Science desk
< July 1	<< Jun \| July \| Aug >>	July 3 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 2

Giving male hormones to transexual (biological) women

Would they grow a beard and change the voice? — Preceding unsigned comment added by Quest09 (talk • contribs)

Yes and yes. See Hormone replacement therapy (female-to-male) for more detail. --Carnildo (talk)

A note that might make it easier to search for future results: it's usual practice, among the people most likely to be discussing this in a scientific way, to refer to a transgender person born with a biologically female body as a transexual, transgender, or even just 'trans' man, based on the view that they are 'really' a man with a woman's body, rather than a 'really' a woman who 'thinks' she's a man. Not only is this less hurtful to trans people (it doesn't involve assuming they are mistaken), understanding this will make it much easier to follow any discussions you see. 86.164.27.124 (talk) 08:06, 4 July 2011 (UTC)[reply]

Light in a tube?

Suppose I have a tube with higly reflective inner walls. If I placed a spotlight in it, aimed directly at opening at one end of tube, would light coming out from it would be any diffrent (like diffrent brighness, diffrent form of light beam or anything) than, if I had just the spotlight? 46.109.116.140 (talk) 02:01, 2 July 2011 (UTC)[reply]

For one thing, it would take longer to get to the other side, as light doesn't travel with infinite velocity. I wonder why no one ever thought of slowing down light with an intricate series of mirrors such that, for example, it has to bounce exactly a million times to reach the observer, which is the same position you flick the switch, just a certain "distance" (as travelled by the light through all those mirrors) away? Then you could measure its speed much more easily... --188.28.55.61 (talk) 02:08, 2 July 2011 (UTC)[reply]

Ohhh... asume also that we are talking at human scale, where light seems to appear inatantly etc. 46.109.116.140 (talk) 02:31, 2 July 2011 (UTC)[reply]

(ec) That's sort of the idea of Speed of light#Cavity resonance. Though in cavity resonance it doesn't have to be the exact same photon bouncing back and forth over and over; the point is that in general the photons bounce once a wavelength. But also note that the speed of light cannot be measured! Because the meter is now defined as a unit of time, oddly enough. You can see how accurate the length of your yardstick really is, in terms of the time light takes to propagate. (User:Brews ohare would love this thread...) Wnt (talk) 02:33, 2 July 2011 (UTC)[reply]

The meter is not defined as a unit of time. It is defined as a unit of length, namely, the length traveled by light in a vacuum in 1/299,792,458 second. So it is defined in terms of time, but not as a unit of time. —Bkell (talk) 13:21, 2 July 2011 (UTC)[reply]

"The speed of light cannot be measured"? That would come as a surprise to Michelson. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:57, 2 July 2011 (UTC)[reply]

The Michelson–Morley experiment didn't actually measure the speed of light. What it did was measure was if there was any speed of light difference between two perpendicular directions (with the direction of Earth's travel and perpendicular to it, for example) by looking at the change in an interference pattern as an apparatus was rotated. However, I believe the point was that although if you have an independent time unit and length unit you can measure the speed of light (see Speed of light#History), the meter (and thus the inch/foot/yard) is currently defined based on the speed of light. So while you could set up a measurement experiment for the speed of light, the answer is a foregone conclusion, and coming up with an answer of even 299,792.4581 m/s (versus 299,792.458 m/s) means that either your distance measurement or your time measurement wasn't accurate enough. -- 174.31.222.225 (talk) 15:14, 2 July 2011 (UTC)[reply]

You might want to look at Light tube and follow some of the links for a real-life example. --TammyMoet (talk) 07:49, 2 July 2011 (UTC)[reply]

See also optical fiber cable, which is essentially the same thing.--Shantavira|^{feed me} 08:20, 2 July 2011 (UTC)[reply]

True, the Michelson–Morley experiment did not measure the speed of light. However, Michelson did experiments to measure it. E.g., this paper from 1927. http://adsabs.harvard.edu/full/1927CMWCI.329....1M

Michelson's result was 0.00118 of one percent higher than the currently accepted speed. This is because the speed of light has slowed due to atmospheric pollution. :::CBHA (talk) 19:53, 2 July 2011 (UTC)[reply]

