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October 6

Nepeta cataria

Hello. Can anyone explain why on Nepeta cataria, there is no phylum or class listed in the taxo box? Brambleclawx 03:12, 6 October 2011 (UTC)

Angiosperms Amborella Nymphaeales Austrobaileyales Mesangiospermae magnoliids Chloranthales monocots Ceratophyllum eudicots

The phylogeny of the flowering plants, as of APG III (2009).

It's not just catnip really. Those (unranked) 'ranks' above the ordinal level in plants are clades, which do not actually have taxonomic ranks. This is because all plant articles in Wikipedia follow the modern APG III system of the Angiosperm Phylogeny Group. This system is more accurate than the old Linnean system because it uses molecular genetic data for grouping plants. Remember that the Linnean system was established before the discovery of evolution and the DNA. So they were traditionally and inaccurately grouped simply by morphological and biochemical characteristics.

For example, flowering plants (angiosperms) were once grouped into two classes - Monocotyledons and Dicotyledons based on the number of cotyledons. Obviously this is a rather unreliable way to classify plants. APG discovered that though monocots are monophyletic (that is, they are all descendants of a common ancestor), dicots are not. Though most dicots are monophyletic (now grouped into the clade Eudicots - 'true dicots'), not all of them descended from a common ancestor. Magnoliids, for example, exhibit two cotyledons and have been traditionally classified under dicots, but they actually diverged earlier than eudicots (see phylogenetic tree on the right). Some genera, like Amborella, are also basal (arising earlier than other clades) and thus can not be classified under any of the traditional orders (as of APG III, the single species of the genus has been classified under their own order, separate from the rest). Others are simply not well understood like members of the family Sabiaceae, etc.-- Obsidi♠n Soul 04:07, 6 October 2011 (UTC)

I don't think it is true that all Wikipedia plant articles use the modern system, although that is probably a goal -- at the moment there is still a lot of variability. Looie496 (talk) 14:53, 6 October 2011 (UTC)

It's preferred (in angiosperms at least), like animal and microbio taxonomy, there's always disagreement on which should be in which among specialists. Add to that good faith editors that use outdated classifications (bananas and plantains for example, were still classified as Musa × sapientum and Musa × paradisiaca a year ago... :/ Using autotaxoboxes helps standardize things at least, though there are necessary exceptions. -- Obsidi♠n Soul 19:23, 6 October 2011 (UTC)

induction motor

can a 3HP three phase induction motor be run at single phase by making the single phase winding inside that 3phase motor?? — Preceding unsigned comment added by 115.242.158.41 (talk) 03:57, 6 October 2011 (UTC)

I have not tried to do that. I have run a 3 phase motor on 2 phase power. That is not very uncommon. When the only power available is 1 phase power, a static 1 phase to 3 phase power converter will produce 3 phase power to get a 3 phase motor started. Then, the static converter will drop to 2 phase power to continue running the motor (yes, this can damage 3 phase motors not designed for 2 phase power). I don't see how a single phase will keep it rotating under any load. Unlike a single phase motor, a three phase motor doesn't have a capacitor to rotate the incoming power and create a second phase (technically, single-phase motors convert the power to 2 phase power internally and are really 2 phase motors). It is possible that some very fancy three phase motors are internally six-phase motors (using the same technology as a single phase motor). Then, I'd be certain that if you got it started, you can keep it spinning on a single phase of power. -- kainaw™ 13:19, 6 October 2011 (UTC)

I've seen three phase motors burn out when only single phase power is furnished to them, but I cannot rule out some motor being capable of being internally rewired to allow single phase operation, perhaps at a reduced HP. I remember hearing one three phase motor driving ventilators slowly wind down over perhaps a 2 minute period when it was single phased while running. It burned out due to the prolonged overload. Engineers have gotten in trouble for failing to provide protection for a motor against such single-phasing, when they specify the protective circuit for a large motor. If the motor is spun up with 3 phase, then "Alternating current fundamentals" by Herman says it will continue to turn if only one phase is powered, with a "greatly reduced capacity." It would overheat and burn out if it were called on to operate the full 3 phase load on 1 phase. A single phase applied to a stopped 3 phase motor would not produce the phase shift or rotating magnetic field needed to start it turning. The question was a bit fuzzy. Did the OP mean "Could a 3 phase motor also be wound with a single phase winding, along with provision for a capacitor?" If so then the answer is likely "Yes." It would not seem efficient or economical to build motors with that capability. Here is an account from 1918 of how someone added an external phase splitter to start a three phase motor, which was then switched to operate direectly from a single phase source when it got up to speed. Edison (talk) 18:41, 6 October 2011 (UTC)

A three phase motor operated from single phase can also be used to produce the missing phases, and thereby power other three phase motors, or produce dangerous and unexpected backfeed on the phases thought to be dead, endangering utility workers. Edison (talk) 15:43, 7 October 2011 (UTC)

homology / analogy of env viral coat proteins, across mammals and Drosophila

I'm designing the beginnings of a selective intercellular transport protocol, and I'd like to take advantage of some of the interesting properties exhibited by HIV env (perhaps make a pseudotype). I note that Drosophila has some endogeneous retroviruses, such as gypsy which too, codes for an "env-like" protein. However, when I actually do a BLAST search between gypsy env and HIV env, the alignment is quite poor, on both a protein level (for gypsy open reading frame 3, which codes for env, and HIV gp120 / gp160 etc.) and a nucleotide level -- often the query coverage is less than 20%. How possible is that HIV env and gypsy env would just keep a few conserved domains and rapidly mutate all the non-critical domains, and that BLAST scores aren't useful for detecting homology between retroviruses of distant species?

Other than the receptors, are there significant differences in the mechanisms of HIV-1 env and gypsy env? Could I use HIV env in Drosophila? This is because the required receptors on the target cell required for gypsy env to induce efficient infections remain poorly-characterised, unlike the receptors/coreceptors required for HIV env. elle _{vécut heureuse} ^{à jamais} (be free) 05:05, 6 October 2011 (UTC)

It may be difficult to identify homology, particularly if the entry process has diverged substantially (i.e. if very little homology exists). For a search like this, I would expect PSI-BLAST (PMID 9254694, available as an algorithm choice on the BLAST page) to be more useful for your purpose than BLAST. PSI-BLAST forms a PSSM from BLAST results, and uses the highest-scoring positions in an iterative BLAST search - it's a remarkably powerful process! -- Scray (talk) 02:05, 7 October 2011 (UTC)

Eating "unpleasant" foods

There are many foods that people eat routinely that are in some sense "unpleasant", such as spicy, sour, and bitter foods. Many of these contain chemical irritants that "burn" your mouth or otherwise might discourage some people from eating them, and yet many of us (myself included) enjoy eating them frequently. Presumably such qualities originally evolved to discourage animals from eating these plants, though now they are paradoxically the reason that we intentionally cultivate many foods for consumption.

Now, what I am really wondering about is whether the irritants in "unpleasant" foods have an impact beyond the mouth and immediate process of eating them. For example, does eating such foods also tend to irritate the stomach or bowel in a way that can make people more prone to digestive problems such as stomach aches, heart burns, diarrhea, etc? I know people who have given such an explanation for not eating spicy food, but I'm not sure if there is good empirical evidence for this or not. Dragons flight (talk) 07:56, 6 October 2011 (UTC)

Strictly hearsay, but I've known people who said they ate stuff that was so strong and spicy they could feel it all the way through their digestive systems. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:42, 6 October 2011 (UTC)

Eating certain spicy foods, irritates the digestive tract. Normally, this is not a problem however, regular consumption of such foods can result in ulceration which may lead to further complications. In fact, it has been proven that daily consumption of curries usually causes the stomach lining to thin considerably. Plasmic Physics (talk) 09:55, 6 October 2011 (UTC)

. For decades it was believed that alcohol and spicy foods caused peptic ulcers, but that was shown to be a myth wasn't it? [1][2][3]. Our article and those external links generally say that spicy food may aggravate an existing ulcer, but they don't cause them. The last link even suggests that spicy food may partially protect against ulcer formation in healthy people. Since the 2005 Nobel prize was awarded for showing that most ulcers are caused by bacteria, I pretty much assumed that we would be discussing other kinds of digestive problems when I asked the question. Also, where are you getting the curry info from? Dragons flight (talk) 18:59, 6 October 2011 (UTC)

It's difficult to track down the original research paper, but the main point is that acute gastritis is caused by the phenolic compounds present in "hot" foods, such as capsaicin, this compound induces the secretion of hydrochloric acid in a similiar way that alcohol does. The increased acidity of the stomach acid erodes the stomach lining, and causes inflamation. Curries have a complex chemical makeup, while they contain many healthy chemicals, they also contain unhealthy ones. It's like a candle, oxygen feeds a flame, but if air flow is too great, it extinguishes the candle. The short of it is, moderation is a virtue. Plasmic Physics (talk) 00:57, 7 October 2011 (UTC)

Within the last ten or so years I read an article about chicken farmers feeding hot pepper to the hens. They (the hens, not the farmers) didn't mind the flavor, it discouraged rodents from eating the feed, and somehow the irritation of the digestive system made the hens healthier. Now when I search for "hen pepper health" all I find are chicken soup recipes. I did find refs for using pepper in bird seed to discourage squirrels, which say that birds do not mind the hot pepper taste:[4] Edison (talk) 15:55, 7 October 2011 (UTC)

Yes, most/all? birds aren't sensitive to capsaicin, it's usually suggested the capsaicin evolved in chillis partially for this reason as it discourages mammals from eating the fruit but not birds who are the better seed dispersal agent (for those plants), see Chili pepper#Evolutionary advantages. Nil Einne (talk) 17:08, 7 October 2011 (UTC)

I saw the headline for this a few hours ago but it just occured to me it has some minor relevence here, there can be acute problems [5] [6] [7]. I noticed Capsaicin#Effects of dietary consumption which is of greater relevence (that article also mentions the acute effecs). Nil Einne (talk) 17:15, 7 October 2011 (UTC)

I don't see what is so unpleansant about sour things. I drink vinegar, and eat lemons as if they were oranges. Plasmic Physics (talk) 23:28, 10 October 2011 (UTC)

Centipedes

Specifically, Scutigera coleoptrata, or the "house centipede". They look like a little mustache running along. Creepy critters. But supposedly they feed on other, creepier critters. One thing is unclear or unstated in the article: Do they pose any threat to humans? That is, do they bite? Or are they harmless? Does anyone here know? Thank you! ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:39, 6 October 2011 (UTC)

Some are toxic. Plasmic Physics (talk) 09:46, 6 October 2011 (UTC)

Technically they sting, not bite since their venom organs are attached to their legs. That sting might be painful to humans. Googlemeister (talk) 13:21, 6 October 2011 (UTC)

They don't seem to be considered dangerous to humans. We have the dangerous scolopendrid centipedes (locally known as ulihipan), among which is Ethmostigmus rubripes which can reach a little over six inches in length (compared to one or two inches in American house centipedes). ;) They have the same reputations out here as scorpions (i.e. if you see one inside the house, kill it). -- Obsidi♠n Soul 19:47, 6 October 2011 (UTC)

Centipede bite amazingly .. For the record I was bitten by the European Centipede - not painful like a wasp sting - but very strong - like being kicked by a mule (I never been kicked by a mule so I'm guessing). 87.102.42.171 (talk) 23:21, 6 October 2011 (UTC)

