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September 25

Controlled Release Medications

I have have certain medications like controlled release melatonin which seem to work mechanically, having an agent that slows there dissolution in the digestive tract. I am curious is this is the sole or typical type of controlled release medicine? Do some CR medicines have a different chemical formulation that changes or slows release or clearing in the bloodstream? I am particularly curious about Zolpidem CR. I don't find any explanation in our article or at the Sanofi website. Thanks. μηδείς (talk) 01:26, 25 September 2013 (UTC)

To clarify, I know from having taken oral morphine after a major abdominal surgery that it is not the morphine itself, but the metabolites that have the most effect. So I wonder if that is the case with controlled release substances--are they designed to take advantage of that phenomenon. μηδείς (talk) 03:57, 25 September 2013 (UTC)

We have a controlled release/time release technology pair of articles. The main methods (by concept, not ordered by popularity or usefulness in certain contexts) are gradually removing a coating to expose the active ingredient, gradually leaching the active ingredient out of a matrix or containment, or chemically cleaving the active ingredient from an inactive-complex precursor. DMacks (talk) 04:07, 25 September 2013 (UTC)

We answered an similar, but unrelated question, a few days ago. The answer can be found in the field of pharmacokinetics. The rate at which a drug enters the blood stream is a matter of a combination of factors, some of it due to the chemistry of the drug compound itself and its natural rate of absorption, and some of it is because of the way the pill is prepared to control how fast the drug is released from the pill, a process called liberation. The so-called "inactive" ingredients (those without pharmacological activity) are actually quite important here; these ingredients are called excipients and they have a lot to do with how the drug is liberated and absorbed. --Jayron32 04:55, 25 September 2013 (UTC)

Okay, so you have both confirmed for me what I expected, there are many means of doing controlled release pills, and it may indeed be a more complicated chemical process than just a physically hard to dissolve tablet, which was the case I ran into when I inadvertently got time release melatonin (anyone who knows how melatonin works would know how silly a product that is) which I had to spend minutes chewing out of their gummy substrate.

So, my specific question is, which of these methods of action applies to Zolpidem CR? Our article doesn't say that they have different formulae or that one is the metabolite of the othert. I couldn't find anything in the Sanofi literature either. So I am curious, can someone find out which of the mentioned mechanisms delays the release of the drug? μηδείς (talk) 05:26, 25 September 2013 (UTC)

PS, to save confusion, I got a BA in Bio as one of my majors as an undergrad, and tested out of Chem 101-102 at an ivy league via my scores in AP chem. So feel free to talk to me about this as a big kid. It help finding the specific info which I am really looking for. Thanks μηδείς (talk) 05:38, 25 September 2013 (UTC)

Zolpidem CR uses hypromellose (hydroxypropyl methylcellulose) for extended release, I think, judging by the difference in ingredients between CR and regular form. Here is some info on the mechanism: http://www.colorcon.com/literature/marketing/mr/Extended%20Release/METHOCEL/English/PTEarticle.pdf Ssscienccce (talk) 05:42, 25 September 2013 (UTC)

Excellent, thanks. μηδείς (talk) 18:50, 25 September 2013 (UTC)

Resolved

Also note that some medications do have slow-acting and fast-acting forms, such as insulin. Our article seems rather deficient on this aspect, so try here, instead, and particularly note the graph at the end: [1]. StuRat (talk) 11:00, 27 September 2013 (UTC)

Yes, just about everyone on my father's side of the family has type II diabetes, so I am familiar with the medications. But my question here was solely regarding oral medications. My experience is that certain oral capsules do and do not work quicker or last less time if chewn, and I was curious what the different mechanisms might be. μηδείς (talk) 04:10, 28 September 2013 (UTC)

Well, chewing it to break it into smaller pieces should certainly reduce the amount of time for it to dissolve and pass through the intestinal walls. However, that isn't necessarily the bottleneck. Some meds may already do this quickly, but then take time to be metabolized by the liver, etc., into a usable form. StuRat (talk) 11:58, 28 September 2013 (UTC)

Sensation in throat

we don't give medical advice
The following discussion has been closed. Please do not modify it.
Whenever I lean my neck and head down, craning my neck I think it's called, while still standing up, I get a tingling feeling in my throat, as if a bubble is passing through it. It almost feels as if my neck is being fractured, but it isn't painful. What is this sensation called and what exactly is going on here anatomically? Bennett Chronister (talk) 05:41, 25 September 2013 (UTC) Sorry - but it is against guidelines to provide medical advice. Please see Wikipedia:Reference desk/Guidelines/Medical advice. Zain Ebrahim (talk) 09:29, 25 September 2013 (UTC) A clarification: I wasn't asking for medical advice. This isn't bringing me pain or injury or anything. I'm just interested, in an academic way, in what this phenomenon is, since I don't think I've ever read about it. Bennett Chronister (talk) 15:10, 25 September 2013 (UTC) Most likely you're compressing a nerve -- that's the usual cause of a tingling sensation when the body is put into a strained posture. Looie496 (talk) 15:33, 25 September 2013 (UTC) It doesn't mater whether the OP feels pain or not, we cannot suggest a cause for his condition. μηδείς (talk) 20:42, 25 September 2013 (UTC) Resurrecting Henny Youngman... Patient: "It hurts when I do this." Doctor: "Then don't do that." ←Baseball Bugs What's up, Doc? carrots→ 21:06, 25 September 2013 (UTC) "Condition"? I thought this was something that happened normally in everybody's body when they stood like that. My question is like asking, "What goes on when I hiccup"? Surely you wouldn't close a hiccup question down.right? Bennett Chronister (talk) 02:30, 26 September 2013 (UTC) The OP has been told we don't do medical advice and no serious answers have been given--feel free to answer with refs outside the hat. μηδείς (talk) 02:44, 26 September 2013 (UTC)

Courting behavior when males ram into each other head first

Is there a scientific term for such a behavior (described in the subject line)? Specifically the rams of bighorn sheep. I was wanting to see a list of other animals that also behaved similarly, but the action doesn't seem to have its own article or category. Rgrds. --64.85.215.13 (talk) 09:05, 25 September 2013 (UTC)

Rutting. Also practised by some breeds of deer and goat (and some humans). --TammyMoet (talk) 09:06, 25 September 2013 (UTC)

I saw that article (Rut (mammalian reproduction)), but figured that ramming was something that was done during the rutting season. So I was hoping there was something on that one specific behavior. --64.85.215.13 (talk) 09:16, 25 September 2013 (UTC)

It is neither courting nor rutting. It's called butting, or locking horns. I also found a nice obsolete word in the OED: to nurt: to push or butt with the horns.--Shantavira|^{feed me} 12:16, 25 September 2013 (UTC)

However, it should be noted that many animals will do a one-sided head-butt at other times, as well, as a means of attack or defense. Thus the comic image of a person bending over when a goat "nurts" them from behind. StuRat (talk) 10:49, 27 September 2013 (UTC)

Mummification

In this distressing case (another link), what exactly does it mean to say that the boy's body was 'mummified', and what could have caused it to happen (as opposed to simply decomposing)? Our article doesn't seem to cover this - it seems to imply that mummification happens as a result of deliberate action or fairly extreme and unusual conditions. AndrewWTaylor (talk) 12:52, 25 September 2013 (UTC)

The body dries out, and the absence of moisture prevents or stops decomposition. The child died in december, in low temperature (near freezing) the decomposition would be slow and with a dry, cold atmosphere and constant draft (open window perhaps) the body could have dried completely. Low bodyweight, absence of food in the digestive system and severe dehydration before death would make it more likely, I assume. Ssscienccce (talk) 13:52, 25 September 2013 (UTC)

<OR here> Based on the first link, it sounds like the word “mummified” was used by the detective constable who discovered the corpse. It is possible he simply misspoke. Based on the description of the smell in the house, it is likely that the body was indeed decomposing. Zain Ebrahim (talk) 14:13, 25 September 2013 (UTC)

(e/c)Yes, mummification is a deliberate preservation of the body, whereas mummify (hence mummified) is used more loosely and can mean "of tissues or organs: to dry or shrivel up." (OED again).--Shantavira|^{feed me} 14:19, 25 September 2013 (UTC)

As I understand it, the smell was coming from rotting food inside the house. They entered the house in september 2011, the boy died in december 2009.

The weather conditions may have contributed as well, see Winter of 2009–10 in Great Britain and Ireland. Very cold air outside would result in very low humidity inside the house. Ssscienccce (talk) 14:41, 25 September 2013 (UTC)

Effect of direction of impact on traumatic brain injury

I heard from a friend that a car crash in which your car is hit from the side is far more likely to kill you then if you were hit from the front. Basically, his explanation was that if the brain experiences sideways acceleration and bounces from left to right instead of from front to back, the middle part of the brain separating the two hemispheres (I believe it's called the Corpus callosum?) is a weak spot and is more likely to tear or suffer damage and you end up with a much worse injury. Is this actually true? If so, would that mean if you were about to drive into a wall, looking away before impact would increase your chance of brain injury?--182.55.86.32 (talk) 14:17, 25 September 2013 (UTC)

If I understand it correctly, PMID 715906 supports the claim that a sideways head acceleration is more damaging than a front-to-back acceleration. However, there are many other factors that come into play when comparing a sideways car crash with a head-on collision. Looie496 (talk) 15:26, 25 September 2013 (UTC)

...the most obvious being that in a head-on collision, you have a nice soft bumper and lots of crumple-zones in front of you to absorb the energy of the collision. Some cars absorb energy by pushing the engine down and behind (which absorbs lots of energy because it's heavy!). In a side impact, there is almost nothing between you and the oncoming vehicle and even with clever design, the car can only crumple in an inch or two before it hits you. Another problem is that your seat back and belt stop you from moving forwards and backwards in a frontal impact - but there is much less there to stop you from sliding sideways in a side impact. Your lap belt will hold your hips in place - but your upper body is hardly restrained at all. A frontal impact in one of the nastiest death-traps ever built - a VW microbus (the last of which is mercifully rolling off the production line in December!) is very often fatal - which is largely because there is nothing between you and the front of the vehicle and it originally had only lap belts. That's a good analogy for a side impact in a modern car. Another issue is that when a car is hit from the front or back, it can usually roll backwards or forwards to retain some kinetic energy and suffer a smaller impact...but the tires on your car strongly resist being pushed sideways in a side impact. Some newer cars now have side-impact airbags to help this situation a bit - but even so, it's not a good way to get into an accident. SteveBaker (talk) 18:04, 25 September 2013 (UTC)

I disagree on your tire argument. While low-speed impacts won't cause a car to move sideways, a high-speed impact will, and there it's just like a frontal or rear impact with the brakes on, in either case the car skids. Also, rolling forwards or backwards (if the brakes are not engaged), can get you into more trouble, with additional impacts, etc., so isn't really a good thing. And, finally, having your car start to move in the opposite direction it was headed only increases the rapid acceleration/deceleration injuries. StuRat (talk) 10:41, 27 September 2013 (UTC)

Schizophrenia rat experiments

You know how some research experiments on Schizophrenia use rats? In order to simulate Schizophrenia in rats, it is known that scientists make an environment that is hopelessly inaccessible for the rat. This presumes that rats have some sort of desire going on. The thing is, how do scientists measure desire in rats? Is it possible that the rat may ever grow tired of the object so that the object will not be desirable at all? Also, how do scientists get access to illegal drugs like PCP in order to perform research on rats and thus simulate schizophrenia? 164.107.103.177 (talk) 15:36, 25 September 2013 (UTC)

As far as I can tell you are describing the paradigm called learned helplessness, but that's considered a model of depression, not a model of schizophrenia. Usually the motivation is to escape from something bad, not to gain access to something good. There are no widely accepted animal models of schizophrenia, but our article will give you an overview of the ideas that have been batted around. And finally, in the USA scientists can get access of controlled substances by getting a license from the FDA, although the process is often difficult. Looie496 (talk) 15:51, 25 September 2013 (UTC)

For more on your final question, see Controlled Substances Act, which governs research access to drugs that are not legally available to the public (at least in the USA, there are similar laws and governing bodies in Europe and elsewhere). Basically, the scientists and the producers of such drugs go through a lot of paperwork and government oversight, involving the Food and Drug Administration, and potentially other agencies. SemanticMantis (talk) 15:54, 25 September 2013 (UTC)

Our article on the economic concept of a Giffen_good mentions an experiment where rats were given water mixed with quinine (which is not tasty to rats). The citation in the article is the 3rd footnote. From memory, the cited book discusses the properties of rat utility functions and how to conceptualize and measure a rat's desire for different things. OldTimeNESter (talk) 15:15, 26 September 2013 (UTC)

Ah, I forgot to address that part of the question. Basically scientists measure desire by the amount of work that an animal is willing to do to obtain something, or the way that it trades off with some other type of reward or (as in the example you mention) punishment. The Behaviorists did a huge amount of work using that approach, generating reams and reams of literature. Looie496 (talk) 15:46, 26 September 2013 (UTC)

aragonite

why are most shells made of calcium carbonate instead of aragonite? — Preceding unsigned comment added by 149.152.20.214 (talk) 15:58, 25 September 2013 (UTC)

Our article on aragonite says that your premise is false, and that most shells are made of a combination of aragonite and calcite. Looie496 (talk) 16:07, 25 September 2013 (UTC)

The presence or absence of magnesium in sea water plays an important role in determining whether aragonite or calcite will be the prevalent form of calcium carbonate present. The levels of magnesium have changed over geologic periods and there were periods in Earth's past when aragonite was the prevalent form. see Aragonite sea and Calcite sea. Dauto (talk) 00:04, 26 September 2013 (UTC)

