Wikipedia:Reference desk/Archives/Science/2008 February 8

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February 8

Does cheap alcohol get worse hangovers?

I have heard, for many years. from a variety of sources about how a good liquor doesn't cause hangover, and how if you consume cheap liquor you will get a hangover the next day. Is it really true? If so then why is it that? What is it about a well made liquor that makes the consumer less susceptible to hangovers? Thanks --Spundun (talk) 03:16, 8 February 2008 (UTC)

I initially thought that it was some stray methanol or something like that, that made it unhealthy, but the article Hangover doesn't even mention methanol. --Spundun (talk) 03:22, 8 February 2008 (UTC)

Really wierd,I was just looking at this article :D. It sort of does mention it:

In addition, it is thought that the presence of other alcohols (such as fusel oils), by-products of the alcoholic fermentation also called congeners, exaggerate many of the symptoms (cogeners may also be zinc or other metals added primarily to sweet liqueurs to enhance their flavor); this probably accounts for the mitigation of the effects when distilled alcohol, particularly vodka, is consumed instead. Other alcohols would include methanol i think.Shniken1 (talk) 03:27, 8 February 2008 (UTC)

Ahh, I just search for methenol and didn't find anything, thanks for pointing this out. So I guess thats it then? --Spundun (talk) 03:57, 8 February 2008 (UTC)

AFAIK, hangovers are caused by a slew of factors. First is the effect of the normal metabolic products of ethanol, specifically acetaldehyde poisoning. This effect will be the same for all qualities of drink, unless there is either already acetaldehyde or acetate in the beverage, or there is some compound in the drink which competes with the normal ligands for alcohol or aldehyde dehydrogenase. (Mmm, flagil beer...) This process utilizes NAD+, thus leading to a relative state of hypoglycemia, which in normal individuals will be very quickly remedied, but may nonetheless result in fatigue. Second, is the dehydration caused by diuresis via ADH suppression. Again, this effect will be the same with any quality of drink. Third, and this is where quality comes in, there are impurities in the beverage. Impurities include congeners, which are impurities coming from the processing and fermentation of the drink. The amount of congeners has less to do with the quality of beverage and more to do with type. Unflavored vodka, for instance, and distilled spirits have fewer congeners than simple fermented products like wine or beer. If I am being vague on explaining exactly what a congener is, it's because it's pretty much a catch-all term for various sugars, glycosylated compounds, metals, and organic junk that either taints or flavors your brew. However, congeners are not the only impurities present. There are also things that can form in wine and spirits after they have been opened, they are not immune to chemical activity after shipment. To go much more into this might constitute original research, but suffice it to say that in a perfect world, I would be sure to evacuate all carbon dioxide from my open bottles before storage. Looking back on this (probably partial) list of hangover causes, only one (the congeners) would have much of anything to do with price, and only then within certain classes of alcohol (one couldn't compare the hangover index of a riesling and a bourbon with respect to price). I suspect that if there is a relationship between price and hangover for certain types of alcohol, it has more to do with the expense than the quality. One does not do shots of maduro tequila, though I'm sure they would be very smooth. Tuckerekcut (talk) 17:53, 8 February 2008 (UTC)

My experience in this field is more on the practical research side rather than with the theoretical aspects, but the usual saying of those who should know is that the darker the alcohol, the more savage the hangover. The very worst is dark rum and brandy, and the most forgiving is the colourless vodka. And yes, it is the thousands of OTHER chemicals in the brew that irritate the system and cause the bad effects. Some drinkers aver (and I am one of them) that you won’t get a hangover on vodka. I also have noticed that red wine is a lot more brutal than white. It’s kind of commonsense really, but there is a good Scientific American article about it from the 1980s. Incidentally, one of the most poisonous of all brews is the famous absinthe (the original, which I don’t think is being produced anymore. Apart from a high alcohol content, it also has wormwood as an ingredient, a poisonous hallucinogen. This little number might just be the worst of those that have been sold legally. Wood alcohol will blind people, and the stuff the Russians and others concoct in illegal stills will do that and more. Myles325a (talk) 06:08, 11 February 2008 (UTC)

The dangers of Absinthe have actually been historically exaggerated. Someguy1221 (talk) 06:27, 11 February 2008 (UTC)

Permille

How is permille pronounced? Is it like per mill? I ask because this would be very confusing as per mL is commonly said as per mill and would be used in very similar contexts....Shniken1 (talk) 03:30, 8 February 2008 (UTC)

Per/ml (Permill) is kinda the colloquial way of pronouncing it - 1/1000 - I'm fairly certain that Permille is pronounced per milly - as "mille" means 1000. Wisdom89 (talk) 03:42, 8 February 2008 (UTC)

Actually, scratch that - mille is pronounced "mill" [1] Wisdom89 (talk) 03:43, 8 February 2008 (UTC)

duration of human pregnancy?

what is the mean and standard deviation of human pregnancy lengths?

