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October 29

Voltage divider.

I'm trying to use a simple voltage divider to allow me to measure a variable resistance that ranges from around 10k ohm down to nearly zero using an Atmel microcontroller (like in an Arduino). The circuit is the one shown at right (from our Voltage divider article - which I've read).

Vin is 5 volts and the analog-to-digital converter is connected to Vout and measures 0 to 5 volts with a precision of one part in 1024. I'm trying to figure out whether I should make R₁ or R₂ be the variable resistor - and what value to use for the other (fixed) resistor. From the math:

V_out/V_in = R₂ / (R₁ + R₂)

Which suggests that if R₁ is the variable resistor, then R₂ should be very small in order to use the entire range of the AtoD converter. (For example, if R₂ is 10k ohms - then all of my results will be in the range 2.5v to 5.0v and I'll be wasting one whole bit of the result...but if it's just 10 ohms, then I'd be using almost the entire range of the AtoD. I'm betting that something will go horribly wrong if I make R₂ be as small as 10 ohms. What's the gotcha and what's the recommended value?

(I'm not really interested in investigating more complicated circuits - I'm engineering down to a price here!).

SteveBaker (talk) 02:57, 29 October 2013 (UTC)

Wouldn't it be simpler to use a three terminal variable resistor, with one end of the resistor connected to +5 V, the other end to ground, and the wiper connected to the A/D converter? This would assure a low (0.5 mA) current through the resistor and a negligible current through the wiper. Jc3s5h (talk) 03:14, 29 October 2013 (UTC)

If I was using a potentiometer - yes. That would be nice because R₁+R₂ is a constant and V_out is directly proportional to R₂ - but I'm not. There is just one external variable resistance that I'm measuring and R₂ is fixed. (Although if there was a good reason to do it, I could make R₂ be the variable one and R₁ be the fixed resistance. SteveBaker (talk) 03:39, 29 October 2013 (UTC)

On the "betting that something will go horribly wrong", you need to watch the potential power dissipation in each of the resistors, e.g. 0.5 A and 2.5 W with your value of 10 ohm. That's a pretty hefty resistor, and may cost a few cents more. If your variable resistor can dissipate less power than the fixed resistor, it may overheat when it is at a similar value. Another gotcha is that over most of the range of the variable resistor (> 10 ohm), your resolution is going to be far worse than if you use a larger fixed resistor. You should plot the resolution over the whole range, and how it is spread over the range compared to where you want it. For example, you may want substantially more resolution at lowish values of resistance at the expense of at the high resistance end, in which case you could use a lowish value (e.g. 1 kiloohm, 90% of your ADC range, quite nonlinear; 10 kiloohm: substantially more linear, 50% of the ADC range). In your diagram, which resistor is which makes no real difference: the results are simply reversed, non-linearities and all (subtract from 1023). — Quondum 03:48, 29 October 2013 (UTC)

Another, slightly more complicated way of doing it (I know you said you're not interested, but it's still cheap) is to convert the resistance into a delay and measure that. 555 timer IC#Example applications gives a good example of how the dirt-cheap and ubiquitous 555 timer (or similar methods) were used to measure the position of joysticks, which produced a variable resistance and had to be read with a digital device. Basically, you charge a capacitor and the resistance determines how long it takes to charge it. You can time that and know what the resistance is. The accuracy isn't great, but it is simple to set up in a way that doesn't damage components with too much current, which can be a serious problem for reading the whole range with a voltage divider. Katie R (talk) 11:47, 29 October 2013 (UTC)

The key thing the 555 brings to the table here is the ability to send a trigger pulse then wait for a response using all digital I/O. Since you have an analog input, you could just watch the voltage of the capacitor directly as it charges from a digital output if you want to avoid the chip. Katie R (talk) 11:49, 29 October 2013 (UTC)

An important piece missing is tolerance and accuracy. If your fixed resistor is 5% but 10k, you can forget being accurate at the low end. You would already be bit limited 10 ohms/bit, but also +/- 500 ohms (50 bits) for resistor tolerance. Without knowing your tolerance for error and where you need accuracy, it's not very tractable. Other alternatives are to use a equal voltage divider to supply the reference voltage to the A/D (zero it out) and then have the same circuit with the DUT in parallel to R2. The more you can ratio out error, the better your accuracy. With just the voltage divider, resistor tolerance, temperature and device selection will all impact your measurement and at the low end, it will be useless. You always want to be close to full scale.--DHeyward (talk) 12:52, 29 October 2013 (UTC)

You know more about this than I do, but my thought is that whatever you're using this for, wasting power is always bad, so you want as high a value as possible for R1 so that no matter what goes wrong with the rest of the circuit, you know your power isn't peeing away through it. You then want your other variable resistor to also be as high as possible so that you can get nearly the full range by turning it up higher than R1. Which gets us to the brass tacks: what is the resistance of your voltmeter really? A hypothetical voltmeter passes zero current, so you could use a chunk of wood for R1 and R2 and move the probe needle back and forth on it. Unfortunately this is not a purely hypothetical voltmeter, so you need R1 << maximum R2 << Rvoltmeter. Wnt (talk) 16:35, 29 October 2013 (UTC)

If you want to use a simple voltage divider, I would choose two fixed resistors, with R₁+R_var in place of R₁, R_var being the variable resistor now. V_out/V_in = R₂ / (R₁ + R_var + R₂). With R₁= 100 R₂ = 1000, R_var between 0 and 10k, Vout will be between 0.45 and 4.55V (assuming 5V input). Absolute precision goes down when the variable resistance rises, but the relative precision will be highest when R_var equals R₁+R₂. Example: Voltage difference between R_var = 100 and = 110 is 0.0344V, between 2000 and 2200 it's 0.098V, between 8000 and 8800 it's 0.044V. Ssscienccce (talk) 08:36, 30 October 2013 (UTC)

Replace R2 with alow value capacitor, make Vin come from an output of the u controller and use software (free) to. work out the restance:)--31.55.113.25 (talk) 22:28, 30 October 2013 (UTC)

Questions about Dietry Fibers

1) Why fibers are not considered Essential nutrients?

2) What is the main source of the most coveted source for insoluble fiber by humans?

3) Is there such a concept "correct ratio between soluble and insoluble fiber in a human's diet?"

Thanks very much for an answer. 109.65.50.176 (talk) 05:48, 29 October 2013 (UTC)

I numbered your Q's for easier response:

1) A nutrient is something you digest. Since fiber is not digested, it's not a nutrient. At least that's true of non-nutritive fiber. StuRat (talk) 21:59, 29 October 2013 (UTC)

What you've said is pretty much correct, but in my opinion nutrients don't *always* need digestion. Depends on your definition of digestion. If you define digestion to be any combination of "ingestion, breakdown, absorption, and egestion," then fiber could be included in digestion. If it is enzymatic breakdown only (which some sources indicate as "digestion" per se), then vitamins, minerals, and water don't qualify as being digested because they don't need that enzymatic breakdown before absorption. If you take it to mean ANY sort of breakdown, then drinking a glass of water and absorbing it would not include any sort of digestion. (However, you could make the argument that either water is NOT a nutrient or that's a unique case.) Doctorcherokee (talk) 18:13, 1 November 2013 (UTC)

Wouldn't retrograde amnesia erase a person's mental illnesses too?

If an adult with several mental illnesses or emotional problems and specific fears had an accident and woke up in the hospital with no memories at all like that was their first second being alive, wouldn't their mental illnesses, emotional problems and specific fears be gone too? — Preceding unsigned comment added by 174.65.23.49 (talk) 07:03, 29 October 2013 (UTC)

No. There are multiple problems with that idea, one of which is that mental illnesses aren't purely based on what's in a person's episodic and declarative memory. See Causes of mental disorders. Red Act (talk) 07:57, 29 October 2013 (UTC)

Life is not like a video game. We can't reset back to an earlier time. Mental disease will no more disappear just because of forgetting than grey hair will turn black. Dmcq (talk) 11:08, 29 October 2013 (UTC)

What would or could be forgotten is whatever was experienced previously. Also, is the hypothetical person able to speak and do other things normally? ←Baseball Bugs carrots→ 11:17, 29 October 2013 (UTC)

It depends on the extent of the damage that caused the amnesia. Different areas of the brain cover different functions, so damage to one (for example, to the ability to recall memories) would not necessarily cause problems for other areas of the brain (for example, language processing or physical coordination). --Jayron32 12:15, 29 October 2013 (UTC)

• The answer is a bit complicated, and involves several factors.

1. It is common in movies and TV shows for somebody to wake up with no memory whatsoever, but that almost never happens in real life. Genuine retrograde amnesia eliminates memory for the recent past -- sometimes extending back for years -- but almost always leaves memory from childhood intact. There are a few exceptions, but most of them have dubious features -- in some cases it is not clear whether people are faking TV-style amnesia in order to avoid answering awkward questions.
2. The idea that all, or most, mental illness results from traumatic experience is a relic of Freudian theory that is now rejected by the great majority of psychiatrists.

So the bottom line is that (a) that doesn't happen, and (b) it wouldn't eliminate most types of mental illness even if it did. Looie496 (talk) 16:59, 29 October 2013 (UTC)

Meck, Su has this kind of retrograde amnesia and though it is rare she isn't the only person to have a complete loss of all memories. Baseball_Bugs, in this case the person would be like an infant and would have to be taught everything again. — Preceding unsigned comment added by 174.65.23.49 (talk) 02:30, 30 October 2013 (UTC)

I remember that happened to Lt. Uhura once. They managed to re-teach her everything by the very next episode! --Trovatore (talk) 02:35, 30 October 2013 (UTC)

I'm sure Kirk volunteered to show her where she sleeps at night. StuRat (talk) 02:40, 30 October 2013 (UTC)

I looked up the Su Meck case, and while it's mostly popular-press stuff, it is very much an impressive story. --Trovatore (talk) 02:53, 30 October 2013 (UTC)

Even in cases where mental illness might be caused (or triggered) by trauma, erasing the memories of the traumatic experiences would not erase the mental effects of the traumatic experiences. My cat doesn't have to specifically remember being sprayed with water to react to the sight of a spray bottle. thx1138 (talk) 18:07, 31 October 2013 (UTC)

Side-stick controls in cockpits

This is just a quick question: when Airbus designed the Airbus A320, the first fly-by-wire airliner, what were the reasons why they decided to use side-stick controls (which, at the time, was probably unheard of for commercial aircraft) instead of the conventional yokes, and what were the reasons why Boeing decided not to use side-stick controls in the Boeing 777 and Boeing 787 Dreamliner? Also, what are the advantages and disadvantages of using side-stick controls in commercial aircraft cockpits? I have read our Misplaced Pages articles for yokes and side-sticks, but they do not elaborate on the information I want answered here. Narutolovehinata5 10:39, 29 October 2013 (UTC)

As a pilot that flies small planes, the Cirrus SR22 vs Cessna 210 (and both are mechanical, not fly-by-wire), the sidestick is out of the way of the display and doesn't feel all that different from the left seat (captains seat) than a traditional center yoke. There is also the feeling of more room. The downside is that the left/right seat switches are reversed (some would be anyway for throttle control while PTT). An obvious advantage of the center yoke is either hand can fly and either pilot can see and reach the other yoke. The requirements for the quick donning mask, for instance, might be easier to accomplish with this feature. Even the fly-by-wire yokes have mechanical feedbacks to mimic what would be felt in a traditional mechanical yoke so the transition is easier like the buffet before a stall is mimicked (I'm not sure about side-stick though). Personally, I like the Cirrus side stick just for the added space. Side stick fighter planes normally have the stick on the right with throttle control either on the stick or left side so opposite the captain's seat. In the end though, it comes down to transition time. If everything looks and works the same and the only difference is fly-by-wire vs hydraulic, a transition will be much easier. If there a number of differences, like how/when the autothrottle engages/disengages or where switches are located (stick or console), transition time can be longer, more expensive and possibly less safe. I suspect the yoke and controls on the yoke, the travel distance for rotation, bank angle for standard rate turn, etc, all match previous Boeing airplanes and makes transitioning easier and quicker (cheaper). The crash in San Francisco recently was attributed initially to a small difference in autothrottle behavior between types. Small things that change can have large consequences even if the change appears good on paper. --DHeyward (talk) 12:04, 29 October 2013 (UTC)

In jet airliners like Airbus and Boeing, the pilots actually spend a very small percentage of the flight with hands on the control - most of the time the aircraft is being flown by the autopilot. Pilots spend a much greater percentage of their time monitoring instruments, monitoring information displays and doing things with documents - hence the attraction of the Airbus strategy of providing a stick at the side of the pilot and a tray table directly in front. All flight controls are fully powered by servo motors so a large stick with a large moment arm is not necessary. And why has Boeing stayed with the conventional control yoke? Probably because Boeing is the market leader so it doesn't need to try new strategies as Airbus does in an attempt to establish its product and then increase market share. Also, Boeing places great importance on what its established customers say and want in their future aircraft. It seems likely to me that when Boeing asks its established customers and their pilots, all say they are entirely happy with what they have at present. Dolphin (t) 12:23, 29 October 2013 (UTC)

It is worth noting that the most important differences between the Boeing and Airbus fly-by-wire control really aren't in the shape and position of the yoke or side-stick, but rather in the way that the aircraft's computer interprets, responds to, and feeds back pressure on the yoke or stick. There is much information and discussion (correct and otherwise) available in online fora; see for instance . (You will find many online flamewars about flight envelope protection philosophies of Boeing versus Airbus.) The Airbus system has a number of unambiguous benefits from a design and economics standpoint—it is lighter and mechanically simpler; it seems to be ergonomically preferable (less tiring for pilots, room for a tray in front of the pilot, no problems with controls obstructing the view of instruments); removing the yoke allows the cockpit to be slightly shallower from front to back.

The safety question is difficult to settle. What you will find fairly readily are a small number of edge-case incidents and crashes which each side's proponents like to cite over and over, saying "in this tiny one-off case, our preferred technology could have/did save(d) the day". TenOfAllTrades(talk) 16:55, 30 October 2013 (UTC)

Animal learning by experiences of other animals without direct exposure themselves...

