Wikipedia:Reference desk/Archives/Science/2007 October 22

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October 22

Immune system chemical synthesis

My knowledge of biology was a rather unfortunate victim of the schooling system, so I'm hoping some more knowledgeable types will be able to point me in the right direction here. I have vague recollection of reading somewhere that the human immune system is capable of synthesising a very wide range of chemical compounds (i think it actually said all, or almost all). Could anybody comment on the varacity of this and maybe give a bit more detail? Had trouble finding anything informative that wasn't in initiate-speak.

For great justice and so forth, 217.43.117.117 01:03, 22 October 2007 (UTC)

Yup, that's pretty accurate. T cells can generate a huge variety of T cell receptors and B cells can generate a wide variety of antibodies. The mechanism for this is called V(D)J recombination. --David Iberri (talk) 01:44, 22 October 2007 (UTC)

See Adaptive immune system. The immune system cannot manufacture all kinds of substance. Instead it makes protein variants that can be combined together in many combinations. These proteins can recognise surface shapes on the invader cells, and trigger an immune reaction. Graeme Bartlett 01:46, 22 October 2007 (UTC)

Humans produce many variants of antibodies and T cell receptors so that they can recognize essentially all possible antigenic structures of chemical compounds...even synthetic ones that may never arise outside of the laboratory. People such as Stuart Kauffman have described how there has been evolutionary selection of gene recombination and somatic cell mutation mechanisms active in cells of the immune system providing the ability to produce "universal coverage" and recognition of all possible chemical structures. There is strong evolutionary selection against long-lived animals that do not have a universal defensive toolkit for recognizing potential pathogens. --JWSchmidt 02:05, 22 October 2007 (UTC)

Ah, universal coverage was probably the capability I read about, which my memory somehow transmuted to synthesis. Maximal "Win" respondence, chumnly-good-thanks 217.43.117.117 00:56, 24 October 2007 (UTC)

Compound light microscope

What part of the compound light microscope is responsible for resolution? Thanks, anon. —Preceding unsigned comment added by 70.23.73.94 (talk) 02:25, 22 October 2007 (UTC)

Not much of an answer but my guess would be the objective lenses. After all, they are the things you look through to observe something... Obviously lens of higher quality (such as certainGerman lenses) have better quality and last longer. Hope this helps. Valens Impérial Császár 93 03:09, 22 October 2007 (UTC)

Resolution is a product of the size of the viewing aparture and the magnification - increasing either of them lets you resolve smaller details. The limiting factors tend to be related to the quality of the lenses - but also the amount of light you can get without cooking the sample (as either aparture or magnification goes up - so does the amount of light you need). At some point, the wavelength of light becomes a limitation - and refraction and interference effects start to be very noticable. Hence electron microscopes for the very highest magnifications. SteveBaker 14:03, 22 October 2007 (UTC)

Time Machine

Theoretically, what parts would be required to create a time machine. Far fetched, I know but just wondering

Valens Impérial Császár 93 02:58, 22 October 2007 (UTC)

Depends what method you plan on travelling in time with. The simplest way to travel in time is ... do nothing, whereupon you will travel through time at a rate of 1 second per second. If you want to travel into the future a bit faster, find yourself a really fast rocket and let special relativity do the rest (see twin paradox). Alternatively, dig yourself a gravitational well and watch the rest of the universe fly past (getting out of the well may prove a little trickier). If you actually plan on travelling into the past, then we're getting into the really theoretical stuff, but theoretically if you can develop a form of exotic matter that doesn't behave like all the matter we know now, you can force open a wormhole and, with a little trickery, have a time machine that will take you back - but only as far back as the wormhole itself has existed. If you're desparate on going back even further, or at least to 1984, better start working on a flux capacitor. Confusing Manifestation 03:20, 22 October 2007 (UTC)

Why don't we have an article on second per second? DirkvdM 08:08, 22 October 2007 (UTC)

We have an article on time travel.--Shantavira|^{feed me} 08:10, 22 October 2007 (UTC)

...and then, of course, there is also memory and imagination. Multimillionaire 10:15, 22 October 2007 (UTC)

In the mean time you can have a look at Stephen Baxter's The Time Ships and Michael Moorcock's The Dancers at the End of Time both exquisite time travel SciFi novels. Keria 13:41, 22 October 2007 (UTC)

Or if you just wanted to have a peak you could teleport a super telescope a few thousand lightyears away and have a look at the earth. No sound and the signal back would have to be teleported too. Keria 13:46, 22 October 2007 (UTC)

