
== Electron energy level in atoms ==
What is the difference between an auxotroph and a fastidious organism? It seems to me the second one would have more requirements than the first one, but the limit between the two definitions is rather unclear to me.
Depending on the excited state of the atoms, some electrons are in a higher energy state than in their ground state. But what is the distance from the nucleus of an electron when its energy level increases, does it move away or does it move closer? Does its angular velocity increase or decrease? ] (]) 11:36, 15 October 2024 (UTC)
:The usual type of excitation is that that electron moves into a different ]. The mathematical definition of an electron's state does include among other things both angular-momentum details and something similar to the average distance from the nucleus. The exact types of change depend on which orbitals are involved. But remember that electrons are not objects that "orbit", so the idea of simple closer vs further or faster vs slower, as one might visualize planetary motion, is an incorrect model that leads to many incorrect thoughts. ] (]) 11:52, 15 October 2024 (UTC)
::As in the naive ], the expected distance of an electron to the nucleus of an atom, given its orbital, is determined by the ] {{mvar|n}} of that orbital. Here, "expected distance" means the mean distance obtained by experimental measurements, which make the orbital wave function collapse. There is a relationship between the energy and this expected distance, although the precise picture is complicated; see {{section link|Electron shell#Subshell energies and filling order}}. --] 06:02, 16 October 2024 (UTC)
:::For the naive person that I am, I understand that the electron is a particle with a mass and moves in a particular probabilistic way around an atomic nucleus having a kinetic energy (<math>\frac{1}{2}mv^2?</math>). So, if the most energetic electrons are the furthest away, what is the force that keeps them with the nucleus, an increase in their electric charge in relation to their energy level, , or whatever else? (I understand that with a soup of electrons rotating around a nucleus we are in a world of probability.) ] (]) 13:18, 16 October 2024 (UTC)
::::It is a vibrating cloud of excitations to which you cannot assign a velocity. Perhaps the answers given will help you. --] 15:38, 16 October 2024 (UTC)
:::::Thanks ] (]) 21:41, 16 October 2024 (UTC)
::::::Another way to think about the energy of an electron in an orbital is by considering its ] - the energy it would take to remove it. For hydrogen atoms, the energy needed to remove a ground state electron is 13.6 {{strikethrough|MeV}} eV, so we say the n=1 energy level has energy -13.6 {{strikethrough|MeV}} eV.
::::::An electron in a higher level requires less work to knock it off. For n=2, the required energy is only 3.4 {{strikethrough|MeV}} eV, meaning an electron at the n=2 level is 10.2 {{strikethrough|MeV}} eV MORE energetic than n=1, at -3.4 {{strikethrough|MeV}} eV. ] (]) 22:46, 16 October 2024 (UTC)
:::::::This is similar to a gravitational orbital system, in which a body in a more distant orbit needs less energy to extract itself from the system. ] (]) 09:28, 17 October 2024 (UTC)
::::::::Quite so. And both the electromagnetic and gravitational forces are inverse square forces.
::::::::Although it is somewhat unsettling to consider a situation where the planets are actually smears of probability in circular harmonics rather than, you know, planets. ] (]) 15:49, 17 October 2024 (UTC)
:::::::::<small>A ] is just a smear in many ways. ] (]) 16:07, 17 October 2024 (UTC)</small>
:::::::::I suspect that electrons all have the same mass and repel each other. In addition, this energy level system must involve another physical phenomenon than that of electric charge. ] (]) 18:16, 17 October 2024 (UTC)
::::::::::All electrons DO have the ] and repel each other. You don't need to "suspect" that, it's settled science.
::::::::::And I was being silly when I compared planets to electrons. While electromagnetism and gravity are both inverse square laws, the energy level system is due to the ], which absolutely does not apply on astronomical scales. ] (]) 20:48, 17 October 2024 (UTC)
:::::::Did you confuse electrons with neutrons? MeV are nuclear, electrons are in the range eV to keV. ] (]) 13:58, 17 October 2024 (UTC)
::::::::No, I just flat used the wrong units. I type "MeV" all day at work. :) ] (]) 15:45, 17 October 2024 (UTC)
Thank you ] (]) 23:17, 27 December 2024 (UTC)
= October 16 =
:I'm not 100% sure, but it seems to me that an auxotroph is a specific type of a fastidious organism. ] (]) 03:02, 28 December 2024 (UTC)
:Symbiosis aside, it would seem that most auxotrophs would be fastidious organisms, but there could be many more fastidious organisms that aren't auxotrophs. Auxotrophs specifically can't produce organic compounds on their own. There are a LOT of organisms that rely on the availability of non-organic nutrients, such as specific elements/minerals. For instance, vertebrates require access to calcium. Calcium is an element; our inability to produce it does not make us auxotrophs.
:But perhaps symbiosis would allow an organism to be an auxotroph without being a fastidious organism? For instance, mammals tend to have bacteria in our guts that can digest nutrients that our bodies can't on their own. Perhaps some of those bacteria also assemble certain nutrients that our bodies can't? -- ] (]) 14:27, 28 December 2024 (UTC)
= December 28 =
== Total global river discharge rate ==
== Paper with wrong enantiomer in a figure ==
Is there an estimate for the total global discharge rate of surface / ground water to the sea? It would be nice to state e.g. the Amazon as a percentage of the global total, just as we do for areas and populations of large countries. ] (]) 06:23, 16 October 2024 (UTC)
:I googled "amazon river total discharge rate" and it led me back to ], which says "The Amazon River has an average discharge of about 215,000–230,000 m3/s (7,600,000–8,100,000 cu ft/s)—approximately 6,591–7,570 km3 (1,581–1,816 cu mi) per year, greater than the next seven largest independent rivers combined." ←] <sup>'']''</sup> ]→ 07:25, 16 October 2024 (UTC)
::Yes, rather amazing. We used to have a circle graph in that article that gave percentages, but the numbers were bullshit so I removed it. It would be nice to have an accurate graph, though: the full circle would be the global total, with pie slices for individual rivers. ] (]) 07:55, 16 October 2024 (UTC)
In the following reference:
:] By a ''global'' discharge do you mean including rivers ending in ]s, like a ]? Not that it would make any noticeable difference... --nitpicking ] (]) 15:28, 17 October 2024 (UTC)
:{{cite journal |last1=Quack |first1=Martin |last2=Seyfang |first2=Georg |last3=Wichmann |first3=Gunther |title=Perspectives on parity violation in chiral molecules: theory, spectroscopic experiment and biomolecular homochirality |journal=Chemical Science |date=2022 |volume=13 |issue=36 |pages=10598–10643 |doi=10.1039/d2sc01323a |pmid=36320700}}
::The Caspian is an ocean, so certainly. As you say, I doubt the others would even be visible on a global scale. I'm not going to quibble with whatever I can find. ] (]) 20:28, 17 October 2024 (UTC)
it is stated in the caption of Fig. 8 that ''S''–] is predicted to be lower in energy due to ], but in the figure the wrong enantiomer is shown on this side. Which enantiomer is more stable, according to the original sources for this data? –] (]]) 08:18, 28 December 2024 (UTC)
:The place to search I would think would be in studies of the ], and to look at the estimates that cut off that segment. Maybe check out some of the sources in that article to start (and their background sections to find sources for wider overviews, that might put down some hard estimates). ] (]) 15:50, 17 October 2024 (UTC)
::Thanks. I haven't had much luck, but I've written a couple of those sources to ask if they know of any estimates. ] (]) 23:59, 17 October 2024 (UTC)
:"{{tq|The estimated total from all rivers, large and small, measured and unmeasured, is about 9200 mi<sup>3</sup> (38,300 km<sup>3</sup>) yearly (25 mi<sup>3</sup> or 105 km<sup>3</sup> daily).}}"<sup></sup> --] 13:38, 19 October 2024 (UTC)
]
::Thanks! That comes out to 1.2 million m3/second, so per our figures the Amazon is ~ 18% of the global total. ] (]) 03:24, 20 October 2024 (UTC)
== Where can I find data on the circulation and citation rates of these journals? ==
:Less than one Sears Tower volume per second, though there are probably times when ice dams break and snow gets rained on and some rivers flood and it is more. ] (]) 20:50, 21 October 2024 (UTC)
Hello everyone, To write an article about a scientist, you need to know, where can I find data on circulation and citation rates of journals from ? ] (]) 09:58, 28 December 2024 (UTC)
== So-called “Hydrogen water” ==
{{clear}}
== Daylight saving time - why change on different dates? ==
I saw an ad promoting a device which presumable splits water into
In the UK & Europe, daylight saving time this year runs from 31 Mar – 27 Oct.
hydrogen and oxygen and infuses water with extra hydrogen, to
a claimed surplus of perhaps 5 ppm, which doesn’t seem like much. I found a review article which looked at several dozen related studies that found benefits:https://pmc.ncbi.nlm.nih.gov/articles/PMC10816294/ .
I’ve noticed that carbon dioxide or chlorine (chloramine?) dissolved in water work their way out pretty easily, so I wonder if dissolved hydrogen could similarly exit hydrogen enriched water and be burped or farted out, rather than entering the blood stream and having health benefits. is it more than the latest snake oil? ] (]) 23:01, 28 December 2024 (UTC)
In the USA & Canada, it's 10 Mar – 3 Nov.
:Yes, the dissolved hydrogen will exit the water just as quickly (even faster, because of its low ] and complete lack of ] or capability for ]), and even if it does enter the bloodstream, it will likewise get back out in short order before it can actually do anything (which, BTW, is why ]s use it in their breathing mixes -- because it gets out of the bloodstream so much faster and therefore doesn't ]) -- so, I don't think it will do much! ] (]) 01:50, 29 December 2024 (UTC)
::It's conceivable it might take out the chloramine, I guess. I don't think there's very much of it, but it tastes awful, which is why I add a tiny bit of vitamin C when I drink tap water. It seems to take very little. Of course it's hard to tell whether it's just being masked by the taste of the vitamin C. --] (]) 02:12, 29 December 2024 (UTC)
:If you just want to split water into hydrogen and oxygen all you need is ]. You don't say where you saw this ad but if it was on a socia media site forget it. ]|] 11:47, 29 December 2024 (UTC)
::If this so-called hydrogen water was emitting hydrogen bubbles, would it be possible to set it afire? ←] <sup>'']''</sup> ]→ 14:03, 1 January 2025 (UTC)
:We once had an article on this topic, but see ]. ] (]) 22:27, 1 January 2025 (UTC)
::I don't know if it is rubbish or not but a quick look on the web indicates to me it is notable enough for Misplaced Pages. I didn't see anything indicating it definitely did anything useful so such an article should definitely have caveats. I haven't seen any expression of a potential worry either so it isn't like we'd be saying bleach is a good medicine for covid. ] (]) 23:07, 1 January 2025 (UTC)
:'']'' does not sound of exceptionally high quality. ] (]) 01:05, 2 January 2025 (UTC)
= December 29 =
In Australia, the opposite changes are 7 Apl – 6 Oct.
== Potential energy vs. kinetic energy. Why not also "]" vs. "]"? E.g. in the following case: ==
Why not make them coincide? Surely there would be cost savings on all sides? <span class="vcard"><span class="fn">]</span> (<span class="nickname">Pigsonthewing</span>); ]; ]</span> 15:12, 16 October 2024 (UTC)
:Why have DST at all? :D
:Speaking a bit more seriously: isn't the debate more about abolishing DST than making it consistent across countries? According to , there are moves to do so in the US and the EU. ] (]) 15:20, 16 October 2024 (UTC)
::There is also discussion in America of making DST permanent. But nothing ever gets done. America and Europe's dates used to be pretty close to coinciding, but America expanded it some years back. ←] <sup>'']''</sup> ]→ 16:17, 16 October 2024 (UTC)
:: In Australia it's determined on a state-by-state basis. It's settled down now to a consistent set of dates, but Queensland and Western Australia both adopted and abandoned it more than once. For some decades now neither state has had DST, which makes it fun and games when working out times in the eastern states, and when travelling east-west or reverse, during the summer period. This is all because our Constitution makes no mention of time as a Commonwealth responsibility, which means it's automatically a state matter. -- ] </sup></span>]] 17:07, 16 October 2024 (UTC)
:::Also state-by-state in America: ]. ←] <sup>'']''</sup> ]→ 00:15, 17 October 2024 (UTC)
:::: Well, sort of. As I understand it, states have the option to observe DST or not, but they do not have the option to choose their own starting/ending dates. I'm not really convinced that this restriction is constitutional (I have a fairly narrow view of the ]) but there doesn't seem to be any great advantage for a state to challenge it. --] (]) 00:21, 17 October 2024 (UTC)
:::::Yes, that's what I was trying to say. And presumably interstate commerce is the justification for the federal law. If I remember correctly, the need for standard time was driven by the railroads, in place of a myriad of local times. And also, if I recall correctly, it used to be that the railroads worked strictly within standard time, even during DST, as DST was only sporadically used until 1967. Once DST became standardized, the railroads could change to DST also. ←] <sup>'']''</sup> ]→ 01:15, 17 October 2024 (UTC)
:While we have an article on ], it is not very detailed. I found what appears at glance to be a reliable and well-researched article on the history of European time zones at "" via timeanddate, which suggests that ] <s>Standard Time</s> as we know it (with its onset date) really began its continuity and spread from the Nazi conquests. (Other countries had been experimenting with daylight saving, but inconsistently, as the article explains.) The incongruity in clock-switch dates would be due to the haphazard nature of daylight saving being adopted in various countries, where countries tend to only finally decide to align their clocks with some treaty or conquest or absolute trade necessity. (Of course there are famous exceptions: the ], despite the rest of the continental U.S., including the entire surrounding time zone, having uniform daylight saving dates.) ] (]) 01:56, 17 October 2024 (UTC)
:::: Be careful — CEST does ''not'' stand for "Central European Standard Time" (easy mistake to make as a North American) but for "Central European ''Summer'' Time". It's the opposite of what you would expect from PST / PDT. CET is UTC+1; CEST is UTC+2. --] (]) 06:08, 17 October 2024 (UTC)
:::: <small>As for Indiana, I assume that's because they're so far west in their time zone, making DST a double misery for night owls and farmers. They really should be on Central Time and then it would be much less of a problem. --] (]) 06:18, 17 October 2024 (UTC) </small>
:::::Indeed. They did it to get the same time and business hours as the East (I've heard New York Stock Exchange is important somehow) and cause the enlatenization lobbies like businesses headquartered in EDT and golf are collectively stronger than the delayzation lobbies like CDT headquarters and nightclubs. Great for us New Yorkers, terrible for the Indianan colonists of the aggrandized UTC-4 Time Empire. So no, permanently stopping leap seconds won't cause 9 to 5 jobs to get later till the night owl torture is really bad like ]. There's probably still 9 to 5 jobs in Urumqi, I wonder if they pay better than similar 12 to 8 jobs. ] (]) 21:11, 21 October 2024 (UTC)
:::::: Leap seconds should have been strangled in the cradle. Horrible idea from the very start. People ''will'' absolutely adjust nominal start and stop times to the Sun, no matter what the clock says. It just takes a while; doesn't usually happen in six months, which is why DST has any effect at all. --] (]) 16:25, 23 October 2024 (UTC)
:::: <small> Oh, and not quite true about "the rest of the Continental US" -- Arizona, except for the Navajo Nation, does not observe DST. I expect that's because they're far enough south that the difference between summer and winter times doesn't justify it. Not sure why other southern states don't do the same thing. --] (]) 06:21, 17 October 2024 (UTC) </small>
:::::<small>It gets even more confusing. Within the Navajo Nation is the separate Hopi Reservation. Which does not observe DST. So, you go from Arizona in general (no DST), enter the Navajo Nation (has DST), and continue onward into the Hopi Reservation (no DST).--] (]) (]) 15:08, 17 October 2024 (UTC)</small>
:::::Yes my mistakes, the article I linked specifies CEST = "Summer Time", not "Standard", so that's on me. Also I knew there were other U.S. states that didn't do daylight saving, but I had only remembered Hawaii, and Indiana has always felt like an odd one out for its area in so many ways (usually good ways, Hoosiers). ] (]) 15:57, 17 October 2024 (UTC)
:::::Even Cuba has DST for some reason. ] (]) 21:52, 21 October 2024 (UTC)
::My nerdy brain tells me that, logically, daylight saving should run for the same amount of time either side of the summer solstice. It doesn't in my state of Australia. My ageing memory tells me that the finishing date was extended further into autumn by a populist state premier who wanted more people to go to the Formula 1 Grand Prix. ] (]) 02:16, 17 October 2024 (UTC)
:::Your logic may fail to take into account that the ] is not symmetrical, owing to that pesky 0.0167 ] of the Earth's orbit: see the end of the ] section. {The poster formerly known as 87.81.230.195} ] (]) 03:47, 17 October 2024 (UTC)
::::What difference would it make? ] (]) 03:53, 17 October 2024 (UTC)
:::::Mid-sunlight isn't 12:00 at 150° East, it's 12:14 in February and 11:44 in early November and 12:00ish in April and December and early September and a few minutes early or late in May and July.
