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July 28

Hearing Distance in humans.

Where would I find out, how far away a 'wanted' sound can be heard by a normal human?

(Context is that when reading about Dutch cycling rules I came across some requirement that cycle bells apparently had to be heard 25m away. I'm assuming that this would be for normal hearing under typical conditions.)

I imagine that determining how far away a specific sound can be heard is more complex than first seems. Sfan00 IMG (talk) 13:03, 28 July 2016 (UTC)

"In a normal three-dimensional setting, with a point source and point receptor, the intensity of sound waves will be attenuated according to the inverse square of the distance from the source." Measure the decibel level of the bell and using the above law calculate the distance where the decibel level is not discernible to humans. 196.213.35.146 (talk) 13:37, 28 July 2016 (UTC)

Yes, but the inverse square law just implies that the attenuation obeys the format I = k * (1/d) where I is intensity and d is the distance from the source. The problem is that k, the constant, is itself a complex function, and will be dependent on both the wavelength of the specific sound (lower frequency sounds travel farther, see for example infrasound) and the medium itself (i.e. the air properties such as density, temperature, pressure, and humidity, all of which change a lot). While bringing up the inverse square law makes it sound simple, the devil is in the details, and the details (the "k" factor here) are quite devilish. --Jayron32 18:26, 28 July 2016 (UTC)

It is indeed quite complex. This may help Decibel#Acoustics. 196.213.35.146 (talk) 13:41, 28 July 2016 (UTC)

The Phon might interest you. 196.213.35.146 (talk) 13:44, 28 July 2016 (UTC)

Silbo_Gomero says (with reference) that that whistled language can be used to send an auditory message 5k in good conditions. SemanticMantis (talk) 13:52, 28 July 2016 (UTC)

5k? Do you mean 5 KM? ←Baseball Bugs carrots→ 17:30, 28 July 2016 (UTC)

Clicking on my link would have clarified that I meant five kilometers. The more appropriate symbols would have been '5 km'. From our kilometre article: "k (pronounced /keɪ/) is occasionally used in some English-speaking countries as an alternative for the word kilometre in colloquial writing and speech." For example, I often hear runners saying "I ran five kay yesterday". SemanticMantis (talk) 18:34, 28 July 2016 (UTC)

Either KM or km work. In the recent Tour de France broadcast, they showed the remaining distance alternating between miles (MI) and kilometers (KM). ←Baseball Bugs carrots→ 22:04, 28 July 2016 (UTC)

After digging around a bit for "peak frequencies", I came across this article, Psychoacoustics, which is rather interesting. DrChrissy 19:07, 28 July 2016 (UTC)

John Tyndall, in "The Science of Sound", devotes chapter 7 to things that affect the propagation of sound through the atmosphere. The motivation seems to have been fog horns and shipping safety. This was in 1875, and understanding has probably advanced some since then.--Wikimedes (talk) 21:01, 28 July 2016 (UTC)

On the subject of foghorns. They were noticeably audible because of the long duration. They made the air vacillate. Bit like what the Alphorn does, and on which one doesn't try to play the Trumpet voluntary as the sound just would not carry so well. So perceivably (subjectively) they were more perceptible . The Buncefield fire explosion in Hemel Hempstead was heard as far a way as Holland but that was probably due to an early morning atmospheric condition (an inversion) which tunnels the sound. It woke me up and I live miles and miles away. So I don't see how we can really answer the OP's question because if one sets up a long duration sign wave sound source it can travel for miles and mile depending on the atmospheric conditions.--Aspro (talk) 22:08, 28 July 2016 (UTC)

Somewhat related, a former prof of mine has extensively studied the propagation of elephant calls under different atmospheric conditions. Although it's about elephants some of the basic ideas are general. Interesting stuff; an article on it is here. Shock Brigade Harvester Boris (talk) 03:22, 29 July 2016 (UTC)

I'm surprised that article did not mention seismic communication in elephants. In some circumstances, they are believed to actually hear through their feet! DrChrissy 21:27, 30 July 2016 (UTC)

I refrained from mentioning that, as the OP's question was about human hearing. But I'm surprised why you DrChrissy did not also mention that elephants can also communicate long distances, by apparently just picking up the telephone and making trunk calls? --Aspro (talk) 12:58, 31 July 2016 (UTC)

Humans can also "hear" through their feet. IIRC, Heather Whitestone listened with her feet for the music when she danced in the Miss America competition. Collect (talk) 23:00, 30 July 2016 (UTC)

Atmospheric conditions can do funny things with sound. The 1980 eruption of Mount St. Helens was audible in some far away places but not audible in some closer places. ←Baseball Bugs carrots→ 03:41, 29 July 2016 (UTC)

EO dates the term "tinny" to 1877, which is shortly after the invention of the telephone. ←Baseball Bugs carrots→ 17:34, 29 July 2016 (UTC)

Identifing sound from batbox

I put this batbox up only a few months ago so I'm surprised to already be hearing activity inside as instructions state it may take years for bats to settle. So I'm not sure if what's inside is a bat - I haven't seen anything leave or enter. I recorded the sound made. https://vid(dot)me/xeHw

Any luck in identifying species? edit: I live in the West Midlands in the UK79.68.175.188 (talk) 17:38, 28 July 2016 (UTC)

