Wikipedia:Reference desk/Archives/Science/2007 May 2

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May 2

Reaching the speed of light

In space since there is no drag, could not one moderatly accelerate to speed of light? —The preceding unsigned comment was added by 75.162.132.156 (talk) 01:05, 2 May 2007 (UTC).

Afraid not! Not through any means we're aware of, at least. By Newtonian mechanics it certainly seems possible, but our understanding of relativity lets us know that it would require infinite energy to accelerate any object with mass to the speed of light, and unfortunately there is only finite energy in the universe. The photon travels at exactly the speed of light, but it has no mass. -- mattb 01:19, 2 May 2007 (UTC)

No. First of all, you can't get to the speed of light if you have any mass. The only thing that can go the speed of light is light itself, and even that has all sorts of philosophical problems (i.e. photons don't experience time, for example). If you want the details you'll have to look over special relativity a bit and perhaps the Lorentz factor (look at what happens when you make v = c). And in any case as you accelerate towards v = c your mass will begin to increase towards infinity, and so will the energy required to accelerate to those speeds — see Mass in special relativity. So it's a losing game: the faster you get, the more energy you will need to go any faster, and at some point it just won't work out from either a practical or theoretical standpoint. At least, that's my understanding of it. Drag doesn't come into it at all in this case. --24.147.86.187 01:25, 2 May 2007 (UTC)

The easiest way to look at the problem is that the faster you go, the heavier you appear to be, and so the more effort you need to put in to accelerate yourself. At the limiting case of your speed actually equaling the speed of light, you would appear to have infinite mass; so you could never reach it. The only way around the problem is to have no mass, as stated above. --h2g2bob (talk) 12:57, 2 May 2007 (UTC)

And there is non-negligible drag in space, anyway, since it is not a perfect vacuum. Nimur 22:37, 2 May 2007 (UTC)

Breast enlargement (herbal supplements)

d they work? ...are they dangerous? what is the scientific status of this stuff? what is the medical status? —The preceding unsigned comment was added by 75.69.194.105 (talk) 01:10, 2 May 2007 (UTC).

I'm speculating here, but (a) no, (b) no, (c) pseudo, and (d) not efficacious. —Steve Summit (talk) 02:11, 2 May 2007 (UTC)

Although there is probably no way we can verify every herbal supplement, herbs and spices should generally be used for cooking, and are unhelpful to a "natural" breast or penis enlargement. I do not believe there is any scientific status. [Mac Δαvιs] ❖ 02:11, 2 May 2007 (UTC)

I think that I will say that (b) possibly. Some herbs can cause damage.--Kirby♥time 02:44, 2 May 2007 (UTC)

Phytosterols do not work for male bodybuilders who wish to grow muscle. So by analogy I do not suppose herbal supplements that encourage female hormones will work. To expand your knowledge I would suggest looking at female hormones and causes of feamle cancers and then decide where you want to go. Paul

thnx, :) i'd rather stay flat :P

Try birth control, it causes enlargement of breasts —The preceding unsigned comment was added by 76.167.159.75 (talk) 21:22, 2 May 2007 (UTC).

Keeping in mind that in some places around the world, "birth control" means properly delivering the baby. V-Man - ^T/_C 01:45, 3 May 2007 (UTC)

Delivering a baby is a sure way to increase your breast size, albeit only temporarily.

Rock identification

Unknown rock found in England.

I need help identifying this rock. It was found (by my mother) a long time ago in England, and has spent many years in faithful service to me as a doorstop. It's fairly heavy/dense, and I was told by someone it could be a meteorite, although I don't know if I believe him. I've looked at many sites for identifying a meteorite, but am still not convinced either way. I know that identification through just an image is still shaky, and should probably still get some more info (density and compositional data (XRF) data in particular). I'm also curious as to what it looks inside, although I don't want to break it open. More pictures, as well as much larger pictures, can be found at my personal website. Thanks --Bennybp 03:23, 2 May 2007 (UTC)

It's brown. See Brown rock.  :) --Tbeatty 06:11, 2 May 2007 (UTC)

Some (not all) meteorites are made largely of iron. Is the rock attracted toa magnet? --Anon, May 2, 2007, 07:57 (UTC).