I seem to have it backwards in my previous post. We are actually living in aragonite sea period currently, so my answer now seems inconsistent. I'm not sure. Dauto (talk) 00:09, 26 September 2013 (UTC)

Turns out your premiss is incorrect and most modern shells include substantial amounts of aragonite which IS a form of calcium carbonate! Dauto (talk) 00:14, 26 September 2013 (UTC)

I'm not sure his premise is wrong, as the calcite article states: "Calcite is often the primary constituent of the shells of marine organisms". Calcite is the more stable form of calcium carbonate, but ultimately the type of crystal will depend on the specific circumstances I suppose. And in old fossils, aragonite originally present will have turned into calcite. Ssscienccce (talk) 07:57, 26 September 2013 (UTC)

Nautical twilight

How many kilometers above you is the daylight when it's nautical dawn at sea level? — Preceding unsigned comment added by 12.196.0.56 (talk) 18:14, 25 September 2013 (UTC)

For starters, Nautical dawn is when the "Sun is 12 degrees below the horizon in the morning" according to Dawn#Nautical_dawn. The earth is roughly 152,098,232 km from the sun, and the Earth's radius is roughly 6,371 km. So you should be able to do some geometry from there to get your general answer. Depending on the accuracy you want, you could take seasonal and latitudinal considerations into account. SemanticMantis (talk) 18:26, 25 September 2013 (UTC)

Why the distance from the sun? Maybe I misinterpret the question, but wouldn't it simply be r*(sec(12°)-1) (about 143 km)? Ssscienccce (talk) 19:15, 25 September 2013 (UTC)

I pictured an ant on a basketball, and a flashlight. It seemed to me that moving the flashlight closer to the basketball would change how high the ant would have to go to see the flashlight, starting from a dark portion of the basketball (i.e. the 12° dark position). But maybe I'm missing something too :) SemanticMantis (talk) 20:17, 25 September 2013 (UTC)

You're missing the fact that the sun is so freaking far away that you can consider it to be at infinite so its actual distance doesn't matter.

Ah...but to know that that is a valid simplification, you need to know how far away the sun actually is!  ;-) --Stephan Schulz (talk) 23:56, 25 September 2013 (UTC)

Yes, it's all about how accurate you want/need the model to be ;) SemanticMantis (talk) 00:57, 26 September 2013 (UTC)

Now you mention it, seems I have ignored that the sun is not a point source and that the atmosphere refracts light downwards to the surface. So the first daylight would be seen when the sun's centre is about 50 minutes of arc below the horizon, making the height r*(sec(11°10')-1) Ssscienccce (talk) 18:55, 28 September 2013 (UTC)

Bestiality and interspecies mating

Did bestiality evolve from the consequences of interspecies mating? In humans, I am not sure if there is a benefit from interspecies mating, because the offspring may neither be viable nor fertile; therefore, the reproduction - as costly as it is - is futile. How did cultural notions of bestiality evolve? 164.107.214.74 (talk) 22:01, 25 September 2013 (UTC)

You might be interested in our article zoophilia, and concepts like ring species and hybrid species. For what it's worth, my opinion is that the answer to your first question is "no." SemanticMantis (talk) 22:34, 25 September 2013 (UTC)

Zoophilia is sufficiently rare that it can be attributed to simply being an abnormality. Just as people often have physical abnormalities which don't increase their chances of reproductive success, they can also have such behavioral abnormalites. StuRat (talk) 10:04, 27 September 2013 (UTC)

According to Kinsey, approximately 40% of farm workers indulged in this practice. Although his methodology has been criticised and his figure may be too high, I don't think it supports the idea that the practice is "rare". Tevildo (talk) 09:12, 28 September 2013 (UTC)

Yes, 40% seems absurd. Not sure how you can draw any conclusions from a study which you admit is flawed. Looking at it the other way, I can't come up with any evolutionary advantage towards zoophilia. Other unusual sexual activities, which involve sex between people, can be argued to provide an evolutionary advantage by creating strong social bonds, much as they do in bonobos, but that doesn't seem to apply here. StuRat (talk) 11:33, 28 September 2013 (UTC)

I doubt zoophilia has anything to do with wanting to reproduce. Although it reminds me of this quote from Tom Lehrer about his friend "Hen3ry": "He majored in animal husbandry... until they caught him at it one day." ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:49, 27 September 2013 (UTC)

Yes, it's most likely a consequence of the domestication of animals and the increased free time available in modern civilization. Production of offspring requires genetic compatibility, none of which any known animal species has. Not even apes. The closest one can get is Feral children. --Auric talk 22:45, 27 September 2013 (UTC)

September 26

Field interaction from photons or other electromagnetic radiation

If an sub-atomic particle like an electron moves through space it will interact with electrostatic and magnetic forces. Now if a photon or other electromagnetic entity moves through space, will it interact with any other force at all? (besides nuclear cores or gravity) Ie, would it be possible to detect or make a readout of vector direction of a photon source without significantly disturb the photon? Electron9 (talk) 01:01, 26 September 2013 (UTC)

Yes, a photon can interact with another photon, see Two-photon physics. The measurement of a photon properties is subject to the same fundamental constraints as any other measurement in quantum mechanics. --Dr Dima (talk) 01:11, 26 September 2013 (UTC)

Does it have to be the same wavelength photon? or amplitude? or even with the same vector/speed direction? Anyway my thinking was to find out the vector direction of photons before entering an object and then compare that with the photons that exit the same object. If possible.. Electron9 (talk) 01:22, 26 September 2013 (UTC)

No, it doesn't have to be the same wavelength. Regarding photons entering and exiting an object, you may want to read Borrmann effect and Mossbauer effect. --Dr Dima (talk) 06:14, 26 September 2013 (UTC) Regarding the momentum vector of the photon before and after, a local measurement of a photon momentum will change its momentum (or, equivalently, destroy the original photon and create a new one), so it is unclear what you would achieve in this case. If you were trying to use an act of Stimulated emission to amplify the photon population in your measurement (having created the population inversion in the medium beforehand), then indeed you may end up with "identical copies" of the original photon, and subsequently measure their distribution of momentum. --Dr Dima (talk) 06:40, 26 September 2013 (UTC)

The easiest way to detect photons is by using electrons. Dauto (talk) 04:20, 26 September 2013 (UTC)

How big is the blue stars in diameters

I was wondering how big is the blue main sequence stars. Because I am ignorant of radius, I dislike the radius usage and rather use diameter instead This shows how can blue main sequence stars O and B have luminosity of 30,000 and 1000 times. I was wondering is blue main sequence stars with planets around can have a substantial atmosphere if they were the diameter of Earth or twice the Earth diameter, or size of Mars. said Blue main sequence stars have luminosity of 2000 for B3 and 1400000 for O3 main sequence stars. When they use the radius of the size of that star, I am confused about the diameter. --69.233.252.198 (talk) 04:40, 26 September 2013 (UTC)

Have you looked at radius and diameter? The diameter is just two times the radius. --Bowlhover (talk) 05:46, 26 September 2013 (UTC)

Can life harbor of planets around white main sequence stars, or yellow-white main sequence stars

Because my college professor told me try to harbor life on planets around white (A) main sequence stars are quite difficult because their time of main sequence only last 1 billion year at the most, so when a planet around A main sequence stars can they have life harboring around the planets, or only simple bacteria can exist if at all? Can yellowish white (F) main sequence harbor intelligence life around their planets if the main sequence only last 3 billion years. I am not sure if F (yellow-white) main sequence star's planets can reach dinosaurs, something like reptiles if the main sequence lasts about 5 billion years. My astronomy professor told me life develop on celestial body needs to take a long time, in just few million years Main sequence is not going to receive any life forms around any planets. To get a intelligence life around celestial bodies to the parent star needs to take billions of years 4 Ga at least.--69.233.252.198 (talk) 04:49, 26 September 2013 (UTC)

Life, probably yes. Bacteria are a form of life, and as far as we know, bacteria came into being essentially as soon as the Earth had cooled enough to have liquid water. Complex life and intelligence are a lot harder - we work from a sample of one, and there seems to be a lot of randomness in the process. No-one knows if intelligence is inevitable or even likely. Maybe without the Chicxulub asteroid, we'd be dominated by stupid T-rexes. Or maybe Jurassic Park had it right and 64800000 BCE the first Velociraptor would have landed on the moon ("It's a small step for a man-eating monster, but a large jump for dinosaurierhood"). --Stephan Schulz (talk) 05:54, 26 September 2013 (UTC)

"What's a man?" "I don't know... man-eating just sounded cool!" MChesterMC (talk) 08:50, 26 September 2013 (UTC)

It's hard to know - but our Sun is 4.57 billion years old - Earth was formed 4.54 billion years ago and life appeared here about 3.5 billion years ago. So it took about a billion years between star/planet formation and first life. So even a star with just a billion years to live has enough time to form planets and jump-start life.

The problem is that we don't really know why life waited around so long before getting going. It's possible that it took that long for the bombardment by big space rocks to slow down enough - or for a stable atmosphere to form - or for the overall temperature to get low enough. There are many possibilities. That being the case, it's plausible that in some other solar system, the orbital dynamics of various gas giants could clear out all of the big rocks much sooner - or that the primordial composition of the future life-bearing planet could allow it to cool off much faster.

Because we still don't have solid knowledge of how life started on earth, it's also possible that the panspermia hypothesis is true and life arrived in the form of complete, working bacteria from some other source. That being the case, we'd have bacteria from the very moment the planet was suitable for them to take hold.

The limiting factor on higher life forms is the rate of evolution. Here on earth, it took at least a billion years for photosynthesis to evolve - which meant that there was no free oxygen in the atmosphere - and that prevented more complex life forms from appearing. Then another two billion years before we started having things that are recognisably plants and animals. On the plus side, it only took half a billion years to get from simple multicellular life to humans.

So what I think would be fair to say is that your college professor is correct if we assume that things around this hypothetical star proceeded like they did here. But: We can make alternative assumptions (such as that panspermia is correct) and that in this hypothetical world, then by chance, they'd have had multicellular, photosynthesizing life deposited onto the surface of an already reasonable planet after (say) a half billion years. That's not entirely unreasonable. If that were the case, then intelligent life and space-faring civilizations could easily evolve before the star died.

SteveBaker (talk) 14:11, 26 September 2013 (UTC)

The late heavy bombardment only ended about 3.8 billion years ago, and may have completely remelted the previously solid surface of the Earth. We have (some, but quite strong) evidence for complex communities of (unicellular) life 3.5 billion years ago. Indeed, some scientists argue that carbon isotope ratios in much older mineral samples (4.25 billion years old) already indicate life back then. It is in no way certain that life did not arise earlier than 3.5 billion years ago, and it may, indeed, have arisen multiple times, being extinguished or reduced to minimal levels again by the late heavy bombardment or similar events. --Stephan Schulz (talk) 14:36, 26 September 2013 (UTC)

Yes - which kinda emphasizes my final point. If you presume that the same sequence of events happens around some other star - then it's reasonable to come to the conclusion that 1 billion years isn't enough to come up with more than primitive single-celled life. The real question at the heart of this is whether life could start sooner and/or develop faster in solar systems where the initial conditions were different. If you read Late_heavy_bombardment#Possible_causes, you'll see that it's very possible for those dangerous rocks to stay put - or to be swept up by some super-Jupiter in a closer orbit to this alternate-Earth. In such a scenario, life could easily have started a half billion years sooner. The next issue is the question of why it took so long for photosynthesis to evolve - which seems to have been the major impediment to intelligent multicellular life. Why that took so long is an interesting question - especially following the discovery of an independently-evolved photosynthetic system in the Oriental hornet - which can't have taken more than a few million years to evolve. SteveBaker (talk) 18:41, 26 September 2013 (UTC)

It's a sample size of one - impossible to know for sure. At a wild guess I would be more skeptical about the redder stars; I'm not so sure life can get started without some hard UV to blast apart and reform polymers over and over again. But there are lots of ideas in the literature (clays, black smokers, all sorts of crazy things) which would disagree with my impression. Wnt (talk) 18:34, 26 September 2013 (UTC)

Yes - it is hard to know for sure. But those red stars could still get life started by panspermia...which is definitely getting increasing respectability in the scientific world as years go by. SteveBaker (talk) 18:41, 26 September 2013 (UTC)

Life may have evolved 3.5 billion years ago, or even earlier. But it was only simple single celled organisms. It took 3 billion years and the evolution of sexual reproduction to occur to allow the evolution of multicellularity in the Cambrian Explosion, which happened only .5 billion years ago. μηδείς (talk) 18:42, 26 September 2013 (UTC)

Of course, the development history of life on another planet may be totally different from the history of Earth. Without the separation of the Moon or late heavy bombardment, life on Earth might have started much earlier - pretty much as soon as the surface had cooled enough. Once life had a foothold on Earth, it had numerous setbacks - extinction event lists at least 15. I can certainly imagine advanced multicelluar organisms evolving in much less than a billion years under ideal conditions; and equally I can imagine multicelluar organisms never getting off to a good start even after many billions of years. Astronaut (talk) 18:53, 26 September 2013 (UTC)

The extinction events only removed the top predators and macrofauna, and can as easily be credited for opening up opportunities for diversity as be blamed for removing the dinosaurs and trilobites. Without the moon's separation there would be no tides, vital for life that cannot live in stagnant water. The delay of that event and the late bombardment hardly effects the overall scheme of 3 Billion years from origin to multicellularity. Most planets with life probably harbor nothing more complex than bacteria. μηδείς (talk) 00:56, 27 September 2013 (UTC)