] ] (]) 21:47, 21 October 2024 (UTC)
:::My nerdy brain tells me that you can't save daylight hours; what you gain at one end of the day, is lost at the other. The intended result of shifting working hours relative to daylight hours can also be reached by shifting working hours, and there's nobody stopping us from doing that. I remember a ferry with the notice "Operating hours: 6:00–20:00 winter time, 7:00–21:00 summer time". Although it would be convenient to put zero o'clock, when the date changes, at a time when most people are asleep. Right, it's one o'clock now here, time to go to bed. ] (]) 23:06, 17 October 2024 (UTC)
::::Here in Australia, one argument against daylight saving is the issue of milking cows. It's hard to tell cows with bursting udders to just hold on a bit longer. ] (]) 23:14, 17 October 2024 (UTC)
:::::British cows concur. ] (]) 23:25, 17 October 2024 (UTC)
::::::We now have ]; they don't care when the cows want to be milked (molken?), although the cows may have to wait for their turn. You can't run a big dairy farm without robotic help. ] (]) 16:14, 18 October 2024 (UTC)
::::::: Aarrgh, AI has struck! We're all doomed! -- ] </sup></span>]] 17:07, 19 October 2024 (UTC)
In a ], reaching the highest point involves - both a minimal kinetic energy - along with a maximal potential energy, whereas reaching the lowest point involves - both a maximal kinetic energy - along with a minimal potential energy. Thus the mechanical energy becomes the sum of kinetic energy + potential energy, and ''is a conserved quantity''.
::What have the Nazis done for us? In the UK - ]. <span class="nowrap">] <sup>]</sup><sub>]</sub></span> 08:53, 18 October 2024 (UTC)
:::The first national daylight saving was courtesy of Kaiser Bill and his minions. ] (]) 09:27, 18 October 2024 (UTC)
::::The more I hear about that man the less I like him. ] (]) 21:54, 21 October 2024 (UTC)
So I wonder if it's reasonable to define also "potential velocity" vs. "kinetic velocity", and claim that in a harmonic oscillator, reaching the highest point involves - both a ''minimal'' "kinetic velocity" (i.e. involves what we usually call ''a rest'') - along with a ''maximal'' "potential velocity", whereas reaching the lowest point involves - both a ''maximal'' "kinetic velocity" (i.e. involves what we usually call ''the actual velocity'') - along with a ''minimal'' "potential velocity". Thus we can also define "mechanical velocity" as the sum of "kinetic velocity" + "potential velocity", and ''claim that the mechanical velocity is a conserved quantity'' - at least as far as a harmonic oscillator is concerned.
The above is all interesting, but almost none of it addresses the question: "Why not make them coincide? Surely there would be cost savings on all sides?". <span class="vcard"><span class="fn">]</span> (<span class="nickname">Pigsonthewing</span>); ]; ]</span> 15:08, 18 October 2024 (UTC)
Reasonable?
:You really expect America to do something that makes it easier to interact with the rest of the world? You know, like we've (the US) so readily done with the metric system? Or date format?--] (]) (]) 20:29, 18 October 2024 (UTC)
::I expect them to do so when it is in their interest, yes. <span class="vcard"><span class="fn">]</span> (<span class="nickname">Pigsonthewing</span>); ]; ]</span> 18:19, 19 October 2024 (UTC)
:::Once again I point to the metric system.--] (]) (]) 20:45, 19 October 2024 (UTC)
::::Europe got tired of copying our extensions. Also Europe time's fucked up maybe they can't take more, 9 degrees West has the time of 30 degrees East in summer just cause they copied Hitler & seem to want all EU same time, (30+9)'s even worse than extreme west Indiana, or the "7.5 degrees plus or minus nearest country border" that it could be. Nov 7 Northwest Iberian sunrise would be late as hell at that latitude. Europe doesn't have many October 31st kids door-to-door afterschool either, Eurolatists can't say "won't someone think of the children!". ] (]) 21:47, 21 October 2024 (UTC)
:::::To make the dates the same would require a treaty - and if so, it would be best for the clock to roll over at the same UTC time everywhere, not just the same date. ←] <sup>'']''</sup> ]→ 02:06, 22 October 2024 (UTC)
::::::A treaty would work, so would the governments of one side unilaterally wanting to shorten the "wrong offset time" from weeks to hours like they did till we extended for trick-or-treaters (and March for some reason) they didn't copy that one. The latism lobby is stronger (i.e. EUST creeped west from this) but they're not omnipotent. DST's 1:00 UT Eurowide (no earlier than 1 to 2/2 to 1 or later than 3 to 4/4 to 3 with intermediate values as disparate as 9.3 West & 31.6 East). If EU copied our dates ] would get Monday to Friday sunrises after 9:16, sunrises as late as ~9:19.0 11/6/88 at the cape (~43°10'N 9°13'W) seeing the Sun would take even longer cause hills/mountains instead of an idealized mirror-smooth globe. I don't know how late Spain starts but this is past where Americans would start saying "think of the children" outside in the dark & some would get miserable if it's too dark when they work, learn or wake. Everyone would hate it but ] DST might be better for unconscientious night owls actually (our dates plus 6 months or centering the 34 weeks on Sunday nearest Dec solstice). At least kids wouldn't go weeks or months without full dark and mornings already suck if you can't sleep in may as well make them night so 16:30 isn't. Half of US time zones wouldn't even get that bad if centered on 75 90 105 120 like they should be only about 8:30 sunrise (nautical dawn would reach the threes though which would suck) ] (]) 21:42, 22 October 2024 (UTC) ] ] (]) 21:42, 22 October 2024 (UTC)
Note that I could also ask an analogous question - as to the concept of "potential momentum", but this term is already used in the theory of ] for another meaning, so for the time being I'm focusing on velocity.
] (]) 12:26, 29 December 2024 (UTC)
{{clear}}
: 'kinetic velocity' is just 'velocity'. 'potential velocity' has no meaning. ] (]) 13:56, 29 December 2024 (UTC)
::Per my suggestion, the ratio between distance and time is not called "velocity" but rather "kinetic velocity".
::Further, per my suggestion, if you don't indicate whether the "velocity" you're talking about is a "kinetic velocity" or a "potential velocity" or a "mechanical velocity", the very concept of "velocity" alone has no meaning!
::On the other hand, "potential velocity" is defined as the difference between the "mechanical velocity" and the "kinetic velocity"! Just as, this is the case if we replace "velocity" by "energy". For more details, see the example above, about the harmonic oscillator. ] (]) 15:14, 29 December 2024 (UTC)
:::You could define the ''potential velocity'' of a body at a particular height as the velocity it would hit the ground at if dropped from that height. But the sum of the potential and kinetic velocities would not be conserved; rather <math>v_{\mathrm{tot}} = \sqrt{v_{p}^{2} + v_{k}^{2}}</math> would be constant. ] (]) 18:54, 29 December 2024 (UTC)
::::Thank you. ] (]) 20:07, 29 December 2024 (UTC)
::: 'Potential velocity' has no meaning. You seem to be arguing that in a system where energy is conserved, but is transforming between kinetic and potential energy, (You might also want to compare this to ].) then you can express that instead through a new conservation law based on velocity. But this doesn't work. There's no relation between velocity and potential energy.
::: In a harmonic oscillator, the potential energy is typically coming from some central restoring force with a relationship to ''position'', nothing at all to do with velocity. Where some axiomatic external rule (such as ] applying, because the system is a mass on a spring) ''happens'' to relate the position and velocity through a suitable relation, then the system will then (]) behave as a harmonic oscillator. But a different system (swap the spring for a ]) doesn't have this, thus won't oscillate. ] (]) 00:00, 30 December 2024 (UTC)
::::Let me quote a sentence from my original post: {{tq|Thus we can also...claim that the mechanical velocity is a conserved quantity - '''at least as far as a harmonic oscillator is concerned'''.}}
::::What's wrong in this quotation? ] (]) 07:52, 30 December 2024 (UTC)
:::::It is true, not only for harmonic oscillators, provided that you define {{math|1='''v'''<sub>pot</sub> = − '''v'''<sub>kin</sub>}}. --] 09:07, 30 December 2024 (UTC)
::::* You have defined some arbitrary values for new 'velocities', where their ''only'' definition is that they then demonstrate some new conservation law. Which is really the conservation of energy, but you're refusing to use that term for some reason.
::::: As Catslash pointed out, the conserved quantity here is proportional to the square of velocity, so your conservation equation has to include that. It's simply wrong that any linear function of velocity would be conserved here. Not merely we can't prove that, but we can prove (the sum of the squares diverges from the sum) that it's actually contradicted. For any definition of 'another velocity' which is a linear function of velocity.
::::: Lambiam's definition isn't a conservation law, it's merely a ]. The sum of any value and its ] is always ]. ] (]) 14:04, 30 December 2024 (UTC)
::::::{{small|It is a law of conservation of ''sanity''. Lacking a definition of potential energy, other than by having been informed that kinetic energy + potential energy is a conserved quantity, there is not much better we can do.}} --] 11:20, 31 December 2024 (UTC)
::::::: We have a perfectly viable definition of potential energy. For a pendulum it's based on the change in height of the pendulum bob against gravity. For some other oscillators it would involve the work done against a spring. ] (]) 16:33, 31 December 2024 (UTC)
::::::::Oops, I mistyped. I meant to write:
:::::::::"{{small|Lacking a definition of potential velocity, other than by having been informed that kinetic velocity + potential velocity is a conserved quantity, there is not much better we can do.}}"
:::::::: --] 23:32, 31 December 2024 (UTC)
= October18 =
= December 30 =
==Gruesome question about injury==
In this (warning: gruesome image) of Sinwar's body, is it a shrapnel stuck in his bow? What caused the hole to its right?
] (]) 13:36, 18 October 2024 (UTC)
:Where are you seeing a bow? ←] <sup>'']''</sup> ]→ 14:34, 20 October 2024 (UTC)
:‘brow’ maybe? ] (]) 18:07, 22 October 2024 (UTC)
== Saltiness comparison ==
= October 19 =
Is there some test one might easily perform in a home ] to compare the ] (due to the concentration of ] ]s) of two liquid preparations, without involving biological ]s? --] 09:22, 30 December 2024 (UTC)
== Falling into Jupiter ==
:Put two equally sized drops, one of each liquid, on a warm surface, wait for them to evaporate, and compare how much salt residue each leaves? Not very precise or measurable, but significant differences should be noticeable. {The poster formerly known as 87.81.230.195} ] (]) 10:21, 30 December 2024 (UTC)
I was thinking one day. Imagine you are an astronaut in free fall to ]. You are in a spacesuit with plenty of oxygen and food available so you are not dying from suffocation or starvation in your spacesuit. You have no way of escaping Jupiter's gravity. There are no other dangers than Jupiter itself. You will eventually enter Jupiter's atmosphere. At which point would you die? ] | ] 09:30, 19 October 2024 (UTC)
:You would be moving so fast, that you would burn up in the upper atmosphere, turning into plasma temporarily. But when the space suit ruptured, by burning through, suffocation and depressurisation would be a terminal issue. ] (]) 10:53, 19 October 2024 (UTC)
::The thing about vague hypotheticals is, they're vague, and hypothetical. The astronaut could bring along a bigass rocket, and once in a stable orbit around Jupiter fire it to cancel out their orbital momentum until they were at rest relative to Jupiter, then "let go" and just let gravity do its thing pulling them towards Jove's center of mass.
::Most spacecraft don't do this b/c hauling reaction mass up a gravity well ]. The "easiest" way to slow down for landing, is to ''slam into the atmosphere and let that bleed off your velocity''. If you can. If not, for ex the atmosphere is very thin, other methods are required: see the ], or ]s.
::(The real non-hypothetical answer: ] of ] before anything else, unless their "spacesuit" was a massive, very dense and multilayered radiation shield chamber) ] (]) 04:30, 20 October 2024 (UTC)
:::The onset of radiation syndrome is slow enough that the fall is over before the radiation really kills. Or the radiation is very high, then that should be said where and why. ] (]) 12:45, 20 October 2024 (UTC)
::The principle is sound, but the residue from one drop won't be measurable using kitchen equipment -- better to put equal amounts of each liquid in two warm pans (use enough liquid to cover the bottom of each pan with a thin layer), wait for them to evaporate and then weigh the residue! Or, if you're not afraid of doing some ], you could also try an indirect method -- bring both liquids to a boil, measure the temperature of both, and then use the formula for ] to calculate the saltiness of each! ] (]) 18:22, 30 December 2024 (UTC)
== Since neutrinos (and dark matter) don't interact with light, so what should happen when light comes across them? ==
:::Presumably the ''liquid preparations'' are not simple saline solutions, but contain other solutes - or else one could simply use a hydrometer. It is unlikely that Lambian is afraid of doing some algebra. ] (]) 18:57, 30 December 2024 (UTC)
I can think about two options:
:<s>Assuming the liquid preparations are water-based and don't contain alcohols and/or detergents one can measure their rates of dispersion. Simply add a drop of food dye to each liquid and then time how rapidly droplets of each liquid disperse in distilled water. Materials needed: food dye, eye dropper, distilled water, small clear containers and a timer.</s> ] (]) 21:09, 30 December 2024 (UTC)
:::The ] of a solution will indicate its molarity, but not identify the solute. ''Liquid preparations'' that might be found in a kitchen are likely to contain both salt and sugar. Electrical conductivity is a property that will be greatly affected by the salt but not the sugar (this does not help in distinguishing Na<sup>+</sup> from K<sup>+</sup> ions though). ] (]) 22:23, 30 December 2024 (UTC)
Option #1: The light keeps travelling "through" them, as if they don't exist. But if this is the case, then what does that mean, in terms of the neutrino's (and dark matter's) refractive index? Is it identical to the vacuum's refractive index?
::::That's what I'm thinking too -- use an ] to measure the ] of the preparation, and compare to that of solutions with known NaCl concentration (using a ]-type method). ] (]) 20:18, 31 December 2024 (UTC)
Option #2: The light experiences absorption or reflection or scattering, in which case the neutrino's (and dark matter's) momentum must be influenced by that encounter with light, due to the conservation of momentum, so we do see them interact with light, in some sense...
:Quantitative urine test-strips for sodium seem to be available. They're probably covering the concentration range of tens to hundreds millimolar. ] (]) 00:58, 2 January 2025 (UTC)
So, what's the correct option? Is it #1 or #2 or another one?