Being kicked by a mule is like being punched in the gut only more painful, it is a truely breathless experience. Plasmic Physics (talk) 02:04, 7 October 2011 (UTC)

How might one get bitten by Scutigera coleoptrata? I've seen them skittering along the floor. I've deliberately stomped out the lives of a few, wearing shoes of course. I can't imagine trying to pick one up in my hands. They move too fast to catch. Bus stop (talk) 02:12, 7 October 2011 (UTC)

A pair of legs on their first trunk segment have been modified into venom-injecting appendages (forcipules). Think of them as poison syringe-tipped hands. This is the origin of the scientific name for their taxon - Chilopoda means "lip leg". Click to see forcipules on Scutigera-- Obsidi♠n Soul 09:14, 7 October 2011 (UTC)

I found myself sharing a bed with one in Turkey once, so I could easily have been 'bitten', although I wasn't. I also managed to catch it in a water bottle and release it in the hotel grounds. Mikenorton (talk) 09:50, 7 October 2011 (UTC)

I think you should be given credit for being kind to centipedes. Did the centipede even say thank you or give you a reduced price coupon to Foot Locker? Bus stop (talk) 16:10, 7 October 2011 (UTC)

Maybe it gave him a "High 100". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:25, 8 October 2011 (UTC)

lol Bus stop (talk) 16:13, 9 October 2011 (UTC)

Day Length and Seasons

I know that the earth's tilted axis is the primary reason that we have seasons, but how much of an effect does the varying day length have? --CGPGrey (talk) 10:07, 6 October 2011 (UTC)

I suggest the articles Season and Seasonal lag. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:22, 6 October 2011 (UTC)

There is no mention of the % effect that day length has on seasons in those articles. --CGPGrey (talk) 10:27, 6 October 2011 (UTC)

That might be a bit more detail than an encyclopedia would get into. OR, it might just be that no one has researched it and added it. Obviously, the length of the day has a qualitative effect on both atmospheric and oceanic temperatures. An exact percentage might be hard to come by, as it's liable to vary from season to season, due to factors such as el nino, la nina, and any number of other things. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:32, 6 October 2011 (UTC)

Part of the problem is that it would essentially be a 3-dimensional table: One dimension would be the average daily temperature. Another would be the number of hours and minutes of sunlight per day. The third dimension would be the latitude. Obviously, a lot of info, and probably beyond the scope of a wikipedia article. Have you tried googling this subject? ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:38, 6 October 2011 (UTC)

The inclination of the Earth's axis relative to the Earth's orbital plane causes the cyclic variation in the duration of daylight and solar heating, and this variation causes the seasons. Therefore it is reasonable to say that the seasons are due entirely (100%) to inclination of the Earth's axis. Dolphin (t) 10:54, 6 October 2011 (UTC)

But that's not the whole story, otherwise the coldest day of the year would be the Winter Solstice and the hottest day would be the Summer Solstice (or the opposite in the southern hemisphere). But thanks to seasonal lag, the coldest day of the year is liable to be in early February, and the hottest day in early August, by which time the days are longer than the winter solstice and shorter than the summer solstice, respectively. And besides, the OP apparently wants numbers rather than qualitative observations. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:00, 6 October 2011 (UTC)

I agree that the seasonal extreme temperatures don't occur on the solstices, but that doesn't detract from the fact that the Earth's seasonal variations are due 100% to the inclination of the Earth's axis relative to its orbital plane. All other observations, such as seasonal variation in duration of solar radiation and seasonal variation in ocean temperatures, are consequences of the Earth's inclination, not independent causes of seasonal variation. Dolphin (t) 11:12, 6 October 2011 (UTC)

OK. So the simple answer to the OP's question is, indeed, 100 percent. One way to look at it is to look at the extremes. The poles never get warm, but they are not as cold in their respective summertimes when they get 24-hour sunlight, vs. wintertimes when they get none. And at the equator, it's pretty much the same all year around, apart from daily variations due to weather changes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:16, 6 October 2011 (UTC)

I understand that the seasons are caused 100% due to the tilt, but that's not my question. There is increased solar radiation during the summer because the hemisphere is 'facing' the sun, but there is also increased radiation because the duration of exposure is also increased. How much of the increase in solar radiation is attributable to the increase in day length? --CGPGrey (talk) 13:49, 6 October 2011 (UTC)

Here's a plot of solar irradiance during the summer and winter solstices for 40° of latitude [[8]]. The increase in solar radiation is the area between the two curves. You're asking which fraction of the area is due to the summer curve being higher, and which fraction of the area is due to the summer curve being wider. I don't think that's mathematically defined. 98.248.42.252 (talk) 15:59, 6 October 2011 (UTC)

Isn't the increased duration of exposure also caused by the axial tilt? The sun is up longer because the hemisphere is tilted toward the sun. thx1138 (talk) 16:46, 6 October 2011 (UTC)

I disagree with Dolphin's assertion that the Earth's axial inclination is responsible for 100% of the seasonal variations. Because the Earth's orbit is also slightly eccentric, its distance from the Sun varies by about 5,000,000km (about 3.34%) between aphelion (currently around 04 July) and perihelion (03 January), resulting in about 6.9% greater insolation at perihelion. This certainly must have some effect on seasonal temperature variations (ameliorating Northern hemisphere winter temperatures, for example), though as our Earth's orbit article states, the effect is not great compared to that of axial tilt. Nevertheless it is important when considering the Milankovitch cycles. {The poster formerly known as 87.81.230.195} 90.197.66.175 (talk) 13:57, 6 October 2011 (UTC)

The Earth's tilt is 100% of the reason for the existing seasons, but yes, winter in the Northern hemisphere would be a few % colder (probably only 1 or 2%, depending on what you measure percentages of) if the Earth were at its furthest point from the sun instead of its nearest point. The proportion that is attributable to angle of incidence, compared with the effect day length, will depend not just on latitude but on cloud cover, wind speed and direction, and probably several other factors, so it is unlikely that we can find an answer to the question. We need to decide what we are measuring the proportion of (probably temperature, but this has a fixed point only at −459.67 °F). I wonder if anyone has published any research comparing angle of incidence effect with day length effect. They would be difficult to separate because they are closely related. Dbfirs 12:07, 7 October 2011 (UTC)

oxidation no. in halogens

my teacher said that oxidation no. of Halogens like fluorine and iodine in their peracids is +7 not -1 like HClO₄ but i want to know the other peracids which i must calculate the oxidation no. of their halogens by +7 not -1 — Preceding unsigned comment added by Mido22 (talk • contribs) 13:00, 6 October 2011 (UTC)

Fluorine does not have a VII oxidation state, only the lower halogens do. All the lower halogens form "peracids" perchloric acid, perbromic acid, periodic acid. It's not just the peracids, where the VII state exits - iodine heptafluoride, dichlorine heptaoxide, the list is really inexhaustive. Plasmic Physics (talk) 13:41, 6 October 2011 (UTC)

Hypofluorous acid is not fluorine in a +7 oxidation state, but it's still pretty damn cool. It's a good source of oxygen radical. elle _{vécut heureuse} ^{à jamais} (be free) 23:01, 6 October 2011 (UTC)

Which is the strongest oxidant, chlorine trifluoride, or fluoroantimonic acid? It has been said that in case of an accidental spill of chlorine trifluoride, the most appropriate response is to run. It eats through concrete, don't you know? Plasmic Physics (talk) 01:05, 7 October 2011 (UTC)

It would be good to have a strongest oxidant redirect. A very good substance for stripping electrons off other atoms would be the U⁹²⁺ ion. Graeme Bartlett (talk) 00:19, 8 October 2011 (UTC)

It's a trick question: The strongest oxidant is a charged capacitor. I think we can get them up to several million volts now. Buddy431 (talk) 04:45, 8 October 2011 (UTC)

I thought that if you work with chemicals, the approperiate response to any accident is to run, because your life is worth more than all the lab devices. In what respect does chlorine trifluoride differ? – b_jonas 18:30, 8 October 2011 (UTC)

What I mean is that it is an unstoppable force, it consumes everything in its path. There is no way for emergency services to control it. It's like perpetually lit thermite, that only stops buring once it is completely consumed. There are very few materials that can withstand it. Plasmic Physics (talk) 23:27, 8 October 2011 (UTC)

Dark energy and the local cluster

Is the local cluster expanding due to dark energy, contracting due to gravity, or at a steady state (by which I mean, whether it's expanding or contracting is statistically insigificant given the margin of error, or that some parts are expanding and others contracting)?

What can this tell us about dark energy and a possible equation for determining the strength of dark matter in a given area? I'm curious if the evidence points to a cosmological constant (i.e., that the vacuum of space necessarily pushes matter apart as an inherent property) or to a scalar field (e.g., a fifth fundamental force, heretofor undetected).

I'm also curious at what point dark energy seems to overpower gravity; am I correct that the equation for gravity is ${\frac {k}{r^{2}}}$ whereas the equation for dark energy is ${\frac {k}{r^{x}}}$ where $0<$$x<2$ (part wherein "$0<x$" stricken; actually, $x$ could theoretically be zero or negative Magog the Ogre (talk) 19:16, 6 October 2011 (UTC)) (it seems most likely to me that $x=1$, but I can't make that assumption precisely)? Magog the Ogre (talk) 16:49, 6 October 2011 (UTC)

A scalar field would lead to an attractive force scaling as ${\frac {k}{r^{2}}}$ if the particle is massless, so that won't work. Dauto (talk) 17:10, 6 October 2011 (UTC)

Galaxies in the local group tend to be orbit around each other, so overall there isn't any significant expansion or contraction. --Tango (talk) 17:51, 6 October 2011 (UTC)

re: Dauto: according to the article dark energy, scalar fields are in fact considered a possibility, with quintessence and moduli considered subpossibilities.

re: Tango: I'm looking for data that's a bit more specific than that. Magog the Ogre (talk) 19:10, 6 October 2011 (UTC)

What data would you like? --Tango (talk) 21:28, 6 October 2011 (UTC)

The simplest form of dark energy, a cosmological constant, can be approximately represented as $F\propto kr$. In other words, the force grows in direct proportion to the separation distance rather than falling off with distance. The effects of dark energy are just barely perceptible on the scale of several billion light years. If dark energy truly has the form given above, then there is no reason to expect that any measurable impact would occur to structures as small as the local cluster. Dragons flight (talk) 19:21, 6 October 2011 (UTC)

re DF: wait - the force actually expands with distance? That means that a galaxy which is 12 billion ly away is pushing on our planet with greater power than a galaxy at 10 billion ly. If this is correct, wouldn't it eventually mean the disintegration of all matter in the universe? (because, as the universe expands, the distance to massive objects becomes greater, and thus more powerful, such that the forces would become incredibly high... or am I wrong?).

re Tango (not responding inline above; honestly I dislike inline comments because it disrupts the flow): what is the redshift/blueshift of other galaxies within the cluster, how does this relate to their distance from ours, and how is this comparable to other galaxies? I'd think that a measurement of the redshift of these galaxies, versus the redshift of other clusters could give us a pretty good estimation of the scales on which dark energy works. Magog the Ogre (talk) 21:37, 6 October 2011 (UTC)

Yes, a cosmological constant dominated universe will eventually enter a period of exponential inflation, and all structures that are not already gravitationally bound will eventually fly so far apart that they are no longer observable. See also: Big Freeze, Dark energy#Implications for the fate of the universe. Dragons flight (talk) 21:46, 6 October 2011 (UTC)