I want to do the maths so I can go to my sister's city (a far trip) with 90% certainty that I will be there early enough for the birth. --Sonjaaa (talk) 04:54, 8 February 2008 (UTC)

Here's one source that says the mean for pregnancies that end in spontaneous labor at a hospital in India is 272 days, s.d. 9 days: [2]. Most other sources seem to give the due date as 40 weeks (280 days) after conception, and our article on pregnancy says that Sally Tracy says that 90% of births occur within two weeks of the due date. --Allen (talk) 05:25, 8 February 2008 (UTC)

Just to complicate things, some sources measure pregnancy from conception, others from the last period. I have also been told that "second babies are usually early", but no-one has ever been able to tell me whether that means that the median falls while the mean stays the same, or that the mean falls, but they can't be bothered to use a different distribution for bigravidity so they use one they know is inaccurate. Bovlb (talk) 06:25, 8 February 2008 (UTC)

Also, even if you determine the mean and standard deviation, I suspect that they might not characterize the distribution sufficiently. A lot more babies are born three months early than three months late. Bovlb (talk) 06:27, 8 February 2008 (UTC)

I don't think you need a mean - I imagine your sister will have a due date, which tells you her "individual" mean. A non-representative sample of my family agrees with the "two weeks either side of due date" window mentioned above, with first babies typically arriving after due date and second babies typically arriving before. In the UK, if a baby is not born by two weeks after due date then delivery is often induced. Gandalf61 (talk) 11:02, 8 February 2008 (UTC)

Which possibly explains why "second babies are usually early" :-) I know my own mother lied to the doctors about her due dates with later babies, since she knew they would induce if she overshot the date by too much. Or perhaps that's just my mum. Rather annoyingly, she then forgot when her actual due dates were, so we can't work out how late/early we were as guidelines for the future. 130.88.140.112 (talk) 14:43, 11 February 2008 (UTC)

Yes, (OR here) a number of mums choose a due date to suit them (to avoid or encourage induction etc); dates based on cycles can be inaccurate if the woman's cycle is anything other than very regular, and scan due-dates are based on average foetal measurements and thus are usually issued with a "+/- 5 days"-type proviso. On top of that, even if you get a precise due date, each woman has a different relationship betwen delivery/due date. eg. "I'm always early". "I'm always late" etc etc. Babies come when they want to. But if you have 4 weeks up your sleeve, then two weeks either side of the due date is your best bet. If less time, err on the side of late: at least then you won't miss meeting the baby. Gwinva (talk) 03:06, 12 February 2008 (UTC)

Just found this thread, hope you are still reading... 90% of pregnancies deliver within 2 weeks either way of the EDD (estimated date of deliver, or "due date"). That's still a window of almost a month to have a 90% chance of being there. --Ginkgo100^talk 03:50, 15 February 2008 (UTC)

Identify this Hibiscus

Which species of hibiscus is in this picture?

http://en.wikipedia.org/wiki/Image:Hibiscus1.jpg —Preceding unsigned comment added by 202.124.215.123 (talk) 08:24, 8 February 2008 (UTC)

Now THAT'S a pistil! Maybe you already guessed it's Hibiscus Rosa Sinensis or Chinese Hibiscus. Looks like they have frilled edges on the petals. Julia Rossi (talk) 10:05, 8 February 2008 (UTC)

Common corpse perception

There's a common idea that a corpse is noticeably heavier than when it was a living person. Tried cadaver/corpse/body but nothing – unless missed it. Is there any truth in that? Julia Rossi (talk) 09:49, 8 February 2008 (UTC)

Philip Marlowe says "Dead men are heavier than broken hearts", but I don't think he means they actually weigh more, they're just difficult to move around as they are an awkward shape (no handles) and don't make any attempt to help you. 163.1.148.158 (talk) 10:17, 8 February 2008 (UTC)

As a nurse of some decades I have had, unfortunately, to deal with corpses and this myth is of long standing. In my experience there is no evidence to show this to be true, I have never experienced any patient that felt heavier after death. What is often surprising is the weight of a limb or a head when the patient is dead - or unconscious - and this this may have led to this idea. You use the word 'noticeably' in your question which implies subjective assessment. This may be one of those self fulfilling myths. Perhaps a friendly morgue technician will be by in a while to give us some scientific evidence. Richard Avery (talk) 11:31, 8 February 2008 (UTC)

Perhaps its like a child that does not want to be picked up, it seems heavier beacause it is no longer supporting any of its limbs and is flopping around (when you move it, not on its own ;-)) 161.222.160.8 (talk) 18:52, 8 February 2008 (UTC)

I couldn't find any part of the decomp process making it heavier... The last time I heard of it was from a nurse who trained then left many years ago. I'm with the idea that an unconscious body is awkward and cumbersome to lift on its own as above, and kids are wise to this for sure. When people express the impression that a corpse is "so much heavier" it's often in connection with how many it takes to carry the coffin yet no-one likes to admit that it's the coffin making the difference! There;s a lot of subjectivity out there. : )) Thanks all, Julia Rossi (talk) 23:40, 8 February 2008 (UTC)

planetary orbit

has the planets in our solar system ever been perfectly aligned in orbit?

I would assume it was possible, since unless two planets are exactly in phase (eg the angle between them never changes), then eventually they ought to align at some point. It may take longer than the age of the universe, but theoretically it should happen. -mattbuck (Talk) 11:39, 8 February 2008 (UTC)

As the orbital elements are (assumed to be) real-valued quantities, there will never be "perfect" alignment (i.e. it's not impossible but the probability is 0). So there are only points in time at which they are very close to perfect alignment.

Now "perfect alignment" could mean several different things, e. g. that they are (or are closest to being) on a straight line or being in a straight line if projected onto some plane (e.g. Jupiter's orbital plane; the two things are not the same because the orbital planes of different planets are inclined against each other (also remember that the inclinations and the longitudes of the ascending nodes change over longer timespans)), or that they are within an angle as small as possible if viewed from the sun.