I know my rocks, and that doesn't look like much, just a typical glacial cobble, probably composed of some sort of granite or gneiss, with some inclusions. --Zeizmic 11:38, 2 May 2007 (UTC)

Or potato? 213.48.15.234 12:04, 2 May 2007 (UTC)

Haha actually potato is probably not too far off. I forgot to put the size info up, but it is about the size of a large potato: about 7" x 4.5" (17.5cm x 11.25cm). It being glacial cobble might explain why it was just found on the side of the road (or so I've heard; I wasn't even alive when it was found). As for the magnet, I'll check, but I don't think a refrigerator magnet sticks to it. --Bennybp 16:55, 2 May 2007 (UTC)

It looks exactly like a sarsen cobble to me - the same stone as the large trilithons at Stonehenge are made of. Some sarsen has an orangey-brown rind on it, similar to what's in your photo. If you ever get to go to Avebury, a lot of the buildings there are made of smashed-up megaliths of sarsen, and they look just like your stone (although some faces have been dressed for masonry). No, I'm Spartacus 11:54, 5 May 2007 (UTC)

Beating Light?

I was wondering if light could beat in the same way sound waves do. If one had two slightly different colours shining at the same time, would they dim and brighten? Thanks in advance, Storeye 07:15, 2 May 2007 (UTC)

Yes. And [1] [2], etc. Light has wave properties, there's no reason it shouldn't behave similarly. -- Consumed Crustacean (talk) 07:17, 2 May 2007 (UTC)

Thankyou!!!Storeye 07:20, 2 May 2007 (UTC)

Also see interference.--Shantavira 07:40, 2 May 2007 (UTC)

Fuse

We know that a fuse wire melts due to overheating.But the practical resistance of a fuse is low. So how does that become equivalent to heat in melting the fuse, because P=i^2r? Also would it not cause a voltage drop??210.212.194.209

as you said, the fuse resistance is low, normally much lower than the resistance of the device which it protects (and with which it is connected serially). Thus, as long as fuse hasn't melted, the voltage drop on the fuse is rather small (but still nonzero, of course). When the fuse melts, the resistance of the fuse increases by several orders of magnitude, and now most of the voltage falls on it. That is how the standard fuse works. Now, your other question was about how the fuse melts. The answer is, the thinner the wire is the less energy (or power) you need to melt it. Thinner wire also means, for same length and material, a higher resistance. Since the current i is determined mostly by the resistance R of the device and not by the resistance r of the fuse (since R >> r), higher resistance r of the fuse means higher power P = i²r of Joule heating of the fuse wire. Thus, the thinner the wire is the lower the max current for the fuse is. BTW, in case of a slowly rising current it is indeed the power of Joule heating that governs the wire temperature (and hence the max current). In an opposite case of a "sudden" current surge it is energy rather than power that is important, hence different melting times for different fuses. (As you know, energy is power multiplied by time interval). Hope this helps. Bear in mind that I am a physicist, not an engineer ;) . Cheers, Dr_Dima.

Adding to what Dr_Dima said, practical fuses actually do have a significant resistance! If your fused circuit is sensitive to IR drop, you must consider the resistance of the fuse as its probably a substantial portion of your resistance "budget". Fuse manufacturers routinely include the resistance data on their data sheets.

Another interesting effect is that fuses, even in normal operation, do heat noticeably, especially if they're operated at a substantial percentage of their current rating. Over time, this can cause crystallization of the fuse wire and perhaps eventual failure of the fuse, even though you never exceeded its current rating. For this reason, you'll occasionally see circuits that appear to be grossly "over-fused" (say, where a 150 mA load is protected by a 2 A fuse); the choice of the fuse may have been made to ensure that it never fails in normal operation as a result of aging but there's still plenty of current available from the source to force blowing in a true short circuit situation.

Atlant 13:49, 2 May 2007 (UTC)

How does the voltage drop suddenly increase when the fuse is about to blow and its negligible when the fuse is operated under max current rating??Also any idea how do same value and different wattage restistace work??~~ —The preceding unsigned comment was added by 210.212.194.209 (talk) 06:15, 5 May 2007 (UTC).

Hypersonic

Any idea how hypersonic waves travel in straight lines??Also is it possible for the same phenomena to exist with electro-magnetic waves??210.212.194.209

Hypersonic can refer to both phonons (vibrations and sound waves) and photons (electromagnetic waves). In either case, hypersonic waves are high-energy waves, at frequencies over about 100 MHz. For phonons, this relates to heat transfer in insulators. For photons, this relates to most electromagnetic waves.