::Thanks, test strips seem more practical in the kitchen setting than an ohmmeter (why not call it a "]meter"?), for which I'd need to devise a way (or so I think) to keep the terminals apart at a steady distance. Test strips require a colour comparison, but I expect that a significant difference in salinity will result in a perceptible colour difference when one strip is placed across the other. Only experiment can tell whether this expectation will come true. Salinity is usually measured in g/L; for kitchen preparations a ballpark figure is 1 g/L. If I'm not mistaken this corresponds to {{nowrap|1=(1 g/L) / (58.443 g/mol) ≈}} {{nowrap|1=0.017 M = 17 ].}} I also see offers for salinity test strips, 0–1000 ppm, for "Science Education". --] 11:40, 2 January 2025 (UTC)
:::Test strips surely come with a printed color-chart. But if all you are trying to do is determine which is more salty, then that's even easier than quantifying each separately. Caveat for what you might find for sale: some "salinity" tests are based on the chloride not the sodium, so a complex matrix that has components other than NaCl could fool it. ] (]) 18:44, 2 January 2025 (UTC)
== The (uncommon?) terms "relativistic length", and "relativistic time". ==
] (]) 16:29, 19 October 2024 (UTC)
:Since neutrinos do not interact with light, the light never collides with them. ]_] 20:42, 19 October 2024 (UTC)
::By "collides" I meant "comes across" (due to your important comment I've just fixed that in the header) So, what should happen if a photon and a neutrino travel towards each other, i.e. on the same route but in opposite directions? Similarly, what should happen when light comes across dark matter? ] (]) 21:04, 19 October 2024 (UTC)
:protons and electrons interact with photons. What is '''their''' refractive index? Short answer: no one can tell, because the refractive index is not of a particle alone. It depends on the interaction. And neutrinos not only do not interact with photons, they don't interact with each other. So you have no interactions to base a refractive index on. ] (]) 22:25, 19 October 2024 (UTC)
::The refractive index of a given medium is only relevant if photons can travel through that medium. In the case of protons-electrons you're talking about, nobody claims photons can travel through a proton or through an electron, so I can't see how any refractive index may be relevant in that case. But a refractive index may be relevant in option #1 I was talking about as you can see above in that option. ] (]) 02:16, 20 October 2024 (UTC)
:Your fundamental problem is you keep trying to think about "]" intuitively, in terms of the familiar everyday big world we all have direct experience of via our senses. You're asking what photons etc "''really'' act like". Billiard balls? Pebbles? Ocean waves etc etc? The correct answer is, they act like none of those things. They act like photons. They don't "take up space" in any way we can visualize, or occupy a definite fixed position in space, or "move" by plodding around from point A to B in a fixed interval of time, or "pass through one another", anything like that. {{br}}
:A necessary precondition to really "]king" "modern physics", is to throw out your preconceptions, and simply start with: what do our observations of things tell us. From those, we make predictions (]), and then ]. That's how science is done. And if you think it's all made up, you're presumably reading this on some kind of electronic device, ] if electrons were ''really'' tiny little balls, ] ''really'' little tiny beams or rays or water waves that "bounced off" other stuff when they "ran into it".{{br}}
:]: {{tpq|Things on a very small scale behave like nothing that you have any direct experience about. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen.}} ] (]) 05:02, 20 October 2024 (UTC)
::What do you mean by {{tq|'''keep''' trying}}? When did I try to do that for the first time?
::When I posted my question in the header, I had already been quite aware of the methodological idea you're describing quite well. Of course what you're depicting is the correct approach, methodologically speaking. But while you're portraying the correct methodological attitude one should take when thinking about modern physics, my question has nothing to do with methodology, because my question is only a practical one, empirically speaking (as follows), so the correct methodological approach you're quite well picturing has nothing to do with what I've practically asked about. To put it in a clear cut way: Just as you can practically ask, what is empirically expected to happen when one actualizes the photoelectric effect - although it heavily involves quantum physics that should be grokked by means of the methodological idea you're describing, so I can practically ask, what is empirically expected to happen when a photon and a neutrino travel towards each other, i.e. on the same route but in opposite directions, although both the photon and the neutrino are described in that quantum physics.
::So, are you claiming that I can't suggest any experiment in which a photon and a neutrino travel towards each other, i.e. on the same route but in opposite directions? Similarly are you claiming, that once Science detects (somehow) any dark matter, still we won't be able to suggest any experiment in which we send light towards dark matter? Or what are you actually claiming, practically speaking? ] (]) 07:53, 20 October 2024 (UTC)
:::you can never design an experiment where a photon travels on a path. Whatever the path maybe. 😁 For example you can do a photon in a fiber travel from a source to a detector. You will never know that the photon really after the first atom leaves the fiber, travels to the black hole in the centre of the Andromeda galaxy, does half a round around the black hole, a quantum leap short of the event horizon, comes back at the last atom of the fiber and hitting the detector bearing the spectral attenuation of a sodium atom in the middle of the fiber it never passed on the way. Okay that is an extreme example for a very improbable but possible event in quantum mechanics. Now to your question. What if "never interacts with" is a code for active avoidance? That would mean a neutrino near another particle (photon, neutrinos...Whatever) goes out of the way and resumed its travel after the particle has passed. What would you do then? Even going out of time is possible. Think about the length of the way to Andromeda! ] (]) 13:13, 20 October 2024 (UTC)
::::According to your attitude, the very concept of "refractive index" of a given medium through which light travels, would have had no meaning. Additionally, please notice that my original post (i.e. the question in the header and under it), mentions no photons, but rather mentions light only, for example a beam of photons. Anyway, thanks to your comment, I've just added "a beam of" before every "photon" mentioned in my later responses (following my original post). To sum up: the main question in my original post still remains. ] (]) 13:36, 20 October 2024 (UTC)
:::::Rewriting "photon" as "a beam of photons" changes the question. The exact path that a photon will follow cannot be predicted. Subsequent detection of a single photon is possible but allows only an estimate of the spread of likely refractive indices the photon has traversed. One increases the accuracy of a determination of refractive index by averaging measurements of many photons i.e. using "a beam of photons". However there will be practical limits to the focusing of both light sources and detectors. ] (]) 14:30, 20 October 2024 (UTC)
::::::{{tq|Rewriting "photon" as "a beam of photons" changes the question.}} Please re-read the second sentence (the one beginning with "Additionally") in my last response.
::::::As for the rest of your response, I agree, but what's the answer to my original question summed up '''in the header'''? ] (]) 15:44, 20 October 2024 (UTC)
:::{{tpq|1=So, are you claiming that I can't suggest any experiment in which a photon and a neutrino travel towards each other, i.e. on the same route but in opposite directions? Similarly are you claiming, that once Science detects (somehow) any dark matter, still we won't be able to suggest any experiment in which we send light towards dark matter?}}
:::Essentially, yes, assuming we're right about dark matter not interacting with the ]. Or, perhaps it could be put as: we can propose sending photons "this way" and neutrinos "that way", such that their ]s at some point intersect, but we would ] (other than the extremely minute effects of their gravitational and weak interactions), because why would we?
:::In this vein: the ] don't interact with the EM field. The question "what if a beam of X and Y" travel towards each other" is still formulated in intuitive "]" terms. Talking in strict QM terms, questions like "a beam of X and beam of Y" are ill-formed questions: to be meaningful (answerable) questions, rephrase them in terms of ]s, ], ] etc.
] has some good advice for people "talking science": :
{{Cot}}What to Do If You Have a Proposal for the Unified Field Theory?…and what not to do{{br}}
Due to volume of e-mail I have received (several thousand at last count) I cannot answer all requests, especially those from individuals who have a new proposal for completing Einstein’s dream of a unified field theory, or a new theory of space and time. However, I would like to give some guidelines for people who have thoughtfully pondered the question of the meaning of space-time.{{br}}
1) Try to summarize the main idea or theme in a single paragraph. As Einstein once said, unless a theory has a simple underlying picture that the layman can understand, the theory is probably worthless. I will try to answer those proposals which are short and succinct, but I simply do not have time for proposals where the main idea is spread over many pages.{{br}}
2) If you have a serious proposal for a new physical theory, submit it to a physics journal, just as {{sic}} ] or ]. There, it will get the referee and serious attention that it deserves.{{br}}
3) Remember that your theory will receive more credibility if your theory builds on top of previous theories, rather than making claims like “Einstein was wrong! ” For example, our current understanding of the quantum theory and relativity, although incomplete, still gives us a framework for which we have not seen any experimental deviation.Even Newtonian gravity works quite well within its domain (e.g. small velocities). Relativity is useful in its domain of velocities near the speed of light. However, even relativity breaks down for atomic distances, or gravitational fields found in the center of a black hole or the Big Bang. Similarly, the quantum theory works quite well at atomic distances, but has problems with gravity. A crude combination of the quantum theory and relativity works quite well from sub-atomic distances (10^-15 cm.) to cosmological distances (10^10 km), so your theory must improve on this!{{br}}
4) '''Try not to use vague expressions that cannot be formulated precisely or mathematically, such as “time is quantized, ” “energy is space, ” or “space is twisted, ” or “energy is a new dimension,” etc. Instead, try to use mathematics to express your ideas. Otherwise, it’s hard to understand what you are saying in a precise manner.''' Many referees will throw out papers which are just a collection of words, equating one mysterious concept (e.g. time) with another (e.g. light). '''The language of nature is mathematics (e.g. ] and ]). Try to formulate your ideas in mathematical form so that the referee has an idea of where you are coming from.'''{{br}}
5) Once formulated mathematically, it’s then relatively easy for a theoretical physicist to determine the precise nature of the theory. At the very least, your theory must contain the tensor equations of Einstein and the quantum theory of the Standard Model. If they lack these two ingredients, then your theory probably cannot describe nature as we know it. The fundamental problem facing physicists is that General Relativity and the quantum theory, when combined into a single theory, is not “], ” i.e. the theory blows up and becomes meaningless. Your proposal, therefore, has to give us a finite theory which combines these two formalisms. So far, only superstring theory can solve this key problem. Important: this means that, at the very minimum, your equations must contain the tensor equations of General Relativity and the Standard Model. If they do not include them, then your theory cannot qualify as a “theory of everything.”{{br}}
6) '''Most important, try to formulate an experiment that can test your idea. All science is based on reproducible results.''' No matter how outlandish your idea is, it must be accepted if it holds up experimentally. So try to think up an experiment which will distinguish your result from others. But remember, your theory has to explain the experiments that have already been done, which vindicate General Relativity and the quantum theory.{{br}}
Good luck!
{{Cob}} --] (]) 16:28, 20 October 2024 (UTC)
1. In Misplaced Pages, the page ] is automatically redirected to our article ], ''which actually doesn't mention the term "relativistic length" at all''. '''I wonder if there is an accepted term for the concept of relativistic length'''.
:<small>In my view, presenting Michio Kaku's advice in this thread is redundant, as follows.</small>
:Introduction: the reason for which I mentioned the photoelectric effect in my last response to you, is because this effect can be formulated, not only in the language of Quantum chemistry, but also in the language of Classical electromagnetism <small>- which indeed disagrees with this effect but can still tell us what it disagrees with</small>.
:The same is true for my original question in the header: It can also be formulated in the language of classical mechanics, as you have done yourself, stating in a classical language (a bit relativistic yet not the language of quantum mechanics): {{tq|we can propose sending photons this way and neutrinos that way, such that their ] at some point intersect, but we would expect to observe nothing}}. To sum up, you agree to option #1 (in my original post), i.e.: We will see the beam of light keep travelling in the same 4D-route without any change, as if this route is not intersected by the 4D-route of the beam of neutrinos. Am I right? ] (]) 17:35, 20 October 2024 (UTC)
::"Doing" ], which ignores gravitation (assumes flat spacetime) and plotting it out on a ], correct, b/c they only interact via the ] and it's called that b/c seriously it's ''really weak''. (Not as weak as gravity though!) Which is why gazillions of ]s are flooding through us and the entire Earth after plowing through half the Sun, like we're all not even there, constantly. (The neat fact being that what changes is simply the direction they come from: at night they're coming ''upwards'' from the ground ''having just zipped through the entire planet'', after calling on Earth's day side!)
::In gen rel, it would still be the same, b/c the only thing changing is adding in gravitation. The neutrino's mass is immensely tiny, thus its ] has accordingly miniscule effect on local spacetime geometry (which ''is'' what we call "gravity", in GR). Photon's mass is, well, zero, so it has even ''less'' effect. And gravitation is '''really''' weak.
::...Unless, you can crank things up to truly mind-and-spacetime-warping energies, and ] of photons into a vanishingly-tiny volume of space. Somehow. Photons are ], which, unlike ] such as quarks (or neutrinos), are "allowed" to have all identical ] if they feel like it. Meaning their ]s can completely overlap and they can all "take up" an arbitrarily small volume. So if you figure how to do that out do tell the scientific journals, preferably before building your death ray and taking over the world.
::'']'': when physicists these days are "talking shop" generally they only ever use "mass" to mean "the invariant or 'rest mass' according to GR": . So I will try to do the same. --] (]) 19:38, 20 October 2024 (UTC)
:::{{tq|Unless, you can crank things up to truly mind-and-spacetime-warping energies, and ] of photons into a vanishingly-tiny volume of space}}. Btw, some weeks ago I read a scientific article (I think in Nature or in Science) that discovered that a Kugelblitz was actually impossible, because it would've started to emit radiation before it became a black hole, so it would never become a black hole...
:::{{tq|when physicists these days are "talking shop" generally they only ever use "mass" to mean "the invariant or 'rest mass' according to GR.}} I think you've noticed (as follows) that this fact is irrelevant, because the geometry of spcetrime is shaped by energy (and momentum) rather than by mass.
:::{{tq|The neutrino's mass is immensely tiny...Photon's mass is, well, zero, so it has even ''less'' effect.}} Correct, less effect but not zero effect, because the geometry of spcetrime is shaped by energy/momentum rather than by mass. Anyway, thank you for noticing the (immensely tiny) generally-relativistic effect being done to the geometry of spacetime by each beam, thus influencing the other beam, so actually they do have some impact on each other after all, yet not via any force other than the fictitious force of gravitation. Well, your noticing this generally-relativistic effect was an important reservation. Anyway, what I'm taking from your answer to my original question is as follows: Both beams don't interact with each other, as far as gravity is ignored. ] (]) 22:35, 20 October 2024 (UTC)
::::{{tpq|I think you've noticed (as follows) that this fact is irrelevant, because the geometry of spcetrime is shaped by energy (and momentum) rather than by mass.}}
::::See ]: a bunch of photons with the same momentum vector have zero effect on spacetime geometry, because a single photon (having no invariant mass) has no ] where it is at rest, no matter what ] are applied to it. This is why a beam of light always travels at ''c'' in vacuum. If you have two+ photons with ''different'' vectors relative to each other (they have a scattering angle) ''then'' you can calc a center-of-momentum frame for the multiple-photon system, and ''then'' the photons have an effect on the spacetime metric. Hence the kugelblitz idea: if hypothetically you could stuff tons (heh) of photons into a tiny volume of space, they can't be all at rest relative to each other, so the whole system would have a CoM frame and the photons would affect the local metric. {{tpq|In general, only changes in energy have physical significance.}} --] (]) 15:10, 22 October 2024 (UTC)
:::::when I wrote that the geometry of spacetime was shaped by energy and momentum rather than by mass, I tried to be brief. actually I meant what I'd already written in my last response of ]: that the geometry of spacetime was shaped by the "density and flux of momentum and of energy".
:::::Anyway, my main point in my last response, was not about energy (or about momentum), but rather about mass, that is: as far as gravity is concerned, mass is irrelevant. ] (]) 15:57, 22 October 2024 (UTC)
: Interactions are predicted. See . ] (]) 22:44, 20 October 2024 (UTC)
::Thank you for this source. ] (]) 23:02, 20 October 2024 (UTC)
2. A similar qusestion arises, at to the concept of relativistic time: The page ], is automatically redirected to our article ], which prefers the abbreviated term "time dilation" (59 times) to the term "relativistic time dilation" (8 times only), and ''nowhere'' mentions the term "relativistic time" alone (i.e. without the third word "dilation") - although it does mention the term "proper time" for the shortest time. Further, this article doesn't even mention the term "dilated time" either. It does mention, though, another term: ], but regardless of time dilation in ''Special'' relativity. '''To sum up, I wonder what's the accepted term used for the dilated time (mainly is Special relativity): Is it "coordinate time"? "Relativistic time"?'''
