Wikipedia:Reference desk/Archives/Science/2008 August 25

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August 25

Frequency of Meiotic Crossover

OK, if human gametes always acquired their chromosomes intact, then I'd have, on average, 11.5 from each of my grandparents, 5.75 from each great-grandparent, etc. Thus if I went back in my pedigree 7 generations—and with the further simplifying assumption that all of my ancestors were unique—then since there are 128 people back there and only 46 opportunities, the expected contribution from any one of them to my genome would be zilch. And seen the other way round, any one of my descendants 7 generations hence could expect to inherit nothing from me.

But, of course, meiosis doesn't work so tidily. So my question is, in practice how far off is the above reasoning? To state it more rigorously, how likely is it that any particular human gamete is free of crossovers, that each of its 23 chromosomes is simply a complete copy of one from the homologous pair?—PaulTanenbaum (talk) 03:41, 25 August 2008 (UTC)

The crossover rate varies by chromosome, but one would expect in general one crossover per chromosome. So one would have to go back more than seven generations to be reasonably certain that at least one ancestor in that generation had no genetic contribution to your makeup. - Nunh-huh 03:52, 25 August 2008 (UTC)

So, for instance my son's X chromosome likely contains some scraps from both of my in-laws?—PaulTanenbaum (talk) 04:04, 25 August 2008 (UTC)

Yes. And, in general, though not invariably, your son's autosomal chromosomes will likely contain some scraps from all four grandparents. The bigger the chromosome, the more likely there was a crossover event. - Nunh-huh 04:22, 25 August 2008 (UTC)

The number of crossover events per chromosome is higher than Nunh-huh suggests. According to this book, "On average, between two and three crossover events occur on each pair of human chromosomes during meiotic division I." I was surprised by the confirmatory answer to the question about the likelihood of crossovers between the X and Y chromosomes, but Nunh-huh is right on this one - there are indeed tiny regions in the Y chromosome which do cross over with their X chromosome counterparts, see this figure from this article. --NorwegianBlue ^talk 18:17, 25 August 2008 (UTC)

While it's true that there is a small area of the Y & X chromosomes that are homologous, and so permit crossover, it's not pertinent to the question asked about Paul's son's X chromosome, which came from Paul's wife (the crossover here occurred between the two X chromosomes of the mother, each of which contain portions of an X chromosome from her mother, and an X chromosome from her father, again due to crossover). - Nunh-huh 03:13, 26 August 2008 (UTC)

Nun-huh is right about the point of my question. But I do appreciate NorwegianBlue's info about crossovers between X and Y, and the pointer to the NIH article is extremely helpful. Muchos gracias to both of you!—PaulTanenbaum (talk) 03:25, 26 August 2008 (UTC)

Human growth hormone production.

Is it possible to have normal growth hormone function without a pituitary gland? Danlius (talk) 05:14, 25 August 2008 (UTC)

Highly unlikely without treatment, considering GH is secreted by somatotropes, which are found in the anterior pituitary. If one has no somatotropes, then one will almost certainly suffer from a Growth hormone deficiency. However, you should ask an endocrinologist if you want a definitive answer about what is and is not medically possible. Dostioffski (talk) 05:36, 25 August 2008 (UTC)

Cooked meat and air in a refrigerator

Take two slices of cooked ham. Put one slice in an open-air container, and put the other slice in a container with a lid. Now put both ham-containing containers inside the refrigerator, and leave the two containers in there for two days. At the end of those two days, the ham in the open-air container will have become hard (in texture), while the ham in the closed container will still be soft. Why? —Lowellian (reply) 08:11, 25 August 2008 (UTC)

Because a refrigerator efficiently removes moisture from the air, and the dry air efficiently removes moisture from the meat. Franamax (talk) 08:28, 25 August 2008 (UTC)

A fridge may speed up the process, but it isn't necessary. See Dried meat. --Shaggorama (talk) 14:14, 25 August 2008 (UTC)