If we ignore the inclinations (because they are relatively small) as well as eccentricities and changes in orbital periods, we can make an estimate the time until they are aligned within an angle φ (as seen from the sun) in the following way:

The two outermost planets, Uranus and Neptune, have a conjunction every 172.7 years, a time which we call T_u. Saturn has a conjunction with Neptune every T_s = 36.2 years, Jupiter every T_j = 12.8 years, Mars every T_ma = 1.90 years, Earth every T_e = 1.01 years, Venus every T_v = 0.618 years, Mercury every T_me = 0.241 years. The alignment of the three outermost planets within an angle φ can statistically be expected after a time of (2*π/φ)*T_u. For all planets and a small angle φ (so small that even the innermost planet will have made a total revolution while the outermost passes the angle) this is (2*π/φ)⁶*T_u. If the angle is 10' = 1/6 ° = 10*π/(180*60) then the time is 1.75*10²² years - it has never happened. Icek (talk) 11:45, 8 February 2008 (UTC)

Actually, we can't assume it has never happened. Sure, the universe has only been around for 1.3*10¹⁰ years, and the solar system for 6*10⁹ or so, but without knowing what the initial conditions of the solar system are, we cannot say for sure that it hasn't happened and won't happen before the solar system is destroyed. Sure it's very very unlikely, but... -mattbuck (Talk) 12:05, 8 February 2008 (UTC)

http://www.abc.net.au/science/news/stories/s122109.htm Gzuckier (talk) 15:49, 8 February 2008 (UTC)

Now it's possible...when Pluto was a planet, it wasn't, because Neptune and Pluto are gravitationally synchronized (if I remember correctly...i think it's a 3:2 orbital ratio). -RunningOnBrains 16:36, 8 February 2008 (UTC)

I started to mention this, but started second-guessing myself. It's not that it's impossible when accounting for the orbital resonance (Pluto and Neptune must still cross paths) but it is highly restrictive in terms of where in the Solar System such an alignment could occur. However, even with that restriction, it's not clear to me that the alignment itself is any more restrictive than adding an arbitrary additional planet to Icek's math would be. Neptune and Pluto still align every X years, and it's just a matter of tacking that onto the MVEMJSUN requirements outlined above. — Lomn 17:14, 8 February 2008 (UTC)

Twisted transistors

I am doing engineering but I'm finding quite a bit of trouble to work with the damn transistors. Can anyone drop some good learning materials or something?Bastard Soap (talk) 11:14, 8 February 2008 (UTC)

What aspect of transistors is giving you trouble? And is it transistors in general, or is your difficulty presently limited to bipolar junction transistors or field-effect transistors/MOSFETs?

Atlant (talk) 12:34, 8 February 2008 (UTC)

Are your problems more along the lines of biasing the transistors, or soldering them? Edison (talk) 00:57, 9 February 2008 (UTC)

My problems are in calculating the currents and voltages in transistor circuits, which states should you assume them to be, that sort of things.Bastard Soap (talk) 15:57, 9 February 2008 (UTC)

Then you probably want to take a look at our article Bipolar transistor biasing. Also relevant are Common source, Common drain and Electronic amplifier. We can probably give you better help if you ask a more specific question, and specify the exact circuit you are trying to deal with. SpinningSpark 16:49, 9 February 2008 (UTC)

More common corpse perception

Similar to a previous question, "Common corpse perception", are there any reports of dead bodies becoming lighter? I once heard that a dead person is 39 grams lighter than when alive, and that this was somehow evidence of the soul (it leaves and less weight) 195.194.74.154 (talk) 13:03, 8 February 2008 (UTC)

ps: I'd like to meet a "friendly" morgue technician. Thus far, only Tru Davies seems friendly. 195.194.74.154 (talk) 13:04, 8 February 2008 (UTC)

Corpses definitely become lighter over time as fluids evaporate, various gases are formed and exit the body, and insects chow down and leave.

Atlant (talk) 13:06, 8 February 2008 (UTC)

See Duncan MacDougall (doctor) for the story of a doctor who 'proved' that the soul weighs 21 grams by weighing patients before and after death. AndrewWTaylor (talk) 13:16, 8 February 2008 (UTC)

MacDougall actually weighed six of his patients while they were dying, which is a bit creepy. He also did "control" experiments on dogs. This page at Snopes.com gives a summary of MacDougall's research methods. As our article on MacDougall says: "Although generally regarded either as meaningless or considered to have had little if any scientific merit, MacDougall's finding that the human soul weighed 21 grams has become a meme in the public consciousness". Gandalf61 (talk) 13:28, 8 February 2008 (UTC)

counselling

counselling has become popular, in all aspects of society, discuss this new trend, citing examples from the work place —Preceding unsigned comment added by 196.202.194.10 (talk) 14:02, 8 February 2008 (UTC)

This reads suspiciously like a homework question, which we won't do for you. What aspects of the counseling article do you find confusing or incomplete? We can assist with specifics. — Lomn 14:30, 8 February 2008 (UTC)

Gamma Radiation's effect on matter

When gamma rays pass through something like lead. The lead absorbs some of the radiation. What does this turn out as? Heat? Can gamma rays heat matter? 64.236.121.129 (talk) 14:29, 8 February 2008 (UTC)

Our article on gamma rays notes that three specific mechanisms occur, largely depending on the energy of the gamma ray. In all cases, though, it serves to ionize the matter it interacts with, often with additional lower-energy radiation produced in the process. Per the second law of thermodynamics, such interactions must result in heat, and thus matter can be heated by gamma rays, but this is not the primary mechanism. — Lomn 14:35, 8 February 2008 (UTC)

So the matter it touches, becomes radioactive? But that very same article says they use gamma rays to sterilize medical equipment, kill bacteria off of stuff, etc. But if gamma rays makes things radioactive, then that means all the stuff they are trying to clean with gamma rays becomes radioactive too. 64.236.121.129 (talk) 16:14, 8 February 2008 (UTC)

It means they tend to give off x-rays, but mostly just when they're being irradiated. They don't stay very radioactive afterwards. 81.174.226.229 (talk) 16:27, 8 February 2008 (UTC)

There's a distinction to be drawn between becoming radioactive and being irradiated. Gamma rays cause the latter, not the former. While the high-energy release is sufficient to mess up life processes (irradiation), it's not sufficient to mess up the fundamental atomic nature of matter (radioactivity). That's why it's safe to use as a sterilization process on non-living stuff. — Lomn 17:10, 8 February 2008 (UTC)

I wish the article on irradiation made that distinction a little clearer. It doesn't actually state that objects don't become contaminated or radioactive. 64.236.121.129 (talk) 18:31, 8 February 2008 (UTC)

So then the effect is mostly heat right? If you were to shoot a strong gamma laser at something... lets say a vehicle or a house, would it blow up? 64.236.121.129 (talk) 17:15, 8 February 2008 (UTC)

No, because there's no such thing as a gamma-ray laser (yet), and because there's no available source of gamma rays that strong, other than maybe a nuclear bomb (in which case the house would be blown up, but not by gamma rays).