Re Magog the Ogre: Quintessence doesn't produce a repulsive force between objects. Not the way you're thinking. We are not being pushed away by distant galaxies. Quintessence creates an expansion of space (In other words, it's a dynamical form of cosmological constant). That's why the further apart galaxies are, the faster they seem to accelerate from us. That happens because there is more space in between to expand. That can be modeled as a repulsive force that is proportional to the distance as Dragons flight pointed out but it isn't an actual force between distant objects. In fact, An actual force between distant objects that increases with the distance would have to propagate faster than light. Dauto (talk) 01:20, 7 October 2011 (UTC)

Different galaxies within the local group have different redshifts/blueshifts (some of each). There is no correlation between redshift and distance. Redshifts change over time (and change from redshifts to blueshifts and back again) as galaxies move around their elliptical orbits. --Tango (talk) 18:35, 7 October 2011 (UTC)

No it wouldn't. If we can see the galaxy, we can feel the force from it. Magog the Ogre (talk) 01:46, 7 October 2011 (UTC)

Yes, that's right, and as Dragons flight explained above, and I quote "all structures that are not already gravitationally bound will eventually fly so far apart that they are no longer observable". Neither will we be able to see those far away galaxies nor will we be able to fill any force produced by them. They will effectively be beyond the horizon. Dauto (talk) 04:23, 7 October 2011 (UTC)

Are you sure about that? I think that the only reason we won't be able to see them not because they're beyond the event horizon, but because they will be redshifted into the CMBR, meaning there will be too much noise. Magog the Ogre (talk) 15:23, 8 October 2011 (UTC)

Yes, I'm sure. At some distant point galaxies become in fact causally disconnected from us. They are moving away from us faster than the speed of light! (without any contradiction with special relativity). That's what makes it possible for the diameter of the observable universe to be larger than twice the age of the universe (c=1). We see the light of those distant galaxies because they were still causally connected to us back when they produced the light we see now. But they are now causally disconnected so we will never see the light they are producing right now (not even a redshifted version of it). See observable universe. Dauto (talk) 15:18, 9 October 2011 (UTC)

Read also Hubble volume and Event horizon#Particle horizon of the observable universe. --Dauto (talk) 15:40, 9 October 2011 (UTC)

More information on the Marbled Lungfish's genome please

I would like more information on the Marbled Lungfish (Protopterus aethiopicus). According to Wikipedia, it has 133 billion base pairs in its genome, which is more than 40x the size of the human genome. My questions are as follows:

• How does it fit all of that in each of its cells? Does this animal have any evolutionary adaptations to maintaining such a large genome (wrapping it up more tightly, larger cells on average, more cell space devoted to the nucleus)?
• How much of it is junk DNA?
• How long does mitosis take for this creature? Any special adaptations for this process?

Thanks. --70.122.116.118 (talk) 18:09, 6 October 2011 (UTC)

Disclaimer: I know next to nothing about the genome of the Marbled Lungfish. However, tracing the references from the citation in the artice, the quoted genome size is based on estimates from cell size published in 1972 (here). I can't find anything more recent and it doesn't seem that the lungfish genome is among the 1215 eukaryotic genome projects currently underway. Since the genome size estimates are based on the larger cell size, it appears that the answer to your first question is "unusually large cell size" (1978 article by the same author). Since we don't have an actual genome sequence for the marbled lungfish, the answer to your second question is likely unknown, although based on other genome sequences, there do seem to have been genome duplication events during the evolution of fishes, which might explain its large size. I would predict that the proportion of the genome that is "junk" (terrible term, it just means we don't really know what it does; perhaps plays a structural role or controls gene expression patterns in very complex ways) is somewhat greater than the more compact genomes. I can't find any references that address the last question. The marbled lungfish, as beautiful as it is, does not seem to be one of the favorite model organisms for cell biologists or molecular biologists. --- Medical geneticist (talk) 00:29, 7 October 2011 (UTC)

Actually a Google Scholar search for "Protopterus aethiopicus DNA" finds quite a bit of stuff, some of it pretty recent. One factor is that the species is apparently tetraploid, meaning that it has four copies of every chromosome instead of the usual two. This recent paper, however, suggests that the quoted genome size value may not be all that reliable -- there seem to be substantial discrepancies between studies. Looie496 (talk) 02:27, 7 October 2011 (UTC)

Damped oscillations in real life

Why do damped oscillations in real life come to a halt when basic damped oscillations studied in physics/differential equations (such as overdamped, underdamped, and critically damped cases arising from second order linear differential equations with constant coefficients) model oscillations that go on forever, even if with decreasing amplitude? — Trevor K. — 20:27, 6 October 2011 (UTC) — Preceding unsigned comment added by Yakeyglee (talk • contribs)

The model of friction, or other energy-dissipation process in the physics models, is simplified. Also, in real life oscillations below a certain level can't be detected because they are overwhelmed by other motions, electrical noise, or electrical noise and vibration inherent in the measuring device. Jc3s5h (talk) 20:32, 6 October 2011 (UTC)

ec Because those models have been simplified. At some point, the oscillation in a damped system will be below that of molecule vibration. For all intents and purposes, it is no longer oscillating, but in the mathematical model, you can say it is still oscillating even if it is only moving 1x10^-50 m per cycle. Googlemeister (talk) 20:33, 6 October 2011 (UTC)

I would say that the most general explanation falls under the description of stick-slip motion. While the surface-mechanics are still an active area of material science research, stick-slip motion is a very well known model of real-world friction behavior. Basically, what it means is, below a certain velocity, the friction becomes much larger and the object "sticks." We have lots of mathematical models to approximate such behavior: various empirical hysteresis curves can be fit to approximate motion.

More generally, a complicated physical model of friction turns simple harmonic oscillation (the most trivial 2nd order, ordinary differential equation) into a complicated nonlinear differential equation. Nimur (talk) 18:03, 7 October 2011 (UTC)

Gulf stream

Is the gulf stream or north atlantic drift really moving southwards if so what is causing this. Would the mid atlantic ridge eventually have an impact the gulf stream and north atlantic drift therefore changing the climates of different regions. — Preceding unsigned comment added by 86.41.89.65 (talk) 20:52, 6 October 2011 (UTC)

Between the articles Gulf Stream and Mid-Atlantic Ridge, it appears the ridge is roughly twice the depth of the bottom part of the stream. That doesn't precisely answer your question, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:43, 7 October 2011 (UTC)

You would think the first question would be answered in Gulf Stream; it isn't but it is covered in Shutdown of thermohaline circulation. (Some evidence, probably natural but not sure.) Don't know about the second question, presumably ridges do affect the deep ocean currents. Itsmejudith (talk) 10:40, 7 October 2011 (UTC)

You may be interested in the article, Latitude of the Gulf Stream and the Gulf Stream north wall index - unfortunately, it is essentially pure data. The Gulf Stream itself is situated mostly on the North American continental shelf, before departing eastwards near the Outer Banks of North Carolina. It is likely that increased oceanic heat content during the past few decades has both altered the strength of the Gulf stream and its position through additional influxes of warm tropical water and cold Arctic fresh meltwater. As for the Mid-Atlantic ridge, bathymetry usually does affect local sea levels, though I'm not sure about the shape of the ocean currents. It appears that you are asking about the recent tectonic/volcanic activity, and whether any extra heat build up is likely to have affected the Gulf Stream. Any such effect is likely to be slow and long-term, though you can check for any correlations in the data, while remembering that correlation does not imply causation. Additionally, the North Atlantic Oscillation, Arctic oscillation, Arctic dipole anomaly, Azores High position, Atlantic Multidecadal Oscillation and other climate oscillations all affect the atmospheric circulation, and likely the position of the Gulf Stream in association. East of the Grand Banks of Newfoundland, the Gulf Stream becomes the North Atlantic Drift. The following journal articles show some link between the ridge, a geological feature, and the Gulf Stream to North Atlantic Drift: JGR, 1991 and DSR, 1988. See also Irminger Current for the area west of Iceland. ~AH1 ^(discuss!) 23:09, 7 October 2011 (UTC)

Spin–lattice relaxation of different substances

I'm looking at T1 and T2 relaxation times in physics labs ... and being experienced in chemical NMR I am rather puzzled over many aspects of NMR that I overlooked. The pathetic strength of the magnetic field we're using means that we have to use 21 MHz signals (rather than say 300 MHz signals) though. For one, though resonance frequency differences between protons in different chemical environments can't really be resolved that well (though we can pick up differences that are sometimes on the order of parts per ten thousand as opposed to million). The other thing is that differences in relaxation times can be very dramatic.

Why would T1 of glycerol (T1 seems to be ~20 ms) be much shorter compared to the T1 of isopropanol and water (both are >1000 ms)? I get the idea that more oily or more solid implies a shorter T1 -- but is glycerol really that much different from ethanol chemically? Why would this be so? And how would chemical properties (solvent effects, chemical activities, densities and so forth) theoretically affect T2?

Also why is glycerol 1200 times more viscous than isopropanol? elle _{vécut heureuse} ^{à jamais} (be free) 20:58, 6 October 2011 (UTC)

More OHs = more hydrogen bonding, so stronger intermolecular forces, so more viscous. --Jayron32 00:04, 7 October 2011 (UTC)

It surely can't be that simple. Water must surely have a stronger and more robust hydrogen-bond network than glycerol. For one, it can pack a lot more hydrogen bonds into a given space. Furthermore, this trend doesn't necessarily hold with other polyols. Furthermore, many viscous liquids aren't even polar. elle _{vécut heureuse} ^{à jamais} (be free) 01:48, 7 October 2011 (UTC)

I don't know the answer to this one. The real question is, how do you predict viscosity (in general) from first principles? I found an abstract [9] which says "So in this work, a virial equation for calculating the viscosity of dense liquid was introduced according to correlating the dimensionless residual viscosity and reduced density. Adopting critical parameter (Tc, Pc), molecular mass (M) and accentric factor (ω) as parameters, the calculation can be accomplished. So the calculation of the viscosity of dense liquid is consistent with the calculation of equilibrium properties perfectly over the entire fluid range." This person has a site here but I couldn't get in. Wnt (talk) 03:09, 7 October 2011 (UTC)

Also in general, what would differ between glycerol and isopropanol (there are both organic alcohols) that would make for very long T1 and T2 relaxation times for isopropanol compared to glycerol? Why would spin-spin relaxation times be affected? elle _{vécut heureuse} ^{à jamais} (be free) 05:11, 7 October 2011 (UTC)

I can't answer this one. I don't even understand how spin echo can be consistent with what I thought would be the quantization of the nuclear spin each moment is being measured. And I'm not entirely clear on what is being transferred to where with T1 and T2 of these materials. It would be kind if you'd humor me with a description of what you know about this system ... I really hope someone answers your question! Wnt (talk) 17:09, 7 October 2011 (UTC)

Is there software that can animate chemical reactions?