= October 20 =
] (]) 09:32, 30 December 2024 (UTC)
== Soap bubbles and flatulence ==
:Are you reading these things as "contraction of relativistic length" etc.? It is "relativistic contraction of length" and "relativistic dilation of time". --] (]) 09:37, 30 December 2024 (UTC)
Let's say that someone ate a whole can of beans for lunch and had a piece of steak, and some milk to wash it all down. A couple of hours later, they're suffering from farting problems, as they have to fart a lot, and the gas doesn't smell good at all. They have filled a bathtub full of water and added a generous amount of soap, and in they go the bathtub. They fart in the there and those bubbles of soap caused by the release of gas travel up onto the surface. If they had a lighter nearby (for whatever reason) and tried to ignite those bubbles, would the bubbles catch on fire? ] (]) 05:16, 20 October 2024 (UTC)
::When I wrote: {{tq|The page ] is automatically redirected to our article ] which...nowhere mentions the term "relativistic time" alone (i.e. without the third word "dilation")}}, I had already guessed that the term "dilation of relativistic time" (i.e, with the word "dilation" preceding the words "relativistic time") existed nowhere (at least in Misplaced Pages), and that this redirected page actually meant "relativistic dilation of time". The same is true for the redirected page "relativistic length contraction": I had already gussed it didn't mean "contraction of relativistic length", because (as I had already written): {{tq|the article ]...doesn't mention the term "relativistic length" at all}}.
::Anyway, I'm still waiting for an answer to my original question: Are there accepted terms for the concepts, of relativistic length - as opposed to ], and of relativistic time - as opposed to ]? ] (]) 10:12, 30 December 2024 (UTC)
:::A term that will be understood in the context of relativistic length contraction is ''relative length'' – that is, length relative to an observer.<sup></sup> --] 10:55, 31 December 2024 (UTC)
::::Thank you. The middle source uses the term "comparative length", rather than "relative length". I couldn't open the third source. ] (]) 08:04, 1 January 2025 (UTC)
:::::The text under the graph labelled '''Comparative length''' on page 20 of the middle source reads:
::::::Graph of the relative length of a stationary rod on earth, as observed from the reference frame of a traveling rod of 100cm proper length.
:::::A similar use of "relative length" can be seen on the preceding page. --] 10:23, 2 January 2025 (UTC)
== What did Juan Maldacena say after "Geometry of" in this video? ==
:I don't think the human digestive system works as fast as that, but leaving that aside, it's well known that human flatulance is inflammable – ] is a widespread activity; I recall a story that one squad of British Army recruits managed to burn down their barracks hut while indulging in it; I would have liked to have been in the Colonel's office the following morning. {The poster formerly known as 87.81.230.195} ] (]) 05:40, 20 October 2024 (UTC)
:I guess? Why wouldn't they? Is there a reason you were expecting them not to? Fun bio facts time the flammable stuff in human ] is mostly hydrogen gas, made by ] fermenting ] that your digestive system can't tackle. And they actually share some of the products with your cells and they're probably good for gut health. (Non-human ] consume ''buttloads'' of fiber, as did all humans ].)
:The rest of it is mostly swallowed air which makes its way down there, along with small amounts of volatile sulfur compounds also produced by your flora, ]s, which your smeller is extremely sensitive to. That's the smelly stuff. ] (]) 19:52, 20 October 2024 (UTC)
::Haha, no reason why I wouldn't think the bubbles were not flammable; after all, the gases are basically trapped inside, but very interesting as well as informative - thank you! A while back I sprayed some gas from a nearly empty alcohol rub bottle into water and ignited it, and so I thought, if it was possible, the same stuff applies to farts. ] (]) 23:16, 20 October 2024 (UTC)
:::A bubble of flammable gas in water is an interesting apparatus where you can see inside the bubble before and during it popping. With an electronic igniter, could be fun to try to ignite the bubble itself to demonstate the effect of ]. Are H2 and methane actually "flammable" when pure? ] (]) 02:11, 21 October 2024 (UTC)
::::"]"/"fire" is a ] reaction, between at least 2 reactants, a fuel and an ]. H2 and ] fill the "fuel" role while most commonly O2 takes the "oxidizer" one. If by "pure" you mean, "a volume of gas which is 100% eg H2 ]", then no, no "flame" can occur without mixing w/ an oxidizer first. ] in environments where lots of "sparky"/"]" stuff is liable to happen; other stuff is simply kept out of said environment (already necessary anyway for things to work right). H2 is hard to beat in terms of ]!
::::This is why if you block an ]'s air intake, it's not going to be running much longer, and why jet engines don't work in space, and why rockets generally need two things, fuel ''and'' oxidizer. (The latter being often O2, sometimes ].) As do most ]s—a rocket is in essence just a bomb that explodes more slowly, if everything goes right. (]) --] (]) 22:28, 22 October 2024 (UTC)
::::For pure hydrogen or methane, not by itself, no. The combustion of the gases inside the bubbles are using the air around it, which doesn't contain too much oxygen. Fun thing is if you managed to inject some oxygen into those fart bubbles, the mixture would be potentially explosive, and when ignited can create a small bang. People do, however, like to weld with fuel and oxidizer mixtures (see ]); the flame of oxygen and ] can go up to {{convert|3500|C}}, hot enough to melt a variety of metals. ] (]) 00:56, 23 October 2024 (UTC)
:::::For the record, I was proposing experiments, not being ignorant of UEL that I had mentioned:) ] (]) 12:01, 24 October 2024 (UTC)
I was watching this video ] and ] as they explore a wealth of developments connecting black holes, string theory etc, ] said something right after "'''Geometry of'''" Here is the spot: https://www.youtube.com/live/yNNXia9IrZs?si=G7S90UT4C8Bb-OnG&t=4484 What is that? ] (]) 20:46, 30 December 2024 (UTC)
== Must every <s>moving</s> body lose energy, namely the energy of the gravitational waves emitted by that body while <s>moving</s> ? ==
:]. --] (]) 21:05, 30 December 2024 (UTC)
::Thank you, its the ]'s accent which made me post here. ] (]) 21:18, 30 December 2024 (UTC)
= December 31 =
] (]) 10:08, 20 October 2024 (UTC)
:Can you accept as a counter example the body envisaged in ] that remains at rest, or in '''motion at a constant speed in a straight line''', except insofar as it is acted upon by a force? ] (]) 13:36, 20 October 2024 (UTC)
:Given a body moving at a constant speed, there is a reference frame in which the body is at rest, from which it follows that it does not emit gravitational waves. Only a change in the gravitational interaction between massive bodies can stir up the gravitational field. --] 15:31, 20 October 2024 (UTC)
== Brightest spot of a discharge tube ==
'''OP's apology''': Sorry for replacing the correct word "accelerating" by the wrong word "moving". I've just fixed that in the header . ] (]) 16:00, 20 October 2024 (UTC)
:Responders can lose interest in freely helping a questioner who keeps changing their question. Can you accept that energy must always be added (or subtracted) to accelerate (or decelerate) a body? Reference: ]. ] (]) 19:45, 20 October 2024 (UTC)
::{{tq|Responders can lose interest in freely helping a questioner who keeps changing their question.}} What do you mean by <q>'''keeps'''</q> changing my question? When did I change my question, excluding this single time (for which I have already apologized)?
::{{tq|Can you accept that energy must always be added (or subtracted) to accelerate (or decelerate) a body?}} Yes, I can, and I do accept. Still, I'm asking if, besides the energy your're talking about, one should also take into account another amount of energy that should actually be subtracted because of the gravitational waves which are always emitted by every accelerating body. ] (]) 22:59, 20 October 2024 (UTC)
:::The term ] rather than gravity wave is used in article space.
:::Energy (luminosity) carried away by gravitational waves is purportedly given by Einstein's ]
:::As yet this has been only partially confirmed by ] (earning the 1993 Nobel Prize in Physics). Research continues and I think we are far from the kind of laboratory demonstration that is needed to cement this theory to the same extent as, for example, the refined measurements of ] G initiated (effectively but not deliberately) by ]. ] (]) 02:11, 21 October 2024 (UTC)
::::{{tq|The term ] rather than gravity wave is used in article space}}. Of course. Has anyone ever used the term "gravity wave", in this thread?
:::::
::::{{tq|Energy (luminosity) carried away by gravitational waves is purportedly given by Einstein's Quadrupole formula}}. Now let's assume that Einstein was correct. So, regardless of the other kind of energy mentioned in your previous response, must every accelerating body '''lose''' the kind of energy you're mentioning in your last response, namely the energy of the gravitational waves emitted by that body while accelerating? ] (]) 09:42, 21 October 2024 (UTC)
:::::According to the theory, a spherically symmetric pulsing body wouldn't emit gravitational waves. ] (]) 10:46, 21 October 2024 (UTC)
::::::Does it mean that spherically '''asymmetric''' pulsing bodies would? ] (]) 14:37, 21 October 2024 (UTC)
:::::::The opposite of "spherically symmetric" is "not spherically symmetric". The pulsation of body needs to respect certain symmetries in order to keep its centre of mass at rest. As the formula says, the quadrupole of the mass distribution needs to change. Think of a wobbling drop of water. A rotating barbell emits gravitational waves, as does (in a similar way) a pair of orbiting black holes. All the detected gravitational wave events are of that type, occasionally with a neutron star in place of a black hole. --] (]) 16:12, 21 October 2024 (UTC)
::::::::I am content that the single counter-example provided by NadVolume answers the OP's question. ] (]) 16:41, 21 October 2024 (UTC)
:::::::::Well, if you're content, I guess I'll just keep my mouth shut in the future. --] (]) 16:45, 21 October 2024 (UTC)
::::::::Thank you for these examples. So, regardless of the kinetic energy added to an accelerating body, do the bodies in your examples also '''lose''' radiant energy - due to the emission of gravitational waves? ] (]) 19:30, 21 October 2024 (UTC)
::::::::::The "bodies" as a whole (barbell, binary BH) are not accelerated (although parts of them are, e.g. the individual BHs), and no kinetic energy is added to them. Yet their rotation causes them to emit gravitational waves and they lose energy through them. The barbell's rotation slows down, the BHs approach each other and finally coalesce. Incidentally, I mentioned the barbell because ] uses that example (in ''Class. Quantum Grav.'' 16, A131 (1999)) to illustrate the strength of the emitted gravitational waves, which is tiny except for the most extreme cases. --] (]) 05:52, 22 October 2024 (UTC)
:::::::::::If the rotating barbell is in vacuum, it's not supposed to slow down, is it? If it doesn't slow down, and it doesn't receive any kinetic energy, then this barbell will keep losing energy "for ever", or rather until it eventually "evaporates" (like a BH), am I right? ] (]) 12:49, 22 October 2024 (UTC)
::::::::::::Emitting gravitational waves slows its rotation. If the reason it emits gravitational waves is that it's rotating, it should cease emitting them (and thus cease losing energy) when it's lost enough energy to stop rotating. Its mass won't evaporate. -- ] (]) 22:40, 22 October 2024 (UTC)
:::::::::::::Why losing energy may make the body slow down or stop rotating? What about the conservation of angular momentum? ] (]) 23:32, 22 October 2024 (UTC)
:::::::::::You are not right, there is no reason for the barbell to evaporate. The rotation slows down because the GWs carry off energy (and angular momentum). If the thing is not in vacuum the GW effect is overwhelmed by friction. But this is a highly idealised example meant to illustrate the momentary emission of GWs. It does not occur as such in nature, and it is not worth thinking it through to the end. --] (]) 13:02, 22 October 2024 (UTC)
::::::::::::I still think, Bernard schultz's example you've mentioned, is interesting, and worth thinking.
:::::::::::::
::::::::::::I've asked about vacuum, in which no friction exists.
:::::::::::::
::::::::::::Apparently, according to the conservation of angular momentum, this momentum is not supposed to change. So, I still wonder, what may prevent the rotating barbell from continuing to rotate "for ever". As long as it rotates, it emits GWs, thus loses energy, without changing the angular momentum, until the barbell loses all of its energy, i.e. until it "evaporates". I wonder where the mistake lies.
:::::::::::::
::::::::::::Is it possible, that I'm wrong with the conservation of angular momentum, so that what I was taught in school about this conservation in vacuum was not that accurate? ] (]) 14:10, 22 October 2024 (UTC)
:::::::::::::]. --] (]) 16:42, 22 October 2024 (UTC)
::::::::::::::Thank you for this clarification. Consequently, all of the basic laws of conservation (i,.e. conservation of energy, of linear momentum and of angular momentum), are only true for spherecal symmetric bodies, or bodies that don't rotate. All other bodies, emit GWs, so they can't satisfy those laws of conservation any more, at least according to the theory. Do you think we should mention this fact (an important one IMO) in the respective articles about those laws? ] (]) 17:36, 22 October 2024 (UTC)
:::::::::::::::No!!!!! Do you not understand how conservation laws work???? --] (]) 18:09, 22 October 2024 (UTC)
::::::::::::::::Our article ] indicates {{tq|"The symmetry associated with conservation of angular momentum is rotational invariance."}}. Does this reservation exclude every non-spherecal symmetric body? If it does then all is fine. But if it doesn't then:
::::::::::::::::AFAIK, if no external forces act, then the angular momentum must be conserved. Correct? However, non-spherecal symmetric bodies that rotate, emit GWs, so the angular momentum of those bodies is not conserved. Correct?
::::::::::::::::If I'm correct, then the conservation of angular momentum does not hold in all cases where no external forces act. What's wrong? ] (]) 18:26, 22 October 2024 (UTC)
:::::::::The single counter-example provided by NadVolume, only answers the question in the header, but I was waiting for an answer to my follow-up question addressed to NadVolume. It seems that Wrongfilter gives a positive answer, by two theoretical examples: the wobbling drop of water, and the rotating barbell (besides the empirical example of a pair of orbiting black holes). ] (]) 19:21, 21 October 2024 (UTC)
::::::::How is the center of mass of the rotating barbell not at rest? The distribution of mass in the volume it rotates within changes, but if it's rotating around the center of mass, isn't the center of mass stationary? -- ] (]) 22:28, 21 October 2024 (UTC)
:::::::::There may be a misunderstanding here about what a gravitational wave is like. It does not push and pull in the direction from which it comes - it is polarized and squishes and stretches at right angles to its path. If what the observer sees is symmetric then they won't see gravitational waves. ] (]) 23:47, 21 October 2024 (UTC)
::::::::::I did not say (or at least tried not to say) that the CM of the barbell is not at rest, quite the opposite. The rotating barbell is not spherically symmetric but still has some symmetry. My comment was triggered by the word "asymmetric", which I think is not entirely appropriate, and then tried to illustrate systems with a varying quadrupole moment. --] (]) 05:52, 22 October 2024 (UTC)
:::::::::::Got it - thanks for the clarification, and sorry for misreading! -- ] (]) 22:34, 22 October 2024 (UTC)
]
= October 21 =
]
What causes the discharge tubes to have their brightest spots at different positions? ] (]) 13:12, 31 December 2024 (UTC)
: See also the pictures at ]. --] (]) 13:26, 31 December 2024 (UTC)
== datetime for cub birth ==
= January 1 =
when did this happen. date? time? story out oct-21 but it doesn't say time of event. .... it's for ]. -- ] (], ]) 04:41, 21 October 2024 (UTC)
== Two unit questions ==
:Such news articles are based on press releases put out by the organizations featured in the news, in this case ]. Large parts of it are taken from a on Cotswold's website. The latter also does not mention when the young was born. The release date of this news item was likely inspired by World Lemur Day being celebrated on the last Friday of October, this year 25 October, and a reasonable guess it was released just before the article in ''The Guardian'' was published, which has publication date 20 October. The "Park News" item features a photo whose caption reads, "The Greater Bamboo Lemur Baby bred at Cotswold Wildlife Park – aged 5 weeks", so the baby probably arrived near mid-September. Since the park has successfully bred more than 70 lemurs,<sup></sup> this is not Earth-shattering news that deserves careful attention. --] 06:10, 21 October 2024 (UTC)
::Thanks for checking. The 5 weeks age helps. ] (], ]) 06:47, 21 October 2024 (UTC)
:: {{Tq|1="successfully bred more than 70 lemurs"}} Different species. As the linked article says, "Only 36 ]s are in captivity globally". <span class="vcard"><span class="fn">]</span> (<span class="nickname">Pigsonthewing</span>); ]; ]</span> 13:25, 22 October 2024 (UTC)
#Is there any metric unit whose ratio is not power of 10, and is divisible by 3? Is there any common use for things like "{{frac|2|3}} km", "{{frac|5|12}} kg", "{{frac|3|1|6}} m"?