Without the Moon's separation there would be tides (note first sentence), though with only about 1/3 the maximum range they have now – people commonly forget that the Sun also has a significant tidal influence on the Earth. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:33, 27 September 2013 (UTC)

It depends what you define "life" as. Non-carbon based life might have a better chance in some circumstances.--Auric talk 20:29, 26 September 2013 (UTC)

Correct me if I'm wrong, but it's not only the main sequence life that counts, but also the variation during that "life." The sun is getting hotter, slowly but steadily, and the faster these changes happen (within 1 vs. 10 billion years) , the harder it would be on life. Even worse, the power laws seem to dictate an orbital radius that's roughly proportional to m² (luminosity is proportional to the 4th power of mass or slightly less, and radius to the square root of luminosity), and that would indicate that a planet orbiting a star of 1.5 solar masses should do so at a radius of 2.25 AU. On top of that, a type F star would be younger and more metallic than the Sun, and I've read that that's bad for the habitable zone in general; it would probably not even exist. - ¡Ouch! (^{hurt me} / _{more pain}) 14:09, 30 September 2013 (UTC)

Everett branch convergence

In the many-worlds interpretation of quantum physics, does anything prevent Everett branches from reconverging (by leading to the same future by different chains of events) at the same rate as they diverge? NeonMerlin 09:19, 26 September 2013 (UTC)

Surely separate branches can never produce exactly the same future because their futures have different pasts. If event A happens in branch 1 but not in branch 2, then all the descendants of branch 1 will have future states in which event A happened, whereas all the descendants of branch 2 will have future states in which event A did not happen. Gandalf61 (talk) 11:41, 26 September 2013 (UTC)

That does't really follow. In the long run the past is no more certain than the future, you only see the current evidence. Dmcq (talk) 11:55, 26 September 2013 (UTC)

Because some branches can gather in a circle or just assemble back in time , it is possible to reconnect .Thanks Water Nosfim — Preceding unsigned comment added by 81.218.91.170 (talk) 13:10, 26 September 2013 (UTC)

We know very little indeed about what the implications of many-worlds truly is. Heck, we don't know whether it's true - or complete bunkum - and there are reasons to believe that it's an unfalsifiable hypothesis anyway. So whether different parallel universes could ever recombine is anyone's guess. Any effort to give you an answer to your question should therefore be ignored!

That said, Gandalf61's answer is clearly incorrect because if two universes are precisely identical - then any past memories would also have to be precisely identical because if they differed then whatever systems stored that past history would have to identical too. There would be no conceivable test to determine whether two universes with wildly different pasts - but no differences whatever in the present that resulted from that, actually had different pasts.

God only knows where User:81.218.91.170 came up with that answer - but I guarantee there are no reliable sources to back it up.

Bottom line: We definitely don't know the answer to your question. We probably can't ever know the answer. It may well be logically impossible for there even to be an answer. SteveBaker (talk) 13:47, 26 September 2013 (UTC)

Steve - maybe I didn't explain myself very clearly above, but I think we are in agreement. Different Everett branches have different pasts so they cannot recombine in some mysterious way to produce a hybrid future state. In the Everett interpretation of Schrodinger's cat, there is a "cat dead" branch and a "cat alive" branch, and their descendants must remain separate. The two branches cannot recombine into a "cat both dead and alive" branch. Gandalf61 (talk) 14:16, 26 September 2013 (UTC)

But if you threw the box, cat and all, into a black hole, surely the resulting universe in both cases would be on a "that information is unknown" branch? MChesterMC (talk) 08:14, 27 September 2013 (UTC)

Different branches do recombine all the time, this is a trivial consequence of unitary time evolution. The entire multiverse in fact does not evolve in time at all, H|psi> = 0. Time doesn't exist at the multiverse level. Count Iblis (talk) 13:55, 26 September 2013 (UTC)

the word "branch" is really a bit misleading, as it suggests that quantum history has a tree structure. What really happens in the multi-world interpretation is that the probability wave function spreads out over a huge-dimensional state space. There are an infinite number of possible history-paths, including an infinite number that diverge and then come together again. Looie496 (talk) 15:41, 26 September 2013 (UTC)

I'm out of my field here, but my impression is that CPT invariance means that there should be multiple pasts for a given moment of time just as there are multiple futures, provided that there are multiple futures for particles of any charge or parity. However, we live in a gradient of entropy with less in the past than in the future, so does that mean there are fewer pasts than futures? Or are there as many pasts, just more 'orderly' on average? Hmmm. In any case, the trivial case of this is the double-slit experiment - there are two worlds, one with the particle going through the one slit, one the other, but we find ourselves in a world where we're looking at a dot and there is no way to tell which was our past. Wnt (talk) 18:29, 26 September 2013 (UTC)

The entropy increases, but this does not mean that the number of future states increases. Unitary time evolution implies that this number stays exactly the same. So, how can entropy increase? Thing is that if you were to define the entropy as logarithm of the number of states an isolated system really can be fund in then that entropy would stay constant. The entropy one uses in thermodynamics is defined in a different way, it is proportional to the logarithm of the number of microstates that have the same macroscopic properties as the given system has.

Consider the following example. If you do a free expansion experiment with an ideal gas that initially fills half of a totally isolated container, then the entropy will increase by N k Log(2), because the number of states each of the N molecules can be in will have doubled. But if you look more carefully, then you see that the number of states the molecules can really be in must be the same as you started out with, because each initial states evolves determinstically according to the Schrodinger equation to a final state, the transform from initial to final state is unitary, which then implies that the number of states actually stays the same.

But what matters for thermodynamic entropy is that the gas when it has expanded has certain macroscopic properties (e.g. in this case it has a larger volume) and given those macroscopic properties there are then a larger number of microstates that are compatible with it, than in case of the initial state (with a smaller volume). But most of those microstates are not states the gas can be found in, clearly almost none of them will evolve back to the initial state under time reversal, while any of the states the gas really can be in would evolve back to the initial volume under time reversal (note that this is thought experiment where we assume perfect isolation). Count Iblis (talk) 20:54, 26 September 2013 (UTC)

Colour variations on displays

Do all screens whether a tv, pc monitor, laptop or tablet have varying colours even on the same model? For example, would all screens of a particular make and model have the same sorts of colour hues or would they differ slightly? Clover345 (talk) 11:13, 26 September 2013 (UTC)

How accurately can you measure (or perceive) color and brightness? All that matters to the manufacturer is that the color accuracy and consistency are as good as its customers need. You can buy scientific-grade equipment, if you're willing to pay a premium; otherwise your products will fall along the spectrum, ranging from "professional consumer" to "bargain basement." Start by reading colorimetry. Nimur (talk) 12:04, 26 September 2013 (UTC)

Colours do vary, even in sets of same make and model. Variation comes primarily from user adjustment and the display technology (CRT, LCD, etc). All due respect to Nimur, but whether a set is a cheapie or an expensive professional item has little or nothing to do with it, providing the set is not defective or maladjusted. There are six basic aspects of colour reproduction in television:-

• Choice of primary colour filters in TV cameras (not applicable perhaps to this question)
• The colour accuracy of photographic film when movies or film-based programmes are televised (not applicable perhaps to this question, however if comparing one receiver with another some time later, may trick you)
• Accuracy of gamma in the televion station cameras
• The choice of primary colour phosphors or pigments in the reciver
• Adjustment of signal strength of each primary colour circuit in the reciever
• Accuracy of gamma in the reciever.

The television industry industry very early in the days of colour television standardised the primary colour filters used in cameras. You can asume variation here is neglible. Standardisation of primary colours is assisted by the fact that although there are a vast number of TV and monitor manufacturers, thaere are only a few manufacturers of the actuall displays in the World, which they sell to the various set makers, along with other critical parts.

The television industry very early in the days of colour television standardised the colour phosphor primary colurs for use in receivers. You could neglect variation here too, however Japan standardised on a slightly different red than Europe and USA. So reception with a Japanese receiver in USA or Europe will be slightly inaccurate. It is unlikely that you would notice it, however I recall comparing a Philips receiver with a Sanyyo TV some years ago and side by side you can see a difference when a full red test signal is used.

The pigments used in LCD and plasma displays are not as accurate as CRT displays, but they are getting very good.

The colour accuracy depends on the adjustment of the TV set ("colour" control and/or "tint control" user controls, and internal controls accessible to technicians. This variation can be significant. Some people never adjust their sets properly. Some shops intentionally missadjust TV sets as a sales technique, as some customers like to say "I'll buy that one, I like it's nice colours."

"Gamma" is the term for the correspondence between the electrical signal and the colour intensity over the range from black to maximum light output. The relationship is not linear. Gamma accuracy can vary depending on the display technology - CRT, LCD, plasma, and on how well teh user adjusts the brightness and contrast controls. — Preceding unsigned comment added by 1.122.206.159 (talk) 13:25, 26 September 2013 (UTC)

The way I was interpreting the question was with regard to the variation you see by feeding identical inputs to multiple units within a single product-model - amongst products that are built from ostensibly identical parts. For example, an LCD panel's backlight brightness is specified in nits; but if you build a hundred units, the actual brightness follows something like a bell-curve. There is absolutely a correspondence between price you pay (as an end consumer) and the product vendor's ability to tightly control the statistical distribution of part quality. Now that we live in a mostly-digital-video-signal, mostly-solid-state technology ecosystem, it is arguable that even cheap products are "good enough..." for users who don't notice minute details. The color and illumination variance is lower in this type of technology, compared to, say, phosphor screens (as Steve mentions below); and analog imperfections are avoided for most of the signal path, right up to the point where you're emitting or collecting photons. Ultimately, though, the degree you can tolerate imperfection depends on how accurately you can actually detect variation. Graphics professionals (like Steve) and image processing scientists (like myself and my colleagues) pay lots of attention to minutia that most people won't even notice; but our efforts manifest, perhaps somewhat ambiguously, as "better overall products." As I recall, somebody famously called our color accuracy "26% better" a few years ago, a stunningly quantitative figure. Nimur (talk) 13:52, 26 September 2013 (UTC)

The TV we have in our living room has a menu option marked "STORE MODE" - which makes the picture much brighter and more vibrant (too much more, I would argue) as well as disabling the controls on the side of the TV. There is a pop-up there that says that using this mode may shorten the life of your TV and consume more electricity! So judging color quality by what you see in the store is at best of dubious value! SteveBaker (talk) 18:06, 26 September 2013 (UTC)

Back in the era of CRT monitors, it was extremely common for the colors to drift over time due to screen burn, miscalibration of the analog parts and just general age. My personal experience has been that modern LCD panels do not seem to exhibit these problems - but our article Screen burn-in has a section on plasma, LCD and OLED displays that suggests that they are also prone to this phenomenon. Using a screen saver should alleviate the issues of certain common patterns being "burned" into the display - but a general overall degradation of brightness and color performance must still occur. So if our article is to be believed (and it does have some pertinent references) - then the answer to your question is "they differ" - but only after the displays have been in use for some large amount of time and with differing degrees of usage. However, I work in computer graphics where it is important to have color consistency between the displays used by (for example) different artists working on 3D models for the same game. Back in the era of CRT's, we'd have little devices that you stuck on the bottom right corner of the display's screen that adjusted the analog signals from the computer to achieve a stable color balance as the CRT aged - and between different CRT's being used by different people. Since we switched over to LCD displays, we haven't had to do that. But perhaps with OLED's becoming popular, we'll have to revisit that decision! SteveBaker (talk) 13:33, 26 September 2013 (UTC)

Steve, we still use those on LCD displays. Unless you are using specific, expensive monitors, color replication is still a problem. Even on a single brand of monitor, you get variation that is enough to warrant it.217.158.236.14 (talk) 14:08, 26 September 2013 (UTC)

• I'd just like to add that all of this is sort of a moot point, because the color that a viewer perceives on a monitor is strongly dependent on the lighting of the room where the viewer sits. Our brains are designed to minimize our awareness of that fact, but it is true nevertheless. So attempting to precisely control monitor properties is a waste of effort unless you can also precisely control the viewer's environment. If that is not possible, then the only way to get consistent perceptions is to calibrate each monitor individually and use it in a place with consistent illumination. Looie496 (talk) 15:36, 26 September 2013 (UTC)

And you need specially calibrated light-bulbs; and you need matte-gray walls painted with calibrated paint; and you need a government certification for every combination of room wall and lightbulb.... Nimur (talk) 17:30, 26 September 2013 (UTC)

Don't forget the monitor hood lined with black velvet. (some of them costing more than what I would spend on a monitor). Ssscienccce (talk) 03:05, 27 September 2013 (UTC)

Yet another factor (at least with LED screens) is the vertical angle between you and the screen, e.g. colour and contrast will both vary depending on whether you sit or stand.--Shantavira|^{feed me} 16:13, 26 September 2013 (UTC)

Tools like the "LaCie blue-eye" has the ability to monitor ambient room light - and that's plenty good enough for what we do. The objective for us is not to have perfect color - because we know that our end-users are using who-knows-what displays and calibrations. The idea is that all of our artists see the same thing - so that they aren't continually correcting and re-correcting the color of each other's work to make it look good with whatever they are building themselves. Doubtless LCD's do have color differences - both between manufacturers and between screens made by the same manufacturer - but the differences are tiny compared to old-school CRT's. SteveBaker (talk) 18:06, 26 September 2013 (UTC)

A Sony leaflet for their Full HD widescreen medical monitors writes: "every LCD panel used in the LMD-2450MD is precisely color calibrated at the factory, providing consistent characteristics. The colorimetry of an LCD display, by nature, can exhibit inaccurate color characteristics and gamma curves, which can make precise color matching between multiple monitors a challenge." So yes, even within the same lot, batch or model, there can be color variations. Ssscienccce (talk) 03:05, 27 September 2013 (UTC)

When dental veneers go wrong...