It may sound like a confusing or misleading title, but what I am getting at is the instance of having an animal experience some sort of distress by a specific type of predator that looks a particular way. Instead of reacting by instinct, the animal that experiences the stress passes on the learning or conditioning by communication or language, no matter how rudimentary it is. That way, successive generations of the same species can learn who to avoid rather than relying on instinct all the time. In a similar story about lyre birds, if I remember correctly, young male lyre birds can learn the songs of older lyre birds and imitate them. I am wondering if there are any more specific cases in the animal kingdom, but are more sophisticated/complex than the ones I've described and are occurring in nonhuman species. I already know that humans can do it. So, please don't list homo sapiens or any member of the homo genus unless it is an exception. 140.254.227.60 (talk) 13:32, 29 October 2013 (UTC)

It has been shown shown that primates do not have an inborn fear of predators such as snakes but they learn this behaviour from other primates. However, although they can be conditioned in the lab to fear predators by showing them videos of other members of their species showing a fear response, the same process won't necessarily condition them to fear other objects. As it says here "When videos were spliced so that identical displays of fear were modeled in response to toy snakes and flowers, or to toy crocodiles and rabbits( (M. Cook & Mineka, 1991), the lab-reared monkeys showed substantial conditioning to toy snakes and crocodiles, but not to flowers and toy rabbits". So they suggest that there is also an evolutionary component to the selective learning. Richerman (talk) 14:23, 29 October 2013 (UTC)

Concidentally or otherwise, the information you're stating was covered in an NPR discussion just yesterday. :) Which means there could be a link to it on their website, if someone wants to hear more about it. ←Baseball Bugs carrots→ 23:19, 29 October 2013 (UTC)

Are you going to link the article? 140.254.226.247 (talk) 16:18, 30 October 2013 (UTC)

We have a moderately lengthy article on observational learning, with some material about animals. A Google Scholar search for "observational learning animals" will give you a lot more material -- for example, rats learning which foods are good to eat by observing other rats. Looie496 (talk) 16:44, 29 October 2013 (UTC)

There was a study of crows which seemed to show that they recognize specific humans and pass a fear to those individual humans on to others. The people wore masks which made identifying them a bit easier, though. StuRat (talk) 22:05, 29 October 2013 (UTC)

Might be the masks made them scarier. As this BBC thing I just read suggests, humans are naturally freaked by not-quite-human faces, due to the expectation of a regular one. Crows have lived among us as long as we have, so it seems (to me) they could have the same issue. Might be why scarecrows exist. InedibleHulk (talk) 06:04, 30 October 2013 (UTC)

One of my psychology students had trained a rat to press a lever repeatedly to get a reward, and wanted to see if a "student rat" could learn to press the lever to get the reward just by watching the "teacher rat" do the act. The result was that Student rat just hung around by the water dipper to enjoy the reward which was earned by the Teacher rat. The Student did not learn that pressing the lever was what brought the reward. Edison (talk) 04:24, 30 October 2013 (UTC)

And did they call this Student Rat a StuRat, for short ? :-) StuRat (talk) 17:07, 31 October 2013 (UTC)

Does anybody know how many citations an article has been cited?

Does anybody know how many citations an article has been cited? I know there is a function on some website that allows people to track how many people have cited the article in their own articles as part of their references/citations/bibliographies. By the way, have there been documented cases where scientists harshly criticized their rivals' work, where both scientific teams are engaged in the same field and both want the glory of making some important distinguished landmark? I seem to recall a story in the field of chemistry about some guy who discovered Helium and then lost to the guy who discovered Hydrogen... or was it the reverse? I forget. 140.254.227.60 (talk) 14:19, 29 October 2013 (UTC)

To answer the first part of your question, the number of times a scientific publication is cited is the main criterion used to decide its quality and it is something academics are obsessed with. There are a number of ways find out see: for example or google "how many times has my article been cited" As for the second part - scientific rivalry often spills over into harsh criticism of one anothers' work, and the awarding of the Nobel prizes are often a great source of controversy as to whether the recipient really should have got the credit - see Nobel Prize controversies. Richerman (talk) 14:37, 29 October 2013 (UTC)

I beg to differ that it is not academics who are obsessed with citation count, but the people who evaluate academics (for allocating university rankings, research funding, etc). I'm sure most academics would happily not care about such dubious measures but are forced to if they are to survive. 31.52.246.217 (talk) 23:17, 30 October 2013 (UTC)

• If you look up an article on Google Scholar, it will show you the number of citations and allow you to list the citing articles. The number is often not completely accurate -- if it is important, you should check through the list to make sure that each entry is legitimate. Looie496 (talk) 16:48, 29 October 2013 (UTC)

Google Scholar is a useful tool but it has the drawback that it only includes journals that have been indexed online. In some fields this can omit the majority of publications. SpinningSpark 17:27, 29 October 2013 (UTC)

The old standard was ISI Web of Science, but in some way that I don't understand they made themselves so much of a pain in the ass for so many researchers to use (both in terms of interface and who was allowed access from where) that for a while they've seemed to have become more obscure. Wnt (talk) 21:11, 29 October 2013 (UTC)

Fighting scientist? doi:10.1029/2011JE003880 against doi:10.1029/2010JE003599. Or an old example: The discovery of thallium doi:10.1098/rsnr.1984.0005. The favorite one is Cassiopeium and Aldebaranium are no elements because the French chemist was heading the naming committee and not the Austrian chemist. The bloody fight about polywater and the devastating resistance about plate tectonics are other examples.--Stone (talk) 12:30, 30 October 2013 (UTC)

If your German is good enough just read what Hermann Kolbe wrote about his colleagues in his journal (one example of many is doi:10.1002/prac.18820260121).--Stone (talk) 12:33, 30 October 2013 (UTC)

My German is extremely poor. A translation of the document or a summary written in English would be helpful. Thanks. 140.254.226.247 (talk) 15:55, 30 October 2013 (UTC)

"...Adolf von Baeyer is an excellent experimentor, but he is only an empiricist, lacking sense and capability, and his interpretations of his experiments show particular deficiency in his familiarity with the principles of true science..." To make it clear 1905 Baeyer was awarded the Nobel Prize in Chemistry.--Stone (talk) 19:01, 30 October 2013 (UTC)

October 30

The term for the tendency for dominant entities to get more dominant

Like Microsoft, planets, armies, wealthy individuals, etc. Being big helps them get bigger. Is it a maths thing? It seems to be everywhere. It seems that on Earth, it's fueled by money, and people jump into exploit the phenomenon. It seems to have a runaway effect. What's the term? It there one? Anna Frodesiak (talk) 05:13, 30 October 2013 (UTC)

Oh, and thank you, by the way. :) Anna Frodesiak (talk) 05:18, 30 October 2013 (UTC)

Well, the opposite and ultimately triumphant tendency is regression to the mean. - Nunh-huh 06:27, 30 October 2013 (UTC)

The rich get richer and the poor get poorer. Clarityfiend (talk) 06:58, 30 October 2013 (UTC)

I'm not 100% certain what it is you are looking for, so here's a bunch of things that might be of interest: Matthew effect, Tipping point (sociology), Network effect, Virtuous circle and vicious circle, Positive feedback, Reflexivity (social theory), Bifurcation theory, Threshold model. Do any of these fit the bill for the type of thing you are looking for? If so, I can help you find more specific details; or if not, what is missing (so i can narrow it down)?Phoenixia1177 (talk) 07:30, 30 October 2013 (UTC)

Wow! Holy moly! Yes, it's all of those, somehow. Those are some of the most interesting articles I've ever seen. I'm just getting started on them and it will take me a while. Thank you very, very much!

Okay, I will return the favour. Here's something I made up: Tell a friend you can make a specific word come to mind. Write down "What???" on a bit of paper and fold it up. Then ask your friend: "Okay, ready? Are you sure? Okay, concentrate. Now, think of an animal between one and ten." Anna Frodesiak (talk) 08:09, 30 October 2013 (UTC)

No problem:-) I'll dig around when I get home and see if I can find something with more details. --I like your trick, I'm going to use it at work:-)Phoenixia1177 (talk) 08:15, 30 October 2013 (UTC)

Where someone might respond, "Between one and ten inclusive or exclusive?" ←Baseball Bugs carrots→ 09:48, 30 October 2013 (UTC)

Or another wise guy might say, "Three-toed sloth." ←Baseball Bugs carrots→ 09:51, 30 October 2013 (UTC)

Or they might say, "My dog." Then you say, "What?" And they say, "My dog just turned seven." ←Baseball Bugs carrots→ 09:53, 30 October 2013 (UTC)

So if you're asking this to a group, you could resort to this Casey Stengelism: "OK, everybody line up... alphabetically by height." ←Baseball Bugs carrots→ 09:53, 30 October 2013 (UTC)

At first I was confused. Then more confused. Then I finally got it. I think your friends think more than mine. Mine all just said "What???" :) Anna Frodesiak (talk) 11:16, 30 October 2013 (UTC)

Economies of scale would be a likely explanation. Ssscienccce (talk) 08:59, 30 October 2013 (UTC)

Money equates to power. Also described as, "The Golden Rule: Whoever has the gold, makes the rules." ←Baseball Bugs carrots→ 09:46, 30 October 2013 (UTC)

Ah, another good article to absorb. Thank you. Anna Frodesiak (talk) 11:16, 30 October 2013 (UTC)

See also Snowball Effect. uhhlive (talk) 13:11, 30 October 2013 (UTC)

It's important to realize that that "Golden Rule" assumes that everyone has at least some theoretical access to gold. If literally one guy had literally all the world's gold, then gold would be come worthless as money. ←Baseball Bugs carrots→ 22:50, 30 October 2013 (UTC)

Economists like to call this Natural monopoly. Jørgen (talk) 13:37, 30 October 2013 (UTC)

Another term is critical mass. Our article is strictly about the nuclear sense of the term, but it also has broader meaning similar to "tipping point". StuRat (talk) 15:07, 30 October 2013 (UTC)

And, another important concept is that all such effects only operate within a certain range. That is, we don't have one person or company that owns everything, on nation that is able to conquer the world, one animal which replaces all the rest, etc. The reason is that at some point a significant diseconomy of scale also kicks in. In the case of business, this leads to a specific ideal firm size. In another field, you also get a stable population size for a given species, even a very successful one. I don't think even black holes are expected to contain the entire universe, due to Hawking radiation and other effects. StuRat (talk) 15:07, 30 October 2013 (UTC)

And we'll throw in logistic growth for a bit more abstract mathematical fun. TenOfAllTrades(talk) 15:52, 30 October 2013 (UTC)

And I'll throw in network effect - the nature of consumers to gravitate toward the most established product/service providers (applies more to some industries than others). Someguy1221 (talk) 22:51, 30 October 2013 (UTC)

I'm going to toss Turing Patterns into the ring. Not strictly examples of this phenomenon, but interesting and related nevertheless. More generally it sounds like you would be interested in reading about pattern formation. If so I can highly recommend the series of books by Philip Ball entitled "Nature's Patterns, A Tapestry in Three Parts" Equisetum (talk | contributions) 23:50, 30 October 2013 (UTC)

I'm absolutely astonished at how much great content there is on this sort of thing. And all these articles get tons of page visits. Misplaced Pages builders are gooooooooooood. Anna Frodesiak (talk) 00:01, 31 October 2013 (UTC)

Heisenberg's delusion of adequately well behaved standard reality?

If you used Heisenberg's box cutter to open the impenetrable cardboard box and dump Schrödinger's cat into a region governed only by classical physics, wouldn't the poor beast die instantly in the flash of an Ultraviolet catastrophe?

I.e. what color of wallpaper is used to paper over the cracks of the run down and condemned poorhouse where classical physics has been left to die in when the physicist makes some sort of effort to separate herself from quantum reality by suggesting that the padded room she's in is not part of all that quantum weirdness "out there"? Is there a well defined "classical model" that actually works, or is it all just Heisenberg's delusion of adequately well behaved standard reality, that breaks down if you poke at any of the walls? Hcobb (talk) 13:19, 30 October 2013 (UTC)

If I not misunderstood your question, some model of a "classic" can be - The movement of the particles back and forth in time many times. Therefore statistics, Therefore possibilities, Therefore the "reality" stabilizing on part of the particles, so the "universes" are multiple . thanks Water Nosfim — Preceding unsigned comment added by 192.116.142.154 (talk) 14:06, 30 October 2013 (UTC)

I don't think you're going to get a better answer than Water Nosfim's to this one. Maybe you could rephrase the question? -- BenRG (talk) 18:14, 30 October 2013 (UTC)

The real question is how classical physics emerges as an approximation of quantum physics in a certain limit. (Just as relativistic kinematics reduce to Newtonian for low relative speeds.) This is a thorny question. The short answer is decoherence, which explains why we see an adequately well behaved standard reality in which interference effects, superposition, etc. are not obvious. It's not that some systems are fundamentally classical instead of quantum, it's just that classical physics is a good enough description of some things and not others. --Amble (talk) 19:45, 30 October 2013 (UTC)

For that matter, much of the Copenhagen interpretation is just pure nonsense, honestly, having done far more harm than good to the advancement of scientific thought. Ideas of superposition, entanglement, and collapsing wavefunctions continue to spur us on into research of fictitious "quantum computers" and the like...meanwhile we just drift further and further from, well, reality. Go figure. Sebastian Garth (talk) 07:23, 31 October 2013 (UTC)

Superposition, entanglement, and quantum computers are in no way dependent on the Copenhagen interpretation. --Amble (talk) 08:37, 31 October 2013 (UTC)

Let me rephrase that: the vast majority of Copenhagen-like interpretations are pure nonsense. More specifically, they all arise from a misinterpretation of the implications of probability with respect to physics; rather than seeing it as the mere necessity to consider all of the probabilistic "degrees of freedom" inherent in a system, they instead take the analogy too far, as it were, constructing a sort of hocus-pocus holographic multiverse of quantum weirdness in the process. Quantum computers are a direct result of such interpretations and thus nothing more than an interesting thought experiment. Sebastian Garth (talk) 15:53, 31 October 2013 (UTC)

That's quite a tangle of misconceptions. --Amble (talk) 18:12, 31 October 2013 (UTC)

You may be surprised to find that a few others agree with my assessment. But hey - what could they possibly know about all that? Sebastian Garth (talk) 19:49, 31 October 2013 (UTC)

Thanks, but I'll take modern experimental and theoretical work in quantum information over a local hidden variables interpretation that has been shown to be inadequate many decades ago. And I have no idea why you believe that quantum computers depend on any particular interpretation of quantum mechanics. They don't. --Amble (talk) 20:16, 31 October 2013 (UTC)

Bell test experiments is the relevant article, although the experiments are unlikely to convince the OP. Tevildo (talk) 21:45, 31 October 2013 (UTC)

Bell's experiments have their own set of problems and besides that don't in any way invalidate what I have said. You can use quantum equations without having to accept that they are inherently "real" (just as you can use probability in many other fields without having to draw any such conclusions). Sebastian Garth (talk) 22:34, 31 October 2013 (UTC)

They most certainly do. To quote the first line of the article, in fact:

"A quantum computer (also known as a quantum supercomputer) is a computation device that makes direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data".