== Why do we use 12 o'clock to represent midnight and noon? ==
#Is a one-tenth of nautical mile (185.2 m) used in English-speaking countries? Is there a name for it?
--] (]) 10:41, 1 January 2025 (UTC)
:1 not that I know of (engineer who has worked with SI for 50 years)
It occurred to me recently that the way we number and label hours is rather odd. We divide the day into two twelve-hour sections, starting at midnight and noon, but we number the hours starting an hour after that. This leads to various oddities: 11am is followed by 12''pm'', not 12am; likewise 11pm is followed by 12''am'' (something that people often get confused about). 11:59pm and 12:01am are different days, despite the numbering logically implying that they are part of the same day. If the 12-hour clock was invented now, I suspect we would define midnight and noon as ''zero'' hours, but the concept of 12-hour semi-days predates the concept of zero. But given the way things were typically numbered in the absence of zero, and the way we still number dates, it occurred to me that it would be more sensible, and more expected, to use 1 o'clock to mark the start of the day, and the start of the afternoon. (That would give us a morning running from 1:00am to 12:59am, and an afternoon running from 1:00pm to 12:59pm. No weird flipping between am and pm at 12, all consecutive numbers are in the same semi-day). So I'm wondering: why was the modern notation adopted? I've looked at ] and ] but they don't explain why this system was adopted, only that it started to become common in the 14th century, displacing the earlier system of using twelve (seasonally-varying) hours for the period of sunrise to sunset. ] (]) 15:12, 21 October 2024 (UTC)
:2 not that I know of (yacht's navigator for many years on and off)
:This doesn't answer your question, but in Japanese usage 午前12時 ("12am") means noon and 午後12時 ("12pm") means midnight. Also possible are 午前0時 ("0am") for midnight and 午後0時 ("0pm") for noon. :) ] (]) 15:17, 21 October 2024 (UTC)
:] (]) 11:35, 1 January 2025 (UTC)
::Japanese time is high IQ! Not only does it do XX:XX to 24:00 like much of the world instead of XX:XX to 0:00 or 00:00 it also does things like this bar's open 16:00 to 28:00 or "trains run till 25:00". Mechanical clocks once had only hour hands and had to have their drift fixed every day with a glance at a sundial, it took a long time for people to stop thinking in Roman numerals and "this is the first hour" instead of "it's 12:27". If all civilizations had 0 clocks would probably not illogically have a 1 at the top instead of 0. Also am and pm mean ante and post meridian, they CAN'T change at 1:00. After the noon meridian not midnight cause the Sun's midnight meridian crossing is invisible unless midnight is in the day. ] (]) 16:15, 21 October 2024 (UTC)
::In Finland, ''kaapelinmitta'' is 185.2 m. Is there an English equivalent? --] (]) 18:11, 1 January 2025 (UTC)
:Time is measured continuously: it's now 8 hours plus 32 minutes plus 7 seconds past midnight and this is only the case for a single moment. Days are counted discretely: it's now the 22nd day of the 10th month of the 2024th year since the epoch and this is the case for the entire day. That's why time starts at 0 and dates at 1. It's also why time is in ] order and date in little endian in most European languages. ] (]) 08:32, 22 October 2024 (UTC)
:::]. --] (]) 18:26, 1 January 2025 (UTC)
: {{Tq|11am is followed by 12''pm''}} It is not, it is followed by noon. And then by 12:01pm.
: {{Tq|11pm is followed by 12''am''}} It is not, it is followed by midnight. And then by 12:01am.
: {{Tq|something that people often get confused about}} Well, quite.
: There are no such things as 12am or 12pm, ''by definition''.
: It may help to clear your confusion if you consider what "am" and "pm" mean. "Before meridian" and "after meridian". In other words, before/after noon. <span class="vcard"><span class="fn">]</span> (<span class="nickname">Pigsonthewing</span>); ]; ]</span> 09:49, 22 October 2024 (UTC)
:::"There are no such things as 12am or 12pm, ''by definition''" - an exception being in the datetime libraires of programming languages where they are defined. ] (]) 10:55, 22 October 2024 (UTC)
::::My dictionary defines various gods. They don't exist either. <span class="vcard"><span class="fn">]</span> (<span class="nickname">Pigsonthewing</span>); ]; ]</span> 13:01, 22 October 2024 (UTC)
:::::There are probably some people out there that approach the whole 12am/12pm issue from a mathematical Platonist perspective. ] (]) 14:51, 22 October 2024 (UTC)
::::::"Time is an illusion; lunchtime, doubly so."
::::::—Douglas Adams, '']''
:::::::--] (]) 15:50, 22 October 2024 (UTC)
::Assistance is available at ]. In some applications of the 24-hour clock, midnight is denoted as 0000 or 00:00, rather than 1200 or 12:00. There is a lot of logic in that! ] ''(])'' 10:49, 22 October 2024 (UTC)
:::''In some applications of the 24-hour clock''. Isn't this the case for all applications of the 24-hour clock? I've never seen one that doesn't use 00:00, and if there was an exception, I would expect it to be using 24:00. ] (]) 12:25, 22 October 2024 (UTC)
::Your typical digital clock will display non as 12:00PM, not 12:00. There is an infinitesimally short period of time at exact noon when it is neither AM nor PM. But for your typical digital clock (with minute-precision) there will be a whole minute (minus that infinitesimal) where it is showing 12:00 post meridian, so use of that PM is probably not unreasonable. ] (]) 12:23, 22 October 2024 (UTC)
:I think the South Koreans used to say people were in their first year when they were born but the west has always said they were no years old until theiy were one year old. Clocks follow that western rule. ] (]) 11:52, 22 October 2024 (UTC)
::Yup, see ]. ] (]) 13:07, 22 October 2024 (UTC)
:::That system is the one used worldwide for horses, irrespective of whether they were foaled in the northern or southern hemisphere. All share a common birthday - 1 January. Lots of previous discussion ] and ] ] (]) 16:17, 22 October 2024 (UTC)
:Timekeeping systems are all ] human systems, defined by humans—though (usually) linked to one or more "real-world" physical referent(s). Which makes this more of a Humanities desk question. This is the thing that people are to some degree going in circles about here. The only stuff that's physically "real" as in, the consequences of underlying invariant physical laws existing outside of humans, time-wise, are ] and the things embedded in it, which we humans model and interpret using tools like ]s and ]. (In ] time passes more quickly than stuck down here, b/c time is relative. So don't take a trip up to orbit if you really wanna "make every minute last"!)
:A "]" if defined as, one full spin of Earth about its major axis, ]; we just pretend it does for convenience (humans like nice simple round numbers) and occasionally arbitrarily adjust our major timekeeping systems to compensate for the accumulating ]. More starkly ]. ] "okay now it's instantly like 2 weeks later. ] based on just, once in a while we change the current "era" and now it's a new one, and still does ceremonially though they cut back on the frequent "time-skips". Etc etc. --] (]) 16:45, 22 October 2024 (UTC)
:::A full spin of Earth about its major axis is a ], which is closer to 23 hours, 56 minutes and 4 seconds. ] adjustments are not made arbitrarily, but to keep our clocks in sync with solar time. --] 06:00, 23 October 2024 (UTC)
::Japan also had a year count that's approaching 2700 now but the Western year count's been more popular for awhile. The era system can cause cool names like calling a skilled sportsman Monster of the Reiwa Era. But also causes 1926-89 to be named for a semi-figurehead who didn't try to reduce evil till he sped up surrender when he was 44. ] (]) 22:15, 22 October 2024 (UTC)
:::Apparent misunderstanding here. All clocks other than atomic clocks (including radio-controlled ones) tick mean solar time. That's because they are not capable of doing anything else. Your sundial, naturally enough, cannot show anything other than apparent solar time, but over the long term that's the same as mean solar time (that's why it's called mean solar time). Coordinated Universal Time is Atomic Time plus an offset (regulated by means of the leap second) which keeps it so close to mean solar time that nobody can tell the difference. This is why all countries (bar a handful that don't) use mean solar time. It avoids argument:
::::Good article. I was wrong ] (]) 22:26, 1 January 2025 (UTC)
:Traffic warden: You are allowed to park for one hour. You overstayed by one second.
:::The answer can be found by looking up '']'' on Wiktionary. --] 00:14, 2 January 2025 (UTC)
:Motorist: No I didn't. I parked at 12 midnight and left at 1 AM.
:Warden: Yes you did. There are sixty minutes in an hour. You parked at 12:00:00 and your time expired at 12:59:60. You left a second later.
== What is more physiological (for a right-hander) left-hand drive or right-hand drive? ==
As little as once or twice a month your radio-controlled clock is adjusted by means of a radio signal to show Coordinated Universal Time. Twice a year the signal adjusts it to show (or stop showing) what is in effect "Coordinated Universal Summer Time" (although nobody calls it that). ] (]) 11:19, 23 October 2024 (UTC)
Has anyone determined whether it is better for a right-hander to have the left hand on the steering wheel and the right hand on the gear shift stick, or the other way round? Are there other tests of whether left-hand drive or right-hand drive is physiologically better (for a right-hander at least)? ] (]) 12:03, 1 January 2025 (UTC)
= October 22 =
:<small>Supplementary question: I've only driven right-hand-drive vehicles (being in the UK) where the light stalk is on the left of the steering column and the wiper & washer controls are (usually) on the right. On a l-h-drive vehicle, is this usually the same, or reversed? {The poster formerly known as 87.81.230.195} ] (]) 12:12, 2 January 2025 (UTC)</small>
== Although neutrinos can't interact with photons, can photons deliver momentum to neutrinos, via electrons as intermediaries which receive it from photons and deliver it to neutrinos? ==
::<small>Modern cars are designed for mass production in RH- and LH-drive versions with a minimum difference of parts. Steering columns with attached controls are therefore unchanged between versions. ] (]) 12:29, 2 January 2025 (UTC)
:::In the UK nowadays, are cars still mostly manual transmission, or has automatic become the norm? ←] <sup>'']''</sup> ]→ 12:38, 2 January 2025 (UTC)
::::In the UK, sales of new automatics have just recently overtaken manuals - so probably still more manuals than automatics on the road. ] (]) 14:37, 2 January 2025 (UTC)</small>
:::::<small>This may be tied to the rise of EVs, since they have automatic transmissions by default. {The poster formerly known as 87.81.230.195} ] (]) 05:29, 3 January 2025 (UTC)</small>
:::In Australia, we drive on the left, and the indicator and wiper stalks are the opposite way to the UK. Having moved back from the UK after 30 years, it took me a while to stop indicating with wipers. ] (]) 05:08, 3 January 2025 (UTC)
::::This depends more on where the car came from I think. For European or American cars it tends to be in the UK direction. For Asian cars or I guess those odd Australian made cars which are out there, it tends to be in the other. See e.g. . The UK being a bigger market I think most manufacturers have come to follow the new UK norm for cars they intend to sell there although I suspect to some extent it's still true in the sense that I think most Asian car brands, at least assemble their cars in the EU or maybe the UK if they're destined for the UK (made a lot of sense pre-Brexit) . It sounds like the new UK norm is fairly recent perhaps arising in the 1980s-1990s after European manufacturers stopped bothering changing that part of the production for the reasons mentioned by Philvoids. As mentioned in one of the Reddit threads, the UK direction does make it difficult to adjust indicators while changing gear which seems a disadvantage which is fairly ironic considering the the UK has much more of a preference for manuals than many other RHD places with the other direction. ] (]) 04:31, 6 January 2025 (UTC)
:::::<small><p>For further clarity, AFAICT, LHD vehicles generally have their indicators on the left and wipers on the right. As mentioned, assuming the gear stick is in the middle which AFAIK it is for most cars by now, this seems the better positioning especially on manual cars since you're much more likely to want to need to indicate while changing gear than you are going to want to adjust your wipers even in the rainy UK. The UK being LHT/RHD especially with their own manufactured cars tended to have the indicators on the right and wipers on the left in the more distant past so again the positions that made most sense. </p><p>While I don't have a source for this going by the history and comments, it sounds to me like what happened is European manufacturers who were primarily making LHD vehicles, with the UK and Ireland their main RHD markets but still small compared to the LHD market stopped bothering changing positions for RHD vehicles as a cost saving measure. So they began to put wipers on the right and indicators on the left even in their RHD vehicles no matter the disadvantage. I'm not so sure what the American manufacturers did or when and likewise the British but I think they were a fairly small part of the market by then and potentially even for them LHD was still a big part of their target market. </p><p>Meanwhile Asian manufacturers however still put their indicators on the right and wipers on the left in RHD vehicles, noting that Japan itself is LHT/RHD. I suspect Japanese manufacturers suspected, correctly, that it well worth the cost of making something else once they began to enter the LHD markets like the US, to help gain acceptance. And so they put the indicators on the left and wipers on the right for LHD vehicles even if they did the opposite in their own home market and continued forever more. Noting that the predominance of RHT/LHD means even for Japanese manufacturers it's generally likely to be their main target by now anyway. </p><p>Later I assume South Korea manufacturers and even later Chinese felt it worth any added cost to increase acceptance of their vehicles in LHT/RHD markets in Asia and Australia+NZ competing against Japanese vehicles which were like this. And this has largely continued even if it means they need to make two different versions of the steering column or whatever. It sounds like the European and American brands didn't bother but they were primarily luxury vehicles in such markets so it didn't matter so much. </p><p>This lead to an interesting case for the UK. For the Asian manufacturer, probably many of them were still making stuff which would allow them to keep putting the indicators on the right and wipers on the left for RHD vehicles as they were doing for other RHD markets mostly Asian. And even if they were assembling them in the EU, I suspect the added cost of needing to ship and keep the different components etc and any difference it made to the assembly line wasn't a big deal. </p><p>So some of did what they were doing for the Asian markets for vehicles destined for UK. If they weren't assembling in the EU, it made even more sense since this was likely what their existing RHD assembly line was doing. But overtime the UK basically adopted the opposite direction as the norm no matter the disadvantages to the extent consumers and vehicle enthusiast magazines etc were complaining about the "wrong" positions. So even Asian manufacturers ended up changing to the opposite for vehicles destined to the UK to keep them happy. So the arguably better position was abandoned even in cases where it wasn't much of a cost saving measure or might have been even adding costs. </p><p>] (]) 05:43, 6 January 2025 (UTC)</p></small>
::I've driven different (automatic) left-hand-drive vehicles with the light stalk on each side, but left side has been more common. Perhaps because the right hand is more likely to be busy with the gear shift? (Even in the US, where automatic has been heavily dominant since before I learned to drive.) -- ] (]) 17:32, 2 January 2025 (UTC)
:It's better for a right-hander to have both hands on the steering wheel regardless of where the gear lever is. See . I suspect the same goes for a left-hander. ] (]) 14:39, 2 January 2025 (UTC)
::I suppose that the question is whether right-handers have an easier time operating the gear stick when changing gears in manual-transmission cars designed for left-hand traffic, with the steering wheel on the right (like in the UK) or right-hand traffic, with the steering wheel on the left (like in most of continental Europe). Obviously, drivers will use their hand at the side where the gear stick is, so if it is in the middle and the driver, behind the wheel, sits in the right front seat, they'll use their left hand, regardless of their handedness. But this may be more awkward for a rightie. Or not.