That just moves the problem one step further down the chain. Instantaneous teleportation is the same thing as time travel to the past - and it's disallowed for the exact same reasons - the information in your teleportation 'beam' can't travel faster than light. If you send the mirror out there by 'normal' means - then when you look back at the earth through it, you'll be looking into the past alright - but you won't ever be able to see back to a time before the mirror was launched. Using a TV camera and a VCR to "record the past" is a much easier way to do that! But forward-direction time travel is not difficult - between having a nice long sleep and waking up 12 hours into the future and zooming around the universe at relativistic speeds - we've got that covered. SteveBaker 13:58, 22 October 2007 (UTC)

Ah, that brings me back a few years. In my early teens I came with this brilliant idea to travel in excess of the speed of light and then look back with a very strong telescope to examine the dinosaurs. Worrying about how to complete this very difficult task gave me sleepless nights. Seriously. :) The problem of how to get the info back didn't even occur to me then. DirkvdM 17:47, 22 October 2007 (UTC)

Yep - but travelling faster than light is as impossible as reverse-direction time travel - and that's because they are (in some respects) the exact same thing. If you can only fly away from the earth at 99.999% of the speed of light - then the light from the moment of your launch will overtake you and can never be caught up with (even without relativity messing you up). So you can never see back in time before the moment of the launch. Staying home and launching a mirror has much the same result. SteveBaker 19:51, 22 October 2007 (UTC)

Or, to spin it another way, reverse-direction time travel is as possible as faster-than-light travel. If you can send something (a physical object, or simply information) faster than light, through Some As Yet Unknown Process, and if the Unknown Process works in a frame-independent way, then you can also send the thing backwards in time. Do we have an article on the tachyonic antitelephone yet? If not, someone should write it, as the question comes up on a somewhat regular basis. --Trovatore 20:37, 22 October 2007 (UTC)

Actually, concerning looking back into the past, we do that already when we look at the stars. The light from the nearest star (excluding the Sun) took several years to reach us. For most stars it's millions or even billions of years. Add to that that space is curved, which means it can (and will?) eventually return to the place it originated from. So if we'd know where to look, we might see an image of our solar system. Of course, if we only find one such place we'd only see one set period in time, going at a normal speed, so we can't fast forward or rewind. And we'd need an exceedingly powerful telescope, and even then the image may be heavily blurred because of what has happened to it in the meantime. It's like looking through a turbulent atmosphere, except much worse. And we wouldn't be traveling in time, just looking back. DirkvdM 06:48, 23 October 2007 (UTC)

Compound light microscope

What part of the compound light microscope is responsible for resolution, the smallest distance at which two points can be distinguished as separate? Thanks, anon. —Preceding unsigned comment added by 70.23.73.94 (talk) 03:47, 22 October 2007 (UTC)

Its down to the objective lens of the Optical_microscope. The wavelength of light and the angle it subtends at the lens combined witht he diameter of the lends determine the resolution. Also the refractive index of the media below the lens affects it, so an oil immesrsion lens can improve resolution. Graeme Bartlett 04:27, 22 October 2007 (UTC)

Nano GOld Reactivity

Any idea why is bulk gold inert but Nano Gold reactive and acts as a catalyst???210.212.194.209 —Preceding comment was added at 05:33, 22 October 2007 (UTC)

Do you mean as in [1]? Without knowing the details of the reaction, I would suggest that (a) while gold is highly inert, that doesn't mean that it's completely unreactive, and compounds such as Gold (II) chloride and Gold (III) chloride do exist, and (b) a substance doesn't have to take part in a reaction to be a catalyst, it can also provide a surface for the reaction to take place. Confusing Manifestation 06:45, 22 October 2007 (UTC)

In general finely divided metals are more reactive because they

have a greater surface area

have a higher surface energy

It's the higher surface energy part that is important here - in general atoms in the centre of the metal are more stableised (have lower energy) than those at the edges - this is because those at the edges are in contact (bonding with) less atoms - there are less atoms around them

So in a nanopowder - because the particle size is very small (<1000 atoms perhaps) there is a greater percentage or higher energy gold atoms..

In the extreme case each gold atom would be totally separated - if this could be done thr gold would be very reactive...87.102.0.6 14:15, 22 October 2007 (UTC)

YECism and alleles

So I was conversing with a creationist relative of mine and she mentioned Ken Ham. I think people familiar with Young Earth creationism can dispute it in many ways but I thought I might approach it in a fairly simple manner. One of the implications of Ham's claims is that the alleles present today for each gene is the same number or less than at the creation of the Adam and Eve. What I'm thinking is that if there is a gene in humans that has 5 or more alleles (because Adam and Eve would only be have 4 or less between them) then that would provide for an easy and straightforward refutation of this explanation that I can then use the next time I go to a family wedding. I'm hoping for something verifiable. Can anyone help me out? Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 07:16, 22 October 2007 (UTC)