The actual reason gamma rays are harmful to living things is that they are ionizing radiation and they can destroy molecules by breaking chemical bonds. If a DNA molecule in a cell is damaged, that can cause radiation poisoning or cancer. If a gamma ray hits some inanimate object, nothing spectacular will happen. —Keenan Pepper 17:36, 8 February 2008 (UTC)

Well first of all, I know gamma lasers or gasers, don't exist yet, but they are entirely possible. Next, I question your conclusion on inanimate objects. We have concluded that gamma rays will heat up matter, so there should be some effect I think. 64.236.121.129 (talk) 18:22, 8 February 2008 (UTC)

You could presumably heat things significantly with a gamma-laser of sufficiently ludicrous power, but you'd need a lot to overcome gamma-rays natural tendency to go straight through objects without noticing they're there. You'd do much better to shoot them with something they'll actually absorb most of. Algebraist 18:45, 8 February 2008 (UTC)

Exactly. If you want to blow stuff up, gamma rays are a nonsensical choice. Radiation damage is important for some applications (computer chips in satellites come to mind), but it's usually invisible to the naked eye. If I take a brick and subject it to the most intense gamma source on Earth for hours and hours, it might heat up a few degrees, but afterward it'll still be an ordinary brick. The only permanent effect the gamma rays will have is creating invisible microscopic defects in the crystals. —Keenan Pepper 19:25, 8 February 2008 (UTC)

To continue this, and use an example in a similar vein, a visible-wavelength laser will be far more effective than a graser because most materials won't pass visible wavelengths but will pass gamma rays. Note that laser cutting is well-established in the visible and near-visible wavelength range. Sci-fi likes applying grasers because it's usually accompanied by materials too tough for ordinary lasers to affect. — Lomn 19:34, 8 February 2008 (UTC)

So what kind of electro magnetic radiation heats stuff up the best in laser form? Just regular lasers? 64.236.121.129 (talk) 19:40, 8 February 2008 (UTC)

Anything that's fully absorbed by the material in question and minimally absorbed by the transmission medium (air). Get into a vacuum and you can chuck out the second concern. However, lasers are significantly inferior to other lower-tech devices when it comes to simply heating an object. Their energy is far too concentrated to be effective in this regard. A laser, for instance, could burn through your hand -- but a candle will warm your entire hand. — Lomn 20:23, 8 February 2008 (UTC)

That didn't really answer my question. 64.236.121.129 (talk) 21:17, 8 February 2008 (UTC)

Well, "regular lasers" is rather vague, and I'm not personally up on all the specifics. It's a matter of wavelength and energy, though. Gamma rays are too high-energy for efficient energy transfer. Radio waves are too long-wavelength. So a graser and a raser would both be poor choices. A red laser would be good (for a laser), as it penetrates air well and is absorbed quickly by most materials. Is it best (for a laser)? I have no idea. And then there's that massive "for a laser" caveat, as all lasers are relatively lousy heating elements. — Lomn 21:38, 8 February 2008 (UTC)

You really have to pick a substance before asking what will heat it up best. If you want to heat up organic matter very quickly, use a good carbon dioxide laser in the infrared band. If you want to heat up water very quickly, a maser in the microwave band does a nice job. And as you can tell with your own eyes, plenty of common substances absorb very well in the visible wavelengths. Someguy1221 (talk) 21:45, 8 February 2008 (UTC)

See Active Denial System. Gandalf61 (talk) 10:56, 9 February 2008 (UTC)

Wind loading

Im trying to find information about wind loading, I have to produce a banner that is 4 metres high by 3 metres wide, the banner will be attached to some poles (havent decided how many) but the overall thing needs to be heavy enough to not get blown over by the wind but light enough to be moved by hand by people. —Preceding unsigned comment added by 194.164.82.35 (talk) 15:25, 8 February 2008 (UTC)

i don't have any hard data, but that's going to be really unwieldly. suggestion: cut a lot of vent flaps into it, litle partial circles like 10 cm in diameter, to let the air through. Gzuckier (talk) 15:46, 8 February 2008 (UTC)

So that's what those holes are for. You learn something new every day, eh? 206.252.74.48 (talk) 16:07, 8 February 2008 (UTC)

Mass death of forest tent caterpillars

I live on (in?) Long Island, New York and every 10 years or so, during the spring, we get a population explosion of disgusting forest tent caterpillars (Malacosoma disstria). Then after a few weeks, they all suddenly die. It's almost as if a virus spreads through them all, causing them to ooze, shrivel up, and die. I guess it's possible that a pesticide was applied, but I don't think it was. Are there any known infections that would cause this? -- MacAddct  1984 ^{(talk • contribs)} 15:25, 8 February 2008 (UTC)

There's maybe something here[3] in the article. Julia Rossi (talk) 02:37, 9 February 2008 (UTC)

Why is 98 degrees uncomfortable?