::--] 16:30, 2 January 2025 (UTC)
:::In my personal experience (more than 10 years driving on each side of the road, in all four combinations of car handedness and road handedness) the question which hand to use for shifting gears is fairly insignificant. Switching from one type of car to the other is a bit awkward though. —] (]) 18:33, 2 January 2025 (UTC)
::::My first car, a ], had the gearstick on the left and the handbreak on the right, which was a bit of a juggle in traffic. ] (]) 19:13, 3 January 2025 (UTC)
== Distinguishing a picture of a sunset from the picture of a sunrise? ==
Something that reminds of ] (yet not exactly of course). ] (]) 16:06, 22 October 2024 (UTC)
Is there a way (if you don't know which way is west and which way is east in a particular location) to distinguish a picture of a sunset from the picture of a sunrise? ] (]) 12:08, 1 January 2025 (UTC)
:This is the kind of thing that ]s were invented for. You can have a neutrino and a photon going in, a neutrino and a photon going out, and all kinds of other particles running around in a loop in the middle. See for example (paywalled unfortunately). --] (]) 17:21, 22 October 2024 (UTC)
::{{small|I gotcha covered on the link there {{;)}} --] (]) 17:32, 22 October 2024 (UTC)}}
:Generally, no, but there are a few tricks that sometimes work. In dry sunny weather, there's more dust in the air at sunset (due to thermals) than at sunrise, making the sky around the sun redder at sunset. But in moist weather, mist has the same effect at sunrise. If the picture is good enough to see ], comparing the distribution of sunspots to the known distribution of that day (this is routinely monitored) tells you where the North Pole of the sun is. At sunset, the North Pole points somewhat to the right; at sunrise, to the left. If you see any ] or ] clouds in the picture, it was a sunset, as such clouds form during the day and disappear around sunset, but absence of such clouds doesn't mean the picture was taken at sunrise. A very large cumulonimbus may survive the night. ] clouds are often very large, expanding into ], in the evening, but are much smaller at dawn as there's more air traffic during the day than at night, making the upper troposphere more moist towards the end of the day. Cirrostratus also contributes to red sunsets and (to lesser extend, as there's only natural cirrostratus) red sunrises. ], ], flowers and flocks of birds may also give an indication. And of course human activity: the beach is busier at sunset than at sunrise. ] (]) 13:41, 1 January 2025 (UTC)
:Why can't they interact? Both photons and neutrinos participate in the ]. Difficulty: that ] is gonna be ''really'' small. ] may be also of interest. But yes, the aforementioned besides, if you have a whole ''lot'' of photons and can make them go where you want and give them arbitrary energies, you can make the photons do all kinds of neat tricks with each other such as popping out other particles: see ]. The ''truly'' "high-energy physics" processes in our universe such as ]s and ]s and ] do plenty of this kind of stuff. (Another whopper is that we're now fairly sure type II supernovas are in essence "powered" mostly '''''by the neutrino burst!''''' The core collapse releases such a staggering amount of neutrinos that, and not have anything else kill you, ''you would be killed by the '''fatal neutrino radiation!''''' As they say there, a phrase that just ''looks wrong'' if you know what it's talking about. Similarly: an "average supernova" releases about {{10^|57}} neutrinos, 10 followed by a mere ''57'' zeroes. Kind of like: a "modest planetary collision" will ]. (And one hypothesis is, the reason ] is that an even bigger impact happened to ''it''!) --] (]) 17:29, 22 October 2024 (UTC)
::Supposing the photograph has high enough resolution to show ]s it can be helpful to know that the pattern of spots at sunrise is reversed left-right at sunset. ] (]) 13:21, 3 January 2025 (UTC)
::{{tq|Why can't they interact? Both photons and neutrinos participate in the ]}} It seems that your question is addressed (also) to yourself, i.e. to what you wrote ] ] (]) 18:17, 22 October 2024 (UTC)
:::At the equinox, the disk of the Sun with its pattern of sunspots appears to rotate clockwise from sunrise to sunset by 180 degrees minus twice your latitude (taking north positive). At my place, that's 75 degrees. Other times of the year it's less; at the start and end of polar day and polar night, there's no rotation. Sunset and sunrise merge then.
::Is it true the Pacific's where the Mars-sized moonmaker hit non-head on splashing off lava and boiled lava? I thought only continental crust can survive that long. ] (]) 22:21, 22 October 2024 (UTC)
:::And I forgot to mention: cirrostratus clouds will turn red just after sunset or just before sunrise. At the exact moment of sunrise or sunset, they appear pretty white. ] (]) 17:06, 3 January 2025 (UTC)
::: If so it's not mentioned at our ] article, nor the ] one. I would have been surprised if that were true; I assumed that the Earth's entire surface was liquid for a while after the impact so there shouldn't be any remaining localized remnant. But I could be completely wrong about that. --] (]) 22:56, 22 October 2024 (UTC)
::::I differ: the same rotation is involved everywhere on Earth. If you stand on tiptoe at a N. or S. pole to take a picture of the Sun it is you who must pirouette 15 degrees per hour to keep facing the Sun. The Earth rotates you at this rate at all non-polar locations. If you stand within the arctic or antarctic circles, for parts of the year the 24-hour night or 24-hour daylight seem to prevent photographs of sunrise or sunset. However the terms "sunrise" and "sunset" can then be interpreted as times that are related to particular timezones which are generally assigned by longitude. In photographing the 24-hour Sun the equatorial rise and set times for your own longitude are significant elevation maxima worth mentioning even though the minimum elevation remains above the horizon. I maintain that the sunspot pattern observed from any location on Earth rotates 360 degrees per 24 hours and that "night", the darkness from sunset to sunrise, is when the Earth's bulk interrupts one's view of the rotation but not the rotation itself which is continuous.
:::That's ] But seeing as >4 bil ybp, there was no such thing as "the Pacific Ocean"... I dunno? Is this based on some specific thing from somewhere? A ''mere'' 220 mya ] with no major landmasses apart from "the one place where all the land is". If I recall right the hypothesized Theia impact is predicted to maybe have re-liquified Earth's entire crust, even ''vaporizing'' some of it to produce a temporary "rock vapor atmosphere", another one of those "phrases that just sound crazy". ('''''Excellent''''' band name up for grabs there btw) --] (]) 23:02, 22 October 2024 (UTC)
:::::Taking the Earth as reference frame, the Sun rotates around the Earth's spin axis. The observer rotates around his own vertical axis. The better both axes are aligned, the smaller the wobble of the Sun. In the northern hemisphere, it rotates clockwise from about 6 till 18 by 180 degrees minus twice your latitude and counterclockwise at night, in the southern hemisphere it's the opposite. Try a planetarium program if you want to see it. ] shows some sunspots, does things right and is free and open source. ] (]) 10:27, 5 January 2025 (UTC)
::::I heard that somewhere maybe whoever thought it was just ignorant? ] (]) 00:20, 23 October 2024 (UTC)
:::::]We deprecate the obselete ] and suggest Misplaced Pages references that are free and just one click away (no extra planetarium software needed). The axes of rotation of the Sun and Earth have never in millions of years aligned: the ] is the orbital plane of Earth around the Sun and Earth currently has an ] of about 23.44° without "wobbling" enough from this to concern us here. ] (]) 14:56, 5 January 2025 (UTC)
::{{Tpq|we can propose sending photons "this way" and neutrinos "that way", such that their worldlines at some point intersect, but we would expect to observe nothing ('''other than the extremely minute effects''' of their gravitational and weak interactions),}} (emphasis added). Okay, I was being a tad pedantic, but, being precise can matter for Science Stuff. You're the one proposing hypothetical scenarious here—you could always say "here, we're gonna fire ''enough'' photons such that their weak interactions w/ matter start adding up" (like in a supernova). Alternately if you just want to ask, "can photons and neutrinos interact with each other at all, directly or indirectly" just ask that and skip the trouble of crafting undergrad physics textbook study problems. (Keep in mind, people here are volunteering to devote some of their own time to responding to questioners' queries.) --] (]) 23:02, 22 October 2024 (UTC)
::::::This isn't my field but sunspots aside, if you know the location and date, I assume the appearance of other astronomical objects like the moon or rarely another star probably Venus, in the photograph should be enough to work out if it's a sunset or sunrise. That said, to some extent by taking into account other details gathered from elsewhere's I wonder if we're going beyond the question. I mean even if you don't personally know which is east or west at the time, if you can see other stuff and you know the location or the stuff you can see is distinctive enough it can be worked out, you can also work out if it's sunset or sunrise just by working out if it's east or west that way. ] (]) 03:54, 6 January 2025 (UTC)
:::Oh sorry, I did read what you had written in parentheses "other than the extremely minute effects of their gravitational... interactions", but for some unknown reason I didn't notice the crucial words "and weak interactions". So you're right, sorry.
:::::In my experience (Southern England) they tend to be pinker at dawn and oranger(!) at dusk. {The poster formerly known as 87.81.230.195} ] (]) 03:23, 4 January 2025 (UTC)
:::As for the two-photon physics you've mentioned: Well, AFAIK, two photons can turn into electron-positron (or muon-antimuon, tauon-anti-tauon), but never (directly) into neutrino-anti-neutrino. The same it true for the opposite direction: If a neutrino collides with its anti-particle, the direct result may be Z-boson, not photons (and with regard to what you wrote in your last parentheses: Of course, indeed you are always invited to remove my misunderstanding, but are never obligated to do that). ] (]) 00:24, 23 October 2024 (UTC)
::::::Pink clouds must result from blending of reddish clouds with the blue sky behind. There's actually more air between the observer and the clouds than behind the clouds, but for that nearby air the sun is below the horizon. ] (]) 10:27, 5 January 2025 (UTC)
::That makes my (new) list of most exotic way to shuffle off this mortal coil. ] (]) 00:07, 23 October 2024 (UTC)
::::The questioner asks for interpretation of a single picture. It is beside the point that more would be revealed by a picture sequence such as of changing cloud colours. ] (]) 12:41, 4 January 2025 (UTC)
<small>
:Recalling Leonard Maltin's comment about the ''Green Berets'' movie, which was filmed in the American state of Georgia: "Don't miss the closing scene, where the sun sets in the east!" ←] <sup>'']''</sup> ]→ 22:37, 5 January 2025 (UTC)
::Victim ]]: Hello?
::Which you can only tell if you know which way is east in the image. Maltin, or his writer, appears to have assumed that Vietnam has a seacoast only on the east, which is wrong. --] (]) 03:46, 6 January 2025 (UTC)
::St. Peter: Sorry, guy. There's no room at the inn for you. Have you tried the Other Place?
:::Georgia has only an eastern seacoast. ←] <sup>'']''</sup> ]→ 10:31, 6 January 2025 (UTC)
::Victim: But, but I'm high up on ]!
::::<small>] ] (]) 14:18, 6 January 2025 (UTC)</small>
::St. Peter: That cuts no ice up here.
::::So what. Bugs? The claim is about the setting, not the filming location. --] (]) 07:30, 7 January 2025 (UTC)
::Victim : Uh, I was struck down by neutrinos!
:::::But as it was filmed in (The US State of) Georgia, it must actually show a sunrise, regardless of what the story line says – how do you know that wasn't what Maltin actually meant? {The poster formerly known as 87.81.230.195} ] (]) 10:35, 7 January 2025 (UTC)
::St. Peter: Way cool, dude! Okay, I can make an exception for you. Just don't tell anyone. ] (]) 03:07, 23 October 2024 (UTC)
</small>
= January 6 =
== Does the energy belonging to an electromagnetic field, also belong (or is considered to belong) to the space carrying that field? ==
= October 24 =
] (]) 18:41, 6 January 2025 (UTC)
== Default multiplication tables in schools worldwide ==
:It would be unusual to express the situation in such terms. Since the notion of energy "belonging to" some entity is not itself a physical concept – any practical approach to energy bookkeeping that satisfies the law of conservation of energy will do – this cannot be said to be wrong. It is, however, (IMO) not helpful. Does an apple belong to the space it occupies? Or does that space belong to the apple? --] 23:37, 6 January 2025 (UTC)
According to ], in the English-speaking world schools use 1-12 multiplication tables, or 1-9. Can this maybe be distinguished between countries? In German-speaking Europe, schools use 1-10 by default. For sure in many countries they start with 0. What's the situation in different countries worldwide? --] (]) 08:37, 24 October 2024 (UTC)
::First, I let you replace the notion of energy "belonging to" some entity, by the notion of energy "attributed to" some entity, or by the notion of energy "carried by" some entity, and the like. In other words, I'm only asking about the abstract relation (no matter what words we use to express it), between the energy and the ''space'' carrying the electromagnetic field, rather than about the specific term "belong to".
::Second, I'm only asking about ''what the common usage is'', rather than about whether such a usage is wrong or helpful.
::The question is actually as follows: Since it's ''accepted'' to attribute energy to an electromagnetic field, is it also ''accepted'' to attribute energy to the ''space'' carrying that field?
::So, is your first sentence a negative answer, also to my question when put in the clearer way I've just put it? ] (]) 03:28, 7 January 2025 (UTC)
= January 7 =
:Wait, why would one start a multiplication table with zero? <span style="border-radius:2px;padding:3px;background:#1E816F">]<span style="color:#fff"> ‥ </span>]</span> 08:43, 24 October 2024 (UTC)
::I guess so that every possible product of two digits is included. ] (]) 09:36, 24 October 2024 (UTC)
:Why would one start multiplication tables with 1? We started with 2. ]|] 09:00, 24 October 2024 (UTC)
::Ok, and where did you go to school, please? --] (]) 11:02, 24 October 2024 (UTC)
:The curriculum in the UK is ].
:The includes multiplication tables up to 12 × 12 (no word on whether 0 or 1 are included as tables, but multiplying by 0 or 1 is included).
:Wales (at least partly English speaking), up to 10x10
:Scotland 12.
:Northern Ireland doesn't explicitly have multiplication tables, but "multiplication facts up to 10 x 10".
:My understanding is that education is a state matter in the USA so maybe there are 50 different curricula?
:] (]) 11:31, 24 October 2024 (UTC)
:US states generally delegate to school districts, so each county or township has its own standards (and then there are tons of non-public schools). But there are a few standard curricula or textbooks that many of them use, and regardless of approach many follow the same or similar broad standards. And finally, it's sometimes just a semantic difference whether it's called part of the "table" or just a loose fact. Some relevant articles:
:*]
:*] (3.OA.C.7 specifies "By the end of Grade 3, know from memory all products of two one-digit numbers.")
:*] (popular in some parts of the US)
:Some lead refs:
:*{{cite book |doi=10.1007/978-3-030-28561-6_6 |chapter=Teaching the Multiplication Table and Its Properties for Learning How to Learn |title=Teaching Multiplication with Lesson Study |date=2021 |last1=Olfos |first1=Raimundo |last2=Isoda |first2=Masami |pages=133–154 |isbn=978-3-030-28560-9 }}
:*{{cite journal |doi=10.1186/s41235-022-00451-0|doi-access=free |title=Elementary math in elementary school: The effect of interference on learning the multiplication table |date=2022 |last1=Dotan |first1=Dror |last2=Zviran-Ginat |first2=Sharon |journal=Cognitive Research: Principles and Implications |volume=7 |issue=1 |page=101 |pmid=36459276 |pmc=9716515 }}
:*{{cite book |doi=10.1007/978-3-030-28561-6 |title=Teaching Multiplication with Lesson Study |date=2021 |isbn=978-3-030-28560-9 |editor-last1=Isoda |editor-last2=Olfos |editor-first1=Masami |editor-first2=Raimundo }}
:] (]) 11:57, 24 October 2024 (UTC)
::It's been a long time since I was at school but I dimly remember the multiplication tables in the booklet went up to 13x13 though we only had to learn up to 12x12. ] (]) 12:40, 24 October 2024 (UTC)
:::The 12 times table had a greater significance in my primary school days, since there were 12 pence in a ] in those days. ] (]) 14:10, 24 October 2024 (UTC)
::::Ditto. Learning the 13 and 17 times tables might be of some value; the others can be trivially derived mentally by doubling (e.g. 9x14 = (9x7)x2) and similar expedients, or for nx19 ((nx10)x2)-n. {The poster formerly known as 87.81.230.195} ] (]) 12:44, 27 October 2024 (UTC)
= October 26 =
== Launch site identification ==
I am currently on a bridge on the ] facing north, getting ready to view the Spacex launch later today.