You'll find more than 5 alleles for most sites studied (for example, one study of phenylketonuria showed 27 mutated PAH alleles representing 19 different haplotypes [2]). Don't expect that to convince young Earth creationists of anything. (Nor should it, really: they by and large don't reject the idea of random mutation, or even natural selection, they just reject the idea that they result in speciation.) - Nunh-huh 07:26, 22 October 2007 (UTC)

Frankly, if you can find a gene out there with less than 4 alleles that's pretty interesting...It must be very new or under high selective pressure. Almost every gene has many variants. CFTR (gene) has more than a 1000. — Scientizzle 15:49, 22 October 2007 (UTC)

On another hand there can't be more than 5 possibilities for a single base locus: A,C,G,T or omission. —Tamfang 19:19, 22 October 2007 (UTC)

Almost true. You can have insertions, too. And they can be of widely variable size, from 1 base to long sequences (see VNTR). But, even if we just go with 5 possibilities, add a second point mutation anywhere in the gene and now there's 25 possible variants. Three? 125. Onward and exponentially upward! — Scientizzle 19:37, 22 October 2007 (UTC)

I'm counting an insertion as something-vs-nothing at a new locus; otherwise the possibilities are infinite. —Tamfang 19:31, 23 October 2007 (UTC)

Yeah - you just can't argue with those guys. The problem is that if nothing changes - and if we're all descended from two people - how come there are so many different skin/eye/hair colours (to take a really obvious example) in modern humans. Modern evolutionary theory says that we are all descended from a single common ancestor - and in that regard, the Bible isn't so far off. So, for the sake of argument, let's call those early humans "Adam" and "Eve" - we don't know their real names - or if they even had names, so these are as good as any.

But the problem comes about if you claim that we haven't evolved since then. If that were so then all genes in all humans would have had to come from those two individuals and been inherited without change. There would be just three different X chromosomes (two from Eve and one from Adam) and just one Y chromosome (from Adam) in the entire population! This would mean that all men would be of three possible genetic types - and there would be just three different kinds of women! Was it Adam or was it Eve who carried the Sickle-cell disease gene? What about the genes for color blindness, dark skin colour, blue eye colour, blonde hair colour? But looking out at the population, we have (i) men who are colour blind, (ii) men who have sickle-cell disease, (iii) men who have both colour-blindness and sickle-cell disease, and (iv) men who have neither. Just on the basis of those two genetic diseases, we know that there must be at least four kinds of male genetic possibilities (way more than that in practice of course!) But right there, you've defeated the idea that all men have the same Y chromosome as Adam and either Adam's or one or the other of Eve's X chromosomes.

So it's very clear that genes MUST have mutated since the first common ancestor of all humans - which means that any complicated argument over alleles is kinda pointless. Once you accept that genes can mutate and are inherited - then evolution and speciation are unavoidable consequences.

However, God (or perhaps the tooth fairy or the FSM) may have just have yelled "Abracadabra" and made it all happen with a wave of a magic wand...so who knows?

SteveBaker 13:49, 22 October 2007 (UTC)

• If you're arguing from reason while she's arguing from faith, you can not possibly win. No matter what ground you gain, she can always retreat to the gaps. My solution to this problem in my own extended family is to limit my biological assertions to things like, "My, what a beautiful turkey!". --Sean 15:43, 22 October 2007 (UTC)

It doesn't matter what you argue with a Creationist, most will just say "goddidit" as an explanation (or rather, a non-explanation, since there is no explanation for how/where/when/why some god supposedly did it nor any objective evidence supporting such an assertion.) If, for example, you point out that there must be more alleles, then they can just say that God added more later. The evidence however, strongly supports the scientific theory that life began with simple single-cell organisms, and the process of evolution is the best explanation for how we ended up with the variety we have today. Evolution is a well tested scientific theory, while creationism is an untestable religious claim. The real question for a YEC is if things were created as they believe, why then is there so much objective evidence to the contrary supporting an older Earth/Universe and the evolution of life? -- HiEv 18:12, 22 October 2007 (UTC)

Thank you for your answers. My aim in regards to my YEC relative is not to shake her faith but to get her to stop asserting that she's spouting science. As a follow up question, Scientizzle said that a gene with less than 4 alleles must be very new. Is my understanding of the genes for blood type missing something? I thought there were just three alleles: A B and O. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 18:57, 22 October 2007 (UTC)