When someone has veneers done - but they end up with a set of teeth that looks like Barney the dinosaur's choppers or that they're wearing a mouthguard. What exactly is it that's gone wrong to cause that? I presume that they didn't go into it expecting their teeth to look like that afterwards... --Kurt Shaped Box (talk) 18:48, 26 September 2013 (UTC)

Our resident dentist can answer this question :) .Count Iblis (talk) 20:37, 26 September 2013 (UTC)

It seems that I've been summoned. :)

Veneers are done by first trimming away the superficial 0.5 or so of enamel on the facial of the teeth being restored, taking impressions of those prepared teeth and then cementing very thin laminates made of porcelain. Depending on the original anatomical relationship of the teeth being restored, the dentist/dental lab may be forced to put porcelain in places that do not necessarily make the veneers appear as though they reflect the normal anatomy associated with teeth. A primary cause of what you refer to as "Barney the Dinosaur teeth" and what dental school educators generally refer to as "teeth that look like Chicklets" is the complete lack or even partial deficiency of the gigival papilla -- the pink triangles of gum tissue that normally exist between teeth. If they are missing or deficient (either due to periodontal disease, etc.) rather than having "black triangles" the dentist/dental lab will often close these spaces with porcelain for esthetic or functional reasons. In terms of esthetics, even though Chicklets look quite unnatural, black triangles between anatomically-shaped teeth might look worse, and in terms of function, black triangles may cause a whistling sound when the patient talks and food particles may be more likely to become trapped, which may lead to cavities along the already more susceptible restorative margin between porcelain and tooth. DRosenbach ^{(Talk | Contribs)} 15:58, 29 September 2013 (UTC)

searching of arm anatomy illustration

I'm looking for an arm anatomy illustration a long time... But it's very important for me that it will be the same same to the real thing as much is possible... (I even agree to pay money for that, particular if it's on 3D format). Until now I've saw only some things that are not real, it says that they does not reflect the real things. My target is to know well the names of the veins of the arm, from the start to the end. thank you. 95.35.246.240 (talk) 21:17, 26 September 2013 (UTC)

http://teleflexhandbook.com/chapter-13-right-heart-cath-from-the-arm has a couple of pictures that might give you most of what you want. Looie496 (talk) 00:26, 27 September 2013 (UTC)

Keep in mind that there is considerable variability in the venous anatomy of the upper extremities (more than in the legs). The number of venous branches and their respective lengths show great inter-individual differences in the arm, so it's unlikely that an illustration will match someone's arm exactly. A Nigerian study noted 10 types of venous patterns (link), the abstract of another study mentioned four patterns. One example is the Median cubital vein between the cephalic and basilic veins in the H-shaped pattern, present in 70% of population, while 30% has the M-pattern, with five segments, the cephalic and basilic veins and the intermediate cephalic, intermediate basilic and intermediate antebrachial veins. 3-D views that you can turn and zoom in can be found at several sites (for example anatomyexpert or healthline). Ssscienccce (talk) 01:26, 27 September 2013 (UTC)

September 27

SF - Some kind of anatomic pathology?

Anyone of you guys heard about a pathology shortly named "SF" ? (Common in runners), Can someone tell me it's actual name? thanks. Ben-Natan (talk) 00:00, 27 September 2013 (UTC)

I'm betting stress fracture. Looie496 (talk) 00:18, 27 September 2013 (UTC)

Agree. I've added it to the SF disambiguation page.--Shantavira|^{feed me} 09:32, 27 September 2013 (UTC)

...and it's been reverted. Oh, well...--Shantavira|^{feed me} 16:12, 27 September 2013 (UTC)

Google search failed to find ANY cases where people had used the abbreviation "SF" in conjunction with running except in the context of San Francisco and Science Fiction. So, yeah - I support that revert - I don't think it belonged in the dab page for SF. SteveBaker (talk) 19:10, 27 September 2013 (UTC)

You probably used the wrong search terms. I got many relevant hits mentioning runners and stress fracture in which "SF" is abbreviation for the latter. Here're some snippets from the hits:

• "Medial tibial stress syndrome (MTSS) and tibial stress fracture (SF) are common lower leg disorders in runners." [2]
• "We assessed CDR in female runners (> or = 20 km/wk) with a recent stress fracture (SF) and with no stress fracture history (NSF)." [3]
• "Anyone who's experienced a stress fracture, please comment. Is the pain from a SF constant or only when it's bearing weight?" [4]
• "Subjects consisted of 10 females with a history of at least one lower extremity stress fracture (SF) .... All subjects were between ages 18-35 and ran between 30-80 miles per week." [5]

--98.114.146.6 (talk) 02:01, 28 September 2013 (UTC)

Waterfall fish kill ?

Do dead fish accumulate at the bottom of waterfalls, having died when they hit rocks at the bottom ? If not, why not ? StuRat (talk) 11:41, 27 September 2013 (UTC)

I'm interested to know why you think fish allow themselves to be carried over waterfalls in any but insignificant numbers. There are other issues to consider. The size of the fish, the depth of the splash pool, the volume of the flow, the speed of the flow, for example. The question is a little vague, but if we take it at face value I suspect the flow of water, local predators and natural decay prevents any accumulation. Richard Avery (talk) 14:01, 27 September 2013 (UTC)

I should think that waterfalls high enough to kill fish would be sufficiently rare that they wouldn't have developed an evolutionary response, that is, an avoidance strategy. Indeed, going over short waterfalls would be in the interest of the species, allowing it to spread to new areas. And can a fish tell how high a waterfall is, from the top side ? Maybe, if they can detect the low frequency sounds generated when the water hits, hundreds of feet below ? StuRat (talk) 14:50, 27 September 2013 (UTC)

I would expect that fish do get carried over waterfalls every so often, but really nothing except rock can accumulate there, because it is constantly scoured by a blast of water. Looie496 (talk) 14:57, 27 September 2013 (UTC)

I don't think that's true, there are often eddies there holding floating objects right against/behind the falls. StuRat (talk) 15:29, 27 September 2013 (UTC)

You mean a recirculating stopper or hole, which can pin a kayak full of buoyancy to the riverbed for a considerable length of time. An eddy (in whitewater terms) is an area of placid water formed at the side of the main current. Alansplodge (talk) 21:59, 27 September 2013 (UTC)

I disagree on "placid". At my link it says "...in very powerful water, eddies can have powerful, swirling currents which can flip boats and from which escape can be very difficult." StuRat (talk) 11:31, 28 September 2013 (UTC)

Yes, but that's prefixed by "However, in very powerful water...". The flipping action is generally on the "eddy line" which divides the eddy from the main flow. I've never seen or heard of an eddy which is dangerous once you get into it. If such a thing exists, then it is a serious exception to the rule. In general terms, eddies are places that paddlers seek out to get their breath back. Trust me, I'm a kayak coach. See Basic Whitewater Kayaking River Features, "Eddys (sic) are usually calm spots that kayaks, rafts, and canoes can sit in while the rest of the river flows downstream." or Whitewater Paddling - Eddy Use & Etiquette, "Eddies are places where paddlers can stop for a while or relax before they start paddling again. Paddlers can rest, eat, or mingle around with other paddlers in eddies, which generally vary in size." Alansplodge (talk) 15:45, 29 September 2013 (UTC)

Sometimes, a little research can be helpful. Bielle (talk) 15:44, 27 September 2013 (UTC)

Interesting. Apparently the falls pose more of a danger to ducks and such. Wouldn't you think they'd just fly away when they went over the top ? StuRat (talk) 17:28, 27 September 2013 (UTC)

I've often see birds hanging around waterfalls. They probably help in collecting whatever edible debris might go over. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:39, 27 September 2013 (UTC)

Algebra

How does n=e/(1+e) become e=n/(1-n). If you rearrange it just becomes n(1+e) = e. am I missing a rule of algebra here? Clover345 (talk) 12:02, 27 September 2013 (UTC)

$n={\frac {e}{1+e}}$

$\Rightarrow n(1+e)=e$

$\Rightarrow n+ne=e$

$\Rightarrow e-ne=n$

$\Rightarrow e(1-n)=n$

$\Rightarrow e={\frac {n}{1-n}}$

Gandalf61 (talk) 12:09, 27 September 2013 (UTC)

And don't forget:

Algebra = Desk_Math

$\Rightarrow$ Algebra <> Desk_Science

StuRat (talk) 12:56, 27 September 2013 (UTC)

Way to get Oils or Oil remnants of the hair?

If regular shampoo's doesn't help, how do you think you would take off (In a generally safe way), oils out of your hair? (Oils that might have got there by oily shampoos or other ways). Thanks. Ben-Natan (talk) 16:47, 27 September 2013 (UTC)

A detergent is what you need. Detergents for hand washing dishes are often strong, yet not too toxic, since they are for cleaning out greasy pots, but also must be safe to touch your hands. Of course, a shampoo designed for oily hair will also have some detergent in it. As always, be careful not to get either in your eyes. Heat will also help, so turn the water temperature up as high as you can stand it. And, after you remove the (presumably dirty) oil, you may want to replace it with clean oil, which is what hair conditioner does. The only exception is if your scalp produces so much oil that your hair will soon be oily again, in any case. StuRat (talk) 17:13, 27 September 2013 (UTC)

Wash, rinse. Repeat. and Repeat. --208.185.21.102 (talk) 17:55, 27 September 2013 (UTC)

A Google search suggests that clarifying shampoos are specially formulated to remove a buildup of product residues and/or oils from hair, where ordinary shampoos may fail to do so. - Karenjc (talk) 18:24, 27 September 2013 (UTC)

Touching a touchscreen

If you were to put a human standing on the top of a huge capacitive touchscreen (the human won't be touching anything else, but has the option of stepping on an isolating material or touching the screen with his skin), could the human activate the touchscreen?̉ OsmanRF34 (talk) 17:37, 27 September 2013 (UTC)

Capacitive sensing does not sound dependent on the user being grounded or having any other specific electrical properties beyond making contact. Could you explain the reason you suspect the person in your scenario would not be able to activate it? DMacks (talk) 17:44, 27 September 2013 (UTC)

I thought that in this scenario the human would acquire the same charge as the capacitive touchscreen, and the touchscreen won't be able to register any contrast. OsmanRF34 (talk) 17:56, 27 September 2013 (UTC)

You're thinking DC. But an AC current can continuously flow to an object (such as the human body) which doesn't appear to be a part of a closed circuit, due to self-capacitance. See also body capacitance. Red Act (talk) 20:45, 27 September 2013 (UTC)

The points on the display are scanned, a pulse is applied to one electrode, and the response in the other electrode is measured. Doesn't matter at what voltage the person is, because it's the change in voltage that is measured (the amplitude of the output signal compared to the amplitude of the input signal), and that will be smaller due to the added capacitance. Ssscienccce (talk) 18:42, 28 September 2013 (UTC)

Why are the babies in need of sleep more than adults?

Why are the babies in need of sleep more than adults (almost twice as adults)? 95.35.246.240 (talk) 19:58, 27 September 2013 (UTC)

We don't understand why humans (or other animals) need sleep - so it's unlikely that there is solid information about why babies need more of it. Our article on sleep says: "Children need more sleep per day in order to develop and function properly" - which doesn't really tell us much.

IMHO, it's evolutionary - if babies didn't give their parents enough time to recover from 6 hours of solid screaming and fussing - they'd never make it past 6 months! SteveBaker (talk) 20:13, 27 September 2013 (UTC)

An interesting fact, and probably an important clue, is that babies spend a much larger fraction of their sleep in the REM (dreaming) state than adults do. Looie496 (talk) 22:15, 27 September 2013 (UTC)

We need sleep because we get sleepy. Babies probably get more sleepy than adults, therefore they sleep more. OsmanRF34 (talk) 22:39, 27 September 2013 (UTC)

Seriously, it is as Steve says, nobody knows exactly. But we know something about sleep: all species do it (=> it has to be pretty old, in evolutionary terms), in one form or the other. Although not all sleep the same. :Other species need more sleep than us. Some bats need 20 hours, elephants 3-4, giraffes need just 2 hours. If you deprive a rat of sleep, it will die in 2 weeks (=> it is biologically necessary).