Not to nitpick, but I highly doubt that pollution is the reason for his experimental error, if it even is error: the speed of light in the atmosphere will depend on many things, most important of which are temperature and humidity. While pollution will change the speed of light in the atmosphere very slightly, pollution varies from place to place, and in many areas has improved greatly since the 1920s (see Great Smog for an extreme example).-RunningOnBrains^(talk) 20:44, 2 July 2011 (UTC)[reply]

(edit conflict)An amusing reason for the error, but the currently accepted speed is that measured in free space. Michelson's result in air should have been slightly less than the current value. Dbfirs 20:46, 2 July 2011 (UTC)[reply]

Really? I ask a practical basic optics question and you start discussing hardly relevant theoretical issue and suggest I explore similar situations on my own? May I argue that the skylight in question is usualy light by an external light source coming in at angle, as a result it might be diffrent as spotlight placed at end of tube as the light source would be inside the tube and spotlights usualy have a curved mirror to aim the light. And according to the article the medium they are made of determines how the lith travels, it is a wire not a hollow tube with air 46.109.116.140 (talk) 02:27, 3 July 2011 (UTC)[reply]

Yes, sorry, we have gone way off topic. The light coming out of your spotlight tube will be almost identical to the light without the tube. Light from any spotlight (coherent lasers excluded) will have considerable spread, so some light will bounce off the inner reflective surfaces of the tube, but the effect, at best, will be similar to just moving the spotlight forward by the length of the tube. A large parabolic reflector and a plain light source at the focus might be more effective at "aiming" the light to producing a sharp beam, but there will always be significant spread of the light beam. Dbfirs 06:36, 3 July 2011 (UTC)[reply]

Just as I thought :) Thanks 46.109.116.140 (talk) 03:14, 4 July 2011 (UTC)[reply]

Tree with purple leaves

Here's a picture I took. The leaves are always purple. Is there something other than chlorophyll in the cells of the leaves of this tree? Why are the leaves purple? Thanks. Peter Michner (talk) 15:34, 2 July 2011 (UTC)[reply]

A) Yes, there are many things other than chlorophyll which give color to leaves. For example, there are the red leaves of the poinsettia.

B) Accessory pigments, which work with chlorophyll, also come in colors other than the common green. StuRat (talk) 15:51, 2 July 2011 (UTC)[reply]

This looks more or less anthocyanin (eggplant) colored, but I won't pretend to recognize the tree, so take that with a grain of salt. But I see that article has a photo of some somewhat similar looking trees. Wnt (talk) 20:22, 2 July 2011 (UTC)[reply]

Not easy to be sure of an i/d from this fuzzy pic, but it seems to have palmate leaves, so my guess is a Norway maple variety like this one. There are a large number of broad-leaved tree varities with purple leaves; they are all cultivars and do not appear naturally. BTW, I think the red parts of a poinsettia are bracts rather than true leaves, but your point stands anyway. Alansplodge (talk) 20:47, 2 July 2011 (UTC)[reply]

D'oh! I've just looked at the Bract article and it says that they are "a modified or specialized leaf", so it seems I was splitting hairs. We live and learn. Alansplodge (talk) 20:54, 2 July 2011 (UTC)[reply]

Yes, I considered saying that, but didn't want to sound argumentative. StuRat (talk) 22:13, 2 July 2011 (UTC)[reply]

ULAS J1120+0641's distance from us... too far?

This is about the farthest quasar that has been discovered up to date.

According to the Wikipedia article, the Quasar is at a comoving distance of 28.85 billion light-years from Earth. Then it states that this light has been traveling for 13 billion years. I suppose that the discrepancy is due to the expansion, but, how do they know the distance? — Preceding unsigned comment added by 186.29.119.171 (talk) 15:50, 2 July 2011 (UTC)[reply]

That question is discussed on the article's talk page. Looie496 (talk) 15:54, 2 July 2011 (UTC)[reply]

Training in the heat

Well basically my question is if it is a good idea to train in the heat, does it make your training more effective? Less? Is it just a hassle with no rewards? Bastard Soap (talk) 18:14, 2 July 2011 (UTC)[reply]