I should have said "likely" rather than "must" to make the statement more accurate, but a small number of alleles is suggestive of very recent evolutionary history (not much time to develop mutations that could spread into the population) and/or strong selective pressure (mutations in said genes tend to be strongly deleterious). As for ABO blood type, it's really not only 3 alleles but 3 groups of alleles (A, B & O) that are very widely distributed in the general population. There are subtypes within each of the 3 groups (examples: PMID 16215642, PMID 16081582, PMID 11896341, PMID 15787730, PMID 14617382). From this paper, the number and type of variants is suggestive of "positive selection for allelic diversity." Interesting stuff, eh? — Scientizzle 19:24, 22 October 2007 (UTC)

The very reason I answered in terms of genetic traits like eye colour, sickle-cell, colour-blindness and such is that these are things you can actually see for yourself every day. You don't need heavy-duty science and counting hard-to-prove things like alleles - you don't need to worry about any of those things. If the Adam-and-Eve story is true - and if genes never mutate/change - then there can only possibly be three kinds of men and three kinds of women in the world - and we all very well know that's not true. I think I remember a StarTrek episode where everyone on the planet was a clone of a handful of survivors of some terrible accident...that's how the world would be with only three X chromosomes and one Y that went forever unchanged. This is MUCH easier to argue - and if your relative can't find a good argument to cover this much easier-to-observe phenomenon - then she's doomed when it comes to deeper stuff. SteveBaker 19:47, 22 October 2007 (UTC)

The three kinds of men is fine, but the three kinds of women, I think, is slightly off. If (between them) Adam & Eve have 3 X chromosomes (let us call them A, B, and C), then one can have 6 kinds of women (leaving out recombination, because that's the kind of ignorant yahoos we are): AA, AB, AC, BB, BC, CC - Nunh-huh 16:47, 23 October 2007 (UTC)

I don't get YEC's. How can the Earth be younger than the time it took to domesticate dogs, cats, and wheat? Like what others have mentioned, it's often fruitless to argue against extreme creationists. At the heart of it, they deny evolution because of the moral implications of it (in their mind). I'd like to pose creationists a question: Prove that the universe wasn't created five minutes ago (all the memories in our heads make it seem like we've been here longer)--the absurdity in the question is the same absurdity in the creationist's mindset about the age of the Earth and evolution despite overwhelming evidence. 128.163.224.222 20:21, 28 October 2007 (UTC)

Electronics

what will happen if you give a dc supply to a a.c machine? —Preceding unsigned comment added by 210.212.241.236 (talk) 08:22, 22 October 2007 (UTC)

Depends on what type of AC equipment it is. If it has a transformer inside or if it's an induction motor, it will simply short out and likely to destroy the coils in it, but if it's something like a newer cell-phone charger which uses PWM to regulate voltage and doesn't contain transformers, I suspect that it would happily run on DC as well. --antilived^{T | C | G} 09:44, 22 October 2007 (UTC)

Your suspicion is absolutely correct; many modern devices that use switching power supplies with high-frequency transformers will run just as happily on a DC input as an AC input; occasionally, it's even specified as permissible.

Atlant 00:09, 23 October 2007 (UTC)

I'd expect an acrid smell, smoke, and fire in that order with increasing capacity of the DC supply and robustness of the AC device, ordinarily. A loud SNAP often accompanies these symptoms. Either the supply or the device or both would be toast, probably. I always shield my eyes when I try things like that. Safety tip. --Milkbreath 11:30, 22 October 2007 (UTC)

It's always good to shield oneself when doing a smoke test. The SNAP would probably be from the noise-emitting diodes referenced in the linked article. --LarryMac | Talk 18:07, 22 October 2007 (UTC)

morbidity/mortality tables - not

I've searched these but they are not what I want. I'm looking for the number of persons still living at various ages rather than those who have died. Not only still living but their weights, how many cigarettes they smoke, etc. For instance I want to be able to ask: how many people are still alive at age 70 that have a BMI of 35, 30, 25, etc. How may at age 65 smoke a pack a day, two packs a day, etc. I feel this will give me a better idea of how to judge how long I might live by matching my habits with those who are still living rather than those who have died. Multimillionaire 09:48, 22 October 2007 (UTC)

Perhaps try one of the death test's? Lanfear's Bane | t 12:18, 22 October 2007 (UTC)

Touch-sensitive fern

I used to own a fern with leaves that folded up and shrank when something (usually my finger) came into contact with them. What species is it? -- _{Escape Artist Swyer} ^{Talk to me} _{Articles touched by my noodly appendage} 11:06, 22 October 2007 (UTC)

Mimosa pudica. - Akamad 11:34, 22 October 2007 (UTC)

This weed isn't a fern BTW. Also you might be thinking of Mimosa diplotricha. This has a fairly similar behaviour to pudica but is more tree like. BTW, for those who haven't seen it before before the M. pudica article has some videos. Having grown up around these things, they are blase but during a biology class at university, it was interesting to see how amazing it was to people who'd never seen one before. Nil Einne 19:09, 23 October 2007 (UTC)