Superposition and entanglement are merely (the Copenhagen-type variety of) interpretations of the possible implications posed by the equations used in quantum mechanics. Furthermore, from the first line from quantum superposition:

"Quantum superposition is a fundamental principle of quantum mechanics that holds that a physical system—such as an electron—exists partly in all its particular theoretically possible states (or, configuration of its properties) simultaneously; but when measured or observed, it gives a result corresponding to only one of the possible configurations (as described in interpretation of quantum mechanics)".

Finally, from the article on quantum entanglement:

"Quantum entanglement is a product of quantum superposition.".

So you see, all of these ideas are indeed connected. It's no wonder people like Stephen Hawking are so much more popular than Einstein in this day and age - science has become a mythological free-for-all, sadly... Sebastian Garth (talk) 21:04, 31 October 2013 (UTC)

To the extent that the theories are predictive and validated by experiment, they are valuable models. Mathematical models describe what we observe. To the extent quantum mechanics lends itself to the description of observation (and the effect observation has on the experiment), is very well documented. I think everyone realizes that a description of a thing is not the thing itself. But if it's sufficiently detailed to predict behavior of the thing, then it's a pretty good model. As far as I can tell, QM's basic premise is the observer is part of the system. Probabilities arise from the uncertainties introduced by the observer. Superposition for example, describes all the observable states for an electron. It's a useful description and model but we can't create an electron from it. We also can't observe a state not part of the superposition description nor can we violate some of the fundamental underpinnings. Until that happens, it's a pretty good model. --DHeyward (talk) 23:33, 31 October 2013 (UTC)

Yes, probability densities and the like are indeed useful and invaluable predictive tools (again, this has much more to do with the "degrees of freedom" present in a system than anything else). What I'm saying is that for whatever reason certain interpretations of QM have assigned an undue measure of "reality" to the equations. For them, probability densities are very real things that actually govern the universe. And because of this, they feel quite justified to jump to all sorts of half-baked conclusions that, frankly, have not produced any truly verified experimental results to speak of and, moreover, are not verifiable to begin with quite simply because they cannot be directly measured! That is, how can we either prove or disprove wavefunction collapse, superposition, entanglement, etc when we can't even even pin down a reasonable method to measure such things? Anyway, my views are obviously not going to be taken seriously as they are in such conflict with present accepted beliefs, so be it. In any case, I'd appreciate it if someone here would quantum teleport me a message whenever they actually get one of those quantum computers up and running. Thanks. Sebastian Garth (talk) 00:32, 1 November 2013 (UTC)

The crux of the problem is are you trying to determine the state of the cat without measuring it? --DHeyward (talk) 07:33, 31 October 2013 (UTC)

Put the cat back in the box and measure the observable O = |dead><alive| + |alive><dead|. Count Iblis (talk) 16:04, 31 October 2013 (UTC)

Division by nothing

I know that division by zero is not mathematical, but what do you get if you divide something with nothing? — Preceding unsigned comment added by 128.214.166.7 (talk) 13:22, 30 October 2013 (UTC)

By this mean insted of 5/0 trying for to do example 5/ — Preceding unsigned comment added by 128.214.166.7 (talk) 13:23, 30 October 2013 (UTC)

According to quantum physics, there is no nothing, so division is well bounded. Alternatively, you can roll up the Complex plane into the Riemann sphere by adding an infinity point, giving a result for every use of the division operator. Hcobb (talk) 13:28, 30 October 2013 (UTC)

Not sure this is a science question more a maths one. But this video has a good explination. Zero and nothing are the same thing.Dja1979 (talk) 13:59, 30 October 2013 (UTC)

• It depends on the system you are operating in. In most programming languages, "5/0" will give you a floating point exception, whereas "5/" will give a syntax error when you try to compile the program. Looie496 (talk) 14:36, 30 October 2013 (UTC)

Looie496's answer is excellent - because at the core, our original question is not well-defined. In English, we use the word "division" to refer to many related mathematical concepts, including the calculation of the multiplicative inverse and the left-multiplication by the adjoint or conjugate. In these cases, we can explicitly define a mathematical result. If you use a programming language to ask the question, you are forced to be very specific; and depending on what you ask, we can provide the result. In English, your words leave enough ambiguity about your intent that we can't answer very specifically.

Speaking of programming - I recently did battle with the innards of a mathematical representation in the C++ Standard Template Library. I was winning the battle, but I realized I had lost the war when I discovered that my predecessor had overloaded arithmetic operations, including /, as unary predicate operators so that he could divide by nothing while iterating over empty sets. I saw red-links, and knew I had crossed over the edge of reason and had reached the limit of human knowledge. Nimur (talk) 15:57, 30 October 2013 (UTC)

http://en.wikipedia.org/Division_by_zero 217.158.236.14 (talk) 14:56, 30 October 2013 (UTC)

You have lack of information about the denominator, so the outcome fo the division is not known. But what you can say is that the amount of information about the outcome will increase by 2 <Log|x|>, where you have to average over all possible inputs. Count Iblis (talk) 15:53, 30 October 2013 (UTC)

What the OP is calling "nothing" is actually the "empty set". Any computer language worth its salt will have a trap for undefined operations like that. I tried it in Oracle SQL, and 5 over null is... surprise! ...null. ←Baseball Bugs carrots→ 16:38, 30 October 2013 (UTC)

The question is not answerable. The OP admits that division by zero is not defined, but then asks what happens when you do it. It's not that it is forbidden, it's simply not defined. Some calculators/computers will raise some type of error that you could catch, like any other logical error. However, you can still approach it as much as you want OsmanRF34 (talk) 19:46, 30 October 2013 (UTC)

Division by zero is well-defined in some contexts — see our article on division by zero for a discussion, or go straight to Riemann sphere for the most important example. But what "division by nothing" is supposed to mean, I'm not sure. Zero is a thing, and the empty set is also a thing, so neither of them is "nothing". Maybe it's more of a language question? If you divide five by nothing, literally speaking, you just didn't do anything, so there is no result of this action, because there wasn't any action. --Trovatore (talk) 19:56, 30 October 2013 (UTC)

In that sense, it's no different from dividing 5 by an apple. That doesn't work either. Most computers and calculators nowadays will pre-empt division by 0 and flag it as an error. But I recall a few decades ago, a mechanical calculator. If you divided X by Y, it would compute it, apparently by figuring out what Z x Y would equate to X. All well and good, until you divided 1 by 0. Then it would start calculating the Z value mechanically. Basically it would just start counting up. The machine had maybe 15 or 20 digits, and although it seemed to be going pretty fast, each power of 10 would naturally take 10 times as long to switch to the next high-order digit as did the next lower-order digit. I figured it would have to have run for days or maybe weeks before it would hit the last digit. So I stopped that experiment, and never did learn what would have happened once it reached all 9's. ←Baseball Bugs carrots→ 22:43, 30 October 2013 (UTC)

Well, no, it is different. Dividing 5 by an apple doesn't make sense, but it could make sense if you specified what new meaning of "divide" you have in mind. Similarly with dividing by zero (though there well-established meanings already exist) or dividing by the empty set (where they don't, as far as I know) — those are both things. But the word "nothing" does not refer to a thing; it has a different linguistic function altogether. --Trovatore (talk) 22:47, 30 October 2013 (UTC)

I think the short, complex answer is infinity. Division by zero is undefined in the real number system, but in Calculus and other higher math, we can argue it is conceptually equal to infinity. Or we might say, "approaching infinity" since it cannot be reached. In other words, how many times does 0 go into some finite number? Infinite number of times. - 76.17.125.137 (talk) 01:59, 31 October 2013 (UTC)

If ∞ = 1/0, then 0 = 1/∞. Count Iblis (talk) 02:06, 31 October 2013 (UTC)

• Let me just say Hcobb's answer is no, good. Concepts are not physical objects, no more than motherhood has a molecular weight. The statement is a category error. μηδείς (talk) 02:31, 31 October 2013 (UTC)

Division by nothing produces the IP address 128.214.166.7, if you want it to. The word "nothing" in mathematics would most commonly mean "0", but not necessarily, and even what "0" means depends on the context. More importantly, the expression "5/" by itself or more generally "x/" by itself doesn't have any well-established mathematical meaning. So by talking about "x/" you're creating new mathematics (which is a perfectly legitimate thing to do), and you're free to define what you mean by "x/" without it even causing confusion due to your meaning being different from some usual meaning of that expression. In particular, you're free to define a function called "division by nothing", which is denoted by the symbol "/" using postfix notation , such that ${\displaystyle /\colon \mathbb {R} \rightarrow \mathbb {IP} }$, where ${\displaystyle \mathbb {R} }$ as usual means the set of reals and ${\displaystyle \mathbb {IP} }$ means the set of IP addresses, and for all x, x/ = 128.214.166.7 . I'm not a mathematician, so a professional mathematician might express the definition of the function a little better than I did, but my point is that you're free to define what "division by nothing" means however you want to. Red Act (talk) 03:10, 31 October 2013 (UTC)

"The word nothing in mathematics would most commonly mean 0"? No. Where do you get that? 0 is very definitely something; it is absolutely not nothing. --Trovatore (talk) 03:40, 31 October 2013 (UTC)

Well, the word "nothing" is certainly sometimes used in mathematical contexts to mean zero; here is the title of an article in Scientific American, as well as the title of book written by a mathematician, that uses "nothing" to mean "zero". The word is also sometimes used to mean the empty set. The word is also sometimes used to mean neither of those things. The whole point of my sentence is that the meaning of the word "nothing" depends on the context. There is no established context I'm aware of in which "division by nothing" is defined, so creating a new context in which it is defined doesn't conflict with any existing definition. Red Act (talk) 04:51, 31 October 2013 (UTC)

The subtitle in your link is just a witticism, not a genuine use of "nothing" to mean "zero".

The thing is that nothing is used as a noun phrase, but it is not interpreted as having a referent; when it appears in a sentence, it's normally to be interpreted as the universal quantification of a negative statement. "I saw nothing" doesn't mean "I saw x, which is nothing"; rather, it means "for every x, I did not see x". So if you divide by zero, you may or may not get a definite answer, depending on the context. But if you divide by nothing, you just don't divide by anything. --Trovatore (talk) 08:26, 31 October 2013 (UTC)

Perhaps the article subtitle can be dismissed as a witticism, but the book title "The Nothing that Is: A Natural History of Zero" mentioned in the article isn't just using a witticism as far as I can tell. But I think it's all moot, because I think the term "nothing" is only used in very informal mathematical contexts, and mainstream math doesn't have a rigorous concept called "nothing". At least, Nothing#Mathematics doesn't list any possible meaning other than zero or the empty set, and I think in formal settings mathematicians would use one of those two terms instead of "nothing", when they want to talk about zero or the empty set. If you're aware of a reliable source containing a rigorous mathematical treatment of "nothing" as being defined as something other than zero or the empty set, please give a citation, so that the Nothing#Mathematics section can be updated. Red Act (talk) 09:51, 31 October 2013 (UTC)

Of course there is no "rigorous mathematical treatment of 'nothing'". That's the whole point of what I was saying — the word "nothing" looks syntactically like something that should have a referent (because it constitutes a noun phrase), but in the actual semantics of the English language, it serves a different function and does not have a referent. So there can't be a mathematical (or, indeed, any) treatment of it, because there is no "it". --Trovatore (talk) 20:26, 31 October 2013 (UTC)

I think I see your point, and to a large extent I agree with what I think your point is. The English sentence "I saw nothing" means something like "the number of objects that I saw was zero", or "the set of objects that I saw was empty", not "I saw the number zero" or "I saw the empty set". To be consistent with that usage of "nothing", the phrase "division by nothing" means something like "the number of numbers being divided by is zero", or "the set of numbers being divided by is empty", not "division by zero" or "division by the empty set". That's consistent with my treatment of the "division by nothing" function above. The function in question is a function that has one argument that's labeled as being a "numerator", and zero arguments that are labeled as being a "denominator", not a function which has one "numerator" argument and one "denominator" argument whose value is zero, or whose value is the empty set.Red Act (talk) 22:09, 31 October 2013 (UTC)

I think you are right that the above usage of "nothing" is the most common way the word is intended to be interpreted in English. However, the word is also used in ways that are inconsistent with that usage. For example, when Billy Preston sings "nothin' from nothin' leaves nothin'", he means something like "0-0=0" or perhaps "Ø∖Ø=Ø". I.e., sometimes in English, "nothing" really does mean zero itself, or the empty set itself. Natural languages are sloppy that way. In this case, the OP made it clear that his usage of "nothing" wasn't to be taken to mean "zero", so I followed the OP's specification, and didn't interpret it that way. Red Act (talk) 00:48, 1 November 2013 (UTC)

Or even better, Kris Kristofferson singing nothin' ain't worth nothin' — but it's free. (This is why I can't abide Janis's version — she ruins the bitter pathos of that line.) Sure. But this is not a mathematical usage. --Trovatore (talk) 03:39, 1 November 2013 (UTC)

It simply doesn't make sense to not have a denominator, it's a non-function. It is possible to have the denominator as undefined, but must still be something. Plasmic Physics (talk) 03:19, 31 October 2013 (UTC)

The "division by nothing" function I defined has a domain of ${\displaystyle \mathbb {R} }$, not ${\displaystyle \mathbb {R} \times \mathbb {R} }$. I.e., the "division by nothing" function doesn't have a denominator, by definition. Red Act (talk) 03:55, 31 October 2013 (UTC)

You've got it wrong, the domain is ${\displaystyle \mathbb {R} \times }$, not ${\displaystyle \mathbb {R} }$. Plasmic Physics (talk) 04:07, 31 October 2013 (UTC)

ERROR: Parsing failure (EXPECTED OPERAND). Plasmic Physics (talk) 06:16, 31 October 2013 (UTC)

It doesn't make sense for the expression "x/" to not have a denominator, if the symbol "/" in that expression is referring to the standard division function whose domain is ${\displaystyle \mathbb {R} \times \mathbb {R} }$. But that doesn't mean that somebody can't define a new function that uses the same symbol, whose domain is just ${\displaystyle \mathbb {R} }$. And if the domain is just ${\displaystyle \mathbb {R} }$, and the symbol for the new function is defined as being used after the function's argument (similar to x! for the factorial function), then the expression "x/", where ${\displaystyle x\in \mathbb {R} }$, is perfectly well defined for that new function. Red Act (talk) 06:21, 31 October 2013 (UTC)

Well, that is bit a useless answer. The OP has already defined / as division. You're basically saying, that hypothetically, if you had a million dollars, then you would have a million dollars. It is a self-evident statement, which has no real bearing on the OP's question. Plasmic Physics (talk) 07:24, 31 October 2013 (UTC)

Baseball, the empty set is no equivalent to nothing. Nothing has no mathematical definition, or any definition for that matter, the empty set is by no means equivalent to nothing - the empty set is a useful mathematical tool.