When I click on the link I get "Server not found". Bus stop (talk) 17:45, 28 July 2016 (UTC)

replace the (dot) with a . 79.68.175.188 (talk) 17:46, 28 July 2016 (UTC)

OK, thanks. Bus stop (talk) 17:49, 28 July 2016 (UTC)

Sounds like a bat to me. Compare e.g. this recording It's not exactly the same, but similar, search youtube for more examples. I'm not sure what specific type of box you used by most bat boxes are designed to be not attractive to e.g. birds, non-flying rodents, and other things that might like a box. It MAY take years, but I think you got lucky and had bats move in more quickly. Keep an eye out near dusk and hope to catch them leaving :D SemanticMantis (talk) 18:29, 28 July 2016 (UTC)

I have often wondered if the microphones built into smart phones have a high enough frequency response to pick up bats. If so, they would only need an app with a software 'heterodyne' to make the ultra sounds audible. Any kick-starters out there (?) as a dedicated bat heterodyne detector can cost over a £100. With one of those one can identify one's bat. Bat Detectors. Mind you, if the critter is weareing a a yellow cape, a green mask, a red jerking and tights, it is probably a Robin.--Aspro (talk) 21:23, 28 July 2016 (UTC)

"Holy mis-identification Asproman!" Another piece of technology you could use is a camera trap, sometimes called trail cameras. DrChrissy 21:33, 28 July 2016 (UTC)

Lol. Images would indeed help for ID, and so would ultrasonic information. For clarity, many bat vocalizations are outside normal human hearing range, but they do plenty of chattering vocalization in the human hearing range too. Also WHAAO trail cameras and camera traps (which are different articles that perhaps should be merged, if anyone is feeling bold). SemanticMantis (talk) 21:45, 28 July 2016 (UTC)

It would (in a perfect world) be advantageous to place a web cam in the box from the out set. One can't (as you will already know) do it after they start roosting, unless one has a license permitting one to handle bats and make adjustments to their habitat. Trail cameras however, are a bit tooo slow for the amateur -me thinks. They have an in built delay which needs some knowhow to adjust. This is because if they fired immediately, all one will see is the snout of a badger or something. So a (typically) ten second delay is built in with the hope that the whole critter is in view buy the time the exposure is taken. I haven't came across one suitable for bats yet. I can't even see bats on my night scope (admittedly it is a cheap one and not a class III military spec). The image is clear but the response is too slow to for the fast moving bats to register. Maybe better to use use a infra red video camera at dusk whilst there is still some light. And anyway, if one could get a image on a Trail cam it would be so blurred that even an expert would not be able-to identify it. Lots of bats look the same. Finally, It would be interesting to know the circumstances of how the OP came by the bat box to start with. He is right that they don't usually get inhabited so quickly. The reason - I think- is that freshly cut wood releases terpenoids and esters, which to a bat, in confide confined space, must be pretty suffocating until the wood has seasoned (about two years minimum). So did the OP by chance get his hands on a old matured box?--Aspro (talk) 23:06, 28 July 2016 (UTC)

Perhaps you could try contacting you local bat group for assistance? https://batlasproject.wordpress.com Their site contains the species found in the West Midlands. --TrogWoolley (talk) 08:59, 29 July 2016 (UTC)

That's a good point about the age of the wood, but the wood pictured in the video does not look young to me. SemanticMantis (talk) 14:41, 29 July 2016 (UTC)

Would the existence gravitational waves imply the possibility of antigravitational waves?

All sources I find about the latter gravitate around sci-fi or cracks who developed anti-gravity-like devices. Hasn't the possibility being seriously considered? Hofhof (talk) 21:58, 28 July 2016 (UTC)

Depends, what do you mean by "antigravitational waves"? As it passes, every gravitational wave will stretch some of space and compresses other parts of space, depending on its orientation. One can also imagine a new gravitational wave that compresses the things the first wave stretched (and vice versa), but that is just a differently polarized gravitational wave. So a gravitational wave with the opposite effects of the first wave is just a different kind of gravitational wave. Is that what you mean, or were you imagining something else by "antigravitational"? Dragons flight (talk) 22:17, 28 July 2016 (UTC)

One thing I was thinking on was what you describe. The other would simply be matter that repels matter, unless of attracting it. --Hofhof (talk) 22:24, 28 July 2016 (UTC)

Matter that gravitationaly repels other matter is not theoretically prohibited by either general relativity or quantum mechanics, but there is no known form of matter with this property. The existence of gravitational waves doesn't change that, since their existence was derived from GR to begin with. The article you're looking for is negative mass. Someguy1221 (talk) 22:37, 28 July 2016 (UTC)

I think that gravitationally repulsive matter is forbidden by field theory (even classically) because it's a perturbation of the vacuum with lower energy than the vacuum itself, and that means the vacuum is unstable. In general relativity, you get weird pathologies (notably closed timelike curves) if you permit locally negative energy density. Probably the deeper theory of gravity that general relativity approximates is fundamentally inconsistent with negative energy. -- BenRG (talk) 06:09, 30 July 2016 (UTC)