Both phonons and photons will generally travel in a straight line unless some sort of force acts on them making them change direction.

You may be thinking of hypersonic photonic crystals or hypersonic phononic crystals. These are more accurately known as left-handed materials and can be used to create superlenses, which allow sub-wavelength resolution of an image (per Berkeley, 2005).

This answer is a bit vague - if you can be more specific about what you mean I'd be happy to help further. --h2g2bob (talk) 12:47, 2 May 2007 (UTC)

Prevalence of Freezing Temperatures on Earth

Hi, everyone. I've asked this question before, so I'm sorry for asking it again. If you've already read it, please don't be angry. I just really want a good answer. So, the question: What proportion of land/earth's surface/plants/organisms have to survive temperatures below freezing (0 C)? If you know of any peripheral statistics around this question, they would be great too. Thanks very much for your help. Aaadddaaammm 08:30, 2 May 2007 (UTC)

I'd say less than one percent. In comparison to the rest of the world, there aren't that many species that live above the frost line. But, that's just my guess, no reference here. [Mac Δαvιs] ❖ 12:40, 2 May 2007 (UTC)

I'm not going to guess because this is a reference desk not a guess desk. But you should specify how much time they need to survive with temperatures below zero, it will make a large difference. —The preceding unsigned comment was added by 204.63.35.15 (talk) 18:02, 2 May 2007 (UTC).

Good questioning—to what extent and how long? Of course, almost any organism can survive at 0 C for a few seconds, but I was thinking a good snowdown in the arctic, where animals live at temperatures around 0˚ for much of their lives. [Mac Δαvιs] ❖ 18:08, 2 May 2007 (UTC)

Yea, sorry, I wasn't very clear. I wasn't very clear because any statistic would do! I was probably thinking about organisms that have special adaptations to survive sub zero temperatures, or what percentage of the Earth's surface has sub zero temperatures measured most years... Thanks for making me clarify the question. Aaadddaaammm 23:51, 2 May 2007 (UTC)

Buddhist relics ?

Removed duplicate question. Answered on Humanities desk.--Shantavira 18:20, 2 May 2007 (UTC)

cells

why are you more likely to see a polar view in animal cells than in plant cells?

Plant cells tend to be more colorful and are easier to see with regular light. Animal cells tend to have less color and their structures can bee seen better using other techniques such as polarized light.-Czmtzc 18:45, 2 May 2007 (UTC)

lewis structure

What is the lewis structure for Li2S (lithium sulfide)? —The preceding unsigned comment was added by 68.191.57.84 (talk) 15:18, 2 May 2007 (UTC).

Hmmm, I really cant draw it and show it to you, because I dont know how. :-) .. but this site is great. It gives you all the steps and everything to form the lewis structure for any compound. Hope it helps! Cheers! Jayant,18 Years, India • contribs 16:16, 2 May 2007 (UTC)

Half Life of a Drug

If the half life of a substance is 60 hours, how many hours does it take for that substance to clear the body completely?

Surely, it depends on the amount of drug ingested. And I must assume that all the drugs we ingest will leave the body one way or another ;-) ..and if certain chemicals in the drugs are absorbed by the body tissues or something, then I guess it'll take a lot of time for the drug to leave the body without any traces. I know I wasn't of much help, but I am just stating the obvious..I guess. :-P .. Jayant,18 Years, India • contribs 16:08, 2 May 2007 (UTC)

I believe that for a "true" half-life (first-order) elimination doesn't depend on the amount ingested. After 60 hours, half is eliminated. So if you take 200mg, after 60 hours, you have 100mg left. If you take 400mg, theoretically, 200mg will be left after 60 hours. But, also theoretically, it will never completely leave since there is a horizontal asymptote in the function. However, half-life formulas break down for a relatively small number of molecules/particles, as is mentioned in the last section of the half-life article. --Bennybp 17:37, 2 May 2007 (UTC)

It may never clear the body completely. There may still be a molecule or two left when you die. However, that doesn't matter, since it will have no effect once it drops below a certain level. For a general estimate, though, you could use this chart:

half lives elapsed   hours elapsed   days elapsed   amount remaining
==================   =============   ============   ================
       10                 600             25                 1/1,024
       20                1200             50             1/1,048,576
       30                1800             75         1/1,073,741,824 

StuRat 17:10, 2 May 2007 (UTC)

the amount of something left after 'n' half lives is 5^n*10^-n+1 :) HS7 17:13, 3 May 2007 (UTC)

Forget that, a much easier way to work it out is 2^-n :) HS7 17:36, 3 May 2007 (UTC)

skin products

do you guys know non prescrition cream for the face that contains the following? : retinol, madecassol,alpha licolic acid and or vitamin C? thank u —The preceding unsigned comment was added by 75.69.194.105 (talk) 17:35, 2 May 2007 (UTC).