The OP most certainly has not defined "/" as being the normal division function. The normal division function is defined as a function whose domain is ${\displaystyle \mathbb {R} \times \mathbb {R} }$. But the OP has explicitly specified that the "division" function being referred to does not involve a denominator of zero. The "division" function being referred to also doesn't have a denominator that's a non-zero real, either; the expression "5/" only shows the function as having one argument, i.e., it doesn't have any kind of denominator (i.e. second argument) at all. It's possible to define a new function that meets the OP's criteria, but none of the standard functions called "division" do. Red Act (talk) 09:23, 31 October 2013 (UTC)

Where has the OP given this liberty to redefine division? Plasmic Physics (talk) 21:27, 31 October 2013 (UTC)

My first post above, at 03:10 31 October 2013, points out to the OP that if he wants to, he can take the liberty of choosing to define "division by nothing" in such a way that his question makes sense, without conflicting with existing mathematics. The function I supplied was merely an example of a function that would work for that purpose. The question is not consistent with the normal division function whose domain is ${\displaystyle \mathbb {R} \times \mathbb {R} }$. If an alternative function is not considered, then the question has no more meaning than "what is the square root of a unicorn?" Red Act (talk) 23:17, 31 October 2013 (UTC)

Then it changes nothing of what I've said. The OP has not made any indication that division has been redefined for this situation, and thus it still makes no sense to have a division with no denominator; and you're explanation is still self-evident. Plasmic Physics (talk) 03:55, 1 November 2013 (UTC)

I'd change nothing of what I've said, either. The question makes no sense with the standard division function, but if the OP should so choose, the OP is still perfectly free to define "division by nothing" in such a way that what he's written makes sense, and doesn't conflict with any existing definitions in mathematics (that I know of). And I would not at all take it for granted that it's self-evident to the OP (I don't care about you) that it's possible to do that. Red Act (talk) 04:30, 1 November 2013 (UTC)

this is more of a mathematics function. Often the answer depends not on the fixed number division, but rather whether the numerator converges faster or slower to 0 than the denominator. --DHeyward (talk) 07:18, 31 October 2013 (UTC)

We customarily use the capital Greek letter Pi ∏ to denote the product of a sequence (see Multiplication#Capital Pi notation). If we wished, we could extend and simplify the notation, defining

${\displaystyle x\cdot \{a_{1},a_{2},\dots a_{n}\}=x\cdot a_{1}\cdot a_{2}\cdot \dots \cdot a_{n}.}$

Then ${\displaystyle 5\cdot \{2,3,4\}=5\cdot 2\cdot 3\cdot 4=120.}$

The empty product is 1 (the multiplicative identity element), so ${\displaystyle x\cdot \{\}=x}$. If we chose to allow the convention of writing ${\displaystyle x\cdot }$ for ${\displaystyle x\cdot \{\}}$, then we would have ${\displaystyle x\cdot =x}$.

Likewise, we could define

${\displaystyle x/\{a_{1},a_{2},\dots a_{n}\}=x/(a_{1}\cdot a_{2}\cdot \dots \cdot a_{n}),}$ where ${\displaystyle a_{i}\neq 0.}$

Then ${\displaystyle 120/\{2,3,4\}=120/(2\cdot 3\cdot 4)=5.}$ Since the empty product is 1, ${\displaystyle x/\{\}=x}$. If we choose the similar convention of ${\displaystyle x/}$ for ${\displaystyle x/\{\}}$, then we would have ${\displaystyle x/=x}$. That is, dividing any number by nothing (in the sense of not dividing it by anything) yields that number unchanged. So in this context, ${\displaystyle 5/=5.}$ -- ToE 03:45, 1 November 2013 (UTC)

Again wrong, your assumption that 'nothing' is logically equivalent to the empty set is false. Plasmic Physics (talk) 04:31, 1 November 2013 (UTC)

"Nothing" could refer to the contents of the empty set. ←Baseball Bugs carrots→ 06:37, 1 November 2013 (UTC)

OK, so you're saying that the OP's supposition is wrong? Nothing is logically equivalent to not _____, such as not 2, not pi, not i, not set, not pink unicorn. Plasmic Physics (talk) 10:49, 1 November 2013 (UTC)

Drinking Ethanol, does it makes you live longer?

I have seem to be found very contradictory claims on alcohol (as a popular beverage) where it says that drinking it will make you live longer, or have healthier life, other claims that drinking alcohol, is bad for health, and should be avoided at all costs.

There doesn't seem to be a consensus about it, so is it really true that drinking alcohol makes you live longer, or it's just a myth? Thank you. 190.60.93.218 (talk) 17:29, 30 October 2013 (UTC)

You may be interested in our articles Long-term effects of alcohol and Health effects of wine. It is true that some studies have found that regular moderate consumers of alcohol (or sometimes specifically wine) seem to live longer, or gain other health benefits. It should also be obvious from the first article that excessive alcohol consumption over a long period of time seems to be extremely bad for you. So the conclusion is less "avoid at all costs" and more "everything in moderation". But you have to keep in mind that most of these long-term studies are looking at correlation only, and correlation does not imply causation. Someguy1221 (talk) 17:57, 30 October 2013 (UTC)

Note that the studies on wine of which I am aware do not cite ethanol as the beneficial substance, but rather other compounds found in wine (see the article cited above for more information) Equisetum (talk | contributions) 23:34, 30 October 2013 (UTC)

Of course excessive consumption in bad for you, that's pretty much the definition of excessive consumption - "the amount which is bad for you" MChesterMC (talk) 09:40, 31 October 2013 (UTC)

And the big difference is what you would be drinking, otherwise. If soda, especially soda with artificial sweeteners, then a bit of alcohol is a favorable alternative. StuRat (talk) 21:55, 30 October 2013 (UTC)

Yeah, if instead of ethanol you decide to drink methanol you'll live a much shorter life. OsmanRF34 (talk) 22:02, 30 October 2013 (UTC)

"especially soda with artificial sweeteners"? Excuse me? citation please... Diet_soda#Health_concerns, mayo clinic "Artificial sweeteners and other sugar substitutes", national cancer institute - Artificial Sweeteners fact sheet Vespine (talk) 23:40, 30 October 2013 (UTC)

Well, you had a citation right in our Wikpedia article: . That concluded that diet soda and regular soda are equally unhealthy. However, they made the assumption that equal quantities were consumed, ignoring the fact that many will drink more diet soda, since they aren't as worried about the calories. When you factor that in, diet sodas are worse. StuRat (talk) 01:38, 31 October 2013 (UTC)

A you say? Oh and speaking of needed citations, where's the one for the claim alcohol is preferable to soft drinks? The link you provided says nothing useful to either query. In fact it doesn't even say what you claimed it said. (It doesn't say they are equally unhealthy, it only says people who consumed diet drinks also had similar health risks and goes on to note the evidence is quite contentious and particularly mentions there are a bunch of confounding factors like people consuming diet drinks because they already had health problems, as μηδείς mentions below. I would also note since the study appears to be an observational study, it seems unlikely any 'assumptions' were made about equal consumption.)

Nil Einne (talk) 04:43, 31 October 2013 (UTC)

Try this one then: . StuRat (talk) 05:01, 31 October 2013 (UTC)

Actually, an antidote to methanol poisoning is ethanol. They compete for the metabolic pathways so it becomes a rate equation as to which wins. The liver clears both but too high of the intermediate metabolites can cause blindness and death for methanol but if you can reduce the rate of methanol metabolism and spread it out through the ingestion of ethanol, you may live and also see the benefits of a beer. The liver prefers metabolizing ethanol over methanol and keeps the intermediate toxins at bay. YMMV and don't try at home. --DHeyward (talk) 08:00, 31 October 2013 (UTC)

I imagine if they catch they methanol poisoning early enough, they would induce vomiting or pump the stomach. StuRat (talk) 17:03, 31 October 2013 (UTC)

• Can you give a mechanism as to why diet soda is worse? Wouldn't it simply make sent that people who drink diet soda do so in a significant part because they are already heavy or diabetic, hence a less healthy cohort? μηδείς (talk) 02:28, 31 October 2013 (UTC)

• I believe the suspected mechanism is as follows: Your body starts to produce insulin as soon as sugar is consumed, so it will be in place as it is digested, to prevent a blood sugar spike. However, artificial sugars fool your body into thinking you consumed sugar, so the insulin is still produced, causing your blood sugar to crash. Your body then responds to this by increasing your cravings for sugar. You then eat some real sugar. You thus suffer all the consequences of consuming sugar, plus the consequences of the blood sugar crash beforehand. StuRat (talk) 04:59, 31 October 2013 (UTC)

I am highly skeptical of this explanation. There are some compounds that can activate GLP-1, but they're not in soda. (Ah, here's a ref. ) My own crank idea (which has no more proof than this) is that people with high blood sugar (even if not meeting the formal definition of diabetes) will find consumption of pure sugar less enjoyable or more distressing in some way, whether it is due to blood sugar spikes, the insulin response, the higher starting level of sugar at the taste receptor, etc.) In any case we should recognize it is an open mystery, despite professional attention. Wnt (talk) 16:58, 1 November 2013 (UTC)

Note that biological responses in anticipation of a future event are widespread. In digestion, we have the salivation response to food smells. There are also sexual preparations for intercourse in response to sexual stimuli, and the adrenaline release in response to perceived threats. StuRat (talk) 18:37, 1 November 2013 (UTC)

The difficulty is that the studies that show that moderate amounts of alcohol are beneficial don't present an underlying mechanism. It's perfectly possible that, for example, people who drink "socially" are getting the benefit from being social - not from the actual alcohol...or that people who are naturally more healthy are happier than people who aren't, and are therefore more likely to drink moderately. It's very difficult to disentangle cause from effect here. SteveBaker (talk) 05:59, 31 October 2013 (UTC)

I know of one abstainer who admits that the only reason he is alive is because he used to drink enormous amounts of booze, it was that or top himself. So he reckons that despite the damage it did him, at least he is alive, 30 years later. (cite: Ross Fitzgerald in The Australian) Greglocock (talk) 23:35, 31 October 2013 (UTC)

Why are we even discussing this? It clearly falls under WP:NOMEDICAL.--ukexpat (talk) 16:12, 1 November 2013 (UTC)

Because it doesn't. Rmhermen (talk) 16:58, 1 November 2013 (UTC)

Correct. Dietary advice is not medical advice. If it was, everyone who writes a diet book would be arrested for practicing medicine without a license. StuRat (talk) 17:05, 1 November 2013 (UTC)

When I come to power, many/most of them will be arrested. It's curious that a GP will routinely refer a patient to an ophthalmologist, a diabetic educator, a physiotherapist, a dietician, a neurologist, an otorhinolaryngologist, a psychiatrist, an oncologist, or various other types of specialist. We can't offer the kinds of advice that any of these people provide, because that would be contravening our No Medical Advice rule - except for the dieticians. Some people go through their entire life without ever needing any of these specialists, but the one thing that every human does every day, eat, is fair game for any and all commentators, including us, no matter how well or poorly qualified they may be to offer such advice. The only thing that threatens to outstrip the ever-increasing obesity and diabetes levels in the West, is the ever-increasing number of supposed solutions (not to mention the ever-increasing number of TV cooking shows which are usually excellent descriptions of what NOT to eat). How any one person can claim to have "the answer" when so many others also have "the answer" is totally beyond me. No wonder virtually all of this advice falls on deaf ears when it comes to their target audiences. How could they possibly believe one over another? It's all just way too horrendously confusing and contradictory for anyone to have confidence in anything anyone says about diet, and that includes so-called scientific studies. Sorry, this turned into a rant, which was not my plan. -- Jack of Oz 19:29, 1 November 2013 (UTC)

Is it possible to start with "When I come to power..." without ending up in a rant ? That's like starting with "With all due respect..." without ending up insulting someone. :-) StuRat (talk) 00:45, 2 November 2013 (UTC)

Which is why I favor the phrase "with all undue respect..." FYI, when I come to power, on the first day I will immediately declare a world-wide holiday. On the second day, I will delegate all activities to others. Then I will go on holiday and leave no forwarding address. ←Baseball Bugs carrots→ 23:18, 2 November 2013 (UTC)

"With all due respect..." doesn't actually say that any respect is due. Indeed, "With all due respect, you're a jerk" implies that no respect is due. StuRat (talk) 17:12, 3 November 2013 (UTC)

Jack and Bugs, please drop me a note when the revolution starts. ;-) 220 of 13:02, 3 November 2013 (UTC)

Practically visible universe stops growing

When will that happen? The visible universe will grow forever (and never exceed 2.36 times the space) but all but our cluster will become too redshifted to detect. What's the real ratio then? — Preceding unsigned comment added by 12.196.0.56 (talk) 20:31, 30 October 2013 (UTC)

Eventually, there will likely be nothing left to detect at all; see Heat death of the universe. For a timeline of what will happen before then, see Future of an expanding universe. And although there is a growing consensus that the universe will continue to expand forever, there are dissenting opinions; see Ultimate fate of the universe. Red Act (talk) 00:55, 31 October 2013 (UTC)

Long after you have died. You will either obtain the answer through divine intervention or simply cease to care. :) --DHeyward (talk) 08:41, 31 October 2013 (UTC)

And as you drift off into eternal oblivion, the last thing you hear will be a voice whispering, "Jackie!" ←Baseball Bugs carrots→ 06:33, 1 November 2013 (UTC)

XENON-100 project regarding dark matter detection?