Human babies need to sleep a lot for proper development. Growth hormones are secreted by the pituitary gland at a much faster rate while babies sleep. However, other baby mammals, like baby dolphins and baby orcas, don't seem to sleep at all, (=> evolution found other ways of making it work). OsmanRF34 (talk) 23:08, 27 September 2013 (UTC)

One valuable clue of the importance of sleep is what happens as a consequence of lack of sleep, as with fatal familial insomnia. Those suffering from that disorder are literally unable to sleep - and it's a death sentence. They eventually suffer dementia and finally they die. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:21, 28 September 2013 (UTC)

It seems to me that this is fundamentally a game theoretical issue. Suppose you start with two identical systems that compete with each other and they also need to repair themselves. Initially they function in a uniform way, they go about their business and do the repairs they need to do to themselves at a constant rate. But then one system can outperform the other by working at a faster rate that on the long run is unsustainable and then having a downtime later to do extra repairs. As a bonus those repairs can be perfomed more efficiently during the downtime. Count Iblis (talk) 01:47, 28 September 2013 (UTC)

And there people who have survived for decades without any sleep at all, e.g. Thai Ngoc, Al Herpin, Paul Kern. Count Iblis (talk) 02:24, 28 September 2013 (UTC)

That's probably a myth. There have been many claims about people who never sleep, but whenever such people have been closely monitored, they did in fact sleep to some degree. There are no documented cases of people who could live with no sleep whatsoever. Looie496 (talk) 06:47, 28 September 2013 (UTC)

Here are my thoughts:

1) The reason for sleep in the first place is it allows us to run our bodies at a faster, unsustainable rate while awake, and make repairs while asleep. Combine this with the rotation of the Earth, which means we get a few hours of light followed by a few hours of darkness, and we get organisms adapted for either the day or night, and sleeping for the period to which they are not well adapted. Humans seem to have a sleep cycle which roughly corresponds with the length of the shortest nights, ensuring we can always be awake during daylight, when we could do all the things needed to ensure our survival. (Of course those living near the poles are an exception.) It would also seem to make sense for us to sleep longer in winter, but our bodies don't appear to have adapted to do this (other species do, however, fully or partially hibernate). And, of course, the introduction of artificial lights mean the evolutionary pressures to avoid activity at night are now gone.

2) In the special case of babies, they have very little they need to do each day which requires that they be awake, just eat and learn (they don't even need to be awake to poop). On the other hand, they are doing a great deal of growing, and this requires a lot of work which can be done in their sleep, like digesting, forming neural connections, etc. So, it makes sense for babies to be asleep more than adults. And the workload on the parents might figure into it, too, as babies which are awake and in need of watching constantly make it hard for their parents to make a living, and they might have tended to not survive, as a result. StuRat (talk) 11:25, 28 September 2013 (UTC)

Interesting fact: hibernation in animals is periodically interrupted, and it seems that they do so in order to be able to sleep. This suggests that sleep has nothing to do with reducing energy expenditure. Ssscienccce (talk) 14:55, 28 September 2013 (UTC)

How does a laser cut glass?

It seems counterintuitive that a laser could cut something that is clear. How is this possible? Specifically, laser cut sapphire glass. --208.185.21.102 (talk) 21:27, 27 September 2013 (UTC)

Are you looking for a technical or a non-technical answer? This absolutely is counter-intuitive; commodity laser cutters can't do it (reliably). Our article describes several distinct physical mechanisms that allow a laser to cut a material. In the case of glass, the procedure is difficult and dangerous; a powerful laser is shined onto a surface that's simultaneously specular and transparent... it takes a lot of engineering to make sure the laser energy gets absorbed, and not wasted, or reflected back into the laser, or accidentally reflected to somewhere else undesirable. Nimur (talk) 21:47, 27 September 2013 (UTC)

Was that the technical or non-technical answer? It seems you didn't answer the question at all except to say, "With difficulty man! It's hard!! In fact commodity lasers can't do it. It takes a lot of engineering." I guess "with a lot of engineering" counts as a nontechnical answer for how does a laser cut glass! :) 178.48.114.143 (talk) 23:07, 27 September 2013 (UTC)

My response wasn't really meant as an answer... it was just a request for clarification. Shall we deep dive into optical physics and evanescent waves now, or should we wait for Steve Baker (who has operated his own laser cutter nearly 24/7 for the last year!) to bring a more pragmatic hands-on style explanation? I have a sort of suspicion that his lasersaur does not cut sapphire glass, but I'd be curious to hear his input. Nimur (talk) 23:15, 27 September 2013 (UTC)

If Steve Baker has operated his own laser cutter nearly 24/7 for the last year, 1) he's probably the world's least qualified person to answer this question 2) give up man, just give up already... 178.48.114.143 (talk) 23:29, 27 September 2013 (UTC)

I've been working with laser optics for over a decade, for many different purposes, ranging from laser cutting to optical probes of chemical species, materials and surface properties; and Steve's one of the reference-desk's best and most well-respected contributors; but if you're unhappy with the quality of our free information and would like me to "give up," perhaps you can find better information by purchasing a textbook on laser physics. My class used an unpublished textbook, and its course webpage is not currently available; but you can purchase Laser Materials Processing at Amazon for the low price of just $350. Nimur (talk) 00:56, 28 September 2013 (UTC)

It's just a joke, Nimur. If Steve's been running a laser non-stop for a year, he's not making very much progress (unless he's trying to break into Fort Knox). Clarityfiend (talk) 01:23, 28 September 2013 (UTC)

Steve's running a small business manufacturing miniature laser-cut figures, and operates out of his living room (or so it appears). His laser cutter, according to his website and his comments, has been highly utilized. He'll probably be happy to discuss it in more detail. Nimur (talk) 01:36, 28 September 2013 (UTC)

I'm far from an expert on lasers, but I presume that at least one consideration is that sapphire glass is only transparent in the wavelength range of about .15-5.5 µm, so it's opaque to the light from lasers outside of that range. There exist commercially available lasers with wavelengths up to 699 µm; see here. Red Act (talk) 21:59, 27 September 2013 (UTC)

A CO2 laser has a wavelength of between 9.4 and 10.6 µm and was the first (and still is the main) laser used for cutting purposes (highest continuous power output, high efficiency). It uses germanium or zinc selenide windows (first windows were made of salt crystals). A popular laser with hobyists because it's easy to make and cheap. Lots of examples on youtube.

For sapphire (like semiconductor wafers), one would probably use a UV pulse laser; the pulses deliver more power, limiting the heat transfer to the rest of the wafer; in effect, a small dot is ablated (evaporated) without putting thermal stresses on the rest of the material. (Dicing sapphire wafers) Ssscienccce (talk) 12:44, 28 September 2013 (UTC)

OK, here is what I know and why. My g/f and I own and operate two lasersaur UV laser cutters. We mostly cut plywood to make model buildings for tabletop gamers. Our CO2 lasers can't cut glass - but they can etch the surface a little. However we can cut acrylic plastic (even the stuff that's optically transparent...but we can't cut polycarbonate - which looks pretty much identical to acrylic! What's going on here is that you're thinking of glass as being transparent - which it is in the visual spectrum. However, in UV, it's totally opaque. Knowing whether something is transparent to visible light really doesn't tell you much about IR, UV, microwaves, radio, etc - which is why acrylic and polycarbonate (which are completely indistiguishable to the naked eye) are so completely different in UV. In fact, the lid of the lasersaur is made from polycarbonate precisely because it's impervious to the laser light and blocks it from wrecking your eyesight. The laser safety goggles we have are also polycarbonate.

Some opaque materials (like plywood) cut nicely because the laser can start a chemical reaction that removes the material bit by bit until it's cut all the way through. Others absorb heat from the laser and melt, others undergo some other kind of reaction. But glass, pretty much just heats up on the surface and cracks a tiny bit...which lets you etch it - but not cut it.

That said, there are lasers that work in other parts of the electromagnetic spectrum that might be able to cut glass. I don't know. (And I'm using a tablet computer which makes it painful to research this for you!!)

SteveBaker (talk) 13:28, 28 September 2013 (UTC)

Glass sheets for flat panel displays used in mobile phones can be cut by a co2 laser. Often the lasers are used to scribe the material, after which it is broken along the scribe line, just as you do with a diamond tip glass "cutter" (the breaking can be done with a second laser reheating the scribe line). Scribing with CO2 lasers can be used on glass from 200 µm to 10 mm thickness. Full body cutting is used on 30 µm to 1 mm glass. There is a marked difference in speed, scribing can be done up to a meter per second or more, full body cutting happens at less than 20 mm per second. In both cases the glass passes under a coolant nozzle right after the laser beam, liquid cooling used for scribing, gas cooling for full body cutting. In scribing, the cooling causes small thermal stress cracks, in full body cutting, the higher energy and lower cooling has the crack propagate through the entire thickness. (Laser glass cutting in flat panel display production) Ssscienccce (talk) 13:51, 28 September 2013 (UTC)

Steve, do you know which of the cutting modes (chemical reaction, local heating, etc.) happens for the CO2 laser on acrylic and why polycarbonate is not affected? It sounds counter-intuitive that polycarbonate absorbs the laser light but does not get affected by it: why doesn't all that energy do...something?. DMacks (talk) 05:38, 29 September 2013 (UTC)

CO2 lasers can be used for cutting polycarbonate, but only with gas-assisted lasers: a nozzle providing 2-6 bar nitrogen or air blowing away the fumes. The smoke will clog up filters, the gas cannot be recycled, basically, it's just messy. See for example this company who mention "Polycarbonate (PC, Lexan) – we stopped cutting Lexan due to the fumes." It's the only material as far as I can see that they initially offered but later abandoned. Ssscienccce (talk) 14:41, 29 September 2013 (UTC)

Steve, I'm a bit confused by your mentioning of UV, don't you mean IR? UV exposure would be the main concern when operating the CO2 cutter, because the high temperature at the target is a significant source of UV radiation (same as with welding), but the laser beam itself is IR of about 10.6 µm. While the Ir is dangerous as well, it doesn't penetrate the eye and get focused on the retina like the UV can. IR damage you would feel when it occurs, unlike the delayed and cumulative effects of the UV, "arc eye" or welders' keratitis. So the emphasis may be on the UV when it comes to safety, but the only CO2 lasers with UV laser light I know of are the CO2/UV laser drilling machines for multi-layer boards that combine diode laser pumped UV lasers and CO2 lasers; the IR used for making 45 to 200 µm holes, the UV for small 18 µm holes. Ssscienccce (talk) 18:48, 29 September 2013 (UTC)

September 28

Mould growth from artificially increased humidity

Can putting water in a bowl on a radiator, to moisturise a room, contribute to mould growth? Clover345 (talk) 00:46, 28 September 2013 (UTC)

No, because putting water in a bowl on a radiator isn't an effective way to moisturise a room. What you need to do is to poor that water on one or more towels and put these wet towels on the radiator. Count Iblis (talk) 01:38, 28 September 2013 (UTC)

That could be a fire hazard, once the towels are dry, depending on how hot that radiator gets. StuRat (talk) 11:07, 28 September 2013 (UTC)

Filled radiators don't get that hot! Electric convector heaters might overheat if covered, and of course electric radiant bars get very hot, but you shouldn't put towels anywhere near these. Dbfirs 15:59, 28 September 2013 (UTC)

A bowlful of water won't increase humidity by much, I agree, but every bit helps the mold grow. BTW, more effective ways to increase humidity, short of buying a humidifier, are to run the shower with a fan blowing air into the bathroom, or to boil water on the stove, but there you have to be careful not to let it go dry. Various forms of cooking also have the side effect of increasing humidity. StuRat (talk) 11:05, 28 September 2013 (UTC)

I doubt that most people would want mold growth, seeing as it is a health hazard. Mold growth, assessment, and remediation has more on the topic. Lack of ventilation, humidity above 50% and cold spots where condensation can form seem to be the main factors; also a previous flooding that caused mold would be a source for fresh mold whenever the conditions are right because the infected spots will have a lot of dormant spores. Ssscienccce (talk) 14:02, 28 September 2013 (UTC)

Agreed. If your room needs "moisturising" then most moulds won't grow there except in damp corners. A bowl of water on a hot radiator will help to gently increase humidity, and is unlikely to have a significant effect on mould growth unless the moisture is then condensing on a cold spot, as explained above. Dbfirs 15:59, 28 September 2013 (UTC)

What animals besides spiders have evolved more than two eyes?

75.75.42.89 (talk) 13:50, 28 September 2013 (UTC)

Anableps Richard Avery (talk) 14:33, 28 September 2013 (UTC)

Those don't really have four eyes, in spite of the name. See however our parietal eye article. Looie496 (talk) 14:44, 28 September 2013 (UTC)

I'm not sure how reasonable it would be to give a complete list of the known animals with more than two eyes. Many, many species of insects have more than two eyes (I think the most common number is two compound eyes and three ocelli). Mollusc eyes says that scallops can have a hundred eyes, and chitons can have thousands. I'm sure there are others. Effovex (talk) 14:43, 28 September 2013 (UTC)

Some echinoderms have multiple eyes, and some use their entire surface as a type of compound eye. μηδείς (talk)

Scyphozoa have multiple eyes; since they are the most diverged animals, it is possible that this is the ancestral condition, and various lineages have settled on two as a matter of natural selection. (Some authorities have suggested that eyes could have evolved and reevolved independently, but the common usage of Pax6-related genes makes me think some authorities just underestimate the Urbilaterian. (Dinoflagellates only have one, so far as I know, and I'll reluctantly accept that one is truly a separate evolution of the structure. :) ) Wnt (talk) 22:17, 28 September 2013 (UTC)

Scallops. Technically, they are animals. Plasmic Physics (talk) 09:30, 29 September 2013 (UTC)

This article might help: Simple eye in invertebrates. Vespine (talk) 03:28, 30 September 2013 (UTC)

Compactified on S₅ or T*S₃

In the context of string theory, in the phrase "compactified on S₅ or T*S₃", what exactly are S₅ and T*S₃? Red Act (talk) 15:13, 28 September 2013 (UTC)

P.S. The phrase is used about 15 seconds into Bohemian Gravity, so I presume the terminology isn't anything too obscure. Our Compactification (physics) article, however, is no help. Red Act (talk) 17:52, 28 September 2013 (UTC)

As a non-physicist and non-mathematician, I would assume that S₅ refers to the Randall–Sundrum model and T*S₃ refers to normal Minkowski space. But this conjecture is not receiving support from any of our articles. Tevildo (talk) 22:27, 28 September 2013 (UTC)

I think S_5 and S_3 are Symmetric groups. I'm not sure about T. Dauto (talk) 13:05, 29 September 2013 (UTC)

Are you sure it wasn't S⁵? I'm guessing that they're talking about the 5-sphere and the join (see [6] for more) of the torus and the 3-sphere. You may have seen ADS₅, in which case take a look at Anti-de Sitter space. Random sources: [7], [8], [9]. Note: I'm guessing that "*" is the join, I'm not familiar with the source you mentioned, it could be something else, but I think the join makes sense.Phoenixia1177 (talk) 13:37, 29 September 2013 (UTC)

I didn't think that one out, T*S3 is the Cotangent bundle, see here [10]. Sorry for that, I don't know why I thought the join made sense...! Anyways, cool video (I realized you linked to it:-) ).Phoenixia1177 (talk) 14:41, 29 September 2013 (UTC)

Thanks! Red Act (talk) 22:25, 29 September 2013 (UTC)

How do you show stacked staircases in a building plan?