Existence of gravitational waves, if confirmed, would raise questions like 1) what is their supporting medium such as an "aether", or have they none other than a mathematical consistency of simultaneous differential equations such as Maxwell's for electromagnetic waves; 2) do they have all the degrees of freedom that we expect in waves (amplitude, frequency, phase); and 3) are there non-linear effects (comparable to dispersion in optics or to diodes, transistors and logic gates in electronics) that we might exploit? A rich source of speculation is that sound waves have already demonstrated ability to manipulate small objects - see Acoustic tweezers - including levitating a few kilograms. However by the rules against speculation on this desk, we should confine the references we give to the First observation of gravitational waves. AllBestFaith (talk) 10:45, 29 July 2016 (UTC)

The existence you propose would allow for regionally suppressing gravity, but not "negative" gravity - repelling things. Just like noise-cancelling headphones car eliminate noise but not create negative noise. -- Q Chris (talk) 11:50, 29 July 2016 (UTC)

Has anyone ever seen anti-sound waves or anti-waves on the sea or anti-light waves or have any idea what any of them would be supposed to be? I guess I could have done with something emitting anti-heat waves recently like Arnold Schwarzenegger as Mr Freeze in a Batman movie ;-) Dmcq (talk) 12:29, 29 July 2016 (UTC)

This not only would be theoretically interesting but would result in a useful commercial product. Something like a "reverse microwave" to cool things quickly. Shock Brigade Harvester Boris (talk) 12:35, 29 July 2016 (UTC)

First, isn't the hypothetical graviton its own anti-particle? Second, I am not aware of anti-electromagnetic waves. While every particle is thought to have an anti-particle unless it is its own anti-particle, not every wave has an anti-wave. Third, negative gravity would require, not negative gravity waves, but negative mass, and I think that does pose technical challenges. Robert McClenon (talk) 12:48, 29 July 2016 (UTC)

July 29

Attracting a float in a pool

Suppose there are a couple of people around a float in a pool and the object is to get the float to move to you without touching it, any ideas what the best way of doing it would be? As far as I can see doing practically anything makes it move away and just doing nothing is the best strategy!, but I'm sure there must be something useful one can do. Dmcq (talk) 12:44, 29 July 2016 (UTC)

• I would guess that if you face the float and row water behind you in a butterfly-like motion, it should bring the float closer. Intuitively you are creating fluid motion in the right direction; less intuitively, an analogy (that is probably deeply flawed anyways) is that you create a "hole" of water in front of you and a "heap" behind you, and so the "hole" will suck water in the front, going by the field lines of a dipole. Even if my reasoning is wrong, in all likelihood this has an effect, positive or negative, and reversing the motion would reverse the effect (for symmetry reasons).

This being said, throwing water directly at the float will likely push it away orders of magnitude more (compared to the amount of water displaced). Of course, any drop that you throw at the float will hit it with a velocity that pushes it away from you. It does not seem unrealistic that, as you perform a vigorous butterfly stroke, you throw enough drops towards it that it more than counteracts the "global effect" of creating a dipole-like motion. The effect of waves is also unclear - just for the lol, I will mention the Casimir effect (which likely does not apply since the damping is too strong).

The best strategy (I assume it is a game) in theory is probably to do some sort of stroke but slowly to limit the drops that you throw. That does not look very fun, and in practice, the best idea is to get the opponents to do the drop-throwing thing. I would try to find a motion that (1) can be done fast, (2) does not throw many drops toward the float. Find this, and you can impress your friends! Tigraan 13:44, 29 July 2016 (UTC)

Thanks. I think I got a bit of motion towards me by pushing water under the float towards or past the opposite side. It is very frustrating how one can try and get a vortex near one or try dragging water back and the float just goes away. Dmcq (talk) 14:21, 29 July 2016 (UTC)

This is sort of vaguely related to the reynolds number, right? Sort of like how you can't easily catch a dandilion's pappus in the air. The problem is that vorticity at all scales prevents much laminar flow. So: I'd try messing with a 4x4' sheet of plywood or stiff plastic. Get a lot of water moving slowly, watch the vortices. Likewise, it should probably be easier to get a ping-ping ball to float toward you, compared to a full-body raft (or maybe that last bit is backwards, I'm groggy, the point is there's a length scale that goes into effective reynolds number, and different sized floats will behave differently in the same water) SemanticMantis (talk) 14:39, 29 July 2016 (UTC)

Don't think it is any good trying to paddle the water in-front towards oneself with one's hands as the water will fill the void sideways. Instead, stand in front and move the water sideways (with both hands in unison) . Flotsam and jetsam will then drift towards you from both the font and rear. Kids instinctively learn to do this in the bath tub.--Aspro (talk) 14:48, 29 July 2016 (UTC)

Thanks, I'll try that next time I'm swimming :) I guess this is a bit like where people compete trying to call a dog or cat to them! Dmcq (talk) 16:27, 29 July 2016 (UTC)

One thing to keep in mind is that any water you move away from one spot, say by pushing it behind you, will find it's way back, sooner or later. So, you may find the float moves towards you initially, but then, as the water flows back in front of you, the float moves back away. The sure-fire cure for this is to move water from the side of the float near you, to the side of the float away from you. This would be easy with a sump pump and hose, but difficult with your hands, as throwing handfuls of water over the float would result in splashing it with water, moving it away from you. But, if you were very close to the float, but not allowed to touch it, cupping hands full of water in front and dropping them behind it might work. This could be an entertaining game, sort of "water curling". Long arms would be an advantage.