Why do people often find it uncomfortable when it's 98 degrees out? Since normal body temperature is 98~ degrees and all. Bellum et Pax (talk) 15:29, 8 February 2008 (UTC)

because your skin likes it to be cooler so it can unload the heat more efficiently. beside, your skin is lower than 98 degrees. Gzuckier (talk) 15:44, 8 February 2008 (UTC)

Remember that you generate body heat too, and need to get rid of it. 81.174.226.229 (talk) 16:15, 8 February 2008 (UTC)

It's 98.6 degrees to be more exact. 64.236.121.129 (talk) 17:13, 8 February 2008 (UTC)

98.6 is blood temperature; not skin temperature (except perhaps in very intimate places).--Shantavira|^{feed me} 17:40, 8 February 2008 (UTC)

When did I say 98.6 degrees was skin temperature? 64.236.121.129 (talk) 18:24, 8 February 2008 (UTC)

Normal human body temperature ranges over several degrees Fahrenheit. 98.6 is false precision. -- BenRG (talk) 20:55, 8 February 2008 (UTC)

Wow, I had no idea 98.6 F was just an exact conversion of 37 C. --Allen (talk) 06:48, 9 February 2008 (UTC)

Yup, and human body temperature fluctuates during the day, and the normal set-point temp. from the Hypothalamus is different for everybody. Mine, for instance, is 97.1 F. Wisdom89 (talk) 07:16, 9 February 2008 (UTC)

Oh, and we also wear clothes. Add the sunlight that is usually present at that temperature, as well as the usual humidity, and the body may very well react as if it was in a state of 150F with no clothes, no sunlight, and no humidity. Clothes keep in the heat that is already in the body, sunlight adds extra heat to the body, and humidity prevents us from sweating much in order to cool us down...and you've got an uncomfortable situation. I just hope I slightly overcalculated on the global warming scenarios, or we could be dealing with an average of approximately 180F of maximum temperatures that the body thinks it feels like annualy where I live. Just some random speculation. Hope this helps. Thanks. ~AH1^(TCU) 18:46, 9 February 2008 (UTC)

Light

I am really confused. If light is a wavelength of the electromagnetic spectrum, then I guess that it is atoms nudging each other in the air. So how on earth can it travel through space? I must be thinking something wrong. (please use short words)KarateKid101 (talk) 16:26, 8 February 2008 (UTC)

Light is not atoms bumping...actually, that's sound. Light (and all parts of the electromagnetic spectrum) are little packets of electric and magnetic vibrations called photons, and they can travel without a medium. For sound, the medium is air (or a wall or any other object you put your ear up to). For ocean waves, the medium is the ocean water. Light is the only wave in nature that doesn't need a medium. Hope this helps! -RunningOnBrains 16:43, 8 February 2008 (UTC)

(edit conflict) This is a great question - it's one that kept scientists in the 19th century very busy for a long time! Before electromagnetism was well understood, scientists only had experience with waves that travelled through stuff - ocean waves travel on the surface of water, sound waves travel through air, waves could travel through stretched ropes (like a jumprope), etc. However, it wasn't clear what Transmission medium light needed to travel through - it didn't seem to depend on any stuff to travel like other waves did. For a while, the best theory available was that there was some mysterious invisible stuff everywhere in the universe that they called the Luminous aether. After lots of careful experimentation and argument, it was proved that there was no aether. So what's the answer to your question? Light is a displacement in the electromagnetic field. If you haven't studied electromagnetism before, it's a tricky concept to grasp at first. The electromagnetic field is a vector field defined everywhere in the universe. Charge cause the electromagnetic field to be non-zero. When you wiggle charges back and forth, it causes a disturbance, or displacement in the electromagnetic (EM) field, which then propagates (travels outwards). And that's essentially what light is. It doesn't need any air, or atoms to travel. Cool, eh? I hope this helped to answer your question. --Bmk (talk) 16:49, 8 February 2008 (UTC)

It's the Luminiferous aether, not luminous. Algebraist 16:52, 8 February 2008 (UTC)

And it wasn't proved there wasn't any aether, it was just proved that if there was an aether, it was indetectable, and thus could be disregarded or not believed in safely. Big difference. --98.217.18.109 (talk) 17:11, 8 February 2008 (UTC)

You make a good point, but in this case, I disagree - since the aether was defined as the medium through which light propagated, and several experiments showed that there was no such medium other than the electromagnetic field, I'd have to say they did prove it didn't exist - but it's a minor point, and really just a sematical question. --Bmk (talk) 19:32, 8 February 2008 (UTC)

Unless you're talking about experimental error, in which case, of course, they could not have actually proved the lack of a luminiferous medium - they merely demonstrated the lack thereof to a high degree of certainty. I guess you could also say that light may be affected by the hypothetical aether, but so weakly that it is as of yet undetectable. --Bmk (talk) 19:35, 8 February 2008 (UTC)

Hello? Lorentz came up with his beautiful contraction equation by showing that if the medium contracted along with the transmission then there would be no way for someone to measure it. It could still be a medium, it just wouldn't be detectable. There were many definitions of the aether—taking one of them as canonical does its own historical injustice. It was the string theory of its day, and it came in many, many flavors. --98.217.18.109 (talk) 17:44, 10 February 2008 (UTC)

Light is the only wave in nature that doesn't need a medium.