But I am not sure which one is the launch site that I should be looking at. I spotted 5 points of interest (labelled A to E), and I can only positively identify A as the kennedy space center (which is not today's launch site).
I would really appreciate it if someone can tell me whether I should be looking at BCD or E. And also I'm interested to learn what BCDE each are. ] (]) 20:09, 26 October 2024 (UTC)
:My exact location is 28.405476616667123, -80.65458604061091. ] (]) 20:31, 26 October 2024 (UTC)
= October 27 =
== Can ]s (if exist) decay, if virtual particles do not really exist? ==
The background of my question is the following two facts:
Our artricle ] states: {{Tq|The production and decay of sterile neutrinos could happen through the mixing with virtual ("off mass shell") neutrinos}}.
While our article ] states: {{Tq|they are by no means a necessary feature of QFT, but rather are mathematical conveniences — as demonstrated by lattice field theory, which avoids using the concept altogether.}}
] (]) 06:34, 27 October 2024 (UTC)
:The statement that "x could happen if y" does not in itself exclude the possibilities that (absent y) x could ''also'' happen if z, or w, etc. Frankly, this is all so deep in the Jungles of Conjecture (that vast expanse beyond the Mountains of Hypotheses) that definitive answers probably don't yet exist, and Nobel prizes will probably be given for finding answers to such questions. Or so I think: perhaps some post-doctoral particle physicist will correct me. {The poster formerly known as 87.81.230.195} ] (]) 12:53, 27 October 2024 (UTC)
::As for your first sentence: Of course. I didn't think otherwise. ] (]) 13:04, 27 October 2024 (UTC)
== Global deforestation runoff ==
What is the global deforestation runoff in km3, which is part of the 40k km3 of global runoff* in general?
*Trenberth KE, Smith L, Qian T, Dai A, Fasulo J (2007). Estimates of Global Water Budget and Its Annual Cycle Using Observational and Model Data. Journal of Hydrometeorolgy 8(4):758-769. DOI: org/10.1175/JHM600.1.
] (]) 07:44, 27 October 2024 (UTC)
Latest revision as of 10:35, 7 January 2025
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I would say not necessarily a Japanese beetle, but almost certainly one of the other Scarab beetles, though with 35,000 species that doesn't help a lot. Looking at the infobox illustration in that article, 16. & 17., "Anisoplia segetum" looks very similar, but evidently we either don't have an article or (if our Anisoplia article is a complete list) it's been renamed. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 14:18, 24 December 2024 (UTC)
Yes, it's not the Japanese beetle for this beetle appears to lack its white-dotted fringe although its condition is deteriorated. Its shape is also more or less more slender; and not as round. Modocc (talk) 15:02, 24 December 2024 (UTC)
Any (flavored) neutrino that is really observed is a superposition of two or three mass eigenstates. This is actually the cause of neutrino oscillations. So, the answer to your question is complicated. Ruslik_Zero19:40, 25 December 2024 (UTC)
Important note: particle physicists today generally only ever use "mass" to mean "invariant mass" and never anything else: . Like the term says, invariant mass is well, invariant, it never changes ever, no matter what "external forces" may or may not be involved. Being proper particle-icans and following the standard practice in the field, then, the three neutrino masses are constant values. ..."Wait, three?" Yeah sure, turns out neutrinos come in three "flavors" but each flavor is a mixture of the three possible mass "states". As mentioned, due to Quantum Weirdness we aren't able to get these different states "alone by themselves" to measure each by itself, so we only know the differences of the squares of the masses. Yeah welcome to quantum mechanics.
Richard Feynman: "Quantum mechanics describes nature as absurd from the point of view of common sense. And yet it fully agrees with experiment. So I hope you can accept nature as She is – absurd." --Slowking Man (talk) 06:06, 26 December 2024 (UTC)
The equation uses invariant mass m0 which is constant if E and p are constant. The traveling neutrino has a varying mass mixture of different flavors with different masses. If a mixture of different masses changes, you would expect the resulting mass to change with it. But somehow this does not happen as the neutrino mass mixture changes. These mixture changes cannot be any changes. The changes must be such that the resulting mass of the traveling neutrino remains constant. My question is whether this is described somewhere. Hevesli (talk) 11:16, 26 December 2024 (UTC)
I freely confess I'm uncertain exactly what's being "asked for" or "gotten at" here. Have you looked at the neutrino oscillation article? From it: That is, the three neutrino states that interact with the charged leptons in weak interactions are each a different superposition of the three (propagating) neutrino states of definite mass. Neutrinos are emitted and absorbed in weak processes in flavor eigenstatesbut travel as mass eigenstates.
What is it that we're "doing" with the energy–momentum relation here? For the neutrino, we don't have a single value of "mass" to plug in for , because we can't "see" the individual mass eigenstates, only some linear combination of them. What you want for describing neutrino interactions is quantum field theory, which is special relativity + QM. (Remember, relativity is a "classical" theory, which presumes everything always has single well-defined values of everything. Which isn't true in quantum-world.) --Slowking Man (talk) 18:41, 26 December 2024 (UTC)
Not all potential evolutions of a linear combination of unequal values produce constant results. Constancy can only be guaranteed by a constraint on the evolutions. Does the fact that this constraint is satisfied in the case of neutrino oscillation follow from the mathematical formulation of the Standard Model, or does this formulation allow evolutions of the mass mixture for which the combination is not constant? If the unequal values are unknown, I have no idea of how such a constraint might be formulated. I think the OP is asking whether this constraint is described somewhere. --Lambiam00:51, 27 December 2024 (UTC)
I wanted to try it just today, but I had to exchange the under-desk elliptical trainer I got for Christmas for a different model with more inclined treadles because with the one I got, my knees would hit the desk at the top of every cycle. Anyway, I was hoping someone else tried it first (preferably as part of a formal scientific study) so I would know if I could control whether I got a runner's high from exercise or not? 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:09, 28 December 2024 (UTC)
Also, sorry for adding to my own question, but here's a related one: is it known whether the length of a person's dopamine receptor D4 (which is inversely correlated with its sensitivity) influences whether said person gets a runner's high from exercise (and especially from low-intensity exercise)? 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:14, 28 December 2024 (UTC)
What is the difference between an auxotroph and a fastidious organism? It seems to me the second one would have more requirements than the first one, but the limit between the two definitions is rather unclear to me.
Symbiosis aside, it would seem that most auxotrophs would be fastidious organisms, but there could be many more fastidious organisms that aren't auxotrophs. Auxotrophs specifically can't produce organic compounds on their own. There are a LOT of organisms that rely on the availability of non-organic nutrients, such as specific elements/minerals. For instance, vertebrates require access to calcium. Calcium is an element; our inability to produce it does not make us auxotrophs.
But perhaps symbiosis would allow an organism to be an auxotroph without being a fastidious organism? For instance, mammals tend to have bacteria in our guts that can digest nutrients that our bodies can't on their own. Perhaps some of those bacteria also assemble certain nutrients that our bodies can't? -- Avocado (talk) 14:27, 28 December 2024 (UTC)
December 28
Paper with wrong enantiomer in a figure
In the following reference:
Quack, Martin; Seyfang, Georg; Wichmann, Gunther (2022). "Perspectives on parity violation in chiral molecules: theory, spectroscopic experiment and biomolecular homochirality". Chemical Science. 13 (36): 10598–10643. doi:10.1039/d2sc01323a. PMID36320700.
I saw an ad promoting a device which presumable splits water into
hydrogen and oxygen and infuses water with extra hydrogen, to
a claimed surplus of perhaps 5 ppm, which doesn’t seem like much. I found a review article which looked at several dozen related studies that found benefits:https://pmc.ncbi.nlm.nih.gov/articles/PMC10816294/ .
I’ve noticed that carbon dioxide or chlorine (chloramine?) dissolved in water work their way out pretty easily, so I wonder if dissolved hydrogen could similarly exit hydrogen enriched water and be burped or farted out, rather than entering the blood stream and having health benefits. is it more than the latest snake oil? Edison (talk) 23:01, 28 December 2024 (UTC)
It's conceivable it might take out the chloramine, I guess. I don't think there's very much of it, but it tastes awful, which is why I add a tiny bit of vitamin C when I drink tap water. It seems to take very little. Of course it's hard to tell whether it's just being masked by the taste of the vitamin C. --Trovatore (talk) 02:12, 29 December 2024 (UTC)
I don't know if it is rubbish or not but a quick look on the web indicates to me it is notable enough for Misplaced Pages. I didn't see anything indicating it definitely did anything useful so such an article should definitely have caveats. I haven't seen any expression of a potential worry either so it isn't like we'd be saying bleach is a good medicine for covid. NadVolum (talk) 23:07, 1 January 2025 (UTC)
In a harmonic oscillator, reaching the highest point involves - both a minimal kinetic energy - along with a maximal potential energy, whereas reaching the lowest point involves - both a maximal kinetic energy - along with a minimal potential energy. Thus the mechanical energy becomes the sum of kinetic energy + potential energy, and is a conserved quantity.
So I wonder if it's reasonable to define also "potential velocity" vs. "kinetic velocity", and claim that in a harmonic oscillator, reaching the highest point involves - both a minimal "kinetic velocity" (i.e. involves what we usually call a rest) - along with a maximal "potential velocity", whereas reaching the lowest point involves - both a maximal "kinetic velocity" (i.e. involves what we usually call the actual velocity) - along with a minimal "potential velocity". Thus we can also define "mechanical velocity" as the sum of "kinetic velocity" + "potential velocity", and claim that the mechanical velocity is a conserved quantity - at least as far as a harmonic oscillator is concerned.
Reasonable?
Note that I could also ask an analogous question - as to the concept of "potential momentum", but this term is already used in the theory of hidden momentum for another meaning, so for the time being I'm focusing on velocity.
Per my suggestion, the ratio between distance and time is not called "velocity" but rather "kinetic velocity".
Further, per my suggestion, if you don't indicate whether the "velocity" you're talking about is a "kinetic velocity" or a "potential velocity" or a "mechanical velocity", the very concept of "velocity" alone has no meaning!
On the other hand, "potential velocity" is defined as the difference between the "mechanical velocity" and the "kinetic velocity"! Just as, this is the case if we replace "velocity" by "energy". For more details, see the example above, about the harmonic oscillator. HOTmag (talk) 15:14, 29 December 2024 (UTC)
You could define the potential velocity of a body at a particular height as the velocity it would hit the ground at if dropped from that height. But the sum of the potential and kinetic velocities would not be conserved; rather would be constant. catslash (talk) 18:54, 29 December 2024 (UTC)
'Potential velocity' has no meaning. You seem to be arguing that in a system where energy is conserved, but is transforming between kinetic and potential energy, (You might also want to compare this to conservation of momentum.) then you can express that instead through a new conservation law based on velocity. But this doesn't work. There's no relation between velocity and potential energy.
In a harmonic oscillator, the potential energy is typically coming from some central restoring force with a relationship to position, nothing at all to do with velocity. Where some axiomatic external rule (such as Hooke's Law applying, because the system is a mass on a spring) happens to relate the position and velocity through a suitable relation, then the system will then (and only then) behave as a harmonic oscillator. But a different system (swap the spring for a dashpot) doesn't have this, thus won't oscillate. Andy Dingley (talk) 00:00, 30 December 2024 (UTC)
Let me quote a sentence from my original post: Thus we can also...claim that the mechanical velocity is a conserved quantity - at least as far as a harmonic oscillator is concerned.
You have defined some arbitrary values for new 'velocities', where their only definition is that they then demonstrate some new conservation law. Which is really the conservation of energy, but you're refusing to use that term for some reason.
As Catslash pointed out, the conserved quantity here is proportional to the square of velocity, so your conservation equation has to include that. It's simply wrong that any linear function of velocity would be conserved here. Not merely we can't prove that, but we can prove (the sum of the squares diverges from the sum) that it's actually contradicted. For any definition of 'another velocity' which is a linear function of velocity.
It is a law of conservation of sanity. Lacking a definition of potential energy, other than by having been informed that kinetic energy + potential energy is a conserved quantity, there is not much better we can do. --Lambiam11:20, 31 December 2024 (UTC)
We have a perfectly viable definition of potential energy. For a pendulum it's based on the change in height of the pendulum bob against gravity. For some other oscillators it would involve the work done against a spring. Andy Dingley (talk) 16:33, 31 December 2024 (UTC)
Oops, I mistyped. I meant to write:
"Lacking a definition of potential velocity, other than by having been informed that kinetic velocity + potential velocity is a conserved quantity, there is not much better we can do."
Put two equally sized drops, one of each liquid, on a warm surface, wait for them to evaporate, and compare how much salt residue each leaves? Not very precise or measurable, but significant differences should be noticeable. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 10:21, 30 December 2024 (UTC)
The principle is sound, but the residue from one drop won't be measurable using kitchen equipment -- better to put equal amounts of each liquid in two warm pans (use enough liquid to cover the bottom of each pan with a thin layer), wait for them to evaporate and then weigh the residue! Or, if you're not afraid of doing some algebra, you could also try an indirect method -- bring both liquids to a boil, measure the temperature of both, and then use the formula for boiling point elevation to calculate the saltiness of each! 2601:646:8082:BA0:BD1B:60D8:96CA:C5B0 (talk) 18:22, 30 December 2024 (UTC)
Presumably the liquid preparations are not simple saline solutions, but contain other solutes - or else one could simply use a hydrometer. It is unlikely that Lambian is afraid of doing some algebra. catslash (talk) 18:57, 30 December 2024 (UTC)
Assuming the liquid preparations are water-based and don't contain alcohols and/or detergents one can measure their rates of dispersion. Simply add a drop of food dye to each liquid and then time how rapidly droplets of each liquid disperse in distilled water. Materials needed: food dye, eye dropper, distilled water, small clear containers and a timer.Modocc (talk) 21:09, 30 December 2024 (UTC)
The colligative properties of a solution will indicate its molarity, but not identify the solute. Liquid preparations that might be found in a kitchen are likely to contain both salt and sugar. Electrical conductivity is a property that will be greatly affected by the salt but not the sugar (this does not help in distinguishing Na from K ions though). catslash (talk) 22:23, 30 December 2024 (UTC)
Quantitative urine test-strips for sodium seem to be available. They're probably covering the concentration range of tens to hundreds millimolar. DMacks (talk) 00:58, 2 January 2025 (UTC)
Thanks, test strips seem more practical in the kitchen setting than an ohmmeter (why not call it a "mhometer"?), for which I'd need to devise a way (or so I think) to keep the terminals apart at a steady distance. Test strips require a colour comparison, but I expect that a significant difference in salinity will result in a perceptible colour difference when one strip is placed across the other. Only experiment can tell whether this expectation will come true. Salinity is usually measured in g/L; for kitchen preparations a ballpark figure is 1 g/L. If I'm not mistaken this corresponds to (1 g/L) / (58.443 g/mol) ≈ 0.017 M = 17 mM. I also see offers for salinity test strips, 0–1000 ppm, for "Science Education". --Lambiam11:40, 2 January 2025 (UTC)
Test strips surely come with a printed color-chart. But if all you are trying to do is determine which is more salty, then that's even easier than quantifying each separately. Caveat for what you might find for sale: some "salinity" tests are based on the chloride not the sodium, so a complex matrix that has components other than NaCl could fool it. DMacks (talk) 18:44, 2 January 2025 (UTC)
The (uncommon?) terms "relativistic length", and "relativistic time".
1. In Misplaced Pages, the page relativistic length contraction is automatically redirected to our article length contraction, which actually doesn't mention the term "relativistic length" at all. I wonder if there is an accepted term for the concept of relativistic length.