Beef aging (in particular, dry-aging) is also close enough to be of interest. -- Coneslayer (talk) 18:04, 25 August 2008 (UTC)

Alcohol-and-cigarette-based human combustion

In the film Better Luck Tomorrow, there is a scene where a character consumes a lot of alcohol, and another character jokingly warns him not to light a cigarette in his mouth because he "might explode". Is it actually possible to drink enough alcohol to combust by lighting a cigarette in one's mouth? —Lowellian (reply) 08:30, 25 August 2008 (UTC)

Does a lighter explode when you light it just because it is full of ethanol and there is a flame at the top? The simple answer is 'no'. You would have to drink pure alcohol (not a dilute like whiskey or vodka), and LOTS of it, because by the time it got into your body it would be diluted by whatever is in there. You would die long before you could drink enough pure alcohol for your body to be over the 'inflammable mark' of 100% proof. Alcohol fumes in the breath may be a very unlikely source of a flame, but certainly no explosion. Like setting your farts on fire.--ChokinBako (talk) 10:06, 25 August 2008 (UTC)

Flammable materials don't always explode. There needs to be just the right mixture of material and air/oxygen. This is why grain silos can explode. I doubt you would ever be in a situation where your body was in danger of exploding due to alcohol consumption. Combustion does not always imply explosions, but more often burning. It is entirely possible to ignite alcohol that is in your mouth, similar to what fire-eaters do, but unlikely that you would be able to ignite the alcohol in your body. --Russoc4 (talk) 14:50, 25 August 2008 (UTC)

According to alcohol poisoning, drinking enough to make alcohol compose 0.55% of one's blood will kill about half the people who try it, so let's use double that (1.1%) as the maximum amount of alcohol you can reasonably have in your blood. Now pour a 1.5 oz shot glass of pure alcohol into a gallon bucket of water, which by RefDesk serendipity comes out to give the mixture a 1.17% alcohol level, and consider trying to light that bucket of water. --Sean 15:53, 25 August 2008 (UTC)

I think "reasonably" is a poor word to use in talking about a probably lethal dose of alcohol. Wanderer57 (talk) 17:24, 25 August 2008 (UTC)

I think you could probably hold enough alcohol vapor in your mouth to give yourself a pretty bad burn. Especially if your nose neighbor was doused. Plasticup ^T/C 18:52, 25 August 2008 (UTC)

I agree with Russoc4 that it's impossible to render a human body flammable by consuming alcohol – we've got too much water in our bodies – but I think we might be choosing the wrong interpretation of the question. Instead of the entire body exploding, could we conceive of a case where there was sufficient high-proof alcohol (and alcohol vapor) remaining in the drinker's mouth to result in a fire or small explosion when triggered with a lit cigarette?

There are a quite a number of alcoholic drinks which are flammable, some which are deliberately set alight, and a few which are even deliberately ignited in the drinker's mouth (e.g. the Sambuca volcano—Attempt at your own risk). In any event, it's certainly possible to ignite some hard liquors in a person's mouth. Can you do it with a cigarette? That's a tougher question. Is is possible to retain enough alcohol and fumes in the mouth after swallowing? Also tough to answer (though high alcohol content would help—think Bacardi 151, or straight grain alcohol...). In principle, if one had the right mix of ethanol and air in one's mouth and lungs, it could ignite violently enough to be described as an explosion. If it also ignited liquid alcohol in the mouth, it could cause serious burns. TenOfAllTrades(talk) 19:11, 25 August 2008 (UTC)

Fire eating might be of interest here. The situation we're talking about would be fire eating gone horribly wrong! --Tango (talk) 19:22, 25 August 2008 (UTC)