Why would retinol and vitamin C be in facial cream? Isn't that Vitamin A and Vitamin C, and quite useless unless digested? Same with ALA, ain't it? [Mac Δαvιs] ❖ 18:04, 2 May 2007 (UTC)

Meat and Dairy and Calcium

Hi! I wonder if anyone help me with something for a school project? I read this article that said "if you drink milk and have meat in the same meal that you don't absorb the calcium from milk" is this correct please help i need it quickly! - Jen

It appears the protein has something to do with it. See here. As an aside, it appears the calcium can decrease the fat absorption (here). So the protein in meat reduces the absorption of calcium, in turn increasing the amount of fat absorbed. At least that's what the site says. --Bennybp 21:59, 2 May 2007 (UTC)

(removed field coloring question since it was asked below under a proper header) --Bennybp 21:59, 2 May 2007 (UTC)

Football grass colors

How are the different colors of the grass on football fields created? Most football fields have different shades of green to help see when players are offside. How are those made? 83.250.67.227 19:19, 2 May 2007 (UTC)

I believe it's due to the grass being mowed in different directions. →Ollie (talk • contribs) 19:47, 2 May 2007 (UTC)

Thats what I thought too but what would happen if someone did a sliding tackle on the grass, will it change color?

If you mean regular patterns you can see even not near the line of scrimmage (e.g., each 10-yard region alternating), then Ollie is right...same thing that gives stripes or checkerboards in the outfield of baseball. For a good time, google for field stripe mowing. If you mean something that always appears for a given play regardless of where that play is, then that's a computer-generated video effect. DMacks 20:00, 2 May 2007 (UTC)

DMacks is correct; no natural grass-cutting effect exists to help determine if players are offsides (either in football or football) since the point at which a player becomes offsides isn't known in advance. Something like 1st & Ten helps determine offsides (at least for the home viewer), but is computer generated and does not exist at field level. — Lomn 20:35, 2 May 2007 (UTC)

10-yard line DMacks? I thought he was talking about real football (soccer). Anyway you see the same thing in baseball fields. I'm pretty sure its largely for decorative/visual appeal purposes. And its not the way its mowed, its the way its grown. its just two different turfs used to make the field. Adam2288 T C 23:56, 2 May 2007 (UTC)

Okay, so it's a Swedish IP, maybe football==soccer instead of ==football, but the distinction of two types of "color on field" stands regardless of whether "football" actually involves foot–ball contact:) DMacks 04:48, 3 May 2007 (UTC)

Okay, surely this is a person asking about the stripes on a football (soccer) pitch, which they believe are there to make it easier to tell if someone is offside? I can see how that would work, since it would be easier to tell who's in front of who if you have some lines to judge by. The short answer is, by mowing in different directions. People playing on the pitch does muck it up slightly, but that's why they pay for experienced people to care for the pitch between games. Skittle 15:47, 3 May 2007 (UTC)

Nitric Acid

Is the bond between the N+ and the O- in HNO3 considered ionic or covalent? I don't really understand how this bonding works. —The preceding unsigned comment was added by 63.249.102.46 (talk) 19:23, 2 May 2007 (UTC).

Our article on nitrate sure makes it look like a covalent bond rather than an ionic bond. Look at all that shared electron density! See also the elements' electronegativity difference for a (perhaps outdated) way to determine bonding types. DMacks 19:50, 2 May 2007 (UTC)

Just a thought, but if you know how to make a Lewis Dot Structure.. this may lead you in the direction of how the bonds form between elements! Otherwise, the electronegativies is your best bet.

As far as I know to be an acid it must always be a covalent bond, other wise the O- ion will be free, and will thus be a baseBastard Soap 13:02, 4 May 2007 (UTC)

Rusting Process

Is the rusting process of iron or steel actually a form of fire?