Using the stomach to clean the blood

Say someone swallows a dangerous substance like a bunch of paracetamol (entirely hypothetically - I've not just poisoned myself and now contemplate the hideous process I'm about to suggest). Gastric lavage (removing the toxic substance from the stomach) is a common first step in treatment, but of course that only gets the poison that's in the stomach - that which has passed into the bloodstream is still there. Now that poison got into the bloodstream by passing through the stomach wall; unless that wall has strong "one-way-street" properties, couldn't one use the stomach to remove the poison? What I'm suggesting is

1. do a full gastric lavage
2. fill the stomach with several litres of water (of a salinity TBD); let's call this "the irrigant" for now
3. the poison will then (hopefully) move across the stomach wall (from the blood into the irrigant) until the blood and the irrigant had the toxin at the same concentration
4. change the irrigant for a fresh supply, and repeat until the concentration of the poison in the recovered irrigant (and hopefully in the blood too) is below the danger level

In practise you'd probably change the irrigant continually, with an inflow and outflow pipe, like the way swimming pool water is processed. And maybe you'd manipulate the salinity of the irrigant to encourange outflow (perhaps making up the shortfall on the blood side with an IV drip).

So, does the stomach lining allow this reverse motion to occur, and has anyone done a procedure like this?

And more extreme yet, couldn't the same thing be done in the lung using liquid breathing (with the breathing fluid as a continually changed irrigant); I guess the advantage being you get a lot more surface area and a different membrane to work with. -- Blobject 13:59, 22 October 2007 (UTC)

I can't quite figure out why people think the reference desk is the place to propose innovative new medical treatments. No, no one uses gastric lavage or liquid breathing to eliminate systemic poisons. One reason would be that hemodialysis or even peritoneal dialysis (a similar process to the one you propose, but effective and less uncomfortable) are available for that purpose. And of course, paracetamol has a specific remedy that is needed to prevent liver damage that would not be addressed by any of these. - Nunh-huh 15:33, 22 October 2007 (UTC)

Who else would you take these ideas to? I certainly wouldn't want to mention this to my doctor in case he agreed that it would be beneficial in my case! (The trouble with this idea is that if the stomach 'worked both ways' as suggested by our OP, then every time you took a drink of plain water on an empty stomach, it would pull all of the nutrients out of your blood! I have no idea why that doesn't happen - but the fact that it obviously doesn't means that this idea won't work.) SteveBaker 19:37, 22 October 2007 (UTC)

The reason it wouldn't work is because the stomach mashes things up: it starts digestion, but doesn't do the absorbtion. Absorption occurs primarily in the small and large intestines. Oh, sure, some stuff gets absorbed in the stomach (some small lipid soluble molecules like aspirin and alcohol - in the process causing a bit of irritation) but it's not a particularly heavily vascularized surface. Since the stomach pH is less than 3, it would hardly do to have a lot of opportunity for exchange between its lumen and the blood, where we do our best to maintain a pH of 7.40. - Nunh-huh 20:31, 22 October 2007 (UTC)

OK - but that only moves the question down an organ or two. Why doesn't this happen in the small intestine for example? SteveBaker 21:04, 22 October 2007 (UTC)

My guess would be that it does happen, but that then the nutrient-filled water gets re-absorbed. There's a natural line of speculation that follows this point, but I'm not going to go there. --Trovatore 21:24, 22 October 2007 (UTC)

You are both assuming that molecules in the intestine are only absorbed passively (down a concentration gradient). This is not at all the case. Active transport by carrier proteins on the apical surface of the intestinal lumen ensures the unidirectional flow of materials into the body. That is not to say that there isn't some degree of bidirectionality possible or present, but that absorption in the intestine is not the same as diffusion in the lungs (where gas exchange is entirely passive). Andrewjuren(talk) 21:44, 22 October 2007 (UTC)

You may be interested in our article on dialysis, especially peritoneal dialysis -- 15:45, 23 October 2007 (UTC) —Preceding unsigned comment added by 128.104.112.63 (talk)

Even under the assumption of passive transport only (yes, some compounds can diffuse through the stomach wall), you would also have to consider the partition coefficient. The chemical environments of the stomach and the bloodstream are quite different. A molecule moving from the stomach into the blood can change (eg. pH change can alter protonation state, which may then lead to further chemical changes) and become "trapped" in the blood because its new state can no longer cross the stomach-blood barrier. A partition coefficient that strongly favours retention in the blood would suggest that your proposal is theoretically possible, but highly unfeasible. Blood is also distributed throughout the body, whereas the stomach contents are localized. 142.103.207.10 00:55, 24 October 2007 (UTC)

Also the effect of Hyperhydration has not been addressed, in your effort of diluting out the poison, what is stopping the rest of your blood electrolytes being diluted to fatal levels? Vespine

Moon observations

On Friday night (20/10/07), I noticed something interesting about the moon and wondered if the science community could explain a thing or two to me.