According to our flash point article, ethanol has an autoignition temperature of 365°C. According to this site, a cigarette has a temperature of 400°C. I'd say that if you held a shot of grain alcohol in your mouth and stuck a lit cigarette in there, you could create the local conditions for autoignition and the ethanol flashpoint of 12.8°C would be more than enough to burn you badly. Just to be sure, have someone else draw on the cigarette when they put it in your mouth - that way you will have a friend in the hospital bed beside you. Franamax (talk) 23:22, 25 August 2008 (UTC)

I would say that the most dangerous part of this is not that the body literally "explodes", but rather that you can get fairly severely burnt. If you drink alot of alcohol, you might pass out to the degree where if the cigarette where to fall out of your mouth and set your clothes on fire, you might not wake up. This could prove fatal, or at the very least leave you with some nasty burns. Be careful with your booze, people! 90.235.4.253 (talk) 02:06, 26 August 2008 (UTC)

power system

why 15 nos. disc insulator connect for 220kv o/h line? —Preceding unsigned comment added by Manir b4u2002 (talk • contribs) 08:45, 25 August 2008 (UTC)

Please write more clearly - it's impossible to understand what the heck your question is! Something about disk insulators on 220 kvolt overhead lines....but what is "15 nos." ? SteveBaker (talk) 13:59, 25 August 2008 (UTC)

(to Manir b4u2002) Also please sign your post in future. Otolemur crassicaudatus (talk) 16:25, 25 August 2008 (UTC)

Guys, there is no need to be so snotty with someone who is asking a good faith question and is just having trouble expressing himself. My interpretation of the question is that it is regarding the stack of insulators used on overhead power transmission lines and why there are that number of them. The insulators are made of glass or ceramic or a modern composite depending on age of the installation. Each disc is able to insulate around 15kV without arcing over. Consequently for the high voltages used in power transmission a stack of them needs to be used. Our article here shows a 275kV pylon with a stack of 18 discs. For 220kV, 15 discs, as Manir states, would be about right, but there are no examples I can go and look at locally as 220kV is not a standard voltage used in the UK. The number of discs required depends also on other factors such as the material and the local climate (damp countries need more than dry deserts). SpinningSpark 18:17, 25 August 2008 (UTC)

And that also accounts for the "crackly" sound you often hear on rainy days when walking near high-voltage lines - current leakage over the surface of the insulators. Franamax (talk) 22:59, 25 August 2008 (UTC)

No. I rather think that sound is caused by corona discharge —Preceding unsigned comment added by ThornCider (talk • contribs) 00:22, 26 August 2008 (UTC)

Medical Term for No Fear in Crisis.

I read in some medical publication of a woman who instead of flight, chose to fight in all emergency situations. There was an example where she was alone in her house and an intruder broke in. Instead of fleeing and getting help, she says that the impulse takes over immediately and she went after the intruder with a wooden spoon. She managed to chase away this intruder but afterwards she realized that she could have put herself in extreme danger. Then this publication named her condition as some medical condition and states than so many percent of Americans have this "disorder". I don't remember the name of this condition. Please help. --Anilmanohar (talk) 13:20, 25 August 2008 (UTC)

I didn't know that the fight-or-flight response was a now considered a 'disorder'; I thought it just meant that her nervous system was working. TenOfAllTrades(talk) 13:38, 25 August 2008 (UTC)

The OP sounds like the article stated that she actually lacks the fight-or-flight response and only possesses a will to fight. -- MacAddct  1984 ^{(talk • contribs)} 14:49, 25 August 2008 (UTC)

Yes, that is correct Macaddct. She only had a will to fight as if she had no choice. --Anilmanohar (talk) 15:14, 25 August 2008 (UTC)

The decision of whether to run or stand and fight is often made in a fraction of a second based on all kinds of things. If you're in your house, you may well not have anywhere to run - presumably the intruder came through the door, so is between you and the door. Deciding to stand and fight when others would most likely run would be an example of courage (possibly combined with stupidity!), I've never heard of it being considered a medical disorder. --Tango (talk) 19:09, 25 August 2008 (UTC)

Ok, I just thought about it more. Is there a medical condition in which a person creates more adrenaline than a normal person would? I mean if you have high amounts than normal of adrenaline coursing through your body, it could lead to unusual aggression? I was also thinking of the Geronimo Syndrome, but that is just an unusual desire to jump, I think. --Anilmanohar (talk) 13:12, 26 August 2008 (UTC)

Is copper(II) ion more stable than copper(I) ion?