--email removed to prevent spam-- —The preceding unsigned comment was added by 63.65.152.94 (talk) 19:26, 2 May 2007 (UTC).

Not really "fire" in the usual "heat, light, flame" sense. But fire and rusting are both examples of oxidation. DMacks 19:41, 2 May 2007 (UTC)

And the oxidation of iron can be made into what is arguably a form of fire by adding a lot of oxygen, see cutting torch. --mglg_(talk) 22:04, 2 May 2007 (UTC)

Even in normal atmosphere, you can even ignite steel wool using a cigarette lighter and then do cool and/or dumb and dangerous things with it. DMacks 22:50, 2 May 2007 (UTC)

good books about instincts/desires and evolutionary psychology?

Lately I have been thinking about evolutionary psychology. I am especially interested in learning about the way that instincts presumably coded in genes become concious (or subconcious) desires. I am also curious about how belief systems, individual or shared, mesh with these instincts/desires.

Can anyone recommend some respected, popular-level books about these issues? Even some links to good articles, or research hints would be appreciated. Thanks -- Diletante 20:42, 2 May 2007 (UTC)

E.O. Wilson's On Human Nature is a classic (emphasis on sociobiology and the development of apparently non-adaptive traits), as is Richard Dawkin's The Selfish Gene (emphasis on the role of genes), Steven Pinker's How the Mind Works (emphasis on cognitive development), and Daniel Dennett's Darwin's Dangerous Idea (emphasis on evolutionary theory). I'm betting that any of those will be highly enjoyable to you in your thinking about this, though they each have problems and are not the end of the discussion. They all take somewhat different approaches and have different emphases so pick the one that seems most up your alley! They're all quite readable. --140.247.250.12 21:29, 2 May 2007 (UTC)

Gaulin, S.J.C. and McBurney, D.H. (2004) Evolutionary Psychology, second edition and Miller, G. (2000) The Mating Mind: How Sexual Selection Shaped the Evolution of Human Naturewere the primary texts for my evolutionary psychology course. With accompanying readings coming from De Waal, Frans (2005) Our Inner Ape: A Leading Primatologist Explains Why We Are Who We Are, Pinker, Steven (1994) The Language Instinct, Pinker, Steven (1997) How the Mind Works, and Pinker, Steven (2002) The blank slate: The modern denial of human nature. Those (plus the ones listed by the previous poster) should provide plenty of reading material on their own, but each also has plenty of citations which you can follow up on your own. You may also want to type in the name of a book or paper that you're interested in into Google Scholar and it will provide a list of papers that cite that work (which may provide contrary perspectives than the authors you're reading). If you have any questions you can always post on my talk page and I will try to help.--droptone 05:29, 3 May 2007 (UTC)

Does the fact that you asked that question here have anything to do with the inclusion of the field "psychology" as a subject of the Science Desk on the header of the desks? A.Z. 08:22, 3 May 2007 (UTC)

Thanks for the suggestions everyone, those look great! -- Diletante 14:46, 3 May 2007 (UTC)

Use of color indicators in titrations.

I have been conducting a lab with an acid and base, and the ending solution is basic. The indicator that I used was phenolphthalein, and at the end of the experiment, the color of the solution is a pale pink color. The question that I have is: Why are titrations typically set up so the ending apperance is colored and does not disappear? Is there a certain reason for this?

I have already read the page about this indicator, but its not quite what I'm looking for. Any comments will help! Thanks! —The preceding unsigned comment was added by 76.188.176.32 (talk) 21:17, 2 May 2007 (UTC).

Titrations based on visual indicators are best done so there is an abrupt, noticible color change. It is much, much, easier to see a clear solution (espectially if you have it against a white background) turn a slight pink rather than go the other way (is there still a little pink? It's hard to tell near the endpoint). At least that's what I've been told (and experienced). Your eyes can play tricks on you. Needless to say, not all titrations are like that. I've seen some where you have to see the solution change from blue to violet. Not easy, but that's why we invented instruments, such as pH meters and spectrophotometers.

You could try a little experiment in the reverse if you want to see it. Just do a base -> acid titration with phenolphthalein. --Bennybp 21:31, 2 May 2007 (UTC)

So is the only reason that titrations are usually set up to turn a different color.. because its easier to see..?