I was walking in London and it was a cloudless night. At approx 7pm I noticed that the moon was almost exactly half/half shining and occluded (is that the right word?), with the line between the two almost immaculately vertical, creating an illusion of a clockface showing 6 o'clock, if you see what I mean.

A couple of hours later, I happened to be walking once more and noticed that the proportion had (of course) remained almost exactly 50-50 light and dark, but the angle had shifted so that using my clock analogy it was more like 5 past 7.

Questions (some of these are a little embarrasing):

• Was my observation accurate?
• Is this a common (even nightly) phemonenon?
• If I'd seen the moon again later on would the angle have become even greater, and if yes, how far will the face appear to rotate?

Cheers. Arrrrooooooo! --Dweller 15:43, 22 October 2007 (UTC)

Yes, yes, and yes. See lunar phase. The moon looks like that at its last quarter (just gone) and first quarter, each of which occur monthly. Its angle with the sun doesn't change much over the course of a couple of hours, so it's still half illuminated by the sun, but the Earth rotates quite a lot in that time and thus the apparent angle with the Earth. The final "angle" at the time it sets depends on the season and your latitude.--Shantavira|^{feed me} 16:39, 22 October 2007 (UTC)

No, No, and No! Dweller - I dispute your observations - and I'm quite sure Shantavira either misunderstood the question or is WAAAAY off the mark (lunar phase says nothing of relevence to this question).

When the moon is exactly half-illuminated, the angle of that 'terminator' line to your local horizon depends on where you are on the surface of the earth. (Using your clock-face analogy...) You'd have to be standing on the North or South pole to get that perfect 6:00 look. If you are on the equator - the moon will appear to be at 3:15 - and somewhere in-between, 7:05 or 8:10. I suspect that if you live in the UK or Canada (oh - yeah - you said "London") - you were seeing it at 7:05 the whole time (it varies a bit through the year because the earth's axis isn't vertical). London is at 51 degrees North latitude - so you're rotated about 39 degrees from the 'vertical' North pole - but since this is winter, the earth's axis is tilted backwards in the northern hemisphere - so you can knock off about another 7.5 degrees for the axial tilt. So I calculate that your head was tilted by about 31.5 degrees to the "vertical" - which would give you the moon looking to be at almost exactly 7:05 per your second observation. (Wow! That worked *perfectly*!! Isn't science wonderful?) - I can't explain your first observation - except to say that I think you were incorrect. But if the moon is high in the sky, it can be hard to judge...perhaps that's it.

I explained some time ago how (when I lived in UK where I was born and lived 40 years), the new moon mostly looked like a slightly tilted letter 'C' - when I moved south to Texas, I was physically shaken to see that the new moon looks more like a 'U' - and that rotation is the same effect we're talking about here. I mean, intellectually, I know it makes perfect sense - but deep down, the Texas moon just seems "wrong" at a very visceral level! I had always wondered why some ancient religions talked of the moon being a 'boat' in which the god travelled across the skies. That made no sense when it was 'C'-shaped - but from closer to the equator, you could easily see how the 'U' shape would approximate the hull of a boat. Of course nothing changes on the moon - it's just that when you are standing on the equator, your head is turned sideways 90 degrees compared to when you are standing on the north pole. SteveBaker 19:23, 22 October 2007 (UTC)

Sorry, Steve, you're quite mistaken. If you play around with Stellarium you can choose the date and location specified by the original poster and see that his observations are exactly right. As the moon is transported across an arc of the sky, its orientation relative to the nearest point of the horizon does indeed change. Geography does go into it, but by no means is the orientation completely fixed for a given geographic location. You can get a "perfect 6:00 look" very far from the poles, with the cutoff latitude depending on how close you require the moon to be to the horizon. --Reuben 21:09, 23 October 2007 (UTC)

Edible mold and fungus (mushrooms)

How did we first discover what's good and what isn't? Did people just literally eat some moldy food, to discover if it made them sick or not? Some mushrooms are poisonous some are edible, but there's no way to know unless you eat it first. Do people just eat everything in sight, then report on whether it is edible or not? 64.236.121.129 16:00, 22 October 2007 (UTC) Did people literally just eat moldy food at random, then remark, wow this tastes great? 64.236.121.129 16:04, 22 October 2007 (UTC)