Unless you are fully adapted to training in the heat, the training will be a lot less effective. Suppose you are used to work out at 250 Watts, you then you produce almost a 1 KW of heat. But if its a lot hotter than normal, you may not be able get rid of 1 KW of heat, so you won't be able to do 250 Watts. Your body thus gets a less effective workout. Count Iblis (talk) 18:26, 2 July 2011 (UTC)[reply]

If you are training for an event that will take place in "heat", training in heat is pretty essential to prepare your body for what you will have to face. CBHA (talk) 19:27, 2 July 2011 (UTC)[reply]

Could you provide physiological mechanisms for what you say? From my knowledge of biology I know that blood is less effective at transporting oxygen in hot temperatures, and when your body is exercising under lack of oxygen it starts burning nutrients anaerobically which is less effective than aerobic metabolism, does that mean that heat training is better for weight loss?78.133.9.177 (talk) 20:00, 2 July 2011 (UTC)[reply]

Also note that training in heat increases the risk of dehydration and heat stroke. StuRat (talk) 20:52, 2 July 2011 (UTC)[reply]

But you notice that don't you? I'm more interested in if it's better or worse for my physical condition. You know I've been living in a hot place all my life so it doesn't really bother me.Bastard Soap (talk) 21:53, 2 July 2011 (UTC) — Preceding unsigned comment added by Bastard Soap (talk • contribs) 21:52, 2 July 2011 (UTC)[reply]

Actually, I don't believe people do always notice the symptoms, or, if they do, they mistakenly think they can do a bit more exercise before they need to do anything about it. StuRat (talk) 22:10, 2 July 2011 (UTC)[reply]

(EC) Not really relevant ~~but~~. I have doubts the heat doesn't really bother you even if you don't appreciate it. When I lived in Malaysia when I was younger, despite being there my whole life I was still far more reluctant and found it harder to carry out vigorous physical activity then I can in NZ. I know I'm not the only one since I've spoken to people in similar situations who feel the same. I suspect most people, even atheletes who've spent their lives and do all their training in such places will find the same (well not necessarily NZ during the current season but a more mild place anyway). Nil Einne (talk) 22:18, 2 July 2011 (UTC)[reply]

I have trouble parsing your first sentence due to (at least) double negatives. StuRat (talk) 22:31, 2 July 2011 (UTC) [reply]

Modified. If you still can't get it I'm saying I suspect the heat does bother the OP even though they may not appreciate it. In other words I have doubts that the op's statement 'it doesn't really bother me' is true, although the op may genuinely believe it to be true. Nil Einne (talk) 22:44, 3 July 2011 (UTC)[reply]

I see. You're probably using "bother me" in a different way. While they meant "cause me an obvious problem", you apparently mean "cause me a hidden problem". StuRat (talk) 00:55, 4 July 2011 (UTC) [reply]

Korey Stringer would have a good answer to this question. Would have a good answer, were he not dead because he trained in the heat. See also the Junction Boys, of whom Bear Bryant later admitted he probably shouldn't have forced them to work out in such heat, as it did not translate directly to better performance in any measurable way. --Jayron32 22:51, 3 July 2011 (UTC)[reply]

This all makes me curious whether minoxidil can be used as a performance enhancing drug. In theory, if the fine hairs on the arms and legs were longer or denser, more sweat would stay on them and cool the body instead of dropping off uselessly... right? And the person would cool himself with less loss of fluid? Wnt (talk) 23:46, 3 July 2011 (UTC)[reply]

When the sweat drops of it's still removing heat, but not enough heat to turn the sweat into steam. The training I do in relatively hot conditions consists of one hour and a half martial arts training, Rugby training is a hell of a lot more strenuous than that.Bastard Soap (talk) 11:21, 4 July 2011 (UTC)[reply]

Athletic heart syndrome?

Surely athletic heart syndrome should be considered to be the normal state of the heart, because until recently we were hunter-gatherers and you needed to run for hours to capture animals? In an NGC documentary it was shown how a bushman persued a kudu in the heat of the day, he run at jogging speed for 8 hours in the heat of the day until the kudu was exhausted and could no longer run away from him.