The whole basis for titration requires knowing when one has reached the endpoint. Need some clearly detectible change to occur, and the clearer the change and the more abruptly it occurs, the easier to detect reliably. "Colorless → colored" is easy, "blue → green" is harder; "precipitate starts to form" is easy, "no more precipitate forms" is hard; etc. DMacks 21:44, 2 May 2007 (UTC)

Thanks for the help!

Nicotine gum and hiccups?

Sometimes when I chew my nicotine gum, I get hiccups. This is listed as a possible side-effect of the gum and the WP article mentions it too (though I'd disagree with the 'excessive use in times of stress' line - I've never been particularly stressed when it's happened to me). What I don't understand is *why* this happens - i.e. how the nicotine works on my body to cause the hics. Anyone know? --Kurt Shaped Box 21:23, 2 May 2007 (UTC)

Do you chew with your mouth open?? Don't suck the air in too fast now!

I don't *think* that I chew the gum with my mouth open (I know that I don't with regular gum). Most of the time the nicotine gum is sat wedged inbetween my teeth and my cheek anyway, so I don't think that's it... --Kurt Shaped Box 21:39, 2 May 2007 (UTC)

Nicotine is a stimulant, and hiccups are muscle spasms of the diaphragm. This is speculative, but it's possible that the nicotine induces tense muscles and spasms. Nimur 22:52, 2 May 2007 (UTC)

In fact, nicotine is known to stimulate gastric receptors, and this is thought to be the mechanism of nicotine hiccups. - Nunh-huh 22:55, 2 May 2007 (UTC)

Have you got a cite for that? If so, I'll add it to the gum article... --Kurt Shaped Box 23:05, 2 May 2007 (UTC)

I was about to say that smoking actually used to occasionally give me hiccups, not very often but once in a while. I haven't smoked for about six months and am very happy to have quit after smoking for about fifteen years. Well done Kurt, you can do it, may many good vibes come your way mate. :) Vespine 23:05, 2 May 2007 (UTC)

I'm still smoking a little. I went cold turkey for a while but I lapsed as soon as I got stressed out enough by something to need a smoke - and was back up to my usual 30-a-day within a couple of days. I've been cutting back a lot now I'm on the gum and I'm planning to quit entirely when my current packet of tobacco is finished. --Kurt Shaped Box 23:46, 2 May 2007 (UTC)

Einarson TR, Einarson A., "Hiccups following nicotine gum use", Ann Pharmacother., 1997 Oct;31(10):1263-4. PMID 9337460 - Nunh-huh 23:48, 2 May 2007 (UTC)

Water drops on outside of bottle

How come if you have a frozen bottle thats sealed (such as a 20 ounce coke bottle), if you take it out the freezer, wipe off the outside so you know theres nothing on the outside, and let it sit, you will see water drops on the outside, why does this happend? Where does the water come from? —The preceding unsigned comment was added by 76.167.159.75 (talk) 21:26, 2 May 2007 (UTC).

The warm air will cause condensation to from on the cold outside of the bottle. The droplets are formed when the coldness tries to evaporate. Perhaps, the air bubbles escaping. They certainly don't like warm!

The hotter the air is, the more water vapor it can hold. So when the surrounding air cools in the vicinity of the bottle, it can retain less water vapor; the excess has to condense/revert to liquid form. (see Water vapor#Condensation; there's a nice little graph showing this temperature dependence.) Clarityfiend 21:36, 2 May 2007 (UTC)

The simple answer to the "where does it come from" part of your question is the air--definately not the water/juice/whatever inside the bottle. When the air in contact with the bottle cools down, the water vapour in it forms little water droplets that stick to the bottle. Adam2288 T C 23:50, 2 May 2007 (UTC) I hope you don't mind Adam, I added a not to your answer. I would normally avoid editing people's comments like the plague, but in this case it seemed incontrovertably what you meant, and likely would cause great confusion to 76.167. Shout at me on my talk page if I did wrong. Skittle 15:41, 3 May 2007 (UTC)

Space

As light approaches a black hole, does it travel faster than the speed of light? Please repond on my talk page or let me know you or someone has reponded, thank you.100110100 22:35, 2 May 2007 (UTC)

Here's that again in a different context, "when a car going its top speed accelerates, is it going faster than its top speed?". See how it doesn't make sense? The "speed of light" is light's top speed. It can't go any faster, no matter what. --TotoBaggins 22:53, 2 May 2007 (UTC)