While there is a degree of trial and error, observation also plays a key role. People can observe what other animals eat (and don't eat) and thereby gain a degree of confidence as to its safety and nutritional merit. Additionally, there's no need to repeat the question -- you can click the "edit" link to the right of the section header to amend, clarify, or otherwise respond. — Lomn 16:56, 22 October 2007 (UTC)

I wasn't repeating my question. Wikipedia was giving me an error message when I was posting it, so I just kept trying to repost the question, but it looks like it did post it after all. 64.236.121.129 18:29, 22 October 2007 (UTC)

An explanation I once heard of how people discovered alcohol it that someone buried some grains somewhere 'for a rainy day'. Then when that day came he discovered the grain had gone off. Being hungry he decided that he would eat it anyway and discovered that it had a rather pleasant side-effect. The moral of the story being that people will eat anything when they're hungry, even if their first impulses tell them not to. Another thing is a survival technique to test food that our ancestors may have figured out too (apart from watching what other animals eat, which is also a standard technique). If you're not sure if something is edible, first rub it between your fingers, then under your armpit, then on your lips, then put some in your mouth, chew and spit. If any of these tests results in a unpleasant feeling, don't eat it. Then swallow a little bit and wait for a few hours (maybe longer). If you don't get sick, you can eat more and wait. If you still don't get sick, it's safe to eat. DirkvdM 18:02, 22 October 2007 (UTC)

There seems to be some kind of assumption that we all woke up one day and had to figure this out. It's not like that at all - we evolved to fit our environment - to be able to eat the things that we need to eat and to seek out the things we've evolved to manage. We evolved from apes (we are apes). Apes that don't have language somehow know not to eat rotten food or unripe fruit...so do we. Human diets didn't suddenly arise - we've been gradually adapting to what's around us for millions of years. The exceptions are fruits and vegetables that came into our environment very suddenly and very artificially from a long way away. When (for example) the Tomato was first introduced into Britain, it was widely believed that they were poisonous unless cooked very completely. There is a story of a guy who grew tomatoes around that time - who knew they were not poisonous even when eaten raw - and in order to publicise this fact, he put up a poster in the town square saying "At such and such time Mr so-and-so will PUBLICALLY EAT A RAW TOMATO on the church steps." - which resulted in a large crowd of people gathering to watch this foolhardy exploit...which (of course) ended without incident. SteveBaker 18:58, 22 October 2007 (UTC)

Yea I heard about that Tomato story. Interesting to say the least, but we did have to figure these things out. Who would honestly eat a moldy piece of cheese? Yes we evolved, yes we are apes, but there's no voice in the back of my head that says eating this moldy thing is not going to make me sick. Some mushrooms are good to eat, others are poisonous, how can we know what's good and what isn't without some expert saying so? There are some mechanisms that help us determine what's good to eat, smell for example, but that doesn't work on everything. Certainly not mold, which is what I'm asking about. 64.236.121.129 19:46, 22 October 2007 (UTC)

Certainly not on death caps either. They apparently taste good. --Kurt Shaped Box 22:13, 22 October 2007 (UTC)

I think a lot of it’s a matter of avoiding starvation. Given a choice between eating a food that one is familiar with and eating something that may or may not work as a food, the obviously preferable choice is to eat the familiar food. But even today, a lot of people are often faced with a choice of eating something that may or may not work as a food, and eating nothing at all. Given that eating nothing at all will lead to certain death, the safer choice is to eat whatever you can, even if you have no clue as to whether it might make you sick or kill you. If you live and it tastes good, then great, you’ve just discovered a new food. If it kills you, then there was no harm in trying it, because you were going to die anyway. MrRedact 06:06, 23 October 2007 (UTC)

Steve, most of the time humans will have had plenty of time (generations) to figure out their surroundings, but especially for humans that would not have been true all the time. Take the original Americans who crossed the Bering Strait and traveled to the southern end, roughly 10,000 km, in roughly 10,000 years. That's on average tens of km per generation. But it will more likely have happened in leaps and bounds. And habitats sometimes change rather abruptly. This is an extreme example, but learning to live in a very different environment is something that humans will have had to do at least every now and then, considering they spread all over the Earth. And it's no coincidence that that is something humans are particularly good at - that's probably the most important reason humans spread all over the world.