Is copper(II) ion more stable than copper(I) ion? If so, why?Tetsuya26 (talk) 14:14, 25 August 2008 (UTC)

Hi Tetsuya! You should check out our ion and copper articles, then get a healthy snack, then go finish your homework. Let us know if you still have questions after reading those articles. --Sean 16:02, 25 August 2008 (UTC)

Yes but why is cu2+ more table? —Preceding unsigned comment added by Tetsuya26 (talk • contribs) 18:13, 25 August 2008 (UTC)

Something to do with its electron configuration. Look for all the usual things: spin multiplicity, filled or half-filled shells, etc. DMacks (talk) 14:44, 27 August 2008 (UTC)

Useful life of commerically packed grated ginger

I've occasionally purchased chopped garlic packed in oil. I'm pretty sure that this product is safe to open, use a little, and store the remainder in the fridge, using it as needed over an extended period of time. Recently, I've purchase grated ginger in a very similar looking package. It is not packed in oil. The ingredient list includes a preservative, the name of which I can't remember. Do you think this product will be stable in the fridge once opened, over a period of months? The labeling doesn't give any indication. ike9898 (talk) 16:54, 25 August 2008 (UTC)

Check the label again, is really should have storage instructions on it. If there is no "use within X weeks of opening", then it should be fine until the best before date. I'm not sure there's any need to refrigerate ginger, but the packet should say. --Tango (talk) 19:13, 25 August 2008 (UTC)

Yeah, but it doesn't which is why I asked. ike9898 (talk) 19:50, 25 August 2008 (UTC)

Unfortunately, personal experience only, it's only "fresh-n-nummy"(c) for 1-2 weeks. Saintrain (talk) 21:40, 25 August 2008 (UTC)

I'm more concerned about the garlic in oil, I thought that was a good place for botulism to develop. Per Saintrain, grated anything will likely oxidize pretty fast and lose its flavour. It will still be "good" in a month, but you won't taste anything. Franamax (talk) 22:55, 25 August 2008 (UTC)

Not strictly answering the question but I can't see why anybody would ever need t buy grated ginger, surely it is always better to simply buy some ginger and grate it yourself? It will be fresher, have more flavour and probably have a much much longer shelf life. Jdrewitt (talk) 10:14, 26 August 2008 (UTC)

The same reason people buy ready grated cheese: convenience. (Admittedly, I don't believe I've ever bought ready grated cheese, but I've seen it in shops, so there must be someone buying it.) --Tango (talk) 20:25, 26 August 2008 (UTC)

Maybe they don't own a grater and are under 18 in the UK, thus unable to buy any knives to chop it instead (although they can join the army and get access to their cutlery and graters)? 79.66.44.182 (talk) 00:27, 27 August 2008 (UTC)

I'm not convinced (unprocessed) ginger would necessarily have a longer shelf life then packed grated/minced/crushed ginger with preservatives. Cost wise, it doesn't make much difference (as opposed to cheese) particularly if you're only using a small amount. Of course convinience as Tango alluded to is the biggest reason. And from my experience it does still have a fair amount of flavour after a month (kept in the fridge of course) Nil Einne (talk) 23:44, 27 August 2008 (UTC)

Ginger powder (grated and dried) lasts at least a few years at room temperature in several households I have visited.Polypipe Wrangler (talk) 08:18, 30 August 2008 (UTC)