Is there any short description of the XENON-100 project? or if someone cares to convert the PhD publications into an wikipedia article.. I'm particulary interested in how they physically accomplish this. Electron9 (talk) 22:00, 30 October 2013 (UTC)

You have already found the short description of the project. "XENON is a next-generation Dark Matter Direct Detection experiment, which will use liquid xenon as a sensitive detector medium to search for WIMPs (Weakly Interacting Massive Particles)." If you are not familiar with gas scintillation, the Misplaced Pages article may help. Nimur (talk) 22:53, 30 October 2013 (UTC)

Makes me wonder if there's other methods to detect dark matter other than scintillation or WIMP. Perhaps like interaction with a field rather than with a mass.. Electron9 (talk) 23:02, 30 October 2013 (UTC)

There are a variety of approaches to direct detection. (Note that WIMPs are a type of dark matter candidate, not a detection method.) Other channels are used to search for WIMPs: XENON-100 uses ionization and scintillation, and other projects also use phonons or heat. COUPP uses bubble nucleation. The Axion Dark Matter Experiment looks for a different candidate, axions, by searching for their interaction with the electromagnetic field in a cavity. --Amble (talk) 00:43, 31 October 2013 (UTC)

We do already have an article for the Xenon family of experiments that includes Xenon100: XENON Dark Matter Search Experiment. Funny that you ask about Xenon-100 on the day that LUX, a very similar but competing experiment, released its first results. --Amble (talk) 06:23, 31 October 2013 (UTC)

October 31

Testing for Pink Noise

I am aware of statistical tests for white noise in a real signal (Box-Pierce, Ljung-Box tests) and red noise (Percival test) but am unaware of any statistical tests for pink noise in a signal and cannot find any literature on this, only properties of pink noise and the generation of pink noise. Does anyone know of any? — Preceding unsigned comment added by 211.31.25.66 (talk) 07:48, 31 October 2013 (UTC)

Articles related to Flicker noise have detection and elimination techniques. Suppressing flicker noise below the thermal noise floor is generally the goal. Double correlated sampling and chopper stabilization are techniques to move the flicker noise below thermal noise. detection is basically all 1/f noise is pink noise. --DHeyward (talk) 08:11, 31 October 2013 (UTC)

I think it's important to point out the distinction between pink noise and flicker noise, which our articles don't make clear. Pink noise is any noise with a 1/f (3 dB per octave) spectral density. Flicker noise is a type of pink noise produced in electronic devices. The two terms aren't synonymous. Tevildo (talk) 22:14, 31 October 2013 (UTC)

Flicker noise does from the description seem to resemble shoot noise but where every single electron contributes and thus it looks different but have the same base? Electron9 (talk) 23:39, 31 October 2013 (UTC)

Shot noise has a white (frequency-independent) spectral density, not a pink (1/f) density. I'm afraid I don't understand the rest of your question. Tevildo (talk) 00:06, 1 November 2013 (UTC)

It is indeed important to realsise that there is a very important difference between flicker noise (also known as 1/f noise) (f for frequency) and pink noise. The Misplaced Pages articles on flicker noise and pink noise are all mixed up - the authors have been confused on the meaning of "1/f".

Flicker noise arises in vacuum tube cathodes, junctions between thin metal films, and junctions between metals and semiconductors, has a power spectrum that drops 6 db for each octave increase in frequency, and rises in proportion to the square of the DC current thru the junction. Saying that it drops 6 dB for each octave increase in frequency is of course the same as saying flicker noise voltage is proportional to 1 / frequency. Since power is proportional to voltage squared, power drops 4:1 for each 2:1 increase in frequency.

Pink noise is white noise that has been filtered to produce a power spectrum that drops 3 dB (ie power halves) for each octave increase in frequency. When expresed as a voltage, pink noise halves for each 4:1 increase in frequency. Because of this, pink noise cannot be produced by a capacitor shunting a noise current source. In analogue circuits, pink noise is produced by a complex network of capacitors and resistors that approximates an impedance proportional to (1/f), not 1/f.

One way to prove out pink noise is to inverse filter it (i.e., use an A = k.f filter) back to white noise in a finite bandwidth and then apply the usual tests for band limited white noise.

Note: Those of us old enough to have worked with vacuum tube operational amplifiers, and those of us who are old enough to have listened to the amplified Low frequency noise from the early junction transistors (eg OC71, AC125, Japanese HJ15, etc) know why popcorn noise is called popcorn noise. And we know it is random, but it sure doesn't sound like pink noise or filtered thermal noise.

A classic textbook that covers white, coloured, and popcorn noise is: Electrical Noise by W R Bennet, McGraw Hill 1960. An oldie but a goodie. Poporn noise discussion starts on Page 87.

127.0.0.1 (talk) 00:24, 1 November 2013 (UTC)

Perhaps some sample sound files (.wav) would make it easier to "get" ? Electron9 (talk) 04:46, 1 November 2013 (UTC)

I had a quick search online for a popcorn noise sample, without success. That's not surprising, as popcorn noise has long been just about a non-problem. It was a problem with the early (1950's) germanium junction transistors. Some were worse than others - you could buy more than you needed and select on test the good ones. To the best of my knowlege, no physicist has figured out a workable theory for popcorn noise yet, but manufacturers have long worked out from experience factory processing methods to all but eliminate it - at least to the degree that shot noise predominates. When you amplify the noise from a good bipolar transistor, it sounds just like white noise (which is of thermal origin - the random movement of charge carriers). It sounds as in "hissssssss.....". It you filter white noise to make pink noise, by comparison it sounds more of an "ahhggrrrrrr....". If you then band limit it to say 0 to 300 Hz, it then sounds like LP record rumble. If you amplify the noise from the early germanium junction transistors (OC71 & the like), and band limit it to the same 0 to 300 Hz to get rid of the masking shot noise, it sounds vaguely like popcorn popping in those big display poppers movie theaters have. It sort of comes and goes a bit like the noise of popping popcorn does.

Incidentally, another name for popcorn noise is burst noise. Misplaced Pages has a short article entitled Burst Noise, apparently written without knowlege of the popcorn / 1/f article (or was it vice versa?)

120.145.135.143 (talk) 05:14, 1 November 2013 (UTC)

Any takers on correcting the relevant articles? ;-) Electron9 (talk) 11:28, 1 November 2013 (UTC)

Certainly not me. If I was to set out to correct all the errors in Misplaced Pages articles that come within scope of my chosen professional field, I'd be doing it full time for years - only to have some peanut revert it again. Certainly not me, not until Wikipeia institutes a system of moderators at at any rate. 120.145.135.143 (talk) 12:07, 1 November 2013 (UTC)

One way to deal with it is to produce a "good version". When peanut lifeforms come around and mess it up other people will find the good version in the change history. Usually the coherent content and solid sources is a sign of good a article. Electron9 (talk) 19:52, 1 November 2013 (UTC)

Agriculture and global food supply

Can you tell me what the current amount of staple foods needed for the world supply is? I want to know the amount of food produced for at least 3 staples and the total world population of those 3 staples.--131.96.121.122 (talk) 13:53, 31 October 2013 (UTC)

• Is meat one staple, grain another staple, and fruits still another staple?

• Also, if meat is one staple, does this mean that beef, mutton, pork, and chicken meat are all one staple?--131.96.121.122 (talk) 14:40, 31 October 2013 (UTC)

I think you misunderstand the concept of a staple food. There is never more than one staple in a given community with a common diet. --Trovatore (talk) 18:31, 31 October 2013 (UTC)

• Is beef a staple food?--98.88.147.108 (talk) 05:45, 1 November 2013 (UTC)
  • Not really, according to the staple food article. Staples are primarily plants rather than animals. ←Baseball Bugs carrots→ 06:24, 1 November 2013 (UTC)
    • Thanks.--98.88.147.108 (talk) 07:08, 1 November 2013 (UTC)

Actually, having looked at the article, I think it fails to define the concept strictly enough. As I understand it, a true "staple" is a single food from which you get the overwhelming majority of your calories, say 80%, day in and day out. That's why there can never be more than one, and for most people, zero. --Trovatore (talk) 17:43, 1 November 2013 (UTC)

World Population in 50 years

What is the projected increase in world population for the next 50 years? (If you can, give me a weblink, too.)--131.96.121.122 (talk) 13:55, 31 October 2013 (UTC)

Population growth has a projection. OsmanRF34 (talk) 14:09, 31 October 2013 (UTC)

So, we're looking at a world population of 10 billion in 2063.--131.96.121.122 (talk) 14:18, 31 October 2013 (UTC)

Trousers

Cuold you please explain me how wearing two trousers (or, in general, wearing multiple layers of clothes) produce warmth?

Sorry for a stupid qestion, but I really don't know. --Roman1969 (talk) 14:44, 31 October 2013 (UTC)

This will trap a layer of air between the clothes, and air has a very low thermal conductivity coefficient. So, what then happens is that the same amount of heat that your body produces must still escape via your clothes, but this heat will escape from the top layer of your clothes, So at that top layer the temperature will be the same (because heat transfer depends on the temperature difference and the heat transfer between the top layer and the air will be the same). Then the hat transfer from your body to that top layer must also be the same in bith cases, but nowwith more air trapped between the top layer and your body, the tamperature difference must be larger, so the temperature at your skin will be larger. Count Iblis (talk) 14:56, 31 October 2013 (UTC)

An air layer is part of the answer, but two layers of the same material also cuts in half the heat transferred by conduction through the fabric, and also decreases the flow of cold wind if the fabric is porous enough to allow any air current. Edison (talk) 18:55, 31 October 2013 (UTC)

Layers also provide another advantage: It's important to prevent sweat from building up, which can then make you very cold and uncomfortable later. With layers, you can add or remove layers as needed, to keep comfortable. If you had a single, thick item of clothing, you would lose this flexibility. StuRat (talk) 16:49, 31 October 2013 (UTC)

This is probably clear, but just in case: Clothing doesn't produce any warmth, it is only your body that produces warmth. Clothes only reduce the heat loss of the body. You can wrap a stone in as many layers as you wish and it will not warm up.86.179.30.226 (talk) 22:41, 31 October 2013 (UTC)

But a hot stone will cool more slowly (to really state the bleedin' obvious). Alansplodge (talk) 13:57, 1 November 2013 (UTC)

A hot stone wrapped in varying layers :-) . {The poster formerly known as 87.81.230.195} 84.21.130.203 (talk) 16:25, 1 November 2013 (UTC)

Some times that kinda stone gets hot because it is missing a particular layer... --Jayron32 20:04, 1 November 2013 (UTC)

RPG-29

I have a curiosity about RPG-29 rocket: in its technical description is said that it could penetrate 750 mm of RHA (Rolled homogenous armour) or 1500 mm of reinforced concrete. This sound to me very strange: the reinforced concrete has a tensile strength of 12-15 megapascal and the RHA of 1000-1200 megapascal (80 times higher). How it's possible so low difference beetwen the two penetration? Isn't maybe the data for RHA overstimed or there is any other reason? 80.116.228.89 (talk) 17:37, 31 October 2013 (UTC)

An RPG uses a shaped charge. The liner of the charge is compressed into a narrow jet of metal moving at speeds up to 14 km/s. At those speeds, the strength of the armor plays a minor role, it's mainly the density or weight that determines how far the charge penetrates, that's why some tanks use depleted uranium in their armor. Ssscienccce (talk) 18:26, 31 October 2013 (UTC)

See also composite armour, that mentions that fused silica glass had a higher stopping power than steel (not sure that can be explained by density). To defend against hollow (shaped) charges, explosive reactive armor has been developed: an explosion moves part of the armor while the jet of the shaped charge is penetrating, disrupting the shape of the jet and diminishing the penetrating depth. To defeat reactive armor, the RPG-29 and other HEAT rockets use two shaped charges, the first will trigger the explosive charge in the armor, the second strikes milliseconds later, when the armor isn't "reactive". Ssscienccce (talk) 19:13, 31 October 2013 (UTC)

A cheaper defence is Slat armour, a heavy grill that detonates the charge before it reaches the body of the target vehicle. It is however, equally vulnerable to the tandem-charge weapons that Ssscienccce describes above. Alansplodge (talk) 13:55, 1 November 2013 (UTC)

'Real world length contraction' moved to archives. Why?

I'm new here... wondering why discussion of my question "'Real World' Length Contraction" was deleted from the current menu and moved to the archives, while, for instance the "vomiting while pregnant" question and others remains on the up-front menu. Wherever I raise the question of a variously contracted Earth diameter, or contracted distances between stars... depending on all varieties of relativistic frames, I am either called a crank (and banned from science forums) or told that challenging mainstream length contraction is inappropriate... or the topic is hidden in the backwaters, like the archives here. Will someone here please explain why my question was brushed aside as above with no answer? Thanks — Preceding unsigned comment added by 63.155.141.178 (talk) 17:58, 31 October 2013 (UTC)

I just asked about the above but forgot the headline... and the question disappeared. — Preceding unsigned comment added by 63.155.141.178 (talk) 18:04, 31 October 2013 (UTC)

Because questions 5 days old are archived automatically. Ssscienccce (talk) 18:12, 31 October 2013 (UTC)

If there's more you feel needs to be explored, feel free to open a new question along those lines. Ideally, don't just ask the same question (unless, say, no one responded at all), but focus on what you feel was not addressed. --Trovatore (talk) 18:16, 31 October 2013 (UTC)

Thanks. The question was left hanging at the challenge of a shrinking Earth diameter, depending on the velocity and direction of relativistic frames observing it. The muon question was also left unanswered. I'll open a new question on those cases of supposed contraction specifically.