I think you could find weird and misleading physics publications which dance around the simple fact (physicists who study black holes are a little weird : ) but the speed of light is constant regardless of the relative environment. Nimur 22:55, 2 May 2007 (UTC)

Not meaning to be picky, but you should say the speed of light in a vacuum is constant regardless of the relative environment, otherwise completely the opposite is true. Of course, sending light through another medium would only slow it down, so embedding a black hole in a giant glass Dyson sphere wouldn't help either! Spiral Wave 23:34, 2 May 2007 (UTC)

To be fair, the speed of light is always the same, whether it's in a vacuum or not. When light passes through a medium it doesn't actually slow down, rather it's absorbed and re-emitted by the medium, over and over again, and that takes extra time. But the photon is still moving at c the entire time--VectorPotential^Talk 23:47, 2 May 2007 (UTC)

Although come to think of it, our article on speed of light lists my explanation as a common misconception ( : the real explanation is much more colorful, and has something to do with the interactions between photons and phonons. My explanation applies only if the medium it's passing through is a star or some other ball of hot plasma ( :--VectorPotential^Talk 23:56, 2 May 2007 (UTC)

Ah, you beat me to it, I was just about to say that's not quite right! But yes, in actuality (from the photon's perspective, as it's sometimes cheekily put) the speed of light is constant. I only meant as we would observe it, which seems to be the useful thing here. Spiral Wave 00:02, 3 May 2007 (UTC)

Light still travels at the speed of light, however, as it approaches the black hole it is blue shifted, so that the frequency is increased. This also applies to light approaching any object with gravity such as the earth, but usually the effect will be too slight to notice. GB 23:31, 2 May 2007 (UTC)

Does that mean it loses energy? I can't remeber the λ formula.100110100 01:39, 3 May 2007 (UTC)

Wouldn't light slow down (as seen by someone on Earth) as it entered a black hole? This would be due to time dilation. --h2g2bob (talk) 23:40, 2 May 2007 (UTC)

Allow me to play the role of a country bumpkin. Any particle traveling at speed S will accelerate further when it drops down a gravity well. So therefore a photon traveling at speed C will accelerate further if it drops downs a gravity well. So does the photon travel faster than the speed of light? 202.168.50.40 00:22, 3 May 2007 (UTC)

Yes, that is my question. That is why I asked if light travels faster than $c$ when approaching a black hole.100110100 01:39, 3 May 2007 (UTC)

Gravity does not work that way. Light always travels at the speed of light, which is constant. Always. It doesn't accelerate as it goes into a black hole. WilyD 03:47, 3 May 2007 (UTC)

To summarise: A photon gains energy as it falls down the gravity well of a black hole. The effect of this increase in energy is not to increase the photon's velocity, which is always c for all observers - instead, the photon's observed wavelength decreases and its frequency increases. Time dilation has no effect because the photon already has an infinite Lorentz factor - in other words, no time passes at all in the photon's frame of reference. Gandalf61 13:05, 3 May 2007 (UTC)

How does it gain energy?100110100 01:28, 4 May 2007 (UTC)

When the photon is far from the black hole it has potential energy due to its position in the gravity well of the black hole. As it approaches the black hole, this potential energy transforms into other forms of energy. For a solid object (like a ball rolling down hill) this potential energy is transformed into kinetic energy, and so the object's velocity increases. A photon's velocity cannot increase, so the potential energy is transformed into relativistic momentum, which decreases the photon's wavelength. So, strictly speaking, the photon does not gain energy - I mispoke - its potential energy is transformed into another form, and it gains relativistic momentum. Gandalf61 08:36, 4 May 2007 (UTC)

the speed of time changes near a black hole, instead of the speed of light.