Another approach you could take is moving water at depth, underneath the float. That should then cause surface water to move in the opposite direction. Actually getting water to move in one direction, at depth, might be difficult. Again assuming electrical pumps are out, how about a manual pump, like a bellows ? I can't picture this method being all that effective, though, in a large pool, as the amount of water moved is tiny and the volume is then distributed over that entire half of the pool. You would do better to aim the nozzle at the far side of the float, toward you, if you could reach that far. StuRat (talk) 18:38, 30 July 2016 (UTC)

There is a video here on how to paddle a coracle. Learning to drive a coracle One can see how they start off trying to paddles the water towards themselves but as I pointed out above, this is of little help. One can see that they get more experienced, they find they only need only swish the paddle from side to side in a figure-of-eight fashion. The coracle moves forwards and the flotsam and jetsam move towards the coracle. Trying to move the water towards one with a paddle or hand only works in a narrow channels. When a kid, a bathtub seems huge and a side to side motion gives instant feed back that ones toy boat is coming closer faster, than trying to drag the water towards oneself. --Aspro (talk) 10:42, 31 July 2016 (UTC)

I'm a kayak coach and can confirm that pulling the water towards yourself (a draw stroke) certainly is effective, but lacks the fine control available with "swish the paddle from side to side in a figure-of-eight fashion" (a sculling draw stroke). The problem with a coracle is that it is very short in every axis (well, circular actually), making the control with an ordinary draw stroke very difficult (but not impossible) and the sculling draw is the easiest with that particular craft. An ordinary draw stroke would be easier with a long boat like a sea kayak and it's the stroke we teach beginners in any craft. My Scouts were perfectly able to move their kayaks sideways using a draw stroke about half-an-hour ago. Alansplodge (talk) 14:37, 31 July 2016 (UTC)

Think you're getting a bit confused. A draw stroke is using the 'resistance' of the paddle through the water to pull the vessel towards the oar. If it was drawing the water towards the vessel, the vessel would end up going in the opposite direction! Some water may come your way but most flows in from the sides due to the hydrodynamics. These things can be counter intuitive to some. Consider a scout attempting to do his first eskimo roll . Muscle memory may we have him lifting the paddle in to the air, because when he is the right way up it is not normal to lift the oar above oneself to paddle fresh air but upside down one has to reverse some of those actions. Try doing a draw stroke in a coracle and you will need a longer paddle which keeps hitting the river bed and is less comfortable to use when it is being held out in-front. The OP's question is how to move a 'floating' object towards one and a draw stroke is not effective. Run this by your scouts and maybe they can teach their Akela a thing or two :-) My swimming coach (a Middlesex Champion circa 1960's) mentioned that in order to pass his coaching exams he had to repeat what he knew was wrong about how to create thrust but he had to write it in order to satisfy the examiners. So don't believe everything you have been taught. Been there – done it – and nearly drowned several times. --Aspro (talk) 23:14, 31 July 2016 (UTC)

Is vision permanently corrected after laser eyes surgery?

Or will eyes deteriorate as normal, just from a starting point of perfect vision? 2.102.187.157 (talk) 12:52, 29 July 2016 (UTC)

The latter. Laser eye surgery (e.g. LASIK) aims to correct current eyesight problems but doesn't prevent the natural aging that results in most people needing glasses later in life. Some people who have had laser surgery in the early days of the technique even choose to repeat it later in life after their eyesight deteriorates due to natural aging. However, I do know one woman who was advised that she had a thin cornea and consequently wouldn't be eligible for a second procedure. Dragons flight (talk) 13:03, 29 July 2016 (UTC)

And yet our lasik article says

For most patients, LASIK provides a permanent alternative to eyeglasses or contact lenses.

although the reference given is apparently to a newspaper article, and clicking it gives an error message. Note also that it does nothing for the loss of reading ability in middle age, so someone who has had lasik will probably need reading glasses eventually. Loraof (talk) 14:58, 29 July 2016 (UTC)

Anecdote is not evidence but both people I know who had LASIK now wear glasses for reading. Greglocock (talk) 15:30, 29 July 2016 (UTC)

Iirc, age related eyesight issues are due to muscle decline, not changes in eye shape that result in early life eye issues. Laser surgery cannot fix muscles. For us myopic folks, it's supposed to be a permanent fix assuming your vision correction is stable (mine isn't sadly). EvergreenFir (talk) 16:06, 29 July 2016 (UTC)

Right, but myopia may delay the onset of presbyopia because your eyes are set up to focus excessively close. So having corrective surgery for a myopic may make presbyopia more likely or at an earlier age. See our articles and for some brief discussion of this. BTW that later ref also has some details on how many people need followup surgery and when it's less likely to succeed. (Note also that stability is one key point of difference where local regulations and specialist views will affect when the surgery will be offered.) Nil Einne (talk) 22:18, 29 July 2016 (UTC)