Except gravitational waves. —Keenan Pepper 17:18, 8 February 2008 (UTC)

Shouldn't there be a non-medium-requiring wave to correspond to any particle or chunk of matter flying through space, per the de Broglie hypothesis? --Allen (talk) 17:35, 8 February 2008 (UTC)

Rofl. Leave it to the reference desk to think "please use short words" means "explain advanced and obscure physics to me". :-P -RunningOnBrains 19:13, 8 February 2008 (UTC)

Good point. I apologize. —Keenan Pepper 19:16, 8 February 2008 (UTC)

Sorry... I figure since you'd already answered the original question using short words, it would be okay to branch out to other, related questions. --Allen (talk) 19:51, 8 February 2008 (UTC)

Not criticizing...just funny. -RunningOnBrains 20:01, 8 February 2008 (UTC)

Cool. So how about it then? Can it be said that medium-less waves aren't the province of a few special cases, but rather a broad category, of which light is just one example? --Allen (talk) 20:32, 8 February 2008 (UTC)

Yes - see wave–particle duality for general concept and electron diffraction and neutron diffraction for specific examples. Gandalf61 (talk) 10:46, 9 February 2008 (UTC)

Show me the light!...for photosynthesis

Ok, I may have asked this before so pleaze forgive as I either don't remember the answer or never got one. Plants photosynthesis in sunlight, right? But can they photosynthesize in artificial light, for example lightbulbs, candels, LEDs... I was told yes but every plant that I've seen kept indoors has died if it has no sunlight. xxx User:Hyper Girl 17:20, 8 February 2008 (UTC)

See Grow light. also, please consider using the add a question link instead of editing the whole page --LarryMac | Talk 17:24, 8 February 2008 (UTC)

LarryMac, how can you tell? Think outside the box 17:29, 8 February 2008 (UTC)

from my watchlist. If somebody edits or adds a section, then I can click on a li'l arrow to go directly to that section. If somebody edits the page, I use the diff link to see what was changed. Also, I believe that it helps prevent edit conflicts, but I could be wrong. On topic, consider also the easily found stories of people arrested for "indoor cultivation". --LarryMac | Talk 17:35, 8 February 2008 (UTC)

Yeah, well, it might help if there was an "add a question" link. What the thing actually says is "+". Easy once you know, but... --Anon, 21:55 UTC, 2008-02-08.

"After reading the above, you may ask a new question by clicking here." But it is below the fold these days, so perhaps not obvious. 130.88.140.112 (talk) 14:34, 11 February 2008 (UTC)

Regular light bulbs and tubes just don't make enough light for most plants. For example, try shining a flashlight on a bright sunny day, and you'll see little or no difference. On the other hand, if you open a blind to an otherwise darkened room in the middle of the day, you'll see a big difference (and might not even notice any more light if you turn on a lamp). Even most grow lights need to be within a few inches of the leaves in order to get healthy growth. --SB_Johnny | ^talk 17:55, 8 February 2008 (UTC)

Photosynthesis also says that the wavelength of the light matters. Friday (talk) 17:58, 8 February 2008 (UTC)

Very true, the wavelength does matter, but visible light produced by a light bulb would be 400nm to 700nm - all visible wavelengths and thus, yes, you could maintain plants without direct sunlight artificially - although it might be less efficacious. Wisdom89 (talk) 19:00, 8 February 2008 (UTC)

Printing a full-scale map of the Earth.

I'd like to print a full-scale map of the Earth, I figure with a laser printer 10,000 sheets (and the equivaelnt amount of paper) only costs a couple of bucks (not hard to store, either, the same as 2 very large 5000 page volumes), so it would be (in real size) like a 1:10 000 scale map, not that large to store, a few bookshelves should do.

But that just Doesn't make Sense, because you'd need thousands of square miles of paper, am I being unreasonable after all? —Preceding unsigned comment added by 212.51.122.27 (talk) 17:52, 8 February 2008 (UTC)

Yeah, you must have miscalculated. 10,000 8.5"x11" sheets is nowhere near even one square mile. --Allen (talk) 18:06, 8 February 2008 (UTC)

Perhaps you can satisfy your map lust by just visiting Eartha in Yarmouth, Maine?

Atlant (talk) 18:08, 8 February 2008 (UTC)

My calculations say you need over eight quadrillion sheets of 8.5x11" paper for this project. --Allen (talk) 18:10, 8 February 2008 (UTC)

I feel someone should point you in the direction of Borges's On Exactitude in Science vis-à-vis the possible point of such a project. Algebraist 18:38, 8 February 2008 (UTC)

Wait -- is this a full-scale map or a 1:10000 map? Because the original question uses both numbers, and that's a factor of 100 million when you get down to sheets of paper. — Lomn 19:27, 8 February 2008 (UTC)

I think that is where the confusion is coming in. I'm assuming he wants a full(complete)-scale 1:10,000 map. -- MacAddct  1984 ^{(talk • contribs)} 19:42, 8 February 2008 (UTC)

My impression was that they wanted a full-scale map, and were suggesting that a full-scale map, stacked into reams of paper, would only take up as much shelf space as a 1:10000 map laid flat. --Allen (talk) 19:54, 8 February 2008 (UTC)

• Ah, I think I get it. I bet it was a hyphenation problem. "Full-scale map of the Earth" (where "full" unambiguously modifies "scale") was a mistake for "full scale map of the Earth", with "full" modifying "Earth". --Anonymous, 22:02:08 UTC, 2002-02-08.

OK, so a complete map of the earth at 1:10000 scale -- Earth, with a mean radius of about 251 million inches, has a surface area of about 8e17 square inches. A 1:10000 scale map is still a surface area of about 8e9 (8 billion) square inches. That's about 85 million sheets of 8.5"x11" paper.