I would like to be able to set up a reaction and be able to watch it in 2D or 3D, for instance in the reaction CO2 + C > 2 CO I'd like to see the O atom breaking from the first C and then attaching to the second C. I know Chemsketch can animate a molecule, but something that did a reaction would be awesome. Does anything like this exist? N^oformation ^Talk 23:17, 6 October 2011 (UTC)

I doubt it, I don't think that the reaction type can be predicted. Reaction rates, and types can only be found through experimental evidence. Plasmic Physics (talk) 01:00, 7 October 2011 (UTC)

Plasmic Physics is way off. Such methods of animating simple chemical reactions have existed for decades. Here is an abstract from J. Chem. Ed. from 1995 which discusses how to animate such chemical reactions. I can also find any of several dozen more recent articles from J. Chem. Ed. which discuss the use of computer animations in a wide variety of applications. Many of these are simple animations of "ball and stick" or "space-filling" models transfering balls from one molecule to another, but trivially one could show electron flows between molecular orbitals (i.e. between HOMO and LUMO orbitals) that show bonds breaking and forming in simple computer animations, which would match expected mechanisms of such reactions. Like say this video which involves a reaction even more complicated than the one the OP came up with. --Jayron32 04:19, 7 October 2011 (UTC)

While there is software that can animate *some* chemical reactions, there is no software that can accurately animate an arbitrary chemical reaction. Because, as Plasmic Physics points out, there's no way to predict a priori how a particular chemical reaction proceeds. You can have a theory, or make analogies to other chemical reactions, but you have to actually do experiments to find out. Even then it can be hard to figure out and contentious. If your reaction is of a class that's been extensively studied (e.g. S_N2, E1, etc.) a program may be able to make a guess of how the reaction goes, but the literature is filled with reactions which look like S_N2 (or E1, etc.) reactions, but were later found to use some other mechanism. If all you have is a list of substrates, a list of products, and a set of reaction conditions, no software in the world will be able to give you an accurate animation, unless someone has already done the lab studies. For example, in the CO2 + C > 2 CO case: yes, a C=O bond needs to be broken and the C needs to form a bond with the O, but how does that happen? Is it dissociative, associative, or coordinated? (What happens first, the old bond breaking, the new bond forming, or do they happen at the same time? The transition state might not be 50%/50%, but something like 20%/30% or 60%/55%.) Is it an end-on attack, or does the new carbon form a three member ring across the C=O bond? (Because the latter is how some halogens add to double bonds.) Additionally, you likely don't have monoatomic carbon - it'll be in some sort of particle, so how does surface effects contribute to the reaction mechanism? - You can animate the reaction any way you like, but you can also draw pentavalent carbons. That doesn't mean that's what happens in the lab. -- 174.24.217.108 (talk) 16:52, 7 October 2011 (UTC)

All very true, but it wasn't readily clear if the OP wanted animations for software which animated known mechanisms, or which itself predicted unknown mechanisms. I read the question as the first; rather than the second. So it's OK. You can be correct too. I don't mind that much. It really doesn't bother me that you are correct. --Jayron32 18:32, 7 October 2011 (UTC)

Is it really meaningful to ask how all those bonds change in time and animate it? I thought all that was so quantum (in the derogatory sense) that all you can really tell with simple reactions is that the old molecules go in and the new molecules come out. Now if you took more complicated reactions from oraganic chemistry and large enzymes, you could as what steps you can break it to, but not with a simple one like that carbon monoxide. – b_jonas 18:25, 8 October 2011 (UTC)

October 7

Largest arthropods: land versus sea

See Largest organisms#Arthropods (Arthropoda). It appears to me that the largest arthropods on land are significantly smaller than the largest under-water arthropods. Is this correct? If so, why? Does it have to do with the ability of the exoskeleton to support its weight or access to oxygen or control of water content or vulnerability to predation or what? More generally, what limits the size of arthropods? JRSpriggs (talk) 03:48, 7 October 2011 (UTC)

For mammals as well, the largest mammal in the sea (the Blue Whale) is orders of magnitude larger than the largest mammal on land (the elephant). The reason for this is buoyancy, and I suspect that for arthropods, the reasoning is similar. --Jayron32 04:04, 7 October 2011 (UTC)

Do you mean that buoyancy reduces the weight of the animal relative to what it would weigh on land? And wouldn't there be another factor in that the ocean is more vast both in surface area but perhaps more importantly in the depth that it offers? Bus stop (talk) 04:15, 7 October 2011 (UTC)

Animals on land are limited in size because beyond a certain limit, they would not be able to support their own weight. Animals in the water are bouyed by the water, which allows for larger animals to exist in the water. --Jayron32 04:23, 7 October 2011 (UTC)

Perhaps nothing illustrates this more clearly then Siphonophorae, some of which can reach 40m-50m in water, but would obviously resemble little more then puddles of goo on dry land. Vespine (talk) 05:45, 7 October 2011 (UTC)

The size of the largest aquatic and land-living arthropods, does not differ that much. The largest ever aquatic arthropod is the Devonian eurypterid Jaekelopterus rhenaniae (8.2 ft). The largest ever land arthropod is the Upper Carboniferous myriapod Arthropleura (8.5 ft). The largest extant arthropod by mass is the American lobster Homarus americanus (3.5 ft). The largest living land arthropod is the coconut crab Birgus latro (3.3 ft). The Japanese spider crab may be considered larger by some, but only because it has amazingly long spindly legs. However, it is true that land arthropods are smaller than aquatic arthropods on average. And yes, you're probably correct on all counts (though the oxygen factor as a limit is still contentious):

• Gravity - exoskeletons cover the exterior of an animal and thus are much heavier than animals with endoskeletons like vertebrates in proportion to size. Proportionally, a smaller arthropod will require a thinner exoskeleton than a larger arthropod to maintain rigidity and motion. Water provides a buoyant support for large aquatic animals. Land animals, however, have to depend on the rigidity of their supports. And in order for exoskeletons to be more rigid it needs to be exponentially thicker and heavier the larger the animal is. There is a point where it becomes mechanically impossible to increase any further (a gravity limit). In addition, exoskeletons need to be molted, they can not grow continuously like endoskeletons. A molting giant arthropod on land would collapse into a squishy mess under its own weight, resulting in deformities when the exoskeleton hardens. Add to this the fact that when molting they are extremely vulnerable (they can't even move as the exoskeletons are the supports for their muscles like our bones are).
• Oxygen - arthropods don't breath with lungs but by direct surface absorption into a network of tracheae. Although crustaceans and arachnids do have gills and book lungs, they also have far more primitive circulatory systems than vertebrates. Tracheal respiration are passive systems. The larger the size of an animal or the thicker the exoskeleton, the harder it is to get oxygen into the deeper internal organs. This is proposed to have been why the hyperoxic conditions of the Carboniferous resulted in land arthropods reaching gigantic sizes. Add to this the problems of water balance. Aquatic arthropods do not have to worry about leaks or evaporation.
• Predation - Paleozoic land arthropods (and aquatic arthropods a little further back) reached very large sizes due to the lack of competition (compare eurypterids which arose before fish and Carboniferous land arthropods which arose before land vertebrate dominance). As vertebrates started taking over some niches, it became too risky for them to increase in size. Per previous reasons, the larger they are, the weaker they are relatively in comparison to animals with endoskeletons. A flea can jump ~200 times its body length, increase their size, and that proportionally becomes much lower.-- Obsidi♠n Soul 08:20, 7 October 2011 (UTC)

I should note that as mentioned in Invertebrate trachea, some insects have air sacs at the end of the tracheae, and air can be forced into and out of the system. However, while arthropods ordinarily should be well capable of using muscular movements to suck in air via the tracheae, during molting the situation is different - those movements shouldn't work, but land arthropods take in air by swallowing it.[10] For small arthropods, I assume the air in the stomach provides a source of oxygen (besides, it takes a long, long time to suffocate an arthropod...) - still, it sounds like a problem. But I don't see why very large insects couldn't evolve some method to permit air to leak into the tracheal system or otherwise to distribute itself from the foregut during that time. Wnt (talk) 11:19, 7 October 2011 (UTC)

Tracheal breathing in bees, grasshoppers, and dragonflies, etc. are actually still heavily mechanical. They only function when the insects are not at rest (e.g. flying, when the metabolic demands are the highest, or when in an alerted state). The rest of the time, it breathes through diffusion. And they did. That's why the largest arthropods today are crustaceans and chelicerates. Because their larger members have gills, branchiostegal lungs, book lungs etc. which do not rely on passive diffusion, and they have blood that can carry oxygen (hemocyanin). But as mentioned, their hearts are still relatively far weaker than vertebrate hearts.-- Obsidi♠n Soul 14:12, 7 October 2011 (UTC)

e/c: Also no. They can not breathe swallowed air. And I'm curious where you got the 'they take a long time to suffocate' bit. Instances of seemingly long suffocation times are merely the result of them still getting oxygen through cutaneous respiration from what would have drowned a vertebrate lung. See [11] -- Obsidi♠n Soul 14:49, 7 October 2011 (UTC)

Well, you can "anesthetize" a caterpillar for purposes of macabre manipulation by keeping it under cold water - given the low metabolic rate, further reduced by the cold, they can survive around an hour that way. This is true even though some effort is made to exclude large external air bubbles, though of course small ones remain.

I would be very surprised if no oxygen makes it out of the stomach, when so much is swallowed that it distends the entire insect. Wnt (talk) 17:01, 7 October 2011 (UTC)

You mention that the lobster and the coconut crab have roughly the same length, but the lobster is more then 4x heavier. I do not see the weights for the prehistoric examples you mention, but the aquatic one looks like it would also have significantly more bulk. Googlemeister (talk) 14:22, 7 October 2011 (UTC)

Probably, though both Arthropleura and Jaekelopterus were dorsoventrally flattened, unlike coconut crabs and lobsters. Also note that some eurypterids may have been amphibious, some of the first animals to set foot on land, really. They are actually the direct ancestors of modern land scorpions and spiders.-- Obsidi♠n Soul 14:49, 7 October 2011 (UTC)

Thank you-all for your replies, especially Obsidian Soul. JRSpriggs (talk) 21:31, 7 October 2011 (UTC)

Collapse of the soft body during molting, or ecdysis provides the critical upper limit in arthropod size. The problem is the regeneration of the entire exoskeleton at once. This does not seem to be mentioned in the article on ecdysis, though. μηδείς (talk) 20:21, 8 October 2011 (UTC)

Official level of radioactivity in Japan

Where can I find official authoritative radioactivity data of Japan? No problem if it's in Japanese. Wikiweek (talk) 11:26, 7 October 2011 (UTC)

I would start by reading nuclear organizations in Japan, and decide what specific sort of data you're looking for. Nimur (talk) 16:59, 7 October 2011 (UTC)

Genetic Population Statistics Question

Where could I find data on what percentage of Filipinos carry a blue allele for OCA2? I once knew a guy with bright blue eyes whose parents were both Filipinos with brown eyes and it struck me as pretty uncommon. His sister had brown eyes like their parents. 20.137.18.53 (talk) 13:38, 7 October 2011 (UTC)

That's probably just a result of mixed ancestry? Some "full Filipinos" tend to not be fully Austronesian. One of my grandfathers had blue-gray eyes (more gray than blue), and one of his sons (my uncle) had gray-greenish brown eyes. But our ancestry is very mixed. And yes, this is very uncommon. -- Obsidi♠n Soul 15:29, 7 October 2011 (UTC)

Here is an article that defines a single SNP that is exquisitely linked to eye color. The SNP in question is rs12913832 and in the HapMap samples the Asian populations have essentially 100% A/A (brown allele). Compare to J. Craig Venter who is G/G and has blue eyes. --- Medical geneticist (talk) 20:41, 7 October 2011 (UTC)

rabbits and radiation

Why are rabbits more resistant to radiation poisoning then humans and most other mammals? Googlemeister (talk) 18:56, 7 October 2011 (UTC)

What makes you think they are? AndyTheGrump (talk) 19:00, 7 October 2011 (UTC)

They are better at self-repair. Why? I don't know. See radioresistance. -- kainaw™ 19:04, 7 October 2011 (UTC)

Note from the article it's not clear rabbits are really better then other mammals. They may be better then humans and dogs but don't see much better then rats or mice. Even compared to humans they only have a LD₅₀ about double although it's not clear to me how reliable the human figure is nor whether the human (or for that matter rats or mice) value is over 30 days. Nil Einne (talk) 20:05, 7 October 2011 (UTC)

Alright, I adjusted the question to state that rabbits are only better then most other mammals, but am looking for a reason as why rodents seem to handle it better then canines, primates etc... Googlemeister (talk) 20:29, 7 October 2011 (UTC)

Why etc? The article doesn't give any figures for cats, or ruminants or ungulates etc. (And it only gives one figure for primates i.e. humans and one figure for canines i.e. dogs so it seems a bit quick to decide all primates and canines are comparable.) Do you have some sources suggesting rodents and rabbits are unusually high among mammals? Nil Einne (talk) 21:01, 7 October 2011 (UTC)

I'm not comfortable drawing the conclusion that rabbits are significantly more radioresistant than other mammals, despite the contents of the table at radioresistance. It's very easy to inadvertently do an apples-to-oranges comparison when trying to estimate LD50 values for ionizing radiation exposure. For one thing, we don't know that all of the test animals used to generate the table were exposed to the same type of radiation. (Indeed, we're certain that the numbers for humans aren't based on systematic testing; they're mostly derived from dose estimates assembled for people bombed at Hiroshima and Nagasaki.)