2. A similar qusestion arises, at to the concept of relativistic time: The page relativistic time dilation, is automatically redirected to our article time dilation, which prefers the abbreviated term "time dilation" (59 times) to the term "relativistic time dilation" (8 times only), and nowhere mentions the term "relativistic time" alone (i.e. without the third word "dilation") - although it does mention the term "proper time" for the shortest time. Further, this article doesn't even mention the term "dilated time" either. It does mention, though, another term: coordinate time, but regardless of time dilation in Special relativity. To sum up, I wonder what's the accepted term used for the dilated time (mainly is Special relativity): Is it "coordinate time"? "Relativistic time"?
Are you reading these things as "contraction of relativistic length" etc.? It is "relativistic contraction of length" and "relativistic dilation of time". --Wrongfilter (talk) 09:37, 30 December 2024 (UTC)
When I wrote: The page relativistic time dilation is automatically redirected to our article time dilation which...nowhere mentions the term "relativistic time" alone (i.e. without the third word "dilation"), I had already guessed that the term "dilation of relativistic time" (i.e, with the word "dilation" preceding the words "relativistic time") existed nowhere (at least in Misplaced Pages), and that this redirected page actually meant "relativistic dilation of time". The same is true for the redirected page "relativistic length contraction": I had already gussed it didn't mean "contraction of relativistic length", because (as I had already written): the article length contraction...doesn't mention the term "relativistic length" at all.
Anyway, I'm still waiting for an answer to my original question: Are there accepted terms for the concepts, of relativistic length - as opposed to proper length, and of relativistic time - as opposed to proper time? HOTmag (talk) 10:12, 30 December 2024 (UTC)
A term that will be understood in the context of relativistic length contraction is relative length – that is, length relative to an observer. --Lambiam10:55, 31 December 2024 (UTC)
Thank you. The middle source uses the term "comparative length", rather than "relative length". I couldn't open the third source. HOTmag (talk) 08:04, 1 January 2025 (UTC)
The text under the graph labelled Comparative length on page 20 of the middle source reads:
Graph of the relative length of a stationary rod on earth, as observed from the reference frame of a traveling rod of 100cm proper length.
Is there any metric unit whose ratio is not power of 10, and is divisible by 3? Is there any common use for things like "2⁄3 km", "5⁄12 kg", "3+1⁄6 m"?
Is a one-tenth of nautical mile (185.2 m) used in English-speaking countries? Is there a name for it?
What is more physiological (for a right-hander) left-hand drive or right-hand drive?
Has anyone determined whether it is better for a right-hander to have the left hand on the steering wheel and the right hand on the gear shift stick, or the other way round? Are there other tests of whether left-hand drive or right-hand drive is physiologically better (for a right-hander at least)? 178.51.7.23 (talk) 12:03, 1 January 2025 (UTC)
Supplementary question: I've only driven right-hand-drive vehicles (being in the UK) where the light stalk is on the left of the steering column and the wiper & washer controls are (usually) on the right. On a l-h-drive vehicle, is this usually the same, or reversed? {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 12:12, 2 January 2025 (UTC)
Modern cars are designed for mass production in RH- and LH-drive versions with a minimum difference of parts. Steering columns with attached controls are therefore unchanged between versions. Philvoids (talk) 12:29, 2 January 2025 (UTC)
In the UK, sales of new automatics have just recently overtaken manuals - so probably still more manuals than automatics on the road. catslash (talk) 14:37, 2 January 2025 (UTC)
This may be tied to the rise of EVs, since they have automatic transmissions by default. {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 05:29, 3 January 2025 (UTC)
In Australia, we drive on the left, and the indicator and wiper stalks are the opposite way to the UK. Having moved back from the UK after 30 years, it took me a while to stop indicating with wipers. TrogWoolley (talk) 05:08, 3 January 2025 (UTC)
This depends more on where the car came from I think. For European or American cars it tends to be in the UK direction. For Asian cars or I guess those odd Australian made cars which are out there, it tends to be in the other. See e.g. . The UK being a bigger market I think most manufacturers have come to follow the new UK norm for cars they intend to sell there although I suspect to some extent it's still true in the sense that I think most Asian car brands, at least assemble their cars in the EU or maybe the UK if they're destined for the UK (made a lot of sense pre-Brexit) . It sounds like the new UK norm is fairly recent perhaps arising in the 1980s-1990s after European manufacturers stopped bothering changing that part of the production for the reasons mentioned by Philvoids. As mentioned in one of the Reddit threads, the UK direction does make it difficult to adjust indicators while changing gear which seems a disadvantage which is fairly ironic considering the the UK has much more of a preference for manuals than many other RHD places with the other direction. Nil Einne (talk) 04:31, 6 January 2025 (UTC)
For further clarity, AFAICT, LHD vehicles generally have their indicators on the left and wipers on the right. As mentioned, assuming the gear stick is in the middle which AFAIK it is for most cars by now, this seems the better positioning especially on manual cars since you're much more likely to want to need to indicate while changing gear than you are going to want to adjust your wipers even in the rainy UK. The UK being LHT/RHD especially with their own manufactured cars tended to have the indicators on the right and wipers on the left in the more distant past so again the positions that made most sense.
While I don't have a source for this going by the history and comments, it sounds to me like what happened is European manufacturers who were primarily making LHD vehicles, with the UK and Ireland their main RHD markets but still small compared to the LHD market stopped bothering changing positions for RHD vehicles as a cost saving measure. So they began to put wipers on the right and indicators on the left even in their RHD vehicles no matter the disadvantage. I'm not so sure what the American manufacturers did or when and likewise the British but I think they were a fairly small part of the market by then and potentially even for them LHD was still a big part of their target market.
Meanwhile Asian manufacturers however still put their indicators on the right and wipers on the left in RHD vehicles, noting that Japan itself is LHT/RHD. I suspect Japanese manufacturers suspected, correctly, that it well worth the cost of making something else once they began to enter the LHD markets like the US, to help gain acceptance. And so they put the indicators on the left and wipers on the right for LHD vehicles even if they did the opposite in their own home market and continued forever more. Noting that the predominance of RHT/LHD means even for Japanese manufacturers it's generally likely to be their main target by now anyway.
Later I assume South Korea manufacturers and even later Chinese felt it worth any added cost to increase acceptance of their vehicles in LHT/RHD markets in Asia and Australia+NZ competing against Japanese vehicles which were like this. And this has largely continued even if it means they need to make two different versions of the steering column or whatever. It sounds like the European and American brands didn't bother but they were primarily luxury vehicles in such markets so it didn't matter so much.
This lead to an interesting case for the UK. For the Asian manufacturer, probably many of them were still making stuff which would allow them to keep putting the indicators on the right and wipers on the left for RHD vehicles as they were doing for other RHD markets mostly Asian. And even if they were assembling them in the EU, I suspect the added cost of needing to ship and keep the different components etc and any difference it made to the assembly line wasn't a big deal.
So some of did what they were doing for the Asian markets for vehicles destined for UK. If they weren't assembling in the EU, it made even more sense since this was likely what their existing RHD assembly line was doing. But overtime the UK basically adopted the opposite direction as the norm no matter the disadvantages to the extent consumers and vehicle enthusiast magazines etc were complaining about the "wrong" positions. So even Asian manufacturers ended up changing to the opposite for vehicles destined to the UK to keep them happy. So the arguably better position was abandoned even in cases where it wasn't much of a cost saving measure or might have been even adding costs.
I've driven different (automatic) left-hand-drive vehicles with the light stalk on each side, but left side has been more common. Perhaps because the right hand is more likely to be busy with the gear shift? (Even in the US, where automatic has been heavily dominant since before I learned to drive.) -- Avocado (talk) 17:32, 2 January 2025 (UTC)
It's better for a right-hander to have both hands on the steering wheel regardless of where the gear lever is. See Rule 160. I suspect the same goes for a left-hander. Bazza 7 (talk) 14:39, 2 January 2025 (UTC)
I suppose that the question is whether right-handers have an easier time operating the gear stick when changing gears in manual-transmission cars designed for left-hand traffic, with the steering wheel on the right (like in the UK) or right-hand traffic, with the steering wheel on the left (like in most of continental Europe). Obviously, drivers will use their hand at the side where the gear stick is, so if it is in the middle and the driver, behind the wheel, sits in the right front seat, they'll use their left hand, regardless of their handedness. But this may be more awkward for a rightie. Or not.
In my personal experience (more than 10 years driving on each side of the road, in all four combinations of car handedness and road handedness) the question which hand to use for shifting gears is fairly insignificant. Switching from one type of car to the other is a bit awkward though. —Kusma (talk) 18:33, 2 January 2025 (UTC)
Distinguishing a picture of a sunset from the picture of a sunrise?
Is there a way (if you don't know which way is west and which way is east in a particular location) to distinguish a picture of a sunset from the picture of a sunrise? 178.51.7.23 (talk) 12:08, 1 January 2025 (UTC)
Generally, no, but there are a few tricks that sometimes work. In dry sunny weather, there's more dust in the air at sunset (due to thermals) than at sunrise, making the sky around the sun redder at sunset. But in moist weather, mist has the same effect at sunrise. If the picture is good enough to see sunspots, comparing the distribution of sunspots to the known distribution of that day (this is routinely monitored) tells you where the North Pole of the sun is. At sunset, the North Pole points somewhat to the right; at sunrise, to the left. If you see any cumulus or cumulonimbus clouds in the picture, it was a sunset, as such clouds form during the day and disappear around sunset, but absence of such clouds doesn't mean the picture was taken at sunrise. A very large cumulonimbus may survive the night. Cirrus aviaticus clouds are often very large, expanding into cirrostratus, in the evening, but are much smaller at dawn as there's more air traffic during the day than at night, making the upper troposphere more moist towards the end of the day. Cirrostratus also contributes to red sunsets and (to lesser extend, as there's only natural cirrostratus) red sunrises. Dew, rime, flowers and flocks of birds may also give an indication. And of course human activity: the beach is busier at sunset than at sunrise. PiusImpavidus (talk) 13:41, 1 January 2025 (UTC)
Supposing the photograph has high enough resolution to show Sunspots it can be helpful to know that the pattern of spots at sunrise is reversed left-right at sunset. Philvoids (talk) 13:21, 3 January 2025 (UTC)
At the equinox, the disk of the Sun with its pattern of sunspots appears to rotate clockwise from sunrise to sunset by 180 degrees minus twice your latitude (taking north positive). At my place, that's 75 degrees. Other times of the year it's less; at the start and end of polar day and polar night, there's no rotation. Sunset and sunrise merge then.
And I forgot to mention: cirrostratus clouds will turn red just after sunset or just before sunrise. At the exact moment of sunrise or sunset, they appear pretty white. PiusImpavidus (talk) 17:06, 3 January 2025 (UTC)
I differ: the same rotation is involved everywhere on Earth. If you stand on tiptoe at a N. or S. pole to take a picture of the Sun it is you who must pirouette 15 degrees per hour to keep facing the Sun. The Earth rotates you at this rate at all non-polar locations. If you stand within the arctic or antarctic circles, for parts of the year the 24-hour night or 24-hour daylight seem to prevent photographs of sunrise or sunset. However the terms "sunrise" and "sunset" can then be interpreted as times that are related to particular timezones which are generally assigned by longitude. In photographing the 24-hour Sun the equatorial rise and set times for your own longitude are significant elevation maxima worth mentioning even though the minimum elevation remains above the horizon. I maintain that the sunspot pattern observed from any location on Earth rotates 360 degrees per 24 hours and that "night", the darkness from sunset to sunrise, is when the Earth's bulk interrupts one's view of the rotation but not the rotation itself which is continuous.
Taking the Earth as reference frame, the Sun rotates around the Earth's spin axis. The observer rotates around his own vertical axis. The better both axes are aligned, the smaller the wobble of the Sun. In the northern hemisphere, it rotates clockwise from about 6 till 18 by 180 degrees minus twice your latitude and counterclockwise at night, in the southern hemisphere it's the opposite. Try a planetarium program if you want to see it. Stellarium shows some sunspots, does things right and is free and open source. PiusImpavidus (talk) 10:27, 5 January 2025 (UTC)
Relationship between Earth's axial tilt (ε) to the tropical and polar circlesWe deprecate the obselete Geocentric model and suggest Misplaced Pages references that are free and just one click away (no extra planetarium software needed). The axes of rotation of the Sun and Earth have never in millions of years aligned: the Ecliptic is the orbital plane of Earth around the Sun and Earth currently has an Axial tilt of about 23.44° without "wobbling" enough from this to concern us here. Philvoids (talk) 14:56, 5 January 2025 (UTC)
This isn't my field but sunspots aside, if you know the location and date, I assume the appearance of other astronomical objects like the moon or rarely another star probably Venus, in the photograph should be enough to work out if it's a sunset or sunrise. That said, to some extent by taking into account other details gathered from elsewhere's I wonder if we're going beyond the question. I mean even if you don't personally know which is east or west at the time, if you can see other stuff and you know the location or the stuff you can see is distinctive enough it can be worked out, you can also work out if it's sunset or sunrise just by working out if it's east or west that way. Nil Einne (talk) 03:54, 6 January 2025 (UTC)
In my experience (Southern England) they tend to be pinker at dawn and oranger(!) at dusk. {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 03:23, 4 January 2025 (UTC)
Pink clouds must result from blending of reddish clouds with the blue sky behind. There's actually more air between the observer and the clouds than behind the clouds, but for that nearby air the sun is below the horizon. PiusImpavidus (talk) 10:27, 5 January 2025 (UTC)
The questioner asks for interpretation of a single picture. It is beside the point that more would be revealed by a picture sequence such as of changing cloud colours. Philvoids (talk) 12:41, 4 January 2025 (UTC)
Recalling Leonard Maltin's comment about the Green Berets movie, which was filmed in the American state of Georgia: "Don't miss the closing scene, where the sun sets in the east!" ←Baseball Bugscarrots→ 22:37, 5 January 2025 (UTC)
Which you can only tell if you know which way is east in the image. Maltin, or his writer, appears to have assumed that Vietnam has a seacoast only on the east, which is wrong. --142.112.149.206 (talk) 03:46, 6 January 2025 (UTC)
But as it was filmed in (The US State of) Georgia, it must actually show a sunrise, regardless of what the story line says – how do you know that wasn't what Maltin actually meant? {The poster formerly known as 87.81.230.195} 94.6.84.253 (talk) 10:35, 7 January 2025 (UTC)
January 6
Does the energy belonging to an electromagnetic field, also belong (or is considered to belong) to the space carrying that field?
It would be unusual to express the situation in such terms. Since the notion of energy "belonging to" some entity is not itself a physical concept – any practical approach to energy bookkeeping that satisfies the law of conservation of energy will do – this cannot be said to be wrong. It is, however, (IMO) not helpful. Does an apple belong to the space it occupies? Or does that space belong to the apple? --Lambiam23:37, 6 January 2025 (UTC)
First, I let you replace the notion of energy "belonging to" some entity, by the notion of energy "attributed to" some entity, or by the notion of energy "carried by" some entity, and the like. In other words, I'm only asking about the abstract relation (no matter what words we use to express it), between the energy and the space carrying the electromagnetic field, rather than about the specific term "belong to".
Second, I'm only asking about what the common usage is, rather than about whether such a usage is wrong or helpful.
The question is actually as follows: Since it's accepted to attribute energy to an electromagnetic field, is it also accepted to attribute energy to the space carrying that field?
So, is your first sentence a negative answer, also to my question when put in the clearer way I've just put it? HOTmag (talk) 03:28, 7 January 2025 (UTC)
this guy is an oriental beetle? I was off-put by the green head at first, but the antennae seem to match. JayCubby 03:00, 24 December 2024 (UTC)
uses invariant mass m0 which is constant if E and p are constant. The traveling neutrino has a varying mass mixture of different flavors with different masses. If a mixture of different masses changes, you would expect the resulting mass to change with it. But somehow this does not happen as the neutrino mass mixture changes. These mixture changes cannot be any changes. The changes must be such that the resulting mass of the traveling neutrino remains constant. My question is whether this is described somewhere. 
, because we can't "see" the individual mass eigenstates, only some 
would be constant. 