In the plan for a floor of a building, how do you graphically show it when the same part of the floor (viewed from the top) has stairs connecting to the floor above and stairs connecting to the floor below? — Preceding unsigned comment added by 173.49.18.74 (talk) 15:35, 28 September 2013 (UTC)

Well the bottom of the stair up and the top of the stair down can't be in exactly the same place, so you show the stairs there, possibly with an right-angled arrow to show which way they turn. Rojomoke (talk) 18:30, 28 September 2013 (UTC)

I think the OP wants to know about a situation like this:

            _|
          _|
        _|
      _|                              
    _|
  _|
_|                              
--------------|
             _|
           _|
         _|
       _|                              
     _|
   _|
 _|                              

where the two staircases are vertically above each other, and "up" is the same direction for both. Our architectural drawing article states that stairs are only shown up to the plan level, and that the plan level is "three feet / one meter" above floor level, without (unfortunately) citing a source for this. (Most of the links from the article are dead, as well.) Based on our article rather than a definitive source, I would therefore say that the plan should show the first three feet of the staircase to the upper floor, and the last [room height - 3'] of the staircase from the lower floor, with arrows indicating the "up" direction on both. However, this may be incorrect. Tevildo (talk) 21:51, 28 September 2013 (UTC)

What does this mean in a floor plan:

____
|===|===|
|===|===|
|===|===|
|===|===|
     ----

? Plasmic Physics (talk) 23:08, 28 September 2013 (UTC)

This is the more conventional arrangement, where the "up" and "down" staircases are next to each other rather than above each other, and the user only has to turn through 180° to get from one to the other, rather than having to walk the length of the corridor. Normally, there should be arrows on each staircase indicating which is "up". Tevildo (talk) 23:26, 28 September 2013 (UTC)

Stairs normally are built in a sort of corkscrew ascending arrangment, requiring small landings where the user makes simple U-turns. Stairs such as the OP apears to describe would be very unusual, and would require a sort of extended mezzanine or landing where the user makes a u-turn, a straight walk, then another u-turn. It would require an excessive number of steps in each flight in order to retain sufficient soffit in the stair well, and so would not pass building regulations. As it is unusual, I would expect it to be drawn as a few steps truncated in each floor plan, with a text notation "Stairwell: See sub-drawing A" and include a special plan of the mezzanine if required and elevation of the stair & landing arrangement. 121.215.63.7 (talk) 23:45, 28 September 2013 (UTC)

Stacked escalators are not uncommon in shopping malls, where they help save floor space , and compelling shoppers to walk the extra number of steps (past some display items) is a desirable feature. A plan drawing for such an arrangement is shown on page 17 of this PDF. Also in houses, the stairs leading to the upper floor and the basement from the "main level" are often stacked (since, again, it saves floor space, and traveling from the basement straight to the upper floor is relatively rare); see plan drawing in Figure 16-70 of this book. Abecedare (talk) 00:21, 29 September 2013 (UTC)

Raisins as cough suppressant?

Hello all, I want to ask you about a strange observation I made the other day: I've been sick for the past couple days and coughing quite a bit; however, the other day, after I ate salad with (raw) raisins in it, my cough and sore throat temporarily disappeared almost immediately! I also observed the same effect later on, after eating boiled rice with (stir-fried) raisins. Which raises the question: What is it about raisins that makes them effective as cough suppressant? 24.23.196.85 (talk) 6:59 pm, Today (UTC−4)

Googling this question provides no evidence raisins are cough suppressants as such. μηδείς (talk) 03:09, 29 September 2013 (UTC)

Eating almost anything when you have a cold can temporarily purge your throat of gunky stuff that builds up. (How's that for techie terminology?) ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:16, 29 September 2013 (UTC)

September 29

The name of a medical condition

First and foremost, this is not a medical question. So, here goes: when I was a teen, there was a family that seemed to have some form of genetic abnormality. Generally, all of the members were short and quite muscular. In fact, my friend went by the nickname "Caveman." As I understand it, he and his brothers entered puberty when they were about 6 years old. They began to develop facial and pubic hair, their testicles descended, voice became deeper, etc. In short, they were physically mature by age 8 (though of short but very muscular stature). They were neither midgets nor dwarfs. Is there a name for this condition? 173.35.158.194 (talk) 01:12, 29 September 2013 (UTC)

Define "short". One thing I know from observation is that those who mature earlier than average seem to be shorter - like their "growth spurt" got too early of a start. Maybe "early maturity" or something like that? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:28, 29 September 2013 (UTC)

We can't know what the specific cause of your friend's condition was, but our article on the topic is Precocious puberty. Deor (talk) 02:55, 29 September 2013 (UTC)

My friend was about 3 feet 11 inches. His brother was a bit taller but generally everyone in his family (i.e. siblings) were all well below the average. His musculature was also very well defined and he even had a bit of a brow ridge. I will read the article Jack suggested. 173.35.158.194 (talk) 04:08, 29 September 2013 (UTC)

Jack has had jack all to do with this question. -- Jack of Oz ^{[pleasantries]} 04:46, 29 September 2013 (UTC)

The OP said nothing about anything remotely like this
The following discussion has been closed. Please do not modify it.
How did your young neighbors' balls feel when you palpated them? Did they hang evenly? Were they sore? Did you have them turn and cough? Where there differences between the boys' ball, left from right or boy to boy? Did they fit in you teenage hands, or where they overlarge? How did they smell? Were they symmetrical? Did they have the same internal texture? μηδείς (talk) 04:50, 29 September 2013 (UTC) I haven't been fiddling with my neighbour's balls lately, but you'll be the first to know when I do. -- Jack of Oz [pleasantries] 05:33, 29 September 2013 (UTC) That was the indentation of laterness, not the indentation of personal address. μηδείς (talk) 20:17, 30 September 2013 (UTC)

When I was at primary school, one of my classmates also started to develop rapidly, his hair started greying aged 8 and he got wrinkles about the same age. I was told then it was progeria. I wonder if this is the condition the OP refers to? --TammyMoet (talk) 08:46, 29 September 2013 (UTC)

The OP speculates on a genetic link, mentions that all family members were short, but specifies that his friend and his brothers were affected by symptoms such as the early development of secondary sex characteristics. Familial male-limited precocious puberty is a type of precocious puberty affecting the males in a family; those with the condition tend to be short as adults because their accelerated development means they stop growing sooner than their peers. This article provides an overview of the genetic mechanism and some useful links. We can't know whether the OP's friend had this condition, but if so then yes, it has a name. - Karenjc (talk) 14:41, 29 September 2013 (UTC)

To correct one point - in human males the testicles normally descend before birth see [11]. Richerman (talk) 22:31, 29 September 2013 (UTC)

Why do we feel colder when lying down?

You're sitting in an armchair watching TV, reading a book, whatever. You're perfectly comfortable, temperature-wise. Then you decide you feel like lying on the even more comfortable sofa and continuing your reading/watching in the supine position. But within a few seconds of lying down you realise you now need a blanket or some cover because you feel cold. The room hasn't changed, the heating arrangements (if any) haven't changed, your clothing hasn't changed, but you still feel colder lying down than you did when you were sitting in a chair.

Why? -- Jack of Oz ^{[pleasantries]} 03:44, 29 September 2013 (UTC)

This discussion has been closed. Please do not modify it.
The following discussion has been closed. Please do not modify it.
This is a totally wild guess, so delete it if it sounds absurd - but could it be that you're more "bunched up" when sitting up, and more "spread out" when lying down, i.e. exposing more of your surface area? Or that maybe your heart becomes a little less active, as it would at night? How often, for example, have you gone to sleep with the cover off and awakened with it on? ←Baseball Bugs What's up, Doc? carrots→ 03:52, 29 September 2013 (UTC) It's not a question of absurdity or otherwise, but I thought it was thoroughly understood by now that guesses of any kind, but particularly wild ones, are the complete antithesis of what the Reference Desk is all about. -- Jack of Oz [pleasantries] 03:57, 29 September 2013 (UTC)

It's easy to find out where the immediate effect comes from, just go lie down on the floor right now and concentrate on where the cold is actually coming from. Clearly what you feel is that while you do start to feel cold generally, the cold is coming from the floor. And that can be easily explained, when you are sitting your clothes will have reached some equilibrium temperature. Your body is in dynamic equilibrium where the heat it produces leakes out into the environment. As much heats enters your clothes per unit time as is dumped by your clothes into the environment, which means that you clothes, while cooler than your body temperature, will be warmer than the environment.

When you lie down on the floor, you will make thermal contact with the floor, the part of the clothes in contact with the floor will cool down. More heat will have to be transported to the floor before a new dynamic equilibrium is reached, the part of the floor directly below you will have to heat up a bit. Whether you will feel warmer or colder on the longer term depends on how efficiently heat is transported away in this new situation compared to the old situation.

In winter you will get the same effect when putting on your winter clothes before going outside. These clothes will initially be at room temperature and you will feel quite cold immediately after putting on all your heavy winter gear (if you do this fast). Count Iblis (talk) 13:59, 29 September 2013 (UTC)

Interesting points. Jack could test this in a different way: Lie on the couch from the get-go, until it feels warm. Then get up and sit in the chair. I would bet a good portion of a dollar that the chair will feel cold. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:11, 29 September 2013 (UTC)

Another thing to consider is that more muscles are relaxed when lying down. So less energy is burnt to maintain the posture. Graeme Bartlett (talk) 22:28, 29 September 2013 (UTC)

Hot air rises...if there is any source of cold air (eg a draft), then the cooler air would pool lower in the room. That could be a contributory factor. SteveBaker (talk) 04:38, 30 September 2013 (UTC)

Assume the room is completely sealed and there are no drafts. I don't experience this effect if I simply move to a different chair, only if I go from the sitting position to the lying position. -- Jack of Oz ^{[pleasantries]} 20:18, 30 September 2013 (UTC)

How to accurately measure how long someone has lived

Given the bones of Li Qing Yun, can it be determined when he was born? Count Iblis (talk) 17:10, 29 September 2013 (UTC)

Radiocarbon dating might be useful for this purpose. DavidLeighEllis (talk) 22:32, 29 September 2013 (UTC)

the teeth might contain some earlier material, but if he really was as old as claimed, there are likely no teeth left! Graeme Bartlett (talk) 22:38, 29 September 2013 (UTC)

I was gonna say radiocarbon dating, but this method is only reliable for telling when someone died -- it's not so reliable for assessing when someone was born. 24.23.196.85 (talk) 22:51, 29 September 2013 (UTC)

Our article says that he produced over 200 descendants during his life span. One could perhaps try to find the remains of his children (using DNA analysis one can verify this), and one can determine when each child died. That would then give a lower limit to his age. Count Iblis (talk) 00:56, 30 September 2013 (UTC)

The problem with bones is that they are remodelled throughout life; slowest in cortical bones, 2%-3% pear year according to this source. Cartilage, on the other hand, seems to stay more or less the same throughout adult life. So if some cartilage is preserved, radiocarbon dating of the DNA of chondrocytes might be possible. Icek (talk) 11:55, 30 September 2013 (UTC)

Hypothermia

OK, this might sound unbelievable, but here goes: I've recently watched an interview with Leonid Bronevoy, where he talked (among other things) about his father who was sent to the Gulag for being a Trotskyite. Well anyway, they sent him to chop wood in some godforsaken place in eastern Siberia, and the foreman of his work crew was a sailor from the cruiser Aurora, who was probably in the Gulag for being too principled and not accepting Stalin's usurpation of power. So the story goes, one frigid winter day when the temperature was -50 degrees, a bunch of fresh fishes arrived, and Bronevoy's father recognized one of them to be his interrogator (this was probably soon after Beria replaced Yezhov, so many of the KGB agents who served under Yezhov were themselves executed or sent to prison). He told this to his foreman, and what the foreman did was very clever (apparently the same agent interrogated the foreman, too): When the interrogator asked to join his crew (a singularly stupid request on his part -- what was he thinking?!), the foreman replied, "No problem, I forgive you, you're welcome here" and put him to work right away; of course, the KGB agent, being unused to physical work, quickly got tired, and when Bronevoy's father noticed that the new guy wasn't keeping up with the work and reported this to the foreman, the foreman gave the chekist permission to take a break, WITHOUT warning him of the need to keep active in order to prevent hypothermia. Anyway, when the two of them came back to the chekist later, not only was he dead, but he was frozen so solid that when one of them struck him with the haft of an ax, he actually shattered into tiny little pieces. My question is: Is this even halfway-plausible, or was Bronevoy making this up? I know that one can easily die from hypothermia in such extreme cold, but is it possible to actually freeze so solid as to shatter??? 24.23.196.85 (talk) 22:41, 29 September 2013 (UTC)