Not having surgery will make it more likely that you can do without glasses later in life as Nil Einne points out above . Currently I don't even need a magnification glass, all I need to do is take off my glasses allowing me to see an object up close just a few centimeters from my eye. Why destroy this supervision ability using laser surgery? Also note that laser surgery will only correct your eyesight to within some tolerance, which may not be good enough e.g. for doing (naked eye) amateur astronomy. You may then need glasses of lower diopter, say -1/2 with a small cylindrical correction for optimal viewing. To actually improve the quality of vision requires using precision glasses that accurately correct for not just the diopter and cylinder, but also higher order aberrations. Carl Zeiss Vision has developed a new system to produce such precision glasses, these allow for perfect sharp vision at night when the pupil is large and vision tends to deteriorate due to these higher order aberrations. Even people who have perfect vision when measured at daytime will not have have perfect vision at night, so they can also drastically improve their vision using such glasses. Count Iblis (talk) 22:17, 29 July 2016 (UTC)

For me, I knew what I was getting into when I had lasik surgery about 20 years ago. I expected before the surgery that it would reverse the situations in which I need glasses, and that's why I wanted it. I didn't like to wear glasses while driving a car, piloting an airplane, riding my bike, or doing any other life-endangering outdoor activity in which I must rely on glasses to see. I didn't (and still don't) give a damn if I need glasses while sedentary: reading, using the computer, etc. 20 years later, that's still true, I can still see distances clearly, but my ability to focus close-range is deteriorating (presbyiopia). So to answer the OP's question, in my case my distant vision was permanently corrected, but my near-vision prescriptions are changing. ~Amatulić (talk) 23:52, 29 July 2016 (UTC)

The most general answer is that there's no procedure that zaps your eyes and magically makes them perfect forever. There are different procedures that can all be considered "laser eye surgery". The most commonly-performed procedures reshape the cornea to compensate for refractive error. This doesn't stop or prevent any changes to the eyes; it just substitutes for corrective lenses. There are many things other than refractive error that can impair vision. A few can be treated with other laser procedures, though there's no medical procedure that's perfect. --71.110.8.102 (talk) 00:26, 30 July 2016 (UTC)

Hitting walls

Does hitting walls with bare fists or wrapped in towel cloth cause any damage to wrist and other joints in long run ? — Preceding unsigned comment added by 182.18.177.78 (talk) 16:02, 29 July 2016 (UTC)

Maybe, maybe not. Answering that question for a specific person and context would constitute medical advice, which we cannot give. You may be interested in reading about repetitive strain injury, sports injury, tendinitis, tendinosis, and maybe bits of sports training, punching or boxing. SemanticMantis (talk) 16:28, 29 July 2016 (UTC)

I think the basic answer is Yes:any impact will cause a certain degree of damage - though whether or not you become aware of the damage caused will depend on the strength of you hand and wrist, and how hard you actually hit the wall. Low levels of damage may have no effect that you are aware of, and should heal easily. Only if the level of damage passes a certain threshold (specific to you) might the damage be severe enough for you to suffer. Wymspen (talk) 16:52, 29 July 2016 (UTC)

If done right, the body will be able to repair it and make itself stronger. This sort of training is necessary to be able to do things shown here and here. Hitting a wall causes a rebound of the shock wave into your hand, as pointed out here this can cause more damage compared to breaking an object. Count Iblis (talk) 20:51, 30 July 2016 (UTC)

Caitlyn Jenner

Every so often, we see Caitlyn Jenner (Bruce Jenner) in the news. I often see photographs that look like this (more or less): . I am struck by the very full head of hair. I assume that is "real hair" and not a wig; am I correct? Also, I see that Jenner is age 66. So, my question is: at that age, why is there no hint of any baldness (when he transitioned to being a woman)? And, if that's the case, doesn't whatever they do with Jenner offer the cure for male baldness? I never see transsexuals (man to woman) who are bald, even in their older age. Is this due to wigs? Or what else is going on? Thanks. Joseph A. Spadaro (talk) 16:56, 29 July 2016 (UTC)

It's probably a wig, though a very well done and natural looking one. --OuroborosCobra (talk) 17:02, 29 July 2016 (UTC)

Your horribly problematic language aside, male pattern baldness (and even baldness in women) is linked to testosterone levels iirc. Hormone replacement therapy trans folks often use would likely affect baldness. It would be inappropriate to speculate on Caitlyn Jenner's medical history though. EvergreenFir (talk) 17:09, 29 July 2016 (UTC)

I thought the OP's language was a little clumsy, but also showed at least some small effort to get it "right"/inoffensive. It seems you think that he did not succeed. So, in the name of edification, can you explain to us which bits are horribly problematic? Not really trying to fight or argue, just understand, thanks. SemanticMantis (talk) 20:47, 29 July 2016 (UTC)

For the record, though, many people of her age, of both genders, wear wigs; c.f. John Travolta with and without his wig. Whether Caitlyn does, or does not, wear a wig or hair extensions or something like that isn't something we should speculate on, and also is not out of the ordinary. At the high school I teach at, more than half of the female students, and a non-zero number of male students, wear some kind of hair extensions, weaves, or something similar. --Jayron32 17:31, 29 July 2016 (UTC)

Google Images results would suggest that it's her own hair. ←Baseball Bugs carrots→ 17:37, 29 July 2016 (UTC)

Or that she has very good wigs. Images are a poor judge. --OuroborosCobra (talk) 18:14, 31 July 2016 (UTC)