Now for storage: 5000 sheets of paper (a standard box of copier paper) measures about 17"x11"x8", or about 1500 cubic inches. 85 million sheets of paper means 17000 such boxes, for about 15000 cubic feet, a cube of paper about 25 feet to a side. — Lomn 20:15, 8 February 2008 (UTC)

• flash* REPLACE TONER CARTRIDGE *flash* -mattbuck (Talk) 01:59, 9 February 2008 (UTC)

Am I missing something? Where are we talking about that 10k of paper + colour laser printer + toner for 10k whole page colour sheets costs $2? Nil Einne (talk) 13:06, 9 February 2008 (UTC)

Square Mercator map

• The equator is around 40,000 km. Scale that by 10,000, you get 4 km. Assume we'll make a square map 4 by 4 km (Mercator projection or whatever). That will be about 12,000 by 20,000 A4 or letter-sized sheets, i.e. 240 million sheets, or close to half a million reams. You'd need quite a bookshelf for that... ;-) Choose another projection, and you'd manage with a bit less... --Janke | Talk 17:54, 9 February 2008 (UTC)

A minor point: The Mercator projection can't be used to map the entire world onto a finite amount of paper. One could choose a latitude range (as implied by Janke with the word "square") or use another projection that can handle the task. Pallida  Mors 20:50, 9 February 2008 (UTC)

Digestion

Approximaetly how long does it take for food to get digested? (i.e. starting from ingestion to egestion?) Thx —Preceding unsigned comment added by 82.46.27.191 (talk) 19:03, 8 February 2008 (UTC)

This varies from individual to individual - the entire digestive tract is roughly 25 feet from mouth to the anus - non digestible material takes roughly 25-36 hours to move this distance. Wisdom89 (talk) 19:16, 8 February 2008 (UTC)

According to the Mayo Clinic, while excretion of undigested material usually begins within 24 hours, it can take up to 72 hours for it to be completely eliminated [4]. And there's a very interesting 70-year-old TIME magazine article here, detailing the time to digest (stomach only) various foods, which should give you a good indication of how much the time it takes to start "eliminating" varries with the content of your meal. Someguy1221 (talk) 19:24, 8 February 2008 (UTC)

On that note, how does the stomach manage to keep one type of food longer than another type? Isn't it all pretty well mashed to a paste by the time it gets in there? --Bmk (talk) 19:37, 8 February 2008 (UTC)

You can probably use a strainer example to visualize how the various food types are "singled out". Imagine mixing chewed meat, mashed potatoes, and a glass of milk in a bowl. Then, you pour the whole mix in a strainer. The milk (and various other liquids) would flow right through. The potatoes would take some encouraging, such as agitation with your hand or a stream of water, but they would slowly make their way through the strainer holes. The meat, not being nearly as soluble or finely divided, would be left in the strainer. Here is where the chemical process in your gut comes in handy, by breaking down the proteins slowly so that eventually it, too, makes its way through the strainer. Tanthalas39 (talk) 21:14, 8 February 2008 (UTC)

To exit the stomach and pass into the intestines, food has to pass through the narrow pyloric sphincter. It passes much more quickly once it has been reduced to liquid or thin paste. ike9898 (talk) 16:32, 10 February 2008 (UTC)

Milk actually takes a while to leave the stomach. Not sure why, but I remember being told as a child that the stomach turns it into something resembling cheese. *shrug* Someguy1221 (talk) 21:56, 8 February 2008 (UTC)

Ever seen a baby burp a while after being breast-fed? ;-) --Janke | Talk 18:16, 9 February 2008 (UTC)

Yes, several times today in fact. It looks like cottage cheese because that's exactly what it is; cheese is just digested milk, after all. Also, baby poop (before solids are introduced) smells exactly like bad cheese, and looks like yellow cottage cheese. And despite all this, I still eat cheese. :P --Ginkgo100^talk 04:04, 15 February 2008 (UTC)

Cheese is traditionally made with an enzyme from cow's stomaches, rennet. Nowadays a vegetable or mold substitute is sometimes used. Rmhermen (talk) 23:01, 8 February 2008 (UTC)

Helicopter Physics

I just saw a U.S. Coast Guard helicopter fly by my window (I have no idea why, this place is landlocked), and it was flying so low that it was level with me on the 8th floor of a 20 story building. I was wondering what is the advantage of flying so low that outweighs the disadvantage of being so close to buildings. A strange theory popped into my head that the air is denser near the ground, thus generating more lift and thus more speed, but I think that is BS. Any ideas? 206.252.74.48 (talk) 19:48, 8 February 2008 (UTC)

The air is slightly denser closer to the ground, but as a practical matter it makes no difference whether the chopper is at your window or five hundred feet further up. (Air pressure declines by about three percent every thousand feet of altitude: [5].) When any aircraft is quite close to the ground ground effect lift comes into play; this effect is only appreciable within a blade-length or so of the ground.

There may have been mission or training requirements that dictated the pilot's choice of altitude, but it wasn't because of thicker air. Maybe your neighbor is an Al Qaeda operative and the Coast Guard was checking him out. TenOfAllTrades(talk) 20:00, 8 February 2008 (UTC)

That's what I thought. Now that I think about it, there is an airport near-by, maybe he had to fly low to keep out of airspace normally used by passenger jets. I wish I knew what he was doing, I've never seen a military helicopter around here before. 206.252.74.48 (talk) 20:38, 8 February 2008 (UTC)

The U.S. Coast Guard isn't part of the military (except when it is, like the U.S. Merchant Marine, during a war). The Coast Guard patrols and protects on navigable waters (some lakes and rivers) as well as blue water operations so you needn't be near the ocean to see them. Rmhermen (talk) 22:37, 8 February 2008 (UTC)

The Coast Guard sure as hell is in the military. Military of the United States lists it as a branch and United States Coast Guard (which you linked to) starts with the sentance "The United States Coast Guard (USCG) is a part of the military of the United States...". And then there is this nice little page on the US military home-page. There was even a dude who received the Medal of Honor for being in the Coast Guard (granted, he was taking part in an operation in Guadalcanal, but still). 83.250.205.56 (talk) 20:48, 9 February 2008 (UTC)