The point is that you come over as quite hostile. You're essentially saying "I don't believe in Special Relativity - it's impossible" - which is not asking us a question. In fact, you're entirely wrong. Special relativity is true - it's one of the better tested scientific theories - and much of what happens in the universe can only be explained by it being true. People have gone so far as to measure the ticking of the clocks on actual, for real spacecraft to see if time is slowed for them - and it is. If you own a GPS unit - you may be surprised to know that there is software inside that little box that has to compensate for both special and general relativity in calculating where you are in the world. This stuff really isn't up for debate.

So we're telling you the answer - "The Truth". It's OK if you don't fully understand it - by all means, ask for clarification. But issuing "challenges" and being generally combative is hostile to our volunteer staff, who's mission here is to tell you the truth and explain it if you don't understand. We're not here to disprove or challenge whatever wonky ideas you may have of your own. If you wish to dismiss all of mainstream science on this point and ignore what 100% of the respondents here are telling you, that's fine - go away and be flat out wrong someplace else. But please don't argue with us. We're telling you the truth as researched most carefully by hundreds of people who were all a lot smarter than any of us here!

Subjects like relativity and quantum theory are strongly contrary to "common sense" - but that's not because they're wrong - it's because we humans have evolved in a world where nothing much moves anywhere near to the speed of light (except light) and all of the objects we deal with routinely are bigger by far than an atom. The "common sense" that we evolved as stone-age hunter-gatherers on the African plains is pretty much useless for explaining what goes on in realms that it did not evolve to handle...so we find it hard to get our heads around the reality of the universe at these crazy speeds and scales. I forget who said it, but: It's not natures' duty to be understandable by mankind.

Perhaps you'd do our volunteers the kindness of toning down your rhetoric - and rather than telling us that this is all wrong and impossible (which it's definitely not), confine yourself to politely requesting clarifications for the parts that you don't understand. Do that, and things will progress more smoothly.

SteveBaker (talk) 21:38, 31 October 2013 (UTC)

I didn't read all that, but you apparently missed his question, the OP asked for an explanation or the underlying mechanisms regarding length contractions. Not that hard is it? And of course, "100% of the respondents here are telling you" is not accurate (reread the thread). --Modocc (talk) 00:17, 1 November 2013 (UTC)

Should we run an experiment with a plane and measure the Earth's various contractions while dog-fighting, we could build a huge database and subject it to supercomputers and produce funky maps, but that would not necessarily change how the data is processed. However, I'm a scientific realist, because our science is evolving (for instance, compare how messed up ancient land maps used to be compared with today's detailed maps) and it's going to take some effort to progress further. Like Steve said, it is OK to ask for clarification on relativity, but this isn't the appropriate place for debate (see the policy guidelines above). -Modocc (talk) 01:40, 1 November 2013 (UTC)

Contracted Earth diameter and atmosphere depth

My "real world length contraction" question was moved to the archives (after the 5 day limit, I'm told... but doesn't seem to apply to other topics), so here are the unanswered challenges from that exchange: If a relativistic frame (future ship or whatever) approaches Earth in the direction of its axis at .866c, special relativity (SR) says that it will measure the polar diameter to be about 4000 miles. Then if it turns around and approaches at the same velocity in the direction of the equatorial diameter, that will now be measured as 4000 miles, and the polar diameter will have restored to its proper length just under 8000 miles. SR insists that all frames are equally valid, so then Earth must "morph" with every possible velocity and direction from which it could (relativistically) be observed. True of false?

Muons traveling through our atmosphere have higher velocities than lab-accelerated muons, so they decay more slowly ("live longer") and therefore travel further than lab muons, so they can reach Earth's surface. SR claims that the depth/thickness of the atmosphere contracts "for those muons." But the atmosphere remains about 1000 km all around Earth at all times, not contracted by what incoming muons would "observe." Different observations can not change physical objects or distances. SR claims that it does. SR advocates now have another 5 days to reply to this challenge. — Preceding unsigned comment added by 63.155.141.178 (talk) 18:51, 31 October 2013 (UTC)

SR says that the squared invariant distance between two points in space-time (x,y,z,t) and (x',y',z',t') is

s^2 = (t-t')^2 -

where the time and the positions are measured in the same units (so the speed of light, is set equal to 1). So, SR disputes the validity of Pythagoras' formula and it disputes that time intervals are invariant. Count Iblis (talk) 19:32, 31 October 2013 (UTC)

I don't see your problem here. Relativity says that sizes, masses, rate of passage of time and a bunch of other things depend on the frame of reference of the observer. In your example, people approaching the earth from different directions and speeds would indeed see the earth as having different sizes and shapes simultaneously. The idea that two people perceive things differently because they are moving at different speeds and directions should come as no surprise to you.

It's not quite a correct analogy - but consider the doppler effect for sound.

There is a person driving a fast car along a straight road and a person standing still at the side of the road. As he's driving along, the first guy leans on the horn and hears a sound of constant pitch as he passes the guy who's standing still. But the guy standing on the side of the road hears a higher pitched sound as the car approaches him and a lower pitched sound as it passes him and heads off into the distance. Ask the two people what pitch the horn had and they'll disagree. The horn doesn't have to have two pitches simultaneously - it's just that the frame of reference for the two observers is different. Position 100 people at different points along the road, all moving at different speeds and you'll get 100 different perceptions of the exact pitch of the car horn.

CAVEAT: This isn't actually a very good analogy because sound exhibits doppler differently from the way light does - but the point is that it's OK that an object can simultaneously be perceived as being many different sizes, masses, etc by different observers.

As I said before, you have to read (and completely understand) things like the Ladder paradox. In that example, a fast-moving 20' ladder fits into a 10' building - from the point of view of an observer standing next to the building - and the 20' ladder moves through the 5' building from the point of view of an observer riding on the ladder. This is entirely non-contradictory - but it is confusing as all hell for people who aren't comfortable with special relativity.

So the answer to your first question is that the earth doesn't "morph" - it simply "is" a whole bunch of different sizes (etc) depending on the frame of reference of the observer.

Your description of what happens with Muons is correct. From our point of view, they are moving ungodly fast, so time for them has slowed down - so they make it through the atmosphere without decaying. From the muons' point of view, time is ticking along normally - but the earth (and it's atmosphere) has contracted to a nearly flat circle and the atmosphere is so thin that it can make it through easily. This is not contradictory - it's an entirely consistent story - and the outcome (that the muon makes it through the atmosphere) is perfectly correct from both viewpoints.

You boldly assert that "Different observations can not change physical objects or distances." - but you are quite wrong. That is exactly what does happen. Consider the behavior of muons to be proof of that. There have been numerous other experiments that demonstrate this kind of thing. Special relativity is a proven fact - weird though it seems. You really can fit a 20' ladder into a 10' building if you move it fast enough...but if you're sitting on the ladder, things seem VERY different.

But think back to my (technically, rather bad) car horn analogy. Different observations of the car horn did change the frequency at which the various observers heard the sound. This is just like that (although the analogy is only perfect for lightwaves - not sound).

SteveBaker (talk) 21:17, 31 October 2013 (UTC)

If I might indulge in a bit of devil's advocacy - the statement "different observations cannot change physical objects" is correct (in this context, although we might get to the Copenhagen Interpretation soon). Different observations change the values of measured times and distances for a given (unchanging) physical object. The object doesn't change, although its length does. Tevildo (talk) 21:23, 31 October 2013 (UTC)

Yes...we should perhaps think of the "rest length" of an object (like it's "rest mass") as being a constant that doesn't change, and that all practical measurements of the object are a combination of the rest-length and a scaling factor that depends on relative motion. Splitting the length into those two parts resolves the confusion. The object's rest-length is an unchanging property of the object itself but it's modified by a factor that is observer-dependent. However, the key point here is that this second factor isn't like an optical illusion or seeing something in a distorted mirror. The point of the Ladder paradox is that a fast-moving object doesn't just look smaller - it will actually fit into a smaller space...from the perspective of some observers.

SteveBaker (talk) 21:46, 31 October 2013 (UTC)

I think it's resolved if you use the unchanging speed of light as the measurement. A 1 meter bar measured with a 1000nm laser is 1 million wavelengths long. I believe it's always 1 million wavelengths long. That fact that an observer will disagree on the wavelength of the laser, but not the speed of light or the number of wavelengths measured by the comoving laser is the invariant physical property. --DHeyward (talk) 09:50, 1 November 2013 (UTC)

Your "challenge" is like saying that the rules of perspective require objects to grow and shrink. The only difference between that case and this one is that there aren't a bunch of dumb popular books telling you that perspective means that the size of objects is "relative to the observer" and that that has profound philosophical implications. Ignore the second-rate philosophy and you'll be fine -- BenRG (talk) 21:39, 31 October 2013 (UTC)

I like that analogy...but we have to be a little careful though. The moon seems like it would fit into a matchbox because of perspective - but we know that it's not "really" that small and that it won't fit into such a small space. With Special Relativity, if the moon were moving so fast that it appeared to be that small, it really would fit into a matchbox. SteveBaker (talk) 21:49, 31 October 2013 (UTC)

Well, no, for a couple of reasons. First of all, length contraction is only in the direction of motion, so you'd need a Moon-sized matchbox in the other two directions. Then, yes, in the matchbox's frame of reference, you could (very briefly!) have the Moon contained within the top and bottom of the matchbox, say a centimeter apart, but only because you don't agree with the Moon about simultaneity. You'd have to let the Moon in, close the box (that might involve moving the top faster than the speed of light, but whatevs), then bask in the satisfaction that the Moon is inside the box before it obliterates the other side. From the point of view of a lunar observer, the events happen in a different order. --Trovatore (talk) 21:55, 31 October 2013 (UTC)

Yeah - sorry, you're right about the contraction being only in one direction - you couldn't get the moon into a matchbox like that - but a pole that's the same diameter as the moon would...and the distinction between that and perspective is significant. SteveBaker (talk) 03:48, 1 November 2013 (UTC)

Only I know of no events that have been measured to have occurred in reversed order due to frame differences. Also, BenRG perspective analogy and Steve's admission objects don't "change" admits to what? Changes in perspective which means what? Apparent change, in a way similar to the way stars go flying about when I turn around. --Modocc (talk) 02:18, 1 November 2013 (UTC)

No! You are completely wrong. The idea that you literally can fit a 20' ladder into a 10' building by moving it fast enough (again, please read ladder paradox) means that this is a very different thing than perspective and things moving in your field of view when you move your head. This is a completely physical dimension change. SteveBaker (talk) 03:48, 1 November 2013 (UTC)

No! You cannot fit a 20' ladder in a 10' room, since fit means "store within unmoving", not "pass through at close to the speed of light". μηδείς (talk) 03:56, 1 November 2013 (UTC)

No? Think about the implications Steve, if that were true then an electron accelerated at our labs (or something bigger in the future) could cause the Earth or our Sun (or some distant star) to be made so thin that it will fit in gigantic envelope. -Modocc (talk) 03:54, 1 November 2013 (UTC)

The implications have been thought of before by some very smart people. See ladder paradox. The sun very well can fit in a very wide envelope, in a certain reference frame, and only briefly. Standing in another reference frame the sun would burst out the back of the envelope and only a small portion would be inside at any one time. There is nothing about this that is either contradictory or which breaks the laws of physics - it's simply a matter a perspective, and its very very weird. Someguy1221 (talk) 04:02, 1 November 2013 (UTC)

More importantly, physical changes only happen with the speed of light, thus the fact that I drove instead of walked to the store yesterday does not mean our neighboring galaxies shrank a tad more during my faster trip than on the previous day even though my frame did change. -Modocc (talk) 04:18, 1 November 2013 (UTC)

• The comment on proper length above reminds me of a question: rather than saying sqrt(x^2+y^2+z^2-c^2t^2), could we define time as an imaginary number t' = ict, so you'd have sqrt(x^2+y^2+z^2+t'^2)? Since this is obvious I imagine there's some reason against it... Wnt (talk) 03:51, 1 November 2013 (UTC)

  That actually was a popular approach for some time; it went out of fashion somewhere in the latter half of the 20th century. The problem with it is, it's a bit too cute; it obscures the difference between a true metric and a pseudometric, which is a real difference. If proper time were a true metric, then you couldn't have two distinct (event) points that have interval 0 between them — but you can. --Trovatore (talk) 04:16, 1 November 2013 (UTC)

Hmmm, can you explain this about the two event points? I see it is mentioned in metric (mathematics) but I'm totally not getting how spacetime isn't a metric (or in general, what "d" means in this context). Wnt (talk) 07:08, 1 November 2013 (UTC)

The metric defines a norm on the vector space and this should then satisfy all the axioms for a norm. One of the axioms is that ||x|| = 0 if and only if x = 0. Now imaginary time is used in quantum field theory, to get nicer behaved path integrals, the amplitude of a process is given as a path integral over exp(i Action of field configuration), and you can change the integrand to this to exp(- Euclidian Action of field configuration). As explained here in the "Alternative" to the WKB approximation, you see that the imaginary term becomes a real term, but the potential changes sign. So, instead of having to consider a tunneling through a potential barrier, the problem is now a particle propagating from one hil to another throug a valley, and then it is immediately clear what the dominat contribution to the path integral is. All you then have to do is to transform the asnwer back from Euclidian time to ordinary time. Count Iblis (talk) 18:40, 1 November 2013 (UTC)