I'm going by pictures of Bruce when he was letting his hair grow long, comparing with Caitlyn's hair now. To me they look similar. Though you're right that a visual check is not 100 percent proof. ←Baseball Bugs carrots→ 18:44, 31 July 2016 (UTC)

I assume, not jokingly, that castration is a good measure against male-pattern baldness. Although Caitlyn Jenner has not undergone sex reassignment surgery, this could still partially explain the alleged non-existence of bald trans-women. Long-term hormone replacement could also be beneficial against male-pattern baldness, since this is caused by the action of androgenic hormones on hair follicles. Add to this that trans-women would be more prone to undergo hair transplantation to look more feminine. Hofhof (talk) 13:10, 30 July 2016 (UTC)

July 30

Perceptions of suicide

Suicide is often viewed either as a selfish act or an act of desperation, and hence not selfish, but ultimately does it not depend on the circumstance and the perspective you look at it from? Why are the general views one or the other? 2A02:C7D:B99F:5300:CAF:A38B:AC61:C4F7 (talk) 12:31, 30 July 2016 (UTC)

Death_and_culture#Suicide and Philosophy of suicide have something about this.Hofhof (talk) 13:11, 30 July 2016 (UTC)

In some cultures suicide is seen as honorable, perhaps as the only honorable option, in some cases. Also, even in cultures where suicide is not seen that way, in cases where death is certain in short order anyway, it is more acceptable. Two such cases are terminal disease and facing capture by an enemy that is certain to torture and kill them. StuRat (talk) 18:28, 30 July 2016 (UTC)

Code of ethics that psychotherapists are supposed to follow

Are psychotherapists allowed to go with patients for a walk during talk therapy? Could they meet over lunch or coffee for a therapy session outside the psychologist office? — Preceding unsigned comment added by Hofhof (talk • contribs) 14:28, 30 July 2016 (UTC)

Different countries, different rules. The main principle seems to be confidentiality - so a walk might be fine but a cafe could present problems. Wymspen (talk) 15:05, 30 July 2016 (UTC)

Sure, the laws and regulations could deal with this in a complete different way around the globe. But I am interested in the scientific part of this. Besides your point, I was asking also while it could imply crossing the line between professional space and private space. That is, mixing two types of roles in the relationship. --Hofhof (talk) 17:28, 30 July 2016 (UTC)

In you'll see the FBI believe they have the right to put bugs anywhere in public spaces without needing special permission and without specially targeting criminals. So yes I'd have thought they should have a reasonable expectation of privacy but that is not what the government thinks. Dmcq (talk) 17:44, 30 July 2016 (UTC)

Do the same areas of a man's brain light up when his nipples are stimulated in comparison to when his genitals are stimulated?

After all, I know that the same areas of a woman's brain light up when her nipples are stimulated and when her genitals are stimulated. Thus, I am wondering if this is also true for men. Futurist110 (talk) 19:21, 30 July 2016 (UTC)

Your premise is in fact based on a false assumption. When different parts of the body are stimulated by tactile contact, they in fact trigger distinct patterns of firing in the somatosensory regions of the brain. Now it may be true that in a given individual, on a given occasion, that this may result in similar responses in other regions of the brain that control a wide variety of other physiological and biopsychological responses, from arousal, to relaxation, to alarm. Then again, they easily may not (and they will certainly never approach being truly identical). But any similarity will vary by individual, by occasion, by state of consciousness, by mood, by pretty much any other mental or physical factor or circumstance. So there is no real concrete, plausible, general answer to your question, because the premise is just too fundamentally flawed. Now, if you're asking if some men are aroused by having their nipples stimulated, the answer is unequivocally yes. But surely that does not come as a surprise to you? Snow 07:53, 31 July 2016 (UTC)

Sahara desert

How long did it take for the non-oasis soil to disappear after the climate became desertic? Sagittarian Milky Way (talk) 21:00, 30 July 2016 (UTC)

Just a point in the right direction as I don't have the time to follow up the primary sources tonight, but I would check out the sources for Chapter 19 (How Africa became Black) of Jared Diamond's Guns, Germs and Steel. I think you should be able to find "further readings" section online; if not, I will transcribe them here for you tomorrow. Numerous of these sources are clearly concerned with the ecological state of the region during the relevant period, so I suspect the answer to your question can be found in one of them! Good luck! Snow 08:04, 31 July 2016 (UTC)

Based on the Dust Bowl, not long. Mikenorton (talk) 09:31, 31 July 2016 (UTC)

Estimating the weight of a dinosaur from its footprint

Is it possible to get an estimate of the weight of this dinosaur using the depth of the footprint, e.g. using the indentation of some small stones or by estimating the softness of the ground the dinosaur was standing on using other means? Count Iblis (talk) 21:21, 30 July 2016 (UTC)

Working out the softness of the ground is the biggest problem I think. This study of producing dinosaur tracks experimentally says "It is impossible to achieve a quantitative test for all fossil dinosaur tracks as there are too many variables to account for. These variables include the moisture content at the time of track formation, the weight of the dinosaur, the true morphology of the dinosaur's foot, and the exact gait of the dinosaur at the time of track formation". Note also that many tracks were left by dinosaurs moving through various depths of shallow water, which may have part-supported their weight. Another factor is that the track may be preserved in a layer that was not actually at the surface at the time, but was below another more easily erodible layer now gone. To sum up, too many variables. Mikenorton (talk) 09:39, 31 July 2016 (UTC)