It seems to me that what is now considered to be a normal heart is perhaps not normal, as it is the typical heart of people who sit at their office desks all day long. Count Iblis (talk) 18:18, 2 July 2011 (UTC)[reply]

Not really an answer, just a comment: a "syndrome" isn't quite a disease - more a combination of symptoms. There are other cases like Aspberger syndrome and Ehlers-Danlos syndrome which, at least in some forms and from the perspective of some people, may not be regarded as disease. The article suggests that athletic heart syndrome might be of interest to physicians who want to distinguish it from other sorts of cardiac hypertrophy that are serious, so in a sense the symptom of wall thickening can be seen as potentially pathological.

I think a certain amount of skepticism might still be appropriate for claims about the athletic prowess of early humans. After all, for every person running down antelopes there was probably someone else hanging around under a fig tree. Running is doubtless an important feature of early human life but I doubt every last one of them was a star athlete, and not every athlete develops this syndrome. Wnt (talk) 20:15, 2 July 2011 (UTC)[reply]

You can't assume that ancient hunter-gatherers had exactly the same lifestyle as hunger-gatherers today. There was probably more game available, and they could also get animal protein by fishing or collecting birds' eggs. Most likely, they walked around a lot, broke into a sprint occasionally, pottered around in camp a lot, sat around telling tall stories in the evenings. But we are talking about thousands of years and right across the globe, so we shouldn't expect it was always exactly the same. Itsmejudith (talk) 21:39, 2 July 2011 (UTC)[reply]

Indeed 'normal' is not a great word in biology anyway. It has some limited use in medicine, if defined in a meaningful way and used properly but outside there? For starters humans haven't stop evolving and we know humans have had some form of agriculture for at least 7000 years so talking solely about hunter-gathers is flawed. (Unless you're going to suggest it's not normal for humans to have our very little body hair because our ancestors had more despite the fact it's likely part of the reason humans can make great persistence hunters.) Further to Wnt's and Itsmejudith point, I'm not sure whether even most advocates of the Endurance running hypothesis would suggest Persistence hunting was used all the time by all humans even after we developed and refined tools like spears. It may have been part of the parcel but probably wasn't used all the time, not to mention it probably wasn't all people (or even all men) that would be doing it. As Wnt has said, note that even when used in medicine, normal or not-normal doesn't have to mean good and bad. Nil Einne (talk) 22:08, 2 July 2011 (UTC)[reply]

Marlin fish question...

I've been watching fishing documentaries recently, as I mentioned in another question a while back. The other day, there was one on that showed guys tag and release fishing for Marlin in the open ocean. One thing that was pointed out was that the Marlin is capable of emitting blue light from its body - there were some really clear shots of the fish being brought closely behind the boat where it was clear through the water that its body was lit up like a DVD player (post-when blue LEDs became more fashionable than red and green). In particular, there were prominent blue lights on the leading edges of its fins - and a series of illuminated stripes on its flanks. It was commented that this is the Marlin's 'attack pattern', indicating that the fish is enraged (as you might expect after being hooked).

Does anyone have any more info about this light and how it is produced? I'm not sure which species of Marlin was shown. They just called it a 'Marlin' on the programme. --Kurt Shaped Box (talk) 23:26, 2 July 2011 (UTC)[reply]

I don't know which method this fish uses, but bioluminescence is the general term. I question their analysis of this as an "attack pattern", though. It seems more likely to be a defense pattern, designed to confuse or scare off the attacker. StuRat (talk) 23:31, 2 July 2011 (UTC)[reply]

From what I can see this is not bioluminscence but rather the fact that partd of the body are silver -- I presume they look like they are shining when the light hits them in certain ways. Looie496 (talk) 00:27, 3 July 2011 (UTC)[reply]

From what the fishermen were saying - along the lines of 'oh crap - look how he's lit up now... you'd better be real careful when you unhook him' (Marlin can jump high out of the water), it would seem that this is something that the Marlin can definitely 'turn on and off' (dunno, maybe it can alter the angling of its scales to reflect light then?)... --Kurt Shaped Box (talk) 00:38, 3 July 2011 (UTC)[reply]

Well, they do have chromatophores, which may give them the ability to change color, but I couldn't find anything that says they actually glow. Looie496 (talk) 00:44, 3 July 2011 (UTC)[reply]

Based on my reading of the info, and your description, it seems like the marlin may alter some chromatophores, and turns it's spikes out rigidly when agitated (like a hedgehog), which makes them sparkle more in the light. SemanticMantis (talk) 23:25, 3 July 2011 (UTC)[reply]