Actually, I believe the proposition of SR is that the only invariant physical property is the speed of light is the same in all frames of reference, energy of light is inversely proportional to wavelength and energy is conserved in all frames of reference. This is the fundamental property that "distorts" lengths, time, and mass. Say you have a laser in spaceship that is moving towards earth in your spaceship. The wavelength in that frame is 440nm. Couple that with the velocity of light and you can measure distance. But another observer in a different frame measures the laser and has the same speed of light. The kinetic energy of motion changes the wavelength of light, though, not the speed. This is counter-intuitive to our normal experience that kinetic energy increases velocity. Let's say the "at rest" observer measures the laser wavelength at 220nm as it moves toward him. If you treat the wavelength of the laser as unit length dimension, how many wavelengths are the two objects apart? If I say the distance between the two objects is 1,000,000 wavelengths because the speed of light is fixed, suddenly the measured distance changes depending on the observer relative velocity. Not only that, but if earth had the same 440nm laser pointed at the spaceship, the spaceship would see a 220nm laser. The consequences of measuring with a fixed speed of light, conservation of energy and the energy of light being inversely proportional to wavelength, gives rise to all the relative weirdness. --DHeyward (talk) 09:34, 1 November 2013 (UTC)

We actually have an article on the postulates of special relativity. As originally formed, Einstein only assumed that the laws of physics (specifically Maxwell's equations) are equally valid in all reference frames, and the speed of light is invariant between reference frames. This is why what the OP is asking for, a mechanism, cannot be provided. As you say, length contraction and all the other weird phenomena that are observable thanks to special relativity are direct consequences of these postulates, and not any complicated physical mechanisms. As that article mentions, there are also other derivations of special relativity that do not require any assumptions about light, but yield the same conclusions (in addition to concluding that the speed of light is invariant). Someguy1221 (talk) 10:09, 1 November 2013 (UTC)

DHeyward and Someguy are correct. In addition, with respect to proof, one also can ignore SR postulates and merely point to the results of direct measurement! So there is no "need" for the postulates in that sense. ;-) So people can be pretty stubborn about this. In addition, unwavering standards are important, thus with the invariant light-speed yardstick relativists have had a substantial degree of success with this, sort of. Consider how we go about measuring the density of gold precisely, one needs pure gold that isn't being periodically contaminated. Likewise, suppose we measure the height of students with a wooden doorframe, and the students' heights vary slightly with time. Suppose too that we don't know what the cause is, but any theorist with this data can certainly conclude that the students' heights are changing periodically simply because of the data and his maths backs him up. He has solid, rock-hard data correlating the changes to something, but he has no idea why, but claims that since his proposed model is correct thus far, it will continue to be (even though he is predicting time reversals too). That's fine, but if someone is predicting measurable time reversals, I'd tell the door frame theorist to back up and rethink the problem and their assumptions from scratch, by studying the dynamics of that door. -Modocc (talk) 14:55, 1 November 2013 (UTC)

My opening paragraphs have not been addressed. The "challenge" is that obviously Earth neither changes diameter lengths (it is a semi-solid/rigid body, and there is no physics explaining physical contraction)... nor does it "have" and infinite number of diameters at the same time as according to all possible frames measuring from all possible speeds and directions of travel. Neither does the atmosphere change in depth (etc.) as a result of the velocity of incoming muons. (See my second opening paragraph.) The philosophical basis implicit in such claims is the idealism (as per Einstein) that there is no "real world" independent of observation. This has come to be expressed in SR's dictum that "there are no preferred frames of reference"... that "all are equally valid," so Earth's diameter "depends on how you look at it," in common vernacular. Realism, on the other hand, "realizes" that the world/cosmos exists "as is" (as formed and naturally changing according to the laws of physics) independent of changes in how it (any given object or distance) might be observed (from relativistic frames in this case.) My contribution to science as a professor of the philosophy of science (retired) has been to contrast Einstein's idealism (that reality depends on observation) with realism (that the world exists and has its intrinsic properties in and of itself independent of observations/measurements.) I ask again that this issue be addressed as a clarification of whether physical objects/distances shrink as a result of various observations, and if so, by what physics. I have been prompted to sign my posts. I was repeatedly insulted as a crackpot and told that my contributions to "disambiguate" length contraction were inappropriate in the editing discussions of the LC section, so I came to the reference desk, as suggested, with this perspective. Again, please address my opening paragraphs. LCcritic (talk) 18:35, 1 November 2013 (UTC)

The line between physics and metaphysics has always been arbitary, but special relativity is comfortably on the scientific side. I'm afraid your statement "Earth neither changes diameter lengths... nor does it have infinite number of diameters" is just wrong - it is not consistent with repeatable observations that can be performed in the real, physical world. The Earth's measured diameter _does_ change, depending on the relative movement of the Earth and the observer. You may deny the truth of this statement, but the Universe (and not just we humble RD editors) doesn't agree with you. A discussion of what "true" and "the physical world" and "reality" mean are within the realms of metaphysics, and more appropriate for the Humanities desk, but, whatever the words mean, the Earth's diameter still shrinks. Eppur si muove. Tevildo (talk) 19:04, 1 November 2013 (UTC)

Special relativity is physics, but it's questionable whether special relativity, per se, has an opinion on whether the Earth "really" shrinks. I'd say that's a bit outside its remit.

The Earth's diameter will be different in the coordinate system of an observer moving relative to the Earth, but, you know, it's just a coordinate system. You can come up with all sorts of silly coordinate systems. The only difference is that it's a coordinate system that's especially convenient for the moving observer; it has some special properties, and these can indeed be confirmed by experiment. But whether those properties equate to a "real" shrinkage is a matter of interpretation, not physics in the strict sense. --Trovatore (talk) 20:54, 1 November 2013 (UTC)

The diameter of the Earth measured by the moving observer _is_ less than the diameter measured by the stationary observer. That's physics. Is this a "real" shrinkage? That's metaphysics, but only as regards the meaning of the word "real". The diameter is smaller, whatever we say about it. Tevildo (talk) 21:08, 1 November 2013 (UTC)

But the "diameter" is just the difference between two coordinates in a coordinate system, and coordinate systems are essentially arbitrary. The only thing that connects the coordinate system used by the observer to the phrase "measured by the observer" is certain coherency properties that it has for that observer. The connection between that and the question of "real shrinkage" is a bit tenuous. --Trovatore (talk) 21:16, 1 November 2013 (UTC)

So, is there a "real diameter", which is not the difference between two sets of coordinates? If so, how is it defined? How can it be measured? Assuming the Lorentz tranform does not apply to this measurement, in what sense is it a "length"? Tevildo (talk) 21:31, 1 November 2013 (UTC)

I didn't say there was a "real diameter". If there is no "real diameter", then there's also no "real shrinkage", n'est-ce pas? But what I think LCcritic is getting at is, the atoms that make up the Earth don't care about the coordinate system of some observer moving relative to them; they just keep their appointed distances from one another, in the coordinate systems convenient for them. The sum of those distances makes up the "diameter of the Earth" in any ordinary sense, irrespective of what observers might do.

I think this is really kind of a good point that is being obscured in this discussion. If I speed up, does it have any effect physical effect on the Earth itself? No, of course not, and I don't think anyone ever really said it did, which is why the point probably doesn't resonate so much with a lot of people who have already internalized SR. They already know that; it seems like a strawman. But we should recognize that it is a point of confusion. --Trovatore (talk) 21:41, 1 November 2013 (UTC)

Yes, I see your point, the presence of the moving observer doesn't affect the stationary observer's measurements, although saying that the Earth shrinks might sound as though it does. My point is that the moving observer's measurements are equally as "real" as the stationary observer's. The cosmic ray muons mentioned earlier really do have a longer lifetime than the laboratory muons, and the atmosphere really is thinner for them - it's not an illusion or a mathematical convenience to explain an "underlying" physical reality where the lengths and times don't change. Such a "reality" doesn't exist. Tevildo (talk) 23:09, 1 November 2013 (UTC)

Yes that about sums up the relativistic perspectives. Classically though, simultaneity is invariant and distances between spacial points don't change either. This classical paradigm actually has nothing to say about whether or not clock rates slow down or speed up due to acceleration, so your last point regarding an absolute time being nonexistent is inapplicable. With such critiques, one must be very careful to distinguish between reality and the model of reality. The latter merely needs to be self-consistent even if not true. -Modocc (talk) 00:38, 2 November 2013 (UTC)

Ironically, Galileo had a classical foundation, whereas the people he said it to whom unsuccessfully censored him were indoctrinated. Hopefully, we are a tad more civilized now, I hope, 'cause sometimes the best knowledge which is grand is hard to come by. --Modocc (talk) 20:43, 1 November 2013 (UTC)

Regarding this exchange: Tevildo: ‘So, is there a "real diameter", which is not the difference between two sets of coordinates? If so, how is it defined? How can it be measured?” Trovatore: ‘I didn't say there was a "real diameter". If there is no "real diameter", then there's also no "real shrinkage"... The proper length as measured from at rest with an object, “hands on,” measuring rod applied directly to the object will be its true physical length without any complications associated with images of the object traveling at light speed meeting an observer approaching the object and its image at near light speed. The Lorentz transformation does a good mathematical job of translating the contracted images into the true, “proper,” at rest length of the object, without measurement distortion via relativistic effects. Even thought this is a criticism of SR interpretation, it does not negate the constant speed of light. That constant does not require physical shrinkage. Yet the basic philosophy is ignored. Is Earth a “real physical object,” (independent of observation.) That question may be too philosophical for relativity idealists who implicitly philosophically (consciously or not) negate a real world independent of observation? But Earth still doesn't physically shrink, regardless of how distorted it might look from a great variety of relativistic frames. (Realism.) — Preceding unsigned comment added by LCcritic (talk • (edit) Sorry, forgot to sign. LCcritic (talk) 00:42, 2 November 2013 (UTC) contribs) 00:38, 2 November 2013 (UTC)

There's a very good book called "Boojums All the Way Down" by David Mermin which addresses the metaphysical implications of special relativity, and which I would recommend to anyone interested in the issue. The main disagreement that we (and received scientific opinion) have with your views is that you distinguish between the "true length of the object" (as measured by the stationary observer) and the "measurement distortion" of the moving observer. Both lengths are equally real/valid/true in their corresponding reference frames, despite their being different. The Earth doesn't just _look_ smaller, it _actually is_ smaller for the moving observer. The problem is (as I see it) in the meaning of the words "smaller" and "length", rather than in physical reality. It may be "intuitively obvious" that the length of an object is constant if the object doesn't change, but this intuition is invalidated by the experimental results, in the same way that a stationary Earth and moving Sun is obvious but invalid. Tevildo (talk) 01:12, 2 November 2013 (UTC)

SSRI/SSNRI WITHDRAWAL

Can someone please add SAVELLA (Milnacipran) withdrawals in with the other SSRI/SSNRI Withdrawal symptoms? It is a fairly new medication, though it has severe withdrawal symptoms, very similar to others you have listed on the page. I would just like others to be informed about coming off this medication.

Thank you kindly,

Laurie Hart — Preceding unsigned comment added by 2602:30A:C0CB:4D60:78B7:92FD:3CA1:56C6 (talk) 19:17, 31 October 2013 (UTC)

If you have a reliable source that supports the change, then be bold and add it, or make a suggestion on the article's talk page. RudolfRed (talk) 20:27, 31 October 2013 (UTC)

I assume you want the article SSRI discontinuation syndrome changed. Milnacipram withdrawal has been studied but doesn't sound impressive. A review financed by Eli Lilly and a bunch of other drug companies says on page 8 that:

"A post hoc analysis of patients abruptly withdrawn from paroxetine or milnacipran as part of a double-blind comparative study showed that paroxetine produced significantly more discontinuation emergent adverse events than milnacipran. In addition, the nature of the adverse events differed between the two antidepressants, with patients withdrawn from paroxetine showing the classical symptoms of dizziness, anxiety, and sleep disturbance (insomnia and nightmares), while those withdrawn from milnacipran showed only increased anxiety. However, some discontinuation symptoms have been reported, and good clinical practice and regulatory authorities always recommend gradual discontinuation from any psychotropic drug."

Honestly, given the spotted history of drugs that have been claimed to lack their predecessors' side effects, I am skeptical to read a statement like this, but I have zero experience in this area and I'm in no position to dispute their statement. Wnt (talk) 03:41, 1 November 2013 (UTC)

Effect of poor Eyesight on life skill development

Can poor eyesight through childhood and adolescence cause any significant lack of life skill development, knowledge etc? Clover345 (talk) 22:25, 31 October 2013 (UTC)

At the very least, it would tend to limit your career options. ←Baseball Bugs carrots→ 11:22, 1 November 2013 (UTC)

November 1

space objects swift motion

hi, why are certain space objects moving so fast in space, while most just float?

You're probably thinking that things float in orbit. They don't. They're actually zipping along pretty quickly. For example, the International Space Station (according to the infobox anyway) is going 27,600 km/h or 17,100 mph around the Earth. It's just that there's not a lot that is stationary up there to give you visual cues.