July 31

Origin of Russian Anthrax

I was reading a recent news story and was wondering whether the anthrax was "natural" in origin, like similar outbreaks in the US and the UK(see Anthrax#Exposure), or whether it's another leak of bio-weapson like the Sverdlovsk anthrax leak. The news story doesn't specify. Crudiv1 (talk) 00:20, 31 July 2016 (UTC)

It specified. "The concern among experts is that global warming thawed a diseased animal carcass at least 75 years old, buried in the melting permafrost, so unleashing the disease." --Tagishsimon (talk) 00:29, 31 July 2016 (UTC)

Yes, I read that, but it doesn't rule out the bio-weapons case since the animal could have contracted the disease from an unintentional lab leak or it could have been infected intentionally as test case like in on Gruinard Island.Crudiv1 (talk) 03:27, 31 July 2016 (UTC)

here is another article. Bear in mind that the Yamal Peninsula is ground zero for global warming - last winter it was the spot that was 11.5 C warmer than normal (see ) and since then, as the news link mentions, they've had a summer heat wave with 95 degree Fahrenheit temperatures as opposed to a normal high of 77. The Arctic is warming faster than anywhere else, and Yamal is warming much more than some other parts of the Arctic. The other thing not mentioned in the first link is that there were 1500 live reindeer infected with anthrax, providing a plausible intermediate step to the humans. Because the cases were not "confirmed", I'll go out on a limb and guess they're gastrointestinal cases from eating infected meat rather than inhalation cases that would trip my paranoia. Wnt (talk) 10:27, 31 July 2016 (UTC)

FTIR machines

I've finally found an FTIR machine which is inexpensive enough (and small enough) for me to buy, but I was surprised to see a disclaimer on the product page saying that "The sale of this item may be subject to regulation by the FDA..." and so on. Is that true? Are sales of FTIR machines really regulated by the FDA, or did they just put this out to be on the safe side? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:12, 31 July 2016 (UTC)

In the section on the use of these, there is a phrase "examining the homogeneity of pharmaceutical tablets" - I suspect something like that would come under the authority of the FDA.You can also get more information by putting FTIR into the search box on the FDA home page - quite a lot of things come up, which I don't have time to read through. Wymspen (talk) 11:46, 31 July 2016 (UTC)

From the official FDA website, "What does FDA regulate? Sale of a device may be regulated by FDA if the seller claims the device is for medical or diagnostic use - and that could be one application of some FTIR machines. (Along the same lines: if you're selling popsicle sticks in an art-and-craft store, you probably won't draw much FDA regulatory attention - but if you sell popsicle sticks for use as a tongue depressor... then you are in clear territory where FDA can and will regulate your sale, even if other applications of ostensibly the same product would fall outside their jurisdiction).

FDA may also regulate a device if it emits electromagnetic radiation - and many FTIR machines make use of a laser, so that could count.

There are many other reasons why FDA or other regulators might have authority to oversee such a product, too. If you aren't sure, and the answer actually matters, you ought to contact an attorney. You can also talk to the vendor - if they are reputable. They can help provide guidance to keep both the seller and the purchaser in clear compliance with all the rules. Nimur (talk) 15:51, 31 July 2016 (UTC)

Blood group

Hi all,

I've had several blood tests and it always showed I'm O+. Yesterday I went to donate blood and they made a quick check by taking a drop of blood from my finger tip. That's the time the nurse told me I was A. How come they can make such a mistake? She checked twice and she couldn't believe me when I said I was O+. Btw the blood tests were made by home in France and also in Dubai, the blood donation was made is a poor hospital in the Philippines. That might explain things but still, I don't get how they can make such a mistake that could kill someone! 203.111.224.94 (talk) —Preceding undated comment added 03:29, 31 July 2016 (UTC)

Blood group

Hi all,

I went to donate blood in a poor hospital in the Philippines. Before that, they took a drop of blood to check my blood group. The lady told me I was A. I am actually O+ (I checked it several times back home in France and also in Dubai for my previous company). The nurse wouldn't believe me. I was just wondering how they cannot find out what is the real blood group? Does this mistake often happens? 122.53.58.54 (talk) 06:26, 31 July 2016 (UTC)

It is difficult to answer this question without seeing actual papers. Ruslik_Zero 07:46, 31 July 2016 (UTC)

We can't diagnose anybody, but I should point out in general that the ABO blood group system is not as simple as in a biology textbook. There are weak A alleles that straddle the boundary with O - see the article for the reference. I would not be surprised if borderline cases are treated differently when donating vs. receiving blood as a matter of safety. Wnt (talk) 10:31, 31 July 2016 (UTC)

If, as a donor, you are O, but get classified as B, that won't threaten the life of anyone. I'd rather worry about the other way round. That is, you could be O, but get classified as B.Hofhof (talk) 12:22, 31 July 2016 (UTC)

Note that per Hofhof and Wnt's points, even if there was some mistake (which is uncertain), for the nurse to refuse to accept that you were O would be correct if the tests say you are B (for example). The concerning thing would be if you are B (for example) but she diagnoses you as O and refuses to accept you are B. In that case it's likely she should either need to accept you are B or since there's some doubt over the test maybe tell you thanks but no thanks.Nil Einne (talk) 14:17, 31 July 2016 (UTC)