Out of curiosity, what city are you in that you saw this helicopter? —Preceding unsigned comment added by 138.29.51.0 (talk) 14:26, 9 February 2008 (UTC)

Schaumburg, IL. 18:42, 9 February 2008 (UTC) —Preceding unsigned comment added by Chris16447 (talk • contribs)

sky digibox

hi all, we have a sky digi box but no service (after a long dispute over a bill, and we wish to no longer use sky) i have tried to 'tune' in a tv channel into freeview to use the box but alas to no avail, i have two of my three children looking at me as thou i am a hopeless father who can not get them the CBBC channel, the third cares not as he only eats, sleeps, poos and giggles (sometimes all at the same time) can anyone help, a poor tired father of three? Perry-mankster (talk) 19:58, 8 February 2008 (UTC)

If you want Freeview you need a Freeview decoder attached to an ordinary (good quality) TV antenna on your roof. You don't get Freeview from a satellite dish using a Sky box. Buuuut a new free service is scheduled to be launched this year - Freesat. It will carry free channels (BBC, ITV, some other stuff, but not everything you get on Freeview). It seems like your current equipment should be able to receive that, but you don't need a viewing card and don't need to pay Sky anything. They're not super clear when exactly they're starting up, only saying "Spring 08". It will carry CBBC, so your kids can watch Charlie and Lola, but won't carry Five, so they can't watch World's most gruesome sexchange mishaps 2. -- Finlay McWalter | Talk 21:22, 8 February 2008 (UTC)

thank you finlay, bloody sky, what have the roman's sky ever done for us? think i might have an old decoder up de loft (sounds painful){mrs mankster has just reminded me about the HUGE fukin' spider that lives in the loft... about time the kids went outside and played}, you think it would work? - i'm not talking to a disgruntled sky worker by any chance?Perry-mankster (talk) 23:07, 8 February 2008 (UTC)

Not all areas can receive Freeview (check the Freeview website)). Cheap set-top boxes are just as good as more expensive ones, and they all handle the tuning automatically, so as long as the reception is good they are simple to set up, though on every tv I've tried, the scart plug has to be pushed in very firmly and wiggled until you get a picture.--Shantavira|^{feed me} 08:23, 9 February 2008 (UTC)

thanks shantavira, will check out coverage, i too have seen v cheap decoders, so might just go for that optPerry-mankster (talk) 10:12, 9 February 2008 (UTC)

Electromagnetic pulse effects on storage devices

According to the Wikipedia article, an electromagnetic bomb would fry (in order from most damage to least damage) integrated circuits, transistors, vacuum tubes, and inductors. My question, which the article says nothing about, is, what would be the effect of an electromagnetic bomb on storage devices like hard drives, flash drives, DVDs, etc.? —Lowellian (reply) 20:36, 8 February 2008 (UTC)

It'll vary depending on the medium. Magnetic storage like a hard drive is absolutely vulnerable. Physical encoding like a DVD or CD is impervious to EMP. Flash memory, as electronic storage, is most likely vulnerable, though it's been a while since I dealt with the specific mechanics that make flash work. — Lomn 20:58, 8 February 2008 (UTC)

I'm not entirely sure, but my guess would be flash and hard drives would be permanently disabled. Flash drives use integrated circuits and hard drives are adversely affected by magnetic fields. Wisdom89 (talk) 20:59, 8 February 2008 (UTC)

How about a practice of doing a daily or weekly backup of critical data to a flashdrive or outboard hard drive, and storing it along with a transistor radio, calculator, and other useful electronic gadgets in a metal box? The question is how much shielding the Faraday cage would have to provide. Is the metal storage cabinet in an office sufficient, or would an old office safe be required, or a box welded out of 1 cm steel? A data room could be maintained in a shielded room by a business enterprise, with opto-isolation and internal UPS. Edison (talk) 00:55, 9 February 2008 (UTC)

Another question: does the metal casing of a typical external hard drive form an adequate Faraday cage? —Lowellian (reply) 01:15, 9 February 2008 (UTC)

The casing almost never encloses the drive electronics, and there are wires leading from the electronics to the read/write heads. I'd expect the data on the platters to survive EMP effects -- it takes a very powerful magnet to erase a hard drive -- but replacing the electronics is a non-trivial operation, and replacing the heads requires opening the case in a cleanroom. --Carnildo (talk) 03:17, 9 February 2008 (UTC)

Nitrocellulose underwear

Would it be possible/practical to make explosive clothing out of nitrocellulose? --67.185.172.158 (talk) 21:10, 8 February 2008 (UTC)

The article has a story about a chemist who made his apron explosive by spilling nitric acid on it. I have a feeling that it's not so much "explosive" but more "highly flammable" and you'd just end up with burned skin. -- MacAddct  1984 ^{(talk • contribs)} 21:40, 8 February 2008 (UTC)

Sounds like Mythbuster's episode on the farmer's exploding pants. Rmhermen (talk) 22:29, 8 February 2008 (UTC)

You would need to combine the Nitrocellulose paper/material with other compounds in order to make it an explosive. Macaddct is correct - it would just be flammable and burn. In the laboratory I constantly use nitrocellulose membranes for western blotting and I've experimented with applying a flame - it simply burns rapidly. Wisdom89 (talk) 22:39, 8 February 2008 (UTC)

Smokeless gunpowder (and old nitrate film) is nitrocellulose. When ignited in open air, it will burn ferociously, but not explode. Confined - BOOM! (Personal experience... ;-) --Janke | Talk 18:00, 9 February 2008 (UTC)

The questioner wouldn't be Lorena Bobbitt by any chance? Clarityfiend (talk) 19:49, 9 February 2008 (UTC)