WTC floor plan

Referring to the floor plan image

A typical floor layout and elevator arrangement of the WTC towers

Why is there so much "empty" space around the actual occupiable space, and what was this "empty" space used for? --82.152.214.49 (talk) 19:47, 25 August 2008 (UTC)

If you mean the section of the diagram that is in yellow, it is labelled for "open plan office", thus would be filled with cubicles or something similar. That is the actual "occupiable space" the central core held elevators, lavatory facilities and such. --LarryMac | Talk 19:51, 25 August 2008 (UTC)

The yellow area might even have walls that look like 'real' walls, but are not structural and can be reconfigured to match the needs of the renter of the space. ike9898 (talk) 19:53, 25 August 2008 (UTC)

And here's a stubby article about Open plan offices. --LarryMac | Talk 20:12, 25 August 2008 (UTC)

A company I worked for had a branch office in one of the twin towers, long before their destruction. On my only visit, I don't know what I had been expecting, but it was not the poky little suite I found. As noted above, on that floor (mid-80s, as I recall), floor-to-ceiling walls had been erected to form offices and suites. The walls served mainly to divide space between tenants, provide privacy, hold up pictures. I'm sure some large organizations had very impressive offices, all built within the framework of the space labeled "open" in the diagram. Cantor-Fitzgerald alone occupied five floors of One World Trade Center. — OtherDave (talk) 01:16, 26 August 2008 (UTC)

Why do we laugh at people who get hurt

http://www.youtube.com/watch?v=B0PEIMGgKH4

^Watch this video. Most people would find it funny even though that kid was pretty hurt. But why is it funny? ScienceApe (talk) 21:25, 25 August 2008 (UTC)

I don't think "most people" would find it funny. Maturity and empathy are big part of one's sense of humour. I'd say that 99% of western under 13s would find it funny. --Mark PEA (talk) 21:32, 25 August 2008 (UTC)

Yeah, I didn't find that funny. Someone just getting hurt isn't generally funny, someone getting hurt in an unusual way (particularly if it's through their own stupidity) can be funny. Schadenfreude will give you some more info. --Tango (talk) 21:42, 25 August 2008 (UTC)

Look at the comments section. Most people did find it funny. ScienceApe (talk) 21:46, 25 August 2008 (UTC)

Most people that post to the comments section of youtube found it funny - hardly a representative sample. --Tango (talk) 22:08, 25 August 2008 (UTC)

Indeed. Comment-posters on youtube aren't considered the sharpest tools in the box. This onion article hits the nail on the head, in my opinion. Fribbler (talk) 23:16, 25 August 2008 (UTC)

If you ever watched America's Funniest Home Videos, most of the videos which are considered funny are accidents where someone appears to get hurt. And adults, many of whom are probably considered mature, laugh at it. Tango, I guess it depends on what you consider to be "most people" of a representative sample. After all, what is representative? In fact by saying "Comment-posters on youtube aren't considered the sharpest tools in the box." could easily be argued that you are drawing an unverified assumption about comment-posters on YouTube. ScienceApe (talk) 00:46, 26 August 2008 (UTC)

Home video shows usually show people getting hurt in interesting or dramatic ways (at least, the ones in the UK do), not just falling off a bike (they might fall off the bike into a swimming pool, or something). "Representative" is a perfectly well defined word, and youtube commenters are not representative of humanity as a whole. Humanity as a whole can spell better, for a start! --Tango (talk) 02:17, 26 August 2008 (UTC)

Nope, they don't. At least not more dramatically than the video I linked. Nope. It isn't. You have to qualify representative. Representative of what demographic? Humanity as a whole? So according to you, a representative sample would be individuals from every single country in the world, which is absurd. Also, you were the one to make the "humanity as a whole" qualifier, not me. I used "most people" in the casual sense, not the literal sense, so really you are nitpicking words which isn't very helpful. With that logic, you made a broad claim that people getting hurt generally isn't funny, while based on what I've observed from other people's behavior, it is. However you don't have a representative demographic to support your viewpoint, other than your own opinion that you thought it wasn't funny. Actually most of humanity can't write in English, so that disproves your last point. ScienceApe (talk) 06:32, 26 August 2008 (UTC)