I believe the comment "Actually, it's not that simple" applies here also, but I am no expert. I suggest that the original poster should consult a doctor who can diagnose whether they have a rare blood type (as Wnt hints at), and that we should close this thread. --69.159.9.219 (talk) 21:22, 31 July 2016 (UTC)

Deriving the subjective arrow of time from entropy

I've been reading through the arrow of time articles, and I've run into a conceptual problem that I didn't see an answer for. I understand the principle that the physical arrow of time, at least above the scale of quantum mechanics and below the scale of cosmology, seems to be entirely a matter of the steady increase in entropy over time. I don't see an explanation of how that would determine the subjective/psychological arrow of time. Why does the steady rise in entropy, which should be a pretty smooth process with little distinction between the near past and near future, produce a subjective experience of time in which there is a perfectly hard line between the past and the future? Specifically, what series of steps would get you from entropy as a physical principle, to a brain in which memories are only formed of events from the entropic past? I came up with a possible solution, and I would like to get feedback on whether it makes sense, or if there is some other obvious explanation that I missed. Taking an action potential in a neuron as the fundamental step of information processing in the nervous system, it seems like it could be viewed as a mechanism for converting entropy into time-irreversible computation. Ignoring the complicated processes for amplifying and propagating an action potential, it is kicked off when channels across a membrane between an area of high sodium concentration and an area of low sodium concentration are opened, allowing the passive diffusion of sodium down the concentration gradient. When enough sodium ions have crossed that the charge passes a threshold, that kicks off the rest of the action potential. So in a world where entropy in fluids of a sufficient volume reliably increases, kicking off an action potential is reliably time-irreversible. In the case of sensory neurons, this allows the transformation of external events that are mostly time-reversible, such as the deformation of a surface or the absorption of a photon, into time-irreversible internal neural events. For instance, in the case of a mechanoreceptor, deforming and then straightening a membrane is time-reversible, ignoring the small amount of heat created. But deforming a membrane which has holes in it that allow segregated fluids to mix, and then straightening it, is time-irreversible, and can kick off a series of events that flow in only one direction in time. As a result of that, regardless of what goes on outside the body, our brains and subjective experiences can only contain information about sensory events that occurred in the strict entropic past, up to the time resolution of a small diffusion event. In terms of the purpose of this process, maybe it protects us from the random noise of events occuring and then de-occuring on small time scales. Black Carrot (talk) 04:29, 31 July 2016 (UTC)

This causal description of irreversible psycho/neurological events is eerily coherent with the Buddhist doctrine of causality: everything we perceive is a result of "dependent origination" that is irreversible, but to the devotee could be rendered void by enlightenment about the fundamental emptiness in all phenomena and experiences. AllBestFaith (talk) 14:45, 31 July 2016 (UTC)

I'm more looking for a scientific explanation for the phenomenon. Black Carrot (talk) 16:35, 31 July 2016 (UTC)

I believe Tenzin Gyatso the spiritual head of Tibetan Buddhism, who seeks common ground between science and Buddhism, has expressed that "If science should demonstrate that Buddhism is in error about something then Buddhism must change." AllBestFaith (talk) 17:04, 31 July 2016 (UTC)

This has to do with the link between entropy and information. To describe a generic past state requires less information than a generic future state. This means that when some (in principle) reversible dynamics of a physical systems works as an information processing device, then in the forward time direction (as defined by the entropy increase) there is no problem, but in the opposite direction, you need to invoke conspirational initial conditions to explain the output. Count Iblis (talk) 18:09, 31 July 2016 (UTC)

I sort of get how that works, but it seems hand-waving to me. I'm comfortable with that level of detail in describing simple systems like ideal gasses, because I see how someone could have gone through the math to verify it, but I'm not confident that the same type of justification is available in a more complicated case like this. How can we verify that the sort of information processing the brain is doing is the kind of thing that that rule would apply to, and how can we verify that the scale of the system and the amount of entropy involved are appropriate to draw that conclusion? Linked from the arrow of time articles are examples of small (micron-scale) systems that experimentally aren't well-behaved on short time scales, so it does make a difference. Black Carrot (talk) 20:31, 31 July 2016 (UTC)

Why'd the box my bear spray shipped in have this end up stickers?

The can doesn't say that. Then again the can also doesn't say anything about spraying the can upside down which would seem more likely to get you eaten (but what do I know, maybe it'd work upside down but if so that'd make the "this end up" stickers even more pointless). Sagittarian Milky Way (talk) 01:05, 1 August 2016 (UTC)

Tips to make my stomach gurgle more

How can I drink water in the way that'll make my stomach gurgle tremendously, including timing it like how often, how much and how fast I drink it? When I drink water, I often hear just little gurgles and growls, which it doesn't annoy me unlike a lot of people and is actually useful for me. Hearing stomach gurgles aid the erection upon thinking of smelling a girl's arm (pleasant body smell, not from any of body treatments such as cologne and body wash) while laying on the floor or bed, and more tremendous gurgles would make me feel lot more erected if I think clearly about that. PlanetStar 01:25, 1 August 2016 (UTC)

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