The pattern of radiation deposition within the body of an animal will depend strongly on the shape of the animal and the energy of the gamma ray photons used. Bones can 'shadow' the tissue behind them if radiation is incident from one side only. Low-energy photons will be strongly absorbed in the first few centimeters of tissue, shielding the organs below; high-energy photons generate showers of secondary electrons that actually deposit more dose a centimeter or two below the surface than is absorbed at the skin. Even though the whole-body LD50 values as presented imply a uniform dose of radiation to the entire volume of the body, in practice such a dose was almost certainly not what was delivered—simplifying radically, the extremities of a larger animal would be 'hotter', while the core would be 'cooler', and the reported figure just an average dose. The mouse would receive a more uniform dose than the dog. TenOfAllTrades(talk) 21:28, 7 October 2011 (UTC)

As I understand it, there's a tradeoff between cancer resistance and radiation resistance. Humans, with a 70+-year lifespan, are highly resistant to cancer, but at the cost of being unusually vulnerable to radiation poisoning: even minor DNA damage tends to trigger cell suicide. Rabbits and other short-lived mammals don't have the strong anti-cancer mechanisms humans do, so it takes a larger dose of radiation to cause the large-scale cell die-offs of acute radiation poisoning (but at the same time, they're more likely to get cancer from radiation). --Carnildo (talk) 01:03, 8 October 2011 (UTC)

2D creatures in a 3D space - could not resist taking it up again

Hi I posted this Q in 2006 - and sorru if it offends anybody also reposted in 2010 - well now I got the inspiration to add to the question instead of reposting : Pasting here

Original 2006 Q link: http://en.wikipedia.org/wiki/Wikipedia:Reference_desk_archive/Mathematics/March_2006#About_2_D_creatures_traveling_on_a_2_D_plane_seen_from_a_3_D_point_of_view

My addition below:

Just googled and found this again - I'm the OP - well now I'm interested in two things. One to see if anybody else but me will notice that I've been here 5 years later, and two : Is there someone out there who can explain in laymans terms why this

“ In this case the maximum factor between the distance of the taxicab traveler and the distance of the Euclidean traveler would be \sqrt{3}, for example going from (0,0,0) to (5,5,5) the taxicab traveler has to move 15 units, as opposed to the Euclidean traveler's 5\sqrt{3} units. But as before, that's a maximum: in going from (0,0,0) to (3,4,12) the taxicab traveler goes 19 units to the Euclidean traveler's 13, but \frac{19}{13}<\sqrt{3}. It's possible to choose a pair of points where the taxicab traveler's distance is exactly \frac{\pi}{2} times as long as the Euclidean traveler's, but that's only because such a pair of points can be found for any number x such that 1 \le x \le \sqrt{3}, which \frac{\pi}{2} happens to satisfy. ”

is right?

As I see it - Going from A to B in 3D is just (always) a straight line. But this C cannot see that so it has to travel from the perspective of the 3D creature in X + Y ie. at the point where it needs to change direction is where the 2D creature actually has traveled the least distance in the X distance (or Y) and then changes direction 90 degrees to be 'the fastest' without changing directions every x/Y mm (or whatever).

So the 3D viewer would, if seeing the 2D creature move along the xy points, percieve the path at some fractional degree from the perfect - Squareroot 2 path - which means the 3D viewer would be able to see the 2D creature's energy expenditure adhere to my postulation.... 2D travelers always expend square root 2 times more energy when the 3D viewer multiply this with hmmm is it cosinus or sinus ? (Perfect angle view that makes a straight line away from the XY plane) That's the hint for ½ PI value. To elaborate : A photon is emitted from somewhere..... this photon is measured at some point and only there you can make the mark that you measured a photon (in whereever space) how it got there (Cab or Helicopter) you don't know - you can just measure the time difference between you emtting the photon - and collecting information about when it hit 'point B' 85.81.121.107 (talk) 19:59, 7 October 2011 (UTC) — Preceding unsigned comment added by 85.81.121.107 (talk)

It looks to me like you are trying to reinvent the basic concepts of Minkowski space Taxicab geometry. -- kainaw™ 20:08, 7 October 2011 (UTC)

OP here, it's not the Manhattan distance I'm "looking" for, my original foundation was when I in my teens read all kind of pop physics books - think stuff like schroedingers cat etc. (http://www.benbest.com/science/quantum.html) BTW Fixed Taxi to Helicopter :-)

I am interested in finding out if there is some merit to the idea that 'my' 3D viewer - if it wanted to travel the same distance as the 2D creature - could do so while expending at least squareroot 2 times less energy as the 2D creature - because the 3D creature would ALWAYS travel in the straight AB line not some xyxyxyyyyyxxyyxyy path as the 2D creature had to...perfect conditions would in my mind suggest this squareroot 2 times less - because the fastest 2D creature would only travbel one X and then one Y. Drawing it up on a XY crossed paper this could look like going from 0,0 to 6,4....but the 3D viewer would just 'measure' the AB distance - The view angle of the 3D creature will if it's not perfectly squareroot 2 times the distance be a candidate to a formula where you can figure out the angle where one observer sees the AB distance for the 2d creature as XY = 5,8 but the actual 3D viever just sess this as the perfect 90 degree travel path for the 2D creature.. so the actual distance/time used traveling would be 1,1 times (co)sinus the angle

I wish I could explain it better....and now I introduced a third 'viewer' or maybe planePOV... in the 3d space observing a 2D creature traveling on a fantasy xy crossed paper....angled so it just looks like a straight line to a human....

So there it is .... redshift is all over me now.... ok going trying once more....

Going from A to B is just start and stop - if you were drawing this path on a piece of paper - it's fairly simple.... just point a and then point B draw a line between these to points.

Ok, so now we introduce a (normal) coordinate system showing XY direction - so the paper now has some kind of information on it that can be used to measure stuff - and we draw a triangle with a 90 degree C angled based on where we put our A and B points - so now there is a triangle with at least one 90 degree angle, independent on the orientation of the 'imaginary' papers xy coordinate lines.

Going from A to B would be straight forward if you could just do it...and here it is - the issue...the 2D creature can only move in XY direction of its own 'coordinate system' being imagined as another virtual coordinate system laying at some angle to what a 3D observer perceives (the '3d' xy paper) so the 2d creatures fastest path is one stop and go in its own coordinate sytem. and in this coordinate system where the 2D creature travels exactly half the distance between point A and B before it does a direction shift. And this half (x2 ) equates to square root 2 of the distance that a 3d creature would use to travel that Ab distance seen from the 3d creatures POV.

So 3d creature can use less time/energy if it should travel the same distance as an observed 2d creature... - it doesn't have to stop and change direction when half the distance is reached...because it just arrives :-)

http:/upwiki/wikipedia/commons/thumb/6/69/Coord_system_CA_0.svg/240px-Coord_system_CA_0.svg.png

Picture link inserted above - The 2D creature only perceives the x and y directions so it cannot travel the direct route throug Z (as observed by the 3D viewer) - btw that picture does not satisfy my idea of the 90 degree rule - = half the distance in X direction and the other half in the Y direction - and now that I think about it - the 2d creature would have no good idea about the Z axis.... which we could imagine to be time :-D

Damn forgot that it also follows that you can then for the 2d creature travel 2 paths.... which have the exact same lenght -> through the 90 degree triangle on the x plane or 90 degree on the y plane... That was my hint for the 3d things going through the 4D stuff and double slith experiment...

85.81.121.107 (talk) 20:58, 7 October 2011 (UTC)

You can think of it in terms of vectors: the "Euclidean" 3-D creature can travel in a direct straight-line distance between all the vectors, while the 2-D creature must travel along all three vectors to get to the same location. ~AH1 ^(discuss!) 22:33, 7 October 2011 (UTC)

OP here - Found an interesting link http://blazelabs.com/f-p-hds.asp helping to visualize seeing the 'world' from a lower/higher dimensional 'space' and the implications. 85.81.121.107 (talk) 06:54, 8 October 2011 (UTC)

I'm sorry, I don't understand. What is your question? The Euclidean distance in 3D is ${\sqrt {x^{2}+y^{2}+z^{2}}}$ and the Taxicab distance is $x+y+z$. What more do you want to know? --Tango (talk) 12:49, 8 October 2011 (UTC)

are stars visable from space.

From the surface of earth a vast quantity of stars are visable with the human eye. 1 if you could move outside the earths exosphere would the same quantity of stars be visable with the human eye. 2 if you could move outside the solar system would the same quantity of stars be visable with the human eye. Cubedmass 21:08, 7 October 2011 (UTC) — Preceding unsigned comment added by Cubedmass (talk • contribs)

1) You would see more, because the earth's atmosphere ruins our view of some stars. That's the reason why the Hubble Space Telescope and devices like it are outside of the atmosphere.

2) You would likely see more stars, as the nearby sun causes some light pollution which interferes with seeing some dim stars. --Jayron32 21:14, 7 October 2011 (UTC)

I recall that around 6000 were visible from Earth. How many could you see where no one can hear you scream? Clarityfiend (talk) 22:15, 7 October 2011 (UTC)

During the daytime on Earth, diffraction of light in the sky causes stars other than the Sun to become invisible. Even when the Sun is visible in space, the stars can still be seen, and the same is true for the Moon as well. ~AH1 ^(discuss!) 22:20, 7 October 2011 (UTC)

It's not diffraction, but Rayleigh scattering. --Carnildo (talk) 01:06, 8 October 2011 (UTC)

Star_catalogue#Full-sky_catalogues suggests that it really depends on what kind of technology you're using, but with good enough terrestrial telescopes you can observe around a billion stars (!!) (e.g. the Guide Star Catalog). --Mr.98 (talk) 01:35, 8 October 2011 (UTC)

1) Definitely would see more in space.