It's all relative anyway. The Earth is speeding around the Sun, the Sun around the Milky Way galaxy, etc. Clarityfiend (talk) 07:30, 1 November 2013 (UTC)

The orbital speed of a an object orbiting Earth depends on the radius of its orbit and its eccentricity. The closer to Earth an object orbits the faster it must be going to stay in orbit. Objects in eccentric orbits speed up as they approach Earth and slow down as they move away. SpinningSpark 09:59, 1 November 2013 (UTC)

i was talking about space debris. In "gravity" movie, when many things float here and there, debris come in great speed. Is that because they are propelled or some objects travel in that speed in space. Not about orbiting, about some moving randomly. — Preceding unsigned comment added by 122.164.80.142 (talk) 13:39, 1 November 2013 (UTC)

Objects in orbit are subject to the earth's gravity at a fairly significant fraction to what you are. That is, the gravitational forces on you if you were, say, on the International Space Station would not be significantly lower than what it is where you are sitting now. So why do objects float along side of you when you let go? For the same reason they would if you jumped out of a plane. Imagine, if you will, that you jump out of a plane. Now, imagine you're holding a pen when you do so. While you're faling towards the earth, let go of the pen. Will the pen go rushing towards the earth as soon as you let go? Well, not any faster than you already are. That is, the pen is already being pulled towards the earth along with you before you let it go, so when you let it go, it keeps the same motion as it already had. When you look at the pen, it appears to float right next to you, but of course, it's rushing towards the ground along side of you, just as you are. Orbit works the same way, except you have enough tangental velocity relative to the earth to avoid hitting it. That is, you're essentially falling in a circle and missing the earth on every pass. If you let go of your pen in orbit, it floats along side of you for the same reason it did when you jumped out of the plane. Because you were both moving together before you let it go, and nothing changed about the forces acting on it and on you when you let it go. --Jayron32 14:43, 1 November 2013 (UTC)

Adding to that, if something is moving fast relative to something else in space (that is, not floating along with it), it is because it is on a significantly different orbit. I haven't seen Gravity, so I don't know the context for the fast moving objects, but things with intersecting orbits can pass each other VERY quickly. 2009 satellite collision is a recent example of a collision. They collided at 26,000 mph. Katie R (talk) 14:53, 1 November 2013 (UTC)

evolution of cancer cells

hi, are cancer cells evolving? They are like bacterial cells, adapting and managing to sustain all these years. — Preceding unsigned comment added by Anandh chennai (talk • contribs) 06:26, 1 November 2013 (UTC)

They do indeed evolve, but the nature of their evolution is a bit different. When lifeforms evolve, they generally don't have a lot of "unused circuitry" to draw on; typically genes that are unused are quickly lost in the course of evolution. But cancer cells have many more genes and developmental programs to draw upon than what they should be using, because they are differentiated and, typically, want to become dedifferentiated, calling on abilities from other tissues such as the ability to degrade extracellular matrix with matrix metalloproteinases, turn on telomerase, and of course to undergo rapid cell cycling and growth with oncogenes. Wnt (talk) 07:14, 1 November 2013 (UTC)

This is the second time you have asked this exact same question - you asked it here on 23 October. It attracted sevearal good answers. What was wrong with them? — Preceding unsigned comment added by 120.145.135.143 (talk) 07:17, 1 November 2013 (UTC)

thanks for assisting. Last time, my question was deleted immediately wanting to discuss such things in an outside forum. I was not aware that it was reactivated. — Preceding unsigned comment added by 122.164.80.142 (talk) 13:35, 1 November 2013 (UTC)

Your previous question is in the archives at WP:Reference desk/Archives/Science/2013 October 23#cancer evolution. Red Act (talk) 14:41, 1 November 2013 (UTC)

The absolute altitude record for a manned spacecraft

• Apollo 13

Because Apollo 13 followed the free-return trajectory, its altitude over the lunar far side was approximately 100 km greater than the orbital altitude on the remaining Apollo lunar missions. Due to this fact, Apollo 13 holds the absolute altitude record for a manned spacecraft, reaching a distance of 400,171 kilometers from Earth on 7:21 pm EST, April 14, 1970.

• Moon

Apogee 405,503 km

Perigee 363,295 km

Apollo 8 entered moon orbit. Apollo 13 only uses moon to capture them and sent them home.

Is it a good idea to say that merely 100 km farther away from the dark side of the moon than previous missions could earn them this world record? -- Toytoy (talk) 11:18, 1 November 2013 (UTC)

Good spot, that's somewhat misleading (it beats Apollo 8 by about 2,800km, not 100km). It was not that they were further from the moon which gained them the record, it was that they were futher from the Earth (and, as it happened, the moon was further from Perigee than during other missions) The fact is cited to Guiness World Records 2010, so I can't be sure if the inference is theirs or not. I don't seem to be able to find it on the GWR website. Either way, it should be changed to remove the misleading "due to this fact". MChesterMC (talk) 13:44, 1 November 2013 (UTC)

Reflection

At quantum level, what causes the difference in reflection of visible light from polished surfaces of, say, silver and copper? Paul venter (talk) 12:13, 1 November 2013 (UTC)

Copper#Physical explains the color of copper on a quantum level, at least rudimentarily. That's the only difference I can think of. --Jayron32 14:30, 1 November 2013 (UTC)

Specifically, from Copper : "Together with caesium and gold (both yellow), and osmium (bluish), copper is one of only four elemental metals with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells is such that it corresponds to orange light. The same mechanism accounts for the yellow color of gold and caesium." loupgarous (talk) 00:12, 2 November 2013 (UTC)

Greatest and Least Surface gravity on inhabitable planet?

Assume a planet with a core and mantle somewhat similar to Earth or one of the other inner planets. What is the Greatest and Least possible *surface* gravity for a planet that Human beings and Earth plants would be otherwise be able to inhabit? I'm wondering because if the planet is much larger than earth then it would seem to be likely to keep it's Hydrogen in a way that would make the planet otherwise unusable and if it was much lower, then the Oxygen would be able to escape relatively quickly in the planet's life. (See Mars, which would be worse if it were closer, I think.)Naraht (talk) 15:17, 1 November 2013 (UTC)

You must take air temperature into consideration.

If the planet is hot (but not too hot to boil living things), then gas molecules would be more likely escape from it.

If the planet is cold (but not too cold), then gas molecules would be less likely escape from it.

The air temperature is determined by TOO MANY factors other than surface gravity:

It may be affected by: the planet's rotational axis, the sun's strength, the distance between the planet and the sun, whether it has a moon or moons, the color of the ground, the existence of sea and the composition of the sea (salinity and color), mountain ranges, the air's color (see Jupiter), greenhouse gases ...... blah blah ...... -- Toytoy (talk) 15:31, 1 November 2013 (UTC)

I agree that temperature would need to be taken into account. However the specifications for survival of both Humans *and Earth Plants* would keep the temperature within a *relatively* narrow range. (Assume on one end for temperature a strip with weather no worse than Calgary along the Equator and on the other with Poles no warmer than Jakarta). The Star would also have to generate enough energy in wavelengths that Earth plants could use to survive. (Let's say F, G, or K class, though that may be too broad).Naraht (talk) 15:43, 1 November 2013 (UTC)

• Surface gravity per se is probably not the dominant factor. For example, Saturn actually has a lower surface gravity than Earth (about 90%, because of its very low density). However, the rate of decrease in gravity with altitude is far slower than on Earth, so Saturn is much better at holding on to its atmosphere. Looie496 (talk) 16:04, 1 November 2013 (UTC)

Saturn is the first thing that came to mind, but if we assume your ecosystem needs ground to stand on (otherwise, Venus is nearly habitable, except for the nasty sulfur making its clouds acid instead of water). So for the largest planet, we're basically supposing it has density of 1 g/cc all the way down to the core, so you can stand on the surface. (The planet could be made out of any number of things, but for purposes of discussion I'll say "turtles".) That means the planet has mass M = 1 g/cm r^3, where r is your distance from the center. Mass of Earth is 6 x 10 g and its radius is 6.36 x 10 cm. For Earth mass of our light planet, you have radius 1.8 x 10 cm (cube root of the volume), which is 2.9 times further, which means you'd actually have only 1/8 the gravity! Yet we know full well the gravity well is as deep, so gas molecules at the top of the atmosphere would need the same escape velocity, and so the planet would lose atmosphere at the same rate as Earth... wait, erm, no, because the top of the atmosphere is so much bigger, it would lose it 8x faster. But then again, it would probably have 24x the gas to start with inside of it. But how much reaches the surface? Hrm, the ugly head of reality noses unwanted into the tent. But gas release ought to be at least 8x more, so surface gravity could be 1/8 Earth's with the same atmosphere. oops, wait, it's just as deep at the center of the planet, but ... The scale height of the atmosphere will be a little teeny bit different, but not much - Earth's atmosphere is so thin that the difference in gravity between top and bottom is miniscule, and for the bigger planet it is even less. Wnt (talk) 16:37, 1 November 2013 (UTC)

But you have a relatively narrow line to walk between losing Hydrogen fast enough and not losing Oxygen. If the functional atmosphere is that much be that much bigger won't it lose Oxygen faster as well?Naraht (talk) 16:46, 1 November 2013 (UTC)

Erm, I might have gone "out of my depth" on this one. Every time I think about it there's some factor I forgot about that throws the whole result off by a factor of 3. Wnt (talk) 17:03, 1 November 2013 (UTC)

How Can the Most Distant Galaxy be 30 Billion ly away when the universe is only 13 Billion ly old?

I can't wrap my head around it. Recently, a most distant galaxy was discovered and its distance given as 30 billion light years from earth. Given that the universe in "only" 13.8 billion light years old, and doesn't expand faster than light speed, how is that possible? (The article also mentions "another" distance as 13.1 billion light years. So what are these two distances?) Even if space has expanded, wouldn't it have expanded at the same rate, i. e. having a maximum radius of 13.8 billion ly? You couldn't fit 30 billion light years in that... Help, please?! -- megA (talk) 22:06, 1 November 2013 (UTC)

Space can expand faster than light. The lead of your linked article Z8 GND 5296 has a link on expansion of the universe which says: "While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, it places no theoretical constraint on changes to the scale of space itself." PrimeHunter (talk) 22:28, 1 November 2013 (UTC)

Are you saying that space expands faster than light and somehow drags galaxies along with it? ←Baseball Bugs carrots→ 23:04, 1 November 2013 (UTC)

Yup, that can happen. The schoolbook analogy is a snail crawling on a rubber band. The snail can only crawl at some maximum speed but that speed is independent of and places no limit on how fast you can stretch the rubber band. 88.112.41.6 (talk) 23:15, 1 November 2013 (UTC)

Especially that damned inflation. Only I wouldn't characterize it as "dragged". The expansion is AFAIK in all directions, not just one. When a balloon is inflated, you wouldn't say a spot on it was dragged. Clarityfiend (talk) 23:35, 1 November 2013 (UTC)

Maybe "pushed" instead of dragged. But either way, the spot on the balloon is just along for the ride. ←Baseball Bugs carrots→ 23:56, 1 November 2013 (UTC)

To say "space expands faster than light" is a confusing (and inappropriate) way to describe it; a better way of saying it is that the total distance between two particular points can increase at more than the speed of light due to the expansion of space, if the points are far enough apart. A nice way pf thinking of it is that the path that the photon from the galaxy traveled in the past got stretched in the time since it went past, but this stretched path length is what we mean when we determine the (current) distance to the galaxy, which is inherently longer than the distance traveled by the photon. — Quondum 00:30, 2 November 2013 (UTC)

There's something innately confusing about that description, because it describes a spacelike interval between two galaxies that are a long way away from one another. The article even says it is beyond the cosmic horizon - does that mean that light from it "now" (whatever "now" involves it 30 billion ly away...) will never reach us? If so, I'm really curious to hear just what frame of reference this distance is measured in... Wnt (talk) 01:00, 2 November 2013 (UTC)

The universe is changing over time. For example, the CMBR temperature is currently about 2.7 K. "Now" in a distant galaxy is whenever the CMBR temperature measured there is 2.7 K. The distance "now" to that galaxy is the minimum, over all chains of galaxies connecting it to ours, of the sum of the distances between consecutive galaxies in that chain, measured in the local frame where the CMBR is isotropic. There are other ways to define it, of course. The important thing is that the Big Bang breaks the symmetry of reference frames.

I'm not sure what it means to say that it's beyond the cosmic horizon, but probably it does mean that light emitted "now" will never reach us. The cutoff distance for that is ${\displaystyle \int _{now}^{\infty }{\frac {c\,dt}{a(t)}}}$, where a(t) is the function given here. I can't remember what that evaluates to but it's more than 18 billion light years and likely less than 28. -- BenRG (talk) 05:45, 2 November 2013 (UTC)

A dumbed down Kindergarten level explanation. Let's take the balloon model as explained above by the IP and others. Then the rate at which two points are receding will be proportional to the distance (if every meter is expanding and becoming larger at some rate then if you have twice as many meters between two points, so the distance must grow at twice the rate). So, you then have Hubble's law that says that the speed v between distant galaxies is v = H d, where d is the distance and H the Hubble constant. If we ignore the new results about the acceleration of the expansion rate due to dark energy and simply consider H to be constant, then that is good enough to roughly understand the two numbers 13.1 billion light years and 30 billion light years.

Then consider what happens when we observe distant galaxies. You don't see them as they are now, rather, you see them as they were when the light left the galaxy. If you measure the distance what you get is not the distance they are from us today, rather you get the distance from us to the point where they were when the light left the galaxy. The Hubble law v = H d based on these distance and speed measurements relates the distance in this sense to the velocity. The farthest you can see in theory is that distance where the velocity would be the speed of light. So H = c/(13.8 billion light years) = 1/(13.8 billion years).

Then we can ask how far away would a galaxy be from us today if d = 13.1 billion lightyears. If the distance at time t is x(t), then the speed is the derivative dx/dt and this must equal H x by the Hubble law, so you have dx/dt = H x. This is a differential equation with the solution x(t) = x(0) exp(H t) = x(0) exp. Then for the galaxy we can take t = 0 the moment when it was at the point where we observe it now. That point is 13.1 billion light years away, so x(0) = 13.1 billion light years. The distance today is then found by taking t = 13.1 billion years, this gives x(13.1 billion years) = 33.8 billion light years. So, this dumbed down model is quite accurate. Count Iblis (talk) 01:21, 2 November 2013 (UTC)

Well, it's an interesting way to calculate things. For example, consider a soda can that has fallen into a black hole and is about to hit the singularity. You track back to a time when it had an observed distance to a spaceship it was tossed out of, track the relative rates of separation, get a distance... But it's not a distance the can can travel to get anywhere. Depending on what frame you looked at them in when they were close together, the distance between them could have been foreshortened to any degree from nothing to practically 100%, yet you could still be in the black hole next to the tin can. Wnt (talk) 04:51, 2 November 2013 (UTC)

I made this picture years ago. It's an illustration of the shape of the expanding universe (earlier times at the bottom), based on cosmological parameters measured by WMAP. The yellow line on the right is a distant object, the brown line on the left is us, the diagonal red line is light from the distant object to us, and the orange line at the top is the separation "now" between us and the distant object. Each grid rectangle is 1 billion years by 1 billion present-day light years. You can check by counting grid rectangles that the object is 28 billion light years away "now" and the light was emitted 12 billion years ago. The light always travels at a 45° angle to the grid lines. -- BenRG (talk) 05:09, 2 November 2013 (UTC)

November 2

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