To me anyway most people does in fact imply humanity as a whole. You don't have to sample people from every single country but I would expect a sample from the major cultures. I don't for example, see how you can say most people do something if few Chinese, Indians and Africans (or perhaps South Americans/Muslims) do it. Thats why I personally avoid saying "most people" unless it's something I don't expect to not have a strong cultural bias. And I often challenge those who say "most people" to question whether they have considered other cultures. IMHO people should be more specific, and not group everyone together without knowing much about them. You could say; most Americans, most English first language speakers, most people from the Western world or whatever. Of course, again you should make sure what you're saying is indeed true. For example, if you're saying most people from the Western world, does it apply to the French, Germans, Spanish or Italians? P.S. And you're right, most people don't speak English P.P.S. I agree we have no way of knowing whether most people find getting hurt funny. P.P.P.S. In this specific case, "a lot of people" or "many people" find this funny would have worked without sandboxing people of large variety of cultures into one box. Nil Einne (talk) 23:32, 27 August 2008 (UTC)

Well that's nitpicking semantics then. Most people on YouTube did find it funny, and I was going off that. If you prefer, you can take the original statement to be based off of that instead of nitpicking semantics, which isn't very helpful. I've noticed some people here taking certain statements too literally, and then dissecting it. That sort of thing should be avoided, it just bogs down discussion into a meaningless debate on semantics. ScienceApe (talk) 02:02, 28 August 2008 (UTC)

I think that people sometimes find it amusing to see someone of a particular group they happen to dislike injuring themselves due to their own stupidity. Suppose that you dislike skateboarder/biker kids doing their stuff on your property (not my view - just an example) - there may be certain pleasure to be taken in seeing a kid, just like the ones who were rude and antisocial to you when you told them to move on getting injured performing a particularly dangerous, ill-thought-out, possibly drunken Jackass-style stunt in a public place... --Kurt Shaped Box (talk) 01:48, 26 August 2008 (UTC)

I would imagine that, for the U.S. immature teenagers who post comments on that video, the "humour" comes from the fact that the kid is described as "fat". There appear (from the side bar recommending other videos) to be a lot of YouTube videos of large children being hurt. Bart133 ^{t c @ How's my driving?} 01:40, 26 August 2008 (UTC)

Sometimes

Re: above; It does seem to be universal, when old farts watch kids (or puppies, fawns etc.) "growing up", the reaction is "Awwww. Hahaha." Toddlers sitting down suddenly, or Bambi on ice or watching a kid cook onions for the first time. When there's actual danger involved, climbing a bookshelf or playing with drano it's an entirely different reaction. Certainly there's empathy but there's something else too. Whatsit? Saintrain (talk) 21:55, 25 August 2008 (UTC)

Sometimes the more excessive or ridiculous the fall the funnier it can be perceived, up to a point. Most people would agree watching a bad car crash is not funny, but watching one of the Marx brothers take a frying pan to the face can be hilarious. Of course the latter is not "real" but the effect is related. Perhaps Slapstick is an article worth citing for that reason. Vespine (talk) 06:37, 26 August 2008 (UTC)

Calls to mind the saying, variously attributed, that comedy is tragedy plus distance. --98.217.8.46 (talk) 23:52, 26 August 2008 (UTC)

why do I look worse in photographs than in mirrors?