2) I don't think light pollution is a significant problem, as long as you are in a shadow, like on the dark side of the Moon when it's not positioned to receive Earthshine. Therefore, I wouldn't expect leaving the solar system to make much difference versus that. (The one exception would be stars near our Sun from your POV. Obviously the farther away you are, the fewer stars our Sun will block, but then again, just moving around within our solar system also fixes that.) StuRat (talk) 22:23, 7 October 2011 (UTC)

Billions and billions. μηδείς (talk) 22:31, 7 October 2011 (UTC)

Light pollution often reduces limiting magnitude by 1 or 2 apparent magnitudes in suburban areas, and up to 5 in city centres. Light pollution-free zones usually get to 6th magnitude visibility for those who have average eyesight. ~AH1 ^(discuss!) 23:11, 7 October 2011 (UTC)

Right. In my answer to part 2 I was talking about light pollution from the Sun, which isn't a problem everywhere in the solar system. Light pollution is more of a problem on Earth, though, due to the large number of light sources and the atmosphere which reflects and refracts that light back into out eyes. StuRat (talk) 00:05, 8 October 2011 (UTC)

Light pollution is a term with a specific meaning; it doesn't apply to natural light sources. You're going to confuse readers if you misuse it.

Even beyond the Earth's atmosphere, however, there are effects of sunlight scattering from dust particles in the solar system. (These effects are visible even to naked-eye observers on Earth under very dark-sky conditions as zodiacal light and gegenschein.) TenOfAllTrades(talk) 02:47, 8 October 2011 (UTC)

Bortle class 0? The best we can get on Earth is Class 1:

Class 1: Excellent dark-sky site. The zodiacal light, gegenschein, and zodiacal band (S&T: October 2000, page 116) are all visible — the zodiacal light to a striking degree, and the zodiacal band spanning the entire sky. Even with direct vision, the galaxy M33 is an obvious naked-eye object. The Scorpius and Sagittarius region of the Milky Way casts obvious diffuse shadows on the ground. To the unaided eye the limiting magnitude is 7.6 to 8.0 (with effort); the presence of Jupiter or Venus in the sky seems to degrade dark adaptation. Airglow (a very faint, naturally occurring glow most evident within about 15° of the horizon) is readily apparent. With a 32-centimeter (12½-inch) scope, stars to magnitude 17.5 can be detected with effort, while a 50-cm (20-inch) instrument used with moderate magnification will reach 19th magnitude. If you are observing on a grass-covered field bordered by trees, your telescope, companions, and vehicle are almost totally invisible. This is an observer's Nirvana!

Count Iblis (talk) 04:25, 8 October 2011 (UTC)

1) You would not see significantly more. On a clear night the atmosphere blocks about 1% of visible light. The Hubble Space Telescope is not in space to get that 1% back; it is there for two reasons: to avoid atmospheric diffraction (does not greatly reduce the number of stars you see, merely makes them twinkle), and to see in non-visible-light frequencies - as mentioned in the HST article. The lost 1% of light can be much more cheaply compensated for by increasing photograph exposure time by 1%.

2) Very very little more. The Sun affects your viewing only if you are looking directly at it. Since there is no atmosphere, there is very little to scatter light from the Sun when looking in any other direction. However, there are places in the galaxy where you would see more stars, such as the galactic center if you are willing to travel that far. 88.112.59.31 (talk) 08:50, 8 October 2011 (UTC)

1) I can see why the atmospheric diffraction wouldn't be an issue with bright stars, but it does seem likely to make a dim star on the edge of perception no longer consistently visible. StuRat (talk) 17:31, 8 October 2011 (UTC)

Petroleum Refinary

There is a fire seen above petroleum refinaries in maxmum photographs of a refinary.can any one help me with what exactly is that fire called .is there any use of that fire?why do we waste energy like that?couldnt that fire be put off? thanks in advance 117.230.71.121 (talk) —Preceding undated comment added 22:18, 7 October 2011 (UTC).

That's intentional, to burn off natural gas which accompanies petroleum. I agree that it's wasteful. Apparently they think the cost of capturing it and selling it is more than they would get. It's burnt because most of the combustion products will be water and carbon dioxide, which are less dangerous in the atmosphere than natural gas. See gas flare. You'd think that if they are going to have a continuous flame like that, that they could at least recover some energy from it to run the refinery. StuRat (talk) 22:26, 7 October 2011 (UTC)

Actually, they mostly do [disclosure: some years ago I worked at this refinery, albeit at a desk job].

The gas burning at the top of refinery flare stacks (as opposed to those sometimes seen at well heads, particularly offshore oil rigs) is not merely the discarded natural gas component of crude oil: such gas is usually also collected and processed at refineries, as can be seen in this diagram, but this and the other distillation and treatment processes going on collectively produce a surplus of mixed inflammable gases, which where I worked were (if I recall correctly) called "refinery gas."

The bulk of this refinery gas is indeed used to generate on-site power, often by burning it to heat water to produce steam which is then piped around the refinery so that its contained heat can be used (and some steam is used directly in some of the chemical processes). However, the distillation and other processes going on in all those distillation towers and other bits of plant are quite sensitive to slight fluctuations in temperature, pressure, and the precise chemical makeup of the crude, so the volume of refinery gas being produced over the whole refinery is subject to unpreditable fluctuations and occasional major "surges." When those occur the sudden large excess of gas cannot be captured (think of an accidentally shaken bottle of beer), and has to be burnt off through the flare stacks.

The quiet, flickering flames normally seen on flare stacks are merely the pilot lights of the stacks. If a surge occurs, the resultant flames are powerful, large and loud (they may be heard for miles) - it's much like the difference between the flickering flame and the roaring flame on a Bunsen burner, except that the 'roaring flame' on a stack is much taller, not smaller, than the 'flickering flame' because it's caused by (much) greater gas volume, not merely by admitting more air to the same volume.

Such surges (at least at the refinery I worked at) are relatively rare, so that the resultant burn-offs can cause some alarm to those in the vicinity unaccustomed to them: they are, however, quite harmless and are indeed a designed safety feature of the system. {The poster formerly known as 87.81.230.195} 90.197.66.142 (talk) 23:50, 7 October 2011 (UTC)

I would like to see some sources about the quantities involved. I spoke with someone today who said that the plant where he worked had to flare off more than 2.5 million cubic feet of refinery gas per day above what they were using to power the plant because even when there was a market for it, which was rare, logistical problems were involved with transmitting it by pipeline. 70.91.171.54 (talk) 01:14, 8 October 2011 (UTC)

I have to wonder if they had to pay the cost of all that pollution, say via carbon credits, if the economics would then favor finding a way to capture it. StuRat (talk) 17:21, 8 October 2011 (UTC)

Simply remove the fossil fuel subsidies. Dualus (talk) 03:30, 9 October 2011 (UTC)

Well, as I understand it, under carbon credits, the refineries would start off with free carbon credits for all their current activities - if they then make one of these natural gas burning stacks, they are transforming methane, a more potent greenhouse gas, into carbon dioxide, which is worth a few extra credits, which they can sell to homeowners who want to purchase the privilege of running a fireplace, a precious keepsake to pass down to future generations... Wnt (talk) 13:38, 10 October 2011 (UTC)

That doesn't seem right. That would mean anyone could get extra credit for leaving the gas tap open with a fire lit above it all the time. Eternal flames at cemetaries should collect lots of credit, then. StuRat (talk) 00:14, 11 October 2011 (UTC)

Only if their previous releases of methane were "grandfathered" into the system with an issuance of free carbon credits - which is not an option for just anyone. Wnt (talk) 19:56, 11 October 2011 (UTC)

October 8

T power?

Hi, I got a little stupid question. Why all of the objects in the universe move in the same direction on the time dimension? I mean why in the space dimension every object is relativity free to move, and on the time dimension in some speed they all move fowards? Exx8 (talk) —Preceding undated comment added 13:50, 8 October 2011 (UTC).

Not a stupid question at all! Some of the greatest minds in history have struggled with it. Short answer: nobody knows for sure. See arrow of time for an overview and some history. SemanticMantis (talk) 15:08, 8 October 2011 (UTC)

I don't think it's clear that everything does move in the same direction. With a subatomic particle, for example, how could you tell ? StuRat (talk) 17:19, 8 October 2011 (UTC)

The concept of "moving through time" is a loose way of speaking that doesn't actually make sense. Moving in space means having different positions at time 0 and time 1. What would moving in time mean? It must mean having different times at time 0 and time 1. Well, duh. Looie496 (talk) 22:59, 8 October 2011 (UTC)

The arrow of time is due to a low entropy initial condition. But if you wait long enough, you'll see arbitrary large downward fluctuations in the entropy. It turns out that such fluctuations away from thermal equilibrium to a lower entropy state are most likely just the time reverse of the evolution back to thermal equilibrium starting from that low entropy state, see here for details, including an example of the most likely way a piano can appear out of a gas of photons and neutrinos. Count Iblis (talk) 00:42, 9 October 2011 (UTC)

Cosmology fact checking

"The universe will expand, then it will collapse back on itself, then will expand again. It will repeat this process forever. What you don't you know is that when the universe expands again, everything will be as it is now." Is that right? (from K-Pax (film)). Quest09 (talk) 16:13, 8 October 2011 (UTC)

As far as we can tell, the universe will not collapse back on itself. It used to be a close call (the universe looks "flat", i.e. as if it would expand at an increasingly slower speed, approaching zero expansion as time goes towards infinity), but we now believe this is an accident of observation time. According to our standard model, the universe will now continue to expand at an increasing rate due to dark energy. See also our article on the ultimate fate of the universe. --Stephan Schulz (talk) 16:22, 8 October 2011 (UTC)

Agreed. The oscillating universe model seems to be out of fashion, these days. StuRat (talk) 17:15, 8 October 2011 (UTC)

Have a look at [12] citing [13] for dark flow. Dualus (talk) 04:03, 9 October 2011 (UTC)

See the ekpyrosis of Stoic physics and Nietzsche's eternal return. μηδείς (talk) 18:10, 8 October 2011 (UTC)

The jury is still out on eternal bleakness. The further out and back, the harder it is to see, and the big bang is in the way, even if it only turns out to be something like a local ultranova. Dualus (talk) 04:12, 9 October 2011 (UTC)

Even if the universe did collapse in on itself, why would there be any reason to assume that the next "big bang" would result in a repeat of the previous one? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:21, 9 October 2011 (UTC)

The stoic and Nietzschean ideas are widespread mystical ones, not scientific. The screenwriter was obviously familiar with them.μηδείς (talk) 15:10, 9 October 2011 (UTC)

That movie (which I haven't seen) came out in 2001, only a few years after the first evidence for accelerating expansion from supernova observations and two years before it was independently confirmed by WMAP. The traditional cyclic universe model seemed more plausible then than it does now. -- BenRG (talk) 08:31, 10 October 2011 (UTC)

Why must it be this set of solutions?

Dear Wikipedians:

While trying to solve the following force diagram scenario:

(Ignoring all vertical forces exerted on pulley by gravity, etc.)

I was able to figure out the following relationship:

${\frac {150-5a_{p}}{2}}=10a+F_{f}$

where a_p is the acceleration the pulley experiences, a is the acceleration the 10 kg mass experiences, and F_f is the force of kinetic friction which I calculate to be 39.2N.