Btw, the point is some humans do eat rotten food, such as french cheese and thousand year eggs, which only illustrates our huge adaptability. DirkvdM 07:15, 23 October 2007 (UTC)

That's the thing, of course we eat rotten food. The question is, how can anyone possibly know it's still edible despite being rotten? It's one thing to just eat something because you are starving, it's another thing to specifically prepare rotten food, which without preparation would be inedible. Those eggs are a good example, because someone has to prepare something like that in order for it to be edible. How could they know how to prepare such a thing? If you eat any other rotten egg, you get sick, but when it's prepared in that specific way, it's ok. How do they figure these bizzare things out? It would be equivilant to just sticking an egg in a bunch of random ingredients for a couple of months, then eating it to see if it tastes good or not... 64.236.121.129 13:34, 23 October 2007 (UTC)

Whoa. Those are some funky-looking eggs. What exactly is the chemistry behind that? --Kurt Shaped Box 07:59, 23 October 2007 (UTC)

On rotten cheese, a friend regularly takes a small cheese and places it under a large glass cover. He then waits for months as the cheese grows white filaments until it has filled the space available. That's when it's good to eat. Quite a delicatessen apparently. . What about when we start to eat and drink food that might not be rotten really hasn't much good in it? To think that Coke is one of the best selling drinks amazes me. I might prefer the mutant cheese option. Keria 08:06, 23 October 2007 (UTC)

Well, the mouldy cheese could be just an example of someone eating it, liking the taste and then deciding to experiment with it, tweaking the taste. Same with beer - most beers taste horrible, but get you drunk. So it makes sense to then start experimenting with the taste until it is also pleasing to drink. The eggs could just originally be a poverty thing. people looked for a way to keep them long, ate them despite the foul taste, and then became used to it. It's certainly an acquired taste. I once saw a documentary in which people who ate such eggs were presented with French cheese and wondered how on Earth anyone could eat something so revolting. Stranger is sago (at least some variety of it, I learn now), which is poisonous and has to be ground and washed to leech out the poison. How do people find that out? I can't imagine someone accidentally doing this, because it's a long and labour-intensive process, without which the sago would remain lethal. DirkvdM 18:50, 23 October 2007 (UTC)

Dirk, by "French cheese" do you mean some particular cheese (the way we use "Swiss cheese" to mean Emmenthaler, or "American cheese" to mean "light-orange colored petroleum byproduct"? The French cheese link just redirects to a list of French cheeses, and I don't know of any particular cheese called French cheese. --Trovatore 20:26, 23 October 2007 (UTC)

Oh, sorry, that may be a dutchism. By French cheese I mean mouldy cheese, such as brie. But there are also mouldy English cheeses such as stilton. And of course Danish blue isn't French either. DirkvdM 06:46, 24 October 2007 (UTC)

I much prefer "French cheese" to Italian maggot cheese. StuRat 22:11, 28 October 2007 (UTC)

Out of curiosity, did the title of this thread set up an echo in anyone else's head, Forty-two pounds of edible fungus/in the wilderness a-growin' ? --Trovatore 07:56, 24 October 2007 (UTC)

One thought on the original question. At a young age, many children will eat or drink just about anything. That would seem to be quite a disadvantage, considering the number of harmful things there are to eat and drink, but it may have been advantageous to the species early on. That is, back when people had a dozen children and most were expected to die in infancy, if they contributed to the survival of their family by finding a new food source before dying, then they would still manage to make their genes more likely to be passed down, despite their short longevity. StuRat 22:11, 28 October 2007 (UTC)

Thelper1 vs Thelper2

How is Th1 and Th2 competition advantageous? Can't a humoural and cytotoxic response complement each other? Th1 promotes macrophage function, Th2 promotes antibody production, but opsonisation by antibodies is supposed to render microbes susceptible to phagocytosis? Competition between proinflammatory and anti-inflammatory response, I can understand, but this is different - the two should go hand in hand... —Preceding unsigned comment added by Seans Potato Business (talk • contribs) 17:37, 22 October 2007 (UTC)

In general, the responses of these two cell types do compliment each other. Certain cytokines will direct the majority of a response either down the cellular or immune routes, but you are right to suspect that opsonization (specifically b-cell mediated Ig opsonization) does aid the macrophages in phagocytosis. However, compliment is effective in opsonizing many typical bacterial molecules even without immunoglobulin. It is advantageous to have multiple ways of attacking bacterial (and other) invaders; that way, there is always a back-up method should a defensive mechanism fail. (and indeed, individuals who lack any one of the immune defensive molecules or routes typically have pronounced immunodeficiencies). Tuckerekcut 20:34, 22 October 2007 (UTC)

Induced C`urrent

How would I calculated the current and voltage induced in a wire a certain distance from a vibrating charge? Thanks, *Max* 23:06, 22 October 2007 (UTC)

Faraday's law of induction. SteveBaker 02:03, 23 October 2007 (UTC)

(edits to repair bot damage) Arakunem 02:20, 23 October 2007 (UTC)

The article on Faraday's Law discusses a coil or wire loop moving relative to a magnetic field. The questioner asked about a moving charge. Edison 17:09, 23 October 2007 (UTC)

Is there a single equasion that I could use with minimal calculus? *Max* 00:13, 24 October 2007 (UTC).