I'm not a very good looking chap but when I look in the mirror do I think that I look okay, and then when I look at photographs of me I think I look bad? I'm the same me, right? So why? —Preceding unsigned comment added by 86.128.219.33 (talk) 21:39, 25 August 2008 (UTC)

I don't really know, but see photogenic for some explanation of the opposite effect, it's probably the same thing in reverse. --Tango (talk) 21:42, 25 August 2008 (UTC)

It's not the same you. The one in the mirror is flipped left to right. Since that's the one you're used to, it can make actual pictures of you look somewhat strange. I don't know how much of the effect is caused by that as opposed to the explanations listed in the photogenic article. — DanielLC 00:38, 26 August 2008 (UTC)

You can experiment by using a photo editor such as the GIMP or photoshop to flip your photos of yorself. -Arch dude (talk)

My theory is that when person A looks at person B, (in general, not in an intimate situation) they usually look less carefully and for a shorter time than is polite or possible if A is looking at a photograph of B. Also, in the first case, B is likely to be moving, whereas a photographic image is fixed and more susceptible to detailed study. Because of these factors, A is less likely to notice "imperfections" of various types in B. Similarly, if A is looking at his or her self in a mirror, they are less likely to notice "imperfections" of which to be critical than when looking at their photo.

As I say, only a theory. Wanderer57 (talk) 05:26, 26 August 2008 (UTC)

But considering that A's image is also fixed when A is looking in the mirror, and A probably is applying detailed study to himself or herself, why would A be less likely to notice imperfections of which to be critical when looking in a mirror rather than in a photo? —Lowellian (reply) 11:49, 26 August 2008 (UTC)

Don't have much time now, but a common saying for the phenomenon 86.128.219.33 is describing is "the camera adds ten pounds". This blog thread has a discussion; I particularly like "your not supposed to eat the camera..." The thread links to this more credible webpage, which has a serious one-page explanation. --Bowlhover (talk) 08:22, 26 August 2008 (UTC)

Also have a look at: Perspective distortion (photography) - the lens itself provides a 'perspective' of reality. Sometimes that distortion is beneficial, sometimes it is not. As also noted a mirror is a constant changing image so doesn't capture 1/100th or 1/500th of a second of your face - at which point any number of problems could be evident such as your pose, lighting etc. I've heard that the 90-110mm range is consider a 'sweet spot' for portrait for photography. I have to agree that I also find most photos of me don't capture me as well as I think I look in real-life! 194.221.133.226 (talk) 13:08, 26 August 2008 (UTC)

It can depend a lot on lighting. Even in natural lighting a camera will perceive light and shadow differently than the naked eye. If care isn't taken with the lighting, Shadows can appear darker and "deeper" on film and change your perception of the shape of a face. Worse is if you're thinking of photographs taken with a flash that is only a couple inches away from the lens, that can cause all sorts of weird effects. APL (talk) 14:47, 26 August 2008 (UTC)

I wonder if the perspective has much to do with it. Most of our visual experience comes to us through binocular vision; someone in front of us (even the mirrored "us") is really composed to two half images (left and right) that our brain interprets as a whole in a complicated way that combines perspective, eye dominance, and other factors. A photo is both static and from a single perspective, which removes the true depth we're used to seeing. Matt Deres (talk) 21:38, 30 August 2008 (UTC)

Human eggs

How many eggs does woman start off with, and what happens to those that are left over after menopause? —Preceding unsigned comment added by ThornCider (talk • contribs) 21:45, 25 August 2008 (UTC)

According to this (from Google), women have one or two million at birth (another, unsourced, Ghit claims they have as many as seven million while still in the womb), are down to four hundred thousand or so by puberty, and are lost at about a thousand a month after that. Menopause occurs when the supply runs out entirely. Algebraist 23:07, 25 August 2008 (UTC)

What mass and volume would that be? 190.244.186.234 (talk) 00:47, 26 August 2008 (UTC)

The human ovum is about 0.1-0.2mm across. I can't find any figures on mass. Algebraist 02:58, 26 August 2008 (UTC)

An ovum would probably have a density close to that of water (it's just a specialized cell - and cells are mostly water) - so we can make a rough estimate - an 0.1 to 0.2mm object will have a volume somewhere around 0.001 to 0.008 cubic millimeters - which is 0.000001 to 0.000008 grams. A million of them would weigh between one and eight grams and take up between one and eight cubic centimeters. For comparison, a US 1 cent coin weighs 2.5 grams. That seems perfectly reasonable.