Given the proportion of the human body which is comprised of water, and the fact that ice can shatter, the story seems plausible. DavidLeighEllis (talk) 22:58, 29 September 2013 (UTC)

From information at The Straight Dope, it doesn't sound like human bodies will shatter even at cryogenic temperatures. Red Act (talk) 23:06, 29 September 2013 (UTC)

I doubt a human being could freeze to that degree of brittleness in nature (if at all). At any rate, cryo-shattering is a thing done in cooking, see here [12], [13], [14], and [15]. These: [16], [17], [18], [19], [20], [21], [22], and [23] all suggest that meat, fruit, chees, and fish can shatter, become brittle, etc. Here's a video of cryo-shattering salmon: [24]. From experience, if you throw a frozen hamburger hard enough, it will break, maybe not into a million pieces, but it fractures in a way that could be described as shattering. However, while this all seems to imply that a human could shatter, I want to stress that it would be under very unnatural circumstances- if you completely froze a person at extremely low temperatures, they'd probably shatter if enough force was used; but nature, or a brief exposure to liquid nitrogen, wouldn't suffice to freeze them to that degree. NOTE: This is not a subject I had prior familiarity with, don't trust my judgement (especially since I'm going with an educated guess based off of the links).Phoenixia1177 (talk) 00:56, 30 September 2013 (UTC)

The Straight Dope may be a great site, but against us they have met their match. Obviously Phoenix deserves our thanks for nailing this, but I'll add that meanwhile I found http://www.youtube.com/watch?v=zLWEemhtdbE and http://www.youtube.com/watch?v=xtHGGPseUqA . The shattering is not as dramatic as filmmakers might imagine it, but it is easy to picture someone swinging an axe and cracking off an arm or even a piece of torso. While Russian winter winds are not as cold as liquid nitrogen, they pass a tremendous volume of cold air quickly past the body, so I can picture it could freeze relatively quickly. The only question is whether the less-than-cryogenic freezing is enough to change the properties of the flesh, and that I can't quite answer. Wnt (talk) 06:11, 30 September 2013 (UTC)

It might be instructive to investigate the gruesome details of the death of Payne Stewart and his associates on an airplane that lost cabin pressure at a high altitude. As I recall, it was difficult to identify body parts of specific persons, and that Stewart's coffin contained only a few bones. Presumably the bodies on board had been frozen as solid as with the OP's premise, yet some bones survived the impact of an airplane crash, which would be way much more force than swinging an axe would be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:34, 30 September 2013 (UTC)

Promession is a proposed method of disposing of corpses by freeze-drying, where the body is frozen with liquid nitrogen and then shattered by vibration (and then there's some additional tidying-up). AndrewWTaylor (talk) 10:20, 30 September 2013 (UTC)

It seems very unlikely that physical activity could make the difference between staying alive and freezing solid in less than a day. For a body to freeze, it would have to cool at least 37°C. Let's assume the body has a thermal mass equivalent of 45 kg water, that would mean losing 45*37= 1665 kcal of heat. In the time it takes a dead body to give off that much heat, a living person would have expended even more, because he has to maintain his high body temperature. Considering that an average daily energy intake for a man is about 2500 kcal, that food rations at the gulag won't have been generous, that "shattering" of the body would not happen at 0°C but much lower, meaning more cooling and implicitly more heat expended by living persons in the same conditions, it seems very implausible that such an event could have happened in mere hours like the story suggests. The conditions required would be so hard that few could survive the day, and even if they survived their energy reserves would be depleted after a few days or weeks. Ssscienccce (talk) 10:31, 30 September 2013 (UTC)

I'd like to make a simple request. Can those posting temperatures here please clarify whether they mean Celsius or Fahrenheit? HiLo48 (talk) 11:07, 30 September 2013 (UTC)

The only ambiguous temperature mentioned, as far as I can see, is the -50 degrees of the OP. Given that the source was an interview, it may not have specified the temperature scale, but since Celcius and Fahrenheit values coincide at -40°, the difference is relatively small: either -50°C = -58°F or -45°C = - 50°F Ssscienccce (talk) 12:06, 30 September 2013 (UTC)

Note that the reason frozen people doesn't readily shatter is the fat they contain. Fats freeze solid at a considerably lower temperature than water. Unlike water, they don't freeze at one temperature, but get gradually thicker and then harder as the temperature drops. Becoming hard enough to shatter requires that they be far colder than when they first start to solidify. You can do an experiment, and cut a chunk of fat off a piece of meat, or maybe use a pat of butter. Put it in the freezer, then try to shatter it with a hammer. Do it outside, as this will make a mess. If you want to try it at colder temps, buy some dry ice and put it in that before you try to shatter it. Many grocery stores carry dry ice. StuRat (talk) 17:30, 30 September 2013 (UTC)

total current in parallel cct

hello, i am stuck on this question:

if four 100 W lamps are connected in parallel across a 120 V source, what is the total current? a) 833 mA b) 3.33A c) 33.3A d) 8.33 A

i dont even know where to begin, help is appreciated. — Preceding unsigned comment added by 208.96.87.57 (talk) 22:56, 29 September 2013 (UTC) unless, is it I(t) = V(t)/R(t)? which is 100/120 = 833mA?

We apply ohms law, E = IR, where E is voltage, I is current, and R is resistance, and the definition of the watt as EI. Now, we determine the amperage of a 100 watt, 120 volt lamp as using W = EI, where W is watts. Thus, W/E = I, so 100/120 = 0.8333... is the amperage of an individual bulb at 120v. But there are four bulbs in parallel, so the total current is (100/120)*4 = 3.333... amps. DavidLeighEllis (talk) 23:12, 29 September 2013 (UTC)

ah yes yes yes thank you, this makes perfect sense.208.96.87.57 (talk) 23:22, 29 September 2013 (UTC)

remember, when you don't know the answer, always choose B. Gzuckier (talk) 05:31, 30 September 2013 (UTC)

Minors' calorie count

Health-related question. Is there a way to figure out how many calories a given minor should consume in a day? All the sources I've found online say that their systems would only apply to adults. Theskinnytypist (talk) 23:51, 29 September 2013 (UTC)

Use Google and search on calorie needs for kids, and you'll get heaps of sites. http://www.weightlossresources.co.uk/children/nutrition_calorie_needs.htm has a good table and information:-

   Calories per day
   ================
 Age       Boys    Girls
------     -----   -----  
 1– 3      1,230   1,165 
 4– 6      1,715   1,545 
 7–10      1,970   1,740 
11–14      2,220   1,845 
15–18      2,755   2,110 
Adults     2,550   1,940 

This can only be a very rough guide designed to keep you skinny and assuming not a lot of exercise. For instance, I am in my 70's, only moderately overweight (80 kg) and eat about 6000 calories per day. How do you format a table in this thing?

121.215.63.7 (talk) 01:13, 30 September 2013 (UTC)

There is a formal table, but I find it easier just to put a space in front and space them out myself. I did this for you above. StuRat (talk) 17:21, 30 September 2013 (UTC)

Anyone know why at every age the suggested calories is lower for girls than for boys? Aren't girls as big or bigger than boys at some ages? Duoduoduo (talk) 15:37, 30 September 2013 (UTC)

Boys have a faster metabolism due to (on average) more muscles and less fat. Count Iblis (talk) 18:10, 30 September 2013 (UTC)

Is that true for pre-pubescent boys vs. girls -- more muscles and less fat? Duoduoduo (talk) 19:04, 30 September 2013 (UTC)

I agree with 121.215.63.7 that the calories are quite low, but then the average child's physical activity is way below what is recommended, and that recommendation is already way too low. The best way one can make sure a child is not going to get obese is to make sure the child gets plenty of exercise every day. At the very least the child needs 2 hours of play time per day which must involve one hour of running, or other strenuous physical activity. Count Iblis (talk) 18:10, 30 September 2013 (UTC)

September 30

Where is East?

My bedroom faces East. In spring the sun rises on the left side of the window. In autumn on the right. It is quite a significant shift. My guesstimate on degrees of a circle would be between 60-90 degrees. I know North changes slightly. My questions are these. What is the range that sunrise covers? Does latitude make a difference? Where is East on the map? And how do aircraft navigate - as East on the map, is actually not a fixed direction? 31.25.4.14 (talk) 09:35, 30 September 2013 (UTC)

A modern nautical compass rose

True east is 90° CW from true north (geodetic north) and does not change. Magnetic east, 90° CW from magnetic north, does change as the North Magnetic Pole slowly moves. The difference (in degrees) between the two is called magnetic variation. Nautical charts include a compass rose which shows both true and magnetic direction, and gives the numerical value of that location's variation in a particular year and the rate of change of that variation to allow for use in subsequent years. "The sun rises in the east." is a general statement, and is not strictly true. (It certainly does't rise in the west, but it doesn't rise due east everywhere on every day of the year.) See Sunrise#Location on the horizon. This sun calculator may be of interest to you. -- ToE 10:20, 30 September 2013 (UTC)

Only around the March and September equinox will the sun rise approximately in the east, between March and September, it will be more to the north, between September and March more to the south, as the sun calculator given by ToE demonstrates. Ssscienccce (talk) 10:45, 30 September 2013 (UTC)

And yes, latitude does make a difference. For any given day, the sun will rise farther from east for locations with greater latitude, but even on the equator it will only rise due east on the equinox. We are currently just one week after the autumnal equinox, and the angles shown in the sun calculator are not large, so you may wish to advance the calculator's date. If you bring it well into the northern winter and choose an extreme northern latitude with only minutes of sunlight per day, you will see that the sun is rising and setting minutes apart in the south. -- ToE 10:56, 30 September 2013 (UTC)

And here is another interesting calculator. 31.25.4.14 geolocates to Harrogate with a latitude of 54°, so the calculator shows that your solstice sunrises are nearly northeast in your summer and southeast in your winter. -- ToE 12:00, 30 September 2013 (UTC)

Why do planet have eliptical orbit?

If sun's gravity at a planet has same in every direction then why a planet moves in eliptical orbit? — Preceding unsigned comment added by 101.217.215.28 (talk) 12:08, 30 September 2013 (UTC)

Elliptic orbit

It would be circular if the planet started at exactly the right speed perpendicular to the Sun, but it doesn't for any of the planets. Kepler orbit has some complicated maths to show how an elliptic orbit happens. Here is a very loose argument not showing why it exactly becomes an ellipsis: Imagine the planet in the drawing is moving down-left falling closer to the Sun for a while. It picks up speed and when it's to the left of the Sun, the speed is maximal and so high that it starts moving further away from the Sun and slow down. At the right edge of the ellipsis, the speed is minimal and so slow that it starts falling closer to the Sun again and increase speed. PrimeHunter (talk) 13:49, 30 September 2013 (UTC)

Note that the planet only moves perpendicular to the Sun at the left and right edge of the ellipsis. At the left edge the speed it too high for a circular orbit so it moves further way. At the right edge the speed is too low for a circular orbit so it moves closer. PrimeHunter (talk) 14:00, 30 September 2013 (UTC)

The orbit is stable if the sum of the gravitational and kinetic energy remains the same throughout the orbit. With a perfect balance like that, no energy is required to be added or removed from the system, so the planet keeps doing the same thing over and over. There is no reason why the planet can't move slowly when further from the sun, and faster as it gets in closer - so long as the sum of gravitational and kinetic energies doesn't change. Such orbits can be perfectly stable over billions of years. A circular orbit certainly has that property - but so does an elliptical one. Statistically, it's extremely unlikely that a planet would happen to be in a perfectly circular orbit - so an ellipse is more likely. Also, the presence of more than one planet in a solar system perturbs orbits slightly - so a circular orbit wouldn't remain perfectly circular for very long. SteveBaker (talk) 14:01, 30 September 2013 (UTC)

In the absence of any perturbing third objects, is it even possible for a very small passing object to be captured into a perfectly circular orbit by a very large object? If yes, under what condition on velocity etc.; if no, why not? Thanks. Duoduoduo (talk) 15:46, 30 September 2013 (UTC)

In the absence of other objects, and in the classical case, two objects either have a positive total energy, or a negative total energy (where total energy is the sum of potential and kinetic energy). Since energy is conserved, this will not change (unless the two smash into each other ;-). In the fist case, they are bound, in the second they are not. In the relativistic case, the system can lose energy via gravitational waves, so in theory they can capture each other. But that is a very small effect. In practice, capture will (nearly) always require a three-body interaction. --Stephan Schulz (talk) 19:48, 30 September 2013 (UTC)

It's worth pointing out to the OP that the diagram is nowhere near to scale for an actual planet. For example, the earth only varies a few percentage points between aphelion and perihelion. The diagram is closer to describing the orbit of a periodic comet such as Halley's - although for a comet it's probably not extreme enough. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:10, 30 September 2013 (UTC)

As Baseball Bugs points out, the orbits of the planets are actually quite close to being circular, so the question should be why that is the case. So, why aren't the orbits of planets a lot more elliptical? The answer is that the solar system is actually unstable, an initial state where you have large eccentricities would lead to collisions and planets being ejected from the solar system. This is precisely what happened during the formation of the solar system. What you are then left with at the end of the planet building phase is a more stable configuration where the orbits are almost circular and the ratios of the orbiting periods are such that resonaces are minimized. So, the perturbations on the very long term will actually steer the orbits toward becoming more circular, but they won't make them exactly circular. The solar system is still unstable, but on a time scale of billions of years.