LIght's behaviour is truly freakish. If I toss a ball towards you at 10 mph, you see it coming towards you at 10mph. But if you run towards me at 5mph when I toss the ball to you at 10mph, you see the ball coming towards you at an effective speed of 15mph (10+5) - and if you run away from me at 5mph - it'll seem to you that the ball is approaching you at only 5mph (10-5). But with light, if I shine a beam of light at you, it'll always seem to be coming towards you at precisely the same speed no matter whether you are running towards me, standing still or running away from me - and it doesn't matter how fast you run either. If you run away from me at 90% of the speed of light, the light still seems to come towards you at the same old speed. This freakish fact is the heart of the weirdness that is relativity. Since I see the light heading towards you at the right speed for me - it seems to me that you ought to see it going slower if you are running away from me. But you don't - and the only way that can be true is if the rate that time passes is different for you and for me...and that it is the literal truth - that's what happens. So as your beam of light drops towards the black hole, from both our perspective and the black hole's perspective, the light is going the same speed. The extreme gravity around the hole warps space - which for an ordinary object like our ball would make it accellerate - but light can't go at different speeds - so time is distorted instead. When you squash up time, the interval between the peaks and the troughs of the light wave gets crunched up instead - which seems to us as if it's changing colour - shifting towards blue - then into the ultraviolet. Since blue light is more energetic than red light - we'd say that the light gained energy. SteveBaker 02:07, 4 May 2007 (UTC)

Hallucinogenic tryptamines and the varaiety of visual patterns produced.

Dear Ref Desk, I am very interested in knowing what structures or mechanisms are responsible for the variation in visual perception among different substances i.e. LSD produces a variety of patterns and while thats true they also happen to be very geometric with well defined shapes while psilocybe mushrooms produce organic shapes in the visual field and furthermore DMT can produce both?

Identify this bizarre fruit?

http://www.pocketmagazine.net/album/wp-content/uploads/2007/05/unknownfruit.jpg

--Sonjaaa 22:53, 2 May 2007 (UTC)

I first thought Kumquat but the cross-section image seems to indicate otherwise. Nimur 22:57, 2 May 2007 (UTC)

I think it's a passionfruit. --Trovatore 23:00, 2 May 2007 (UTC)

Even though its skin appears orange? Nimur 23:01, 2 May 2007 (UTC)

It's a Passion fruit, they come in different colours and I think this is a relatively unripe one. Also known as a grenadilla. --YFB ¿ 23:02, 2 May 2007 (UTC)

Blood Type Possibility

My Mother claims to be AB+ and on my birth certificate it says I am AB+. Seems to fit, however my father claims to be O. If my mother is AB and my father is O then I should be A or B. Is this possible? —The preceding unsigned comment was added by 75.74.140.121 (talk) 23:12, 2 May 2007 (UTC).

It's not possible under ordinary circumstances. One very rare explanation for the results would be if your putative father were not a "true" type O, but rather had the Bombay phenotype. Another, even rarer, explanation might be a spontaneous mutation. But as you recognize, those are not the most likely explanations, the most benign of which is that one of your parents' (or your own) blood type is mistaken. - Nunh-huh 23:18, 2 May 2007 (UTC)

See also the cis-AB case, described along with the other more common blood types. The reference cited specifically mentions the AB->O case you describe. --Tardis 23:39, 2 May 2007 (UTC)

If you're curious about what this may mean, you should speak to your parents and to your physician. Another – relatively unlikely – possibility is that one of your parents is a chimera; see the case of Lydia Fairchild for a famous example. TenOfAllTrades(talk) 02:27, 3 May 2007 (UTC)

That would pretty much mean your mother is Lydia Fairchild. Might as well suggest he got hit by lightning 10 times and it changed his blood type while waiting in line to collect his lottery winnings. A much more likely scenario (about 100%) is that his dad is not O. --Tbeatty 15:01, 3 May 2007 (UTC)

A far more likely cause is, sorry, that your father is not your father. —Preceding unsigned comment added by 84.187.43.190 (talk • contribs)

Well, that possibility is the elephant in the room that everyone is carefully not mentioning. But knowing so little about the circumstances, we clearly have no basis on which to claim that this explanation is more likely than any other. Occam's razor would suggest that the possibility of a mistake in records or recollections should be investigated before considering other more complicated explanations. Gandalf61 12:47, 3 May 2007 (UTC)

And in any case, if paternity were being questioned, it would be determined through a (genetic) paternity test, not via blood typing. - Nunh-huh 00:41, 4 May 2007 (UTC)

Sadly, this isn't too unlikely. I've read that there's about 30 million fathers in America, and out of them about 1 million are raising kids that aren't biologically theirs. Which is what, 3-5% chance? Basically, most likely answers: Your mother/father/you isn't really AB+/O/AB+, or your father isn't your father. -- Phoeba Wright^OBJECTION! 10:27, 5 May 2007 (UTC)