SteveBaker (talk) 15:52, 26 August 2008 (UTC)

What, you're saying a woman is worth three cents? Well, I never! ;) Franamax (talk) 09:02, 27 August 2008 (UTC)

I'm pretty sure that's not what I said...um let me check...no?!?! SteveBaker (talk) 13:49, 27 August 2008 (UTC)

Infinity

I am aware of the mathematical idea of infinity, but what I want to know is: is there any physical entity in the universe that can be said to be infinite? —Preceding unsigned comment added by ThornCider (talk • contribs) 23:38, 25 August 2008 (UTC)

"Only two things are infinite - the universe and human stupidity, and I'm not sure about the former." (and variants, attributed to Albert Einstein). Confusing Manifestation(Say hi!) 23:43, 25 August 2008 (UTC)

"There is no limit to stupidity. Space itself is said to be bounded by its own curvature, but stupidity continues beyond infinity." (Gene Wolfe) Algebraist 00:16, 26 August 2008 (UTC)

Spacetime itself, possibly (it's unknown if it's infinite, and I don't know if you would count it as an entity). Other than that, I don't think so. There are some things in physics that end up with infinities in the maths, but that usually means we don't properly understand it (the density of a singularity in a black hole, for example). Negative temperature can, apparently, be thought of as infinite (or even more than infinite) temperature, but I've never understood that myself. The ranges of electromagnetism and gravity are infinite, but they both move at finite speed and the universe is a finite age, so no EM or gravitational field is actually infinite. That's about all I can think of that even comes close. --Tango (talk) 23:48, 25 August 2008 (UTC)

We don't really know. There might be. Infinite divisibility parallel universes and multiverse are interesting hypothesis's. ScienceApe (talk) 01:06, 26 August 2008 (UTC)

It a little tough to draw the line with "physical entity". The basic "measurements" of physical entities are the fundamental units: Mass, Length, Time, Current, Temperature, Amount of substance and Brightness. But clearly there can't be infinite lengths or times because the universe isn't old enough. Infinite amounts of the other things imply infinite mass/energy and therefore infinite gravity - and we couldn't stand that.

So - what's left? We pretty much have to resort to measurements that boil down to ratios of things where one of the things is literally zero.

We can say (for example) that the singularity at the heart of a black hole is infinitely dense. But that comes about from a boringly finite mass and a literally zero size - so the infinity really comes about because density is mass divided by size.

So anytime you can find something that has a property that is zero you can probably find a ratio that'll pop up an infinity. The ratio of mass of a photon to it's rest mass is infinite for example.

Dunno - it's a bit of a stretch. SteveBaker (talk) 02:18, 26 August 2008 (UTC)

Although a physical measurable property cannot literally be infinite, mathematical models of reality may in some circumstances give an infinite answer, and it may sometimes be possible to assign a physical meaning to these "infinities". There is a story of a mathematician, a physicist and an engineer who were each asked by a firm of architects to calculate the strength of an especially complex structure. All three got the answer "infinity". The mathematician recommended that one of his graduate students should research better mathematical models for solving the relevant non-linear differential equations. The physicist recommended that the architects should design a simpler structure. The engineer wrote a report which concluded "There appears to be an adequate factor of safety for almost all feasible scenarios". Gandalf61 (talk) 09:10, 26 August 2008 (UTC)

Renormalization is one example of that - if you "do the math" relating to things like quantum electrodynamics, then all sorts of ikky infinities keep popping up - but the mathematical "trick" of renormalization fixes that problem and gives you nice, finite results. That's not really an example of a physical infinity though - the infinity appears in the math - but NOT in reality. SteveBaker (talk) 21:39, 26 August 2008 (UTC)