The mechanism here is similar to how thermal equilibrium is approached in many body systems. In a state of thermal equilibrium a particle will still experience thermal fluctuations, but you will have equipartition of energy, the energy transfer from one particle to the rest of the system another will then average out to zero on the long term. Count Iblis (talk) 16:32, 30 September 2013 (UTC)

I think the person asking wants a more basic answer, so let's take a try at being simple: At its closest point to the sun, a planet is a lot like a ball you throw up into the air. Even though it is at its lowest point, it is moving quickly on a line that will take it further away from the sun. Its course bends from that line because of the sun's gravity, and eventually, like a ball tossed in the air, it runs out of energy and starts falling back again. That point where it starts falling back is the furthest point from the sun, but because the planet is still moving perpendicular to the sun at that point, it's going to miss it on the way in. After the planet finishes falling back, it has the extra speed it started out with all over again (this is conservation of energy). Now it happens, mathematically, that this curve is almost an ellipse - (Kepler's law says exactly, but the theory of relativity corrects this a little). In a sense, that's just how the math works out, but there's a deeper meaning too: an ellipse (and more precisely the path corrected for relativity) are shapes that allow the combined angular momentum of planet and sun spinning around one another to remain the same as the planet moves in and moves out. Like an ice skater going into a spin, the planet has to change the angle it has relative to the sun fastest when it is closest to the sun, slowest when it is furthest away. The near-ellipse allows for this change to match the change in the planet's speed as it goes in and out. The only way that the ellipse turns out to be a simple circle is if at its moment of being closest to the sun, the planet has exactly the right speed to keep swinging around in a circle at the same speed. If you could "hit the brakes" on the planet for a moment, it would start falling with that being the highest point in a new ellipse, and if you could "hit the gas" we'd be back to what I described above. Wnt (talk) 19:50, 30 September 2013 (UTC)

Work done by a person carrying a bag on his head

What is the work done by a person while moving and carrying a bag on his head? Scientist456 (talk) 12:29, 30 September 2013 (UTC)

Should be none at all theoretically disregarding friction etc. It's no different from sticking a load onto a trolley and giving it a push to send it away. Actually many people find this a very convenient way to carry loads. Dmcq (talk) 12:37, 30 September 2013 (UTC)

I strongly disagree. It's certainly not true that this is no different than using a trolley (although you're right about the fact that a lot of people prefer to carry loads like this).

As you walk, your head bobs up and down a little (see animation at right). That requires you to lift the load against gravity (expending muscular chemical energy to do so) and lower it again (requiring you to cancel the resulting kinetic energy with more muscle power)...repeated with every step you take. Pushing it on a trolley leaves it at the same height - so the only additional expenditure of energy is the friction of the wheels. I'm not sure whether one or the other is more work. There are much more complicated things at play if you're moving around on uneven ground - so using your head instead of a trolley might well make sense. But there is certainly a profound difference.

In reality, it's even more complicated because a human body isn't like a robot. In theory, a robot with a hydraulically powered arm could hold it outstretched with a heavy weight on it for years without expending any energy whatever to do so. But for a human, that kind of activity is exhausting! So merely placing the weight on someone's head and having them stand still must incur some energy consumption beyond the extra energy required for head-bobbing during walking.

The answer here is very complicated. We shouldn't over-simplify it. What's needed for a good answer here is some kind of study into the biometrics of the thing.

SteveBaker (talk) 13:42, 30 September 2013 (UTC)

(ec) No. How would you walk without lifting your feet? The friction would be enormous if you tried to slide them. The work is the same as if you carried it any other way. The real advantage is that the center of gravity of the load is roughly the same as the center of gravity for the person. This counters the effect of having to lean into the load so you don't topple over. 196.214.78.114 (talk) 13:44, 30 September 2013 (UTC)

Check out this clip to see what I mean. http://www.youtube.com/watch?v=lV-iP1jSMlI 196.214.78.114 (talk) 13:49, 30 September 2013 (UTC)

Old studies claimed that it was more efficient than other ways of carrying loads, a recent publication suggests that it may be less efficient, and is used mostly to traverse difficult terrain (although that seems strange to me, considering the odds of dropping it). I would have thought that it had something to do with keeping the center of mass "centered" so it's supported by the skeleton instead of the muscles, but primarily with the fact that you don't need "grip" to hold the object. Without straps, ropes or a suitable shape with handles, it's hard to support large objects with your hands or arms. But the old theory that they could carry 20% of their body weight without spending more energy seems in doubt. Here are some studies mentioned, one that found Nepalese porters carried loads more efficiently than African women. Ssscienccce (talk) 14:30, 30 September 2013 (UTC)

There is an article Carrying on the head about this. It doesn't describe there but when doing this one normally moves the head in a level way like those Russian dancers so the weight doesn't go up and down much. If we had sinews that were as good as kangaroos I guess even that would be unnecessary as we'd get most of the energy back after each step. Dmcq (talk) 15:07, 30 September 2013 (UTC)

Why is the speed of light in vacuum not relative?

Suppose if the earth were moving toward a star, the light from that star should seem faster than if the earth were moving away from that star. But it does not happen, why? If something is moving with a speed of 100,000 km/s, then it still experiences the speed of light to be 300,000 km/s. Why is it so? Why don't it experience light to be moving at 200,000 km/s (=300,000 - 100,000) or 400,000 km/s(=300,000 + 100,000)? Britannica User (talk) 13:32, 30 September 2013 (UTC)

The speed of light is constant to the observer. What can vary is the frequency, i.e. the light-wave version of the Doppler effect. If a galaxy is approaching, its light should be blue-shifted. If it's receding (the typical situation) it should be red-shifted. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:44, 30 September 2013 (UTC)

Eh? What does that have to do with it? SteveBaker (talk) 13:51, 30 September 2013 (UTC)

I'm giving you the explanation my Physics teacher gave. Feel free to make corrections. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:05, 30 September 2013 (UTC)

Read Special relativity, which explains some of the consequences of the constancy of the speed of light. But, in simplest terms, every observer does measure the speed of light at the same speed, regardless of how fast they are moving. This seems counterintuitive to people who have only experienced measuring the speed of objects like cars and trains and things, but none-the-less it is how the universe actually works. The consequences of this lead to several apparent paradoxes, such as concepts like the relativity of simultaneity and the like, but again these are not paradoxes except in the sense of "I don't experience this so it doesn't make sense" as opposed to "this isn't how experimental observation shows the Universe to work." Concepts like special relativity are a good demonstration of why relying on ones own senses and "common sense" and not on the collective results of experimental science often leads one astray. --Jayron32 13:50, 30 September 2013 (UTC)

I'm not sure we know why this is. Physics is relatively poor at answering "Why?" questions. We know that the universe operates in this manner...but why it does that is hard to say. You can construct arguments like the fact that photons have a zero rest-mass and a measurable mass when in motion, and because of the laws of relativity, that means that they have to be moving at the speed of light in any reference frame...but that only turns things around from "Why is the speed of light constant?" to "Why do photons have a rest mass of zero?" and "Why do the laws of relativity hold as true?". There doesn't appear to be a root cause - it is simply what we've observed in countless careful experiments and measurements of how the universe appears to operate. We know that the universe would be a drastically different place if this were not true. We can probably make a valid claim that life would not exist if it were not true. Hence we can probably invoke the Anthropic principle to say that if this were not true, we wouldn't be here to observe it - so it has to be true...but that's always considered a weak explanation for such things. SteveBaker (talk) 13:51, 30 September 2013 (UTC)

The "why" of any fact about science can sometimes be determined by further experimentation. Why the speed of light is constant is the OP's question. My question would be why is the speed of light what it is, i.e. about 186,000 miles per second? What is it about the nature of light that determines that that is its speed rather than some significantly larger or smaller number? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:04, 30 September 2013 (UTC)

What is this thing about science not answering "why" questions? It's never been true or made any sense. Why is the sky blue? Why don't oil and water mix? Why do most of the stars move as though affixed to a sphere, except for a few (the "wanderers", Greek planetes) that move in complicated patterns in a narrow strip called the ecliptic? Science answers most of the "why" questions that early people probably had about the world.

There's no reason velocities shouldn't behave as they do. Draw a horizontal line. Draw a second line crossing it with a slope of 1/2. Draw a third line with a slope of 1/2 using the second as a base. What is its slope relative to the first? The answer is not 1, but 4/3. You can work out that in general the combined slope is (m + n) / (1 − m·n). That looks a lot like the "velocity addition formula", and that's not a coincidence. If you had used angles instead, you could have just added them. The angle version of speed is called rapidity. You're just measuring speed in a funny way and then complaining that you get weird results. Yes, in a way, it's a mystery why anything is the way it is, but not in a way that's relevant to this question. We actually understand the nature of speed pretty well. -- BenRG (talk) 20:53, 30 September 2013 (UTC)

I would mostly agree with Jayron. You can go a bit further and argue that any local theory of physics where things that will happen here in, say, one second from now isn't going to depend on what is happening now elsewhere at arbitrary large distances, must have this property. Count Iblis (talk) 14:40, 30 September 2013 (UTC)

Also note that sub-light speeds don't add and subtract as you may expect. Relative velocity#Special relativity theory shows the formula $v_{\mathrm {BA} }={\frac {v_{\mathrm {B} }-v_{\mathrm {A} }}{1-{\frac {v_{\mathrm {A} }v_{\mathrm {B} }}{c^{2}}}}}$. If two cars drive towards eachother at each 100 km/h from the reference frame of the road then each car sees the other approaching at ${\frac {100{\text{km/h}}-(-100){\text{km/h}}}{1-{\frac {100{\text{km/h}}\times (-100){\text{km/h}}}{c^{2}}}}}$. c = 1079252848.8 km/h is so large that the result becomes 199.9999999999983 km/h. Humans don't notice the difference from 200 km/h but advanced instruments can measure relativistic effects at Earth speeds. If we consider the lights from the two cars instead of the cars themselves and plug the speed c into the same formula then we get (c - -c)/(1 - (c × -c)/c²) = (c+c)/(1+1) = c. PrimeHunter (talk) 14:45, 30 September 2013 (UTC)

It's very surprising to people but in fact we don't live in a euclidean world. So it makes sense that any intuition based on a expectation that the world is euclidean might turn out to be incorrect. That includes the intuitive - but incorrect - simple addition of velocities the OP thought should apply - but doesn't. Ultimately, the geometric nature of the universe must be decided experimentally - not intuitively - and the experiments have been done. Turns out the universe is not euclidean. Dauto (talk) 21:00, 30 September 2013 (UTC)

Why do razor blades dull so quickly ?

They are steel, after all, and are only used to cut through hair, not corundum. I can think of a couple possible explanations:

1) The manufacturers intentionally use a soft steel, so they will dull quickly, and you will need to buy replacements.

2) The blades oxidize, and this dulls them. The blades often seem dull even with no sign of rust, so that seems to contradict this explanation, unless rust can dull blades before it becomes visible.

StuRat (talk) 17:44, 30 September 2013 (UTC)

My experience is that expensive razor blades can last for quite a while (dozens of uses), but cheap ones are only good for one or two uses (if that). Looie496 (talk) 18:14, 30 September 2013 (UTC)

I remember hearing that it is corrosion, with the advice to dry the blade with a towel after use. I've done that since and I feel like it helps, but I never kept track of uses or anything so it is subjective. I'll second the advice on cheap blades. I once decided to try a pack of cheap disposable razors. They could barely make it through one use, and they started out at the point where I would start considering tossing a nice blade. If anyone can find good information on making a blade last longer, I would greatly appreciate it - I don't get too many uses (certainly not dozens) out of a nice blade either. Katie R (talk) 19:22, 30 September 2013 (UTC)

You could try this approach, which (if it works) is probably a variant of stropping or honing. Assuming that shaving can bend or fold the edge of the blade, this would straighten it again. Ssscienccce (talk) 19:46, 30 September 2013 (UTC)

You could also try a pyramid surrounded by crystals under the full moon. (Disclaimer: It won't actually work but you'll have fun trying.) -- Jack of Oz ^{[pleasantries]} 20:13, 30 September 2013 (UTC)

If soap cleans by removing sebum oil from your skin, and the palms of your hands don't have sebaceous glands, which are the glands that produce sebum oil, does that mean soap never cleans the palms of your hands?

If soap cleans by removing sebum oil from your skin, and the palms of your hands don't have sebaceous glands, which are the glands that produce sebum oil, does that mean soap never cleans the palms of your hands? If soap still cleans the palms of your hands, how does that work despite the absence of sebum oil of the palms of your hands? Rebel Yeh (talk) 19:41, 30 September 2013 (UTC)

Soap is a like detergent (strictly, it's a "Surfactant"). It reduces the surface tension of the water and allows it to flow more easily into small spaces and to mix more easily with oils - and also to encapsulate small particulates. That helps to remove whatever it is that's adhering to your hands...not just sebum, but any kind of oil, fat or other similar residue. SteveBaker (talk) 20:09, 30 September 2013 (UTC)

Just to clarify a bit, soap doesn't clean by removing sebum. Soap cleans by allowing the water to dissolve more substances than it otherwise would. (this is a gross oversimplification, but right enough for a discussion of this level). Sebum may be one of those substances, but there's lots of other things of greater concern than sebum. Indeed, preferably, you want to keep your sebum, as removing that leads to problems with dry skin. Good hand soap strikes a balance between removing dirt and leaving behind your own oils. --Jayron32 20:37, 30 September 2013 (UTC)