However, the problem with this is that multiple sets of a_p, a, and T (tension in string) would satisfy the relationship above. The official textbook answer is:

a = 3.18m/s², a_p=1.59m/s², T = 71N which would of course satisfy the above relationship, but I have calculated an alternative set a = 3m/s², a_p=2.83m/s², T = 69.2N which would also satisfy the above relationship. Of course there are an infinite number of other sets that would also satisfy the above relationship.

Am I missing something?

Thank you for your help.

L33th4x0r (talk) 17:06, 8 October 2011 (UTC)

Well, more force produces more acceleration, of course. They usually specify the desired accel to restrict it to one answer. That 2nd answer seems wrong, though, as the accel on the pulley should always be half that of the mass, unless we are stretching the cable. StuRat (talk) 17:10, 8 October 2011 (UTC)

Hmm...but 1.59m/s² is not half of 5 kg either... But thanks for your help, I'm all ears for more information. 70.31.153.136 (talk) 17:35, 8 October 2011 (UTC)

1.59 m/s^2 is half of 3.18 m/s^2, which is what he means. $a=2a_{p}$. Dragons flight (talk) 17:41, 8 October 2011 (UTC)

Oh yeah! That was the elusive 2nd restraint that I was looking for!!! In order for the cable to remain rigid body this restraint must be there!!! Thanks so much. 70.31.153.136 (talk) 17:46, 8 October 2011 (UTC)

Resolved

Defibrillation

Can a downed power line be used as a defibrillator? --70.129.191.75 (talk) 17:18, 8 October 2011 (UTC)

No, pounding on their chest and administering CPR would be far better. StuRat (talk) 17:26, 8 October 2011 (UTC)

Not that that will re-start their hard heart (except on very rare occasions). CPR just keeps their brain from dying while you wait for a defibrillator to arrive. --Tango (talk) 17:50, 8 October 2011 (UTC)

Their hard what ? :-) StuRat (talk) 18:04, 8 October 2011 (UTC)

That's a strange typo... not even close! --Tango (talk) 21:37, 8 October 2011 (UTC)

I often make that type of mistake, where I type a word that sounds like the word I meant, even though it may not be spelled anything alike or mean anything similar. It seems to me that this shows something about how our brains work. We must first think of the words as audio, then convert it to writing in our minds. I wonder if those who have been deaf from birth are immune to this particular type of error. StuRat (talk) 02:11, 10 October 2011 (UTC)

No. There is a chance it could work, but it's highly unlikely. The voltage is completely wrong, you won't be able to accurately apply it to the right place and, without the ECG that's built into a defibrillator, you won't know if it is appropriate to shock the casualty at all. --Tango (talk) 17:50, 8 October 2011 (UTC)

No. Defibrillators use a charge of direct current stored in a large capacitor to apply current through electrodes which spread out the current to reduce damage to the tissues. A power line would supply alternating current, found in the 1880's to cause electrocution rather than to revive people. Edison (talk) 19:32, 8 October 2011 (UTC)

LOL Joepnl (talk) 21:40, 8 October 2011 (UTC)

MacGyver would manage that. Wikiweek (talk) 21:45, 8 October 2011 (UTC)

Chuck Norris can do it. Plasmic Physics (talk) 23:13, 8 October 2011 (UTC)

No, he can't. Only MacGyver can.Wikiweek (talk) 00:59, 9 October 2011 (UTC)

Chuck Norris would probably favour the precordial thump. --Tango (talk) 01:13, 9 October 2011 (UTC)

Jack Byrnes defibrillates himself using household-mains power (I think that's the source, or maybe from something else in his home, but definitely not overhead-transmission). But MacGyver can build an AED out of a downed power line and two scratch&sniff stickers. And Chuck Norris doesn't need to use an AED machine--he has electricity in his hands. DMacks (talk) 17:02, 9 October 2011 (UTC)

You guys act like it takes a wonder person to build a defibrilattor out of some random AC power source. It's not, even Mr. Bean can do it. The difficult part is remembering not to shake the person's hand with the jumper cable when you're done. Nil Einne (talk) 22:08, 9 October 2011 (UTC)

Clearly you are biased against the high frequency power-to-heart aerial transmission system. Dualus (talk) 03:38, 9 October 2011 (UTC)

Study claiming immortality bad for evolution

Did the simulation model used for the study described in this article assume, as those I've seen do, that behaviour is entirely genetic and individuals can't learn? NeonMerlin 17:56, 8 October 2011 (UTC)

It wouldn't need to make any such assumption. This newspaper article has the common flaw of articles based on press releases: it takes an idea that has been around for ages and pretends that it is brand new. The idea that immortality is bad for evolution is obvious as soon as you assume that individuals cannot change their genes -- whether they are capable of learning is irrelevant unless tjhe learning can be passed on in the genome. Looie496 (talk) 23:20, 8 October 2011 (UTC)

Immortal beings would not need to reproduce, and true evolutionary change occurs through reproduction. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:24, 8 October 2011 (UTC)

It's impossible for a reproducing species to be immortal in a finite world. If they were indeed immortal, their population would increase exponentially with time and all of the world's resources would quickly disappear, at which point they can't possibly obtain resources to survive.

Note that it IS possible for a species to have biological immortality, which is just the absence of cell senescence. Those organisms still die due to predation, starvation, disease, natural disasters, etc., just not due to old age. --140.180.16.144 (talk) 06:28, 9 October 2011 (UTC)

Like plants that put out shoots, maybe? That raises a possibly interesting question: Does anyone know what the oldest known domestic plants are that are the result of taking "cuttings" and rooting them? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:44, 9 October 2011 (UTC)

Baseball Bugs: look at our List of long-living organisms. – b_jonas 09:43, 9 October 2011 (UTC)

This is a bit speculative, but: Without addressing "immortality" per se, a long lifespan tends to allow a long time for mutations to accumulate in the germline. Natural selection can only remove a certain amount of undesirable mutation per generation, depending on its intensity (i.e. the number of offspring - though certainly I'd expect the competition of sperm and atresis of eggs to be most helpful). It follows that there are limits to lifespan for a species to survive in the long term, though these limits are somewhat elastic. I suspect it would be interesting to see whether slow-dispersing organisms in places like Ramsar, Mazandaran evolve a shorter lifespan, and if so what genes are involved. Wnt (talk) 11:42, 9 October 2011 (UTC)

Hearing loss

Is there a term for someone who seems to generally have good hearing, yet is unable to distinguish the voice of the person they are conversing with from other background noises, as in a crowded restaurant ? StuRat (talk) 18:03, 8 October 2011 (UTC)

Cocktail party effect describes the ability to filter out irrelevant background noise, but the article doesn't seem to have a name for when this fails. AndrewWTaylor (talk) 18:14, 8 October 2011 (UTC)

Auditory processing disorder may be what you are looking for 86.189.14.58 (talk) 19:34, 8 October 2011 (UTC)

That term seems to be a catch-all for many different conditions, of which, King–Kopetzky syndrome seems to be the one I mean. StuRat (talk) 19:42, 8 October 2011 (UTC)

Reading that article (and I must admit I had forgotten all about that condition) it seems K-K syndrome is also an umbrella term for several possible pathologies. There is so much about APD and auditory neuropathy that we just don't understand 86.189.14.58 (talk) 19:56, 8 October 2011 (UTC)

Remediation using directional microphone ?

This is a follow-up Q. I've seen ads on TV for a directional hearing aid specifically designed to isolate the speaker from background noises. Are there any studies measuring the effectiveness of this strategy ? StuRat (talk) 19:46, 8 October 2011 (UTC)

Indeed there are. The hearing aid industry is a very lucrative and competitive market, and the effectiveness of a manufacturer's directional microphone is a big selling point. Directional microphones do significantly improve the signal to noise ratio. I found an article on it from Audiology Online; I don't know how to link to it but googling "polar plot hearing aid" returned in on the first page 86.189.14.58 (talk) 20:03, 8 October 2011 (UTC)

This is a medical question which should be directed to a professional who can perform both hearing and physical examinations because the decision tree is likely to require essentially all the information in a hearing test and physical. The details of the physical would be pertinent if a cochlear implant is indicated, and they are increasingly performing above all other options for a wide variety of hearing issues. Please see the heck also http://io9.com/5846275/ Dualus (talk) 03:46, 9 October 2011 (UTC)

Can Mount Teide really be seen from the African coast?

Canary Islands in pre-colonial times contains the (unsourced) claim that it is possible to see the peak of Mount Teide from the African coast (no specific location is named, though) – presumably from ground level. I find that claim quite implausible. I even tried Google Earth and it does not support the claim at all – Fuerteventura and perhaps Lanzarote or Gran Canaria I could believe, but Teneriffa is too far away from the coast. Anyone being able to provide calculations or real-life experiences, perhaps? --Florian Blaschke (talk) 21:17, 8 October 2011 (UTC)

I calculate that the line of sight from sea level to the peak falls below the horizon at a distance of less than 150 miles, and it's almost 200 miles from the peak to the nearest point on the coast -- also the coast is pretty much flat in that vicinity. So I don't see how it would be possible. Looie496 (talk) 22:40, 8 October 2011 (UTC)

Could mirage be an explanation? 86.189.14.58 (talk) 23:02, 8 October 2011 (UTC)

The article horizon gives several formulae to calculate the distance to the horizon. The distance to the horizon from the top of Mount Teide at 3718 meters should be between 218 and 235 kilometers, if my calculations are right. Let's say it is 235 kilometers for further calculations. If, from a point on the African coast you would see a horizon that is closer to Mount Teide than 235 km when looking in the right direction, you should also be able to see the top of Mount Teide. The distance from Tenerife to the closest locations in Africa is approximately 350 km 320 km (measured using google earth). So if you are at an altitude where your distance to the horizon is 320 - 235 kilometers = 85 km, and are looking towards mount Teide, you should be able to see its top. That would require that you are standing on a hill that is 485 meters above sea level, by the same calculations. The highest point in West Sahara is 805 meters, but appears to be quite a bit from the ocean, increasing the distance considerably. So I find the claim somewhat dubious not necessarily impossible. Given special atmospheric conditions, it might be possible. edit: The horizon article mentions that atmospheric conditions tend to increase the distance to the horizon compared to a straightforward geometric calculation, but I was using a formula that was supposed to take this into account. --NorwegianBlue ^talk 23:05, 8 October 2011 (UTC)

The typical conditons near the coast may lead to favorable atmospherical conditions. Inland it is very warm while on sea it is a lot cooler. The warm air from the land rises above the colder air from the sea, creating an inversion. That's why it's bone dry so close to the ocean there. This inversion layer can reflect light back to the ground. Count Iblis (talk) 15:22, 9 October 2011 (UTC)

This book says African can reputedly be seen from the summit of Teide on a clear day. μηδείς (talk) 19:15, 9 October 2011 (UTC)

I'm not seeing the assertion in that linked entry, μηδείς, although neither do I have any reason to contradict it. With respect to seeing Tiede from the African coast, I have read that characteristic clouds often form above islands, particularly mountainous ones, and this is sufficiently common for it to have been used in antiquity to aid navigation in various parts of the world (it's briefly mentioned in Polynesian navigation), so anyone familiar with such clouds (one of whose properties being that they reflect the colour of the vegetation, sand or rock beneathe them distinguishably from clouds above bare ocean) would be able to deduce that an island was present even if the mountain itself was not quite visible. {The poster formerly known as 87.81.230.195} 90.193.78.18 (talk) 23:33, 9 October 2011 (UTC)

The book μηδείς apparently means is the second book appearing in the list, "Astronomy now: Volume 7". The snippet view says: Tenerife is dominated by the majestic snowbound peak of Mount Teide and at 12177 ft it is classified as the highest peak in ... From the summit all the remaining islands and the African coast are reputed to be visible on a clear day.

Fascinating. Thanks, everyone, for your calculations and explanations. I feel much enlightened. --Florian Blaschke (talk) 20:14, 10 October 2011 (UTC)

Egg ID (snake?)

Hello, looking for help on identifying this egg. My cousin thinks it's from a snake. It is large, ~3 in long, pale translucent green & feels rubbery. Found in the past few weeks in NE Ohio. Picture found here [14]. Not sure how many are in nest, but can find out if that will help. Thanks! SemanticMantis (talk) 22:15, 8 October 2011 (UTC)

Actually, it looks like a "witch's egg", which isn't an egg at all, but the immature underground form of a mushroom called the stinkhorn. Check that article out and type "witch's egg" into google images for more pictures. Dominus Vobisdu (talk) 22:55, 8 October 2011 (UTC)

Thanks, but we're pretty sure they are eggs (I have not personally investigated). A fungus would change appearance over a 2 week period, and these have remained more or less the same. SemanticMantis (talk) 23:00, 8 October 2011 (UTC)

Maybe place the egg under a chicken and see what develops. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:18, 9 October 2011 (UTC)

AFAIK, no reptile lays that kind of smooth, shiny, translucent bright green eggs. :/ Reptile eggs are usually chalky white to a dirty kind of yellow and leathery, not rubbery. Unless these have a bad case of DDT poisoning or something. Moreover, at three inches, that's huge. Can you roll it around to see if it's attached to the ground? Are you sure there are others near it? Are they all similarly round and large? It could be some kind of fruit or industrial waste. Or it could be aliens! :D -- Obsidi♠n Soul 11:02, 9 October 2011 (UTC)

If it's translucent, i.e. light shines through it, put it over a strong light source and see what is inside. Maybe take a picture and upload it if you can? --TammyMoet (talk) 10:46, 9 October 2011 (UTC)

"choked with a board"

how exactly would someone be killed by being "choked with a board"? I am aware it is a serious murder but don't really understand how it is done! Harley Spleet (talk) 23:06, 8 October 2011 (UTC)

Are you sure it's not "choked on board"? Wikiweek (talk) 23:38, 8 October 2011 (UTC)

Hmm.. I'm begining to regret trying to help with this one. I assume this refers to John Wayne Gacy who would abduct youths and boys; "Once back at Gacy's house, the victims would be handcuffed or otherwise bound, then choked with a rope or a board as they were sexually assaulted." This article says that Gacy confessed that he would "kill them by pulling a rope or board against their throats." Don't try this at home. Alansplodge (talk) 00:04, 9 October 2011 (UTC)

October 9

Mucokinetics

The article on Mucokinetics says these drugs make mucus much easier for a patient to cough up (or I assume sneeze out). But what is done for patients who, due to injury or disease, are unable to cough up or sneeze ut mucus? Are there drugs that dissolve it so much they can easily swallow it?--178.167.189.6 (talk) 00:31, 9 October 2011 (UTC)

Normally, when you cough it up you do swallow it. You can't swallow it until you've got it out of your throat. The trachea (breathing tube) and oesophagus (eating tube) are only connected at the mouth. There are special massage techniques that can be used to move mucus up to the mouth. They are often used for people with cystic fibrosis. --Tango (talk) 01:17, 9 October 2011 (UTC)

Agree with Tango; I just want to add a link to mucociliary clearance, which I was taught to call the "mucociliary escalator". We normally swallow quite a bit of mucus, one of the reasons public spitting seems so unnecessary and selfish (no benefit, and some risk to others). -- Scray (talk) 03:20, 9 October 2011 (UTC)

Immune system strength

Is there any way or scale to measure immune system's strength (overall or against specific infections)? --178.182.107.62 (talk) 11:31, 9 October 2011 (UTC)

I am in no way an expert old chap, but I imagine there are two key criteria - one is the count of antibodies that are specific to the infective agent in question and second is the overall white blood cell count. The more antibodies the quicker they will latch on the infective agent and the more white blood cells the faster the agent will be attacked and destroyed. Quintessential British Gentleman (talk) 13:45, 9 October 2011 (UTC)

To measure reactivity against a specific antigen, the level of antibody activity is the most oftenly used parameter. If the response is primarily of the IgM isotype, it indicates that the infection may have taken place recently, if it is predominantly of the IgG isotype, it indicates that the response may be caused by an infection in the past. Some tests also measure cellular responses, such as the Mantoux test, which depends on T cell activity.

There is no simple way of presenting someone's "immune system's strength" as a number or anything like that. The immune system is complex, many things can go wrong, and it is when a patient has an abnormal frequency of infections, and especially of infections that are rarely seen in healthy people, that doctors will suspect that the individual has an immune deficiency. An incomple list of things to check:

• Immunoglobulin (IgG, IgA, IgM and IgE) levels. Some doctors would also like to test the IgG subtypes at this point (IgG1, IgG2, IgG3, IgG4).
• A blood count, to see whether the leves of lymphocytes, monocytes and granulocytes are normal.
• A test of specific lymphocyte subsets (CD3, CD19, CD4, CD8, various combinations with other markers).
• Measurement of complement levels and functional activity in both the classical, alternative, and Lectin complement activation pathway.
• Depending on symptoms, various functional defects might be suspected. In chronic granulomatous disease there is a functional defect in the granulocytes, which can be measured.
• Some lab's measure proliferative responses (mainly T cells) to antigens and mitogens, other's don't, and it is not universally agreed that this is a useful parameter.

I'm sure I've left something out. Check out the article Primary immunodeficiency, and its "diagnosis" section. --NorwegianBlue ^talk 21:31, 9 October 2011 (UTC)

Weight-guessing

This is supposedly a skill displayed at county fairs and so on, though I've never actually witnessed it. How does one go about guessing a person's weight based solely on visual clues? I think it would be an interesting skill to have. 198.228.193.194 (talk) 14:44, 9 October 2011 (UTC)

I don't see much use, unless at places like county fairs. For describing people, categories like round figure, skinny, etc would be more than enough. Quest09 (talk) 15:19, 9 October 2011 (UTC)

I've not heard of guessing the weight of people at fairs - usually it's guessing the weight of cake. If you wanted to guess the weight of a person, you could do pretty well by guessing their height and then making a rough estimate of their build and comparing those against memorised numbers (perhaps based on Body Mass Index - if you can get a reasonably close guess of someone's height and BMI, you can calculate their weight). One thing to be careful of is that there are two ways to be heavy for your height - lots of fat or lots of muscle (or, I suppose, lots of both, but that's rare). You need to allow for both. --Tango (talk) 15:24, 9 October 2011 (UTC)

"Weight guessers" basically give out cheap prizes if they are wrong <g> The idea is that they actually try to be accurate on men, but always guess low on women -- who rarely are unhappy. They are entertainers, not more. That said, they can be within 10% on men just by looking at height and face ... Cheers. Collect (talk) 15:54, 9 October 2011 (UTC)

Weight guessing seems like a very fundamental capability which would be of great importance for some animals. I bet if you ran fMRI you'd find a special part of the brain assigned to do it, which I bet is much enlarged in raptors that snatch up their prey in flight. But it's hard to search for this in the literature... Wnt (talk) 16:45, 9 October 2011 (UTC)

It's clearly important, but I don't think they are all that accurate at it. One of the standard pieces of advice if you are threatened by a large predator is to try to make yourself look bigger. If animals were good at estimating weight, that wouldn't work. Looie496 (talk) 18:36, 9 October 2011 (UTC)

Hmmm, but is the animal estimating weight there? I think an animal that projects power further into the environment - for example, a porcupine or a boxer with a long reach - is more dangerous despite equal mass. Wnt (talk) 01:30, 10 October 2011 (UTC)

Even if there were an evolutionary advantage, you can be sure that evolution wasn't using pounds (or kilograms) when it was invented. A weight guessing person would still need to train themselves to express their judgments in the units we use. Dragons flight (talk) 18:49, 9 October 2011 (UTC)

Of course I'm just speculating, but the amygdala contributes to the verbal or written expression of emotions in humans, not (in a narrow sense) an option in other animals. Wnt (talk) 01:30, 10 October 2011 (UTC)

Here's a brief NPR segment on weight guessers, It doesn't really go into specifics, but it does touch on the idea that the prizes are worth less than the price to play the game. [15]

APL (talk) 04:53, 10 October 2011 (UTC)

Integrity of the Cryogenically Preserved Brain

When a rich person has one of the various companies in existence nowadays cryogenically preserve their brain, is there any evidence that the currently most-widely-used procedures succeed at maintaining the brain's network of synapses and their associated activation thresholds? Peter Michner (talk) 17:14, 9 October 2011 (UTC)

Has anything subject to that type of "preservation" ever been reanimated? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:24, 9 October 2011 (UTC)

Yeah, frogs thaw out all the time naturally, but apparently large mammalian cells such as some connective tissue, spindle neurons and ova are subject to ice damage. Thawed mice remember how to run mazes, but the females are sterile and they all have substantially reduced lifespans. 64.134.157.164 (talk) 19:59, 9 October 2011 (UTC)

I don't see how there could be evidence, because currently we can't even come close to reactivating a brain that has been frozen -- far too much tissue damage. But in principle, nearly all the information ought still to be in there -- synapses are pretty large structures in molecular terms, and the receptor molecules that determine synapse activation thrshold ought to survive freezing pretty well. Looie496 (talk) 18:32, 9 October 2011 (UTC)

I suspect we can't even come close to reactivating the brain of a dead mammal in any case, whether or not it's been frozen (pace Mary Shelley). Tonywalton ^Talk 22:30, 9 October 2011 (UTC)

That would depend on your definition of death. If we use the old "heart has stopped" def, then plenty of people have been revived from death, brains included. StuRat (talk) 01:59, 10 October 2011 (UTC)

The question "does the technology to reactivate the brain currently exist?" is a different question than "is the information that is contained in the synapse network and the activation energy levels in each synapse preserved?" I don't pretend to think that the two factors alone in the latter question (which was the only question I was asking) are sufficient for retaining the information necessary to preserve a human mind, but I'd bet that those two things are necessary if it is at all possible. Peter Michner (talk) 22:58, 9 October 2011 (UTC)

I'm not sure that cyryogenically preserved brains are any better than chemically preserved brains, as far as retaining the information in the brain. Has anyone ever compared the two ? I'd think that the risk of power failures (perhaps from the bankrupt company no longer paying the bill) over centuries would also be a major concern for cryogenically preserved brains. StuRat (talk) 02:03, 10 October 2011 (UTC)

arthritis

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

→Στc. 19:33, 9 October 2011 (UTC)

Although, I don't think a healthcare professional would advice someone living in Florida to climb the Appalachian Mountains to get rid of his arthritis :) .Count Iblis (talk) 21:05, 9 October 2011 (UTC)

coin drop

I love this illustration so much.

if, say, we can dig a hole from north pole up to south pole, and drop a coin (or anything you would like to drop) in that hole, ignoring whats in earth's core, what will happen to the coin? — Preceding unsigned comment added by 203.112.82.128 (talk) 22:13, 9 October 2011 (UTC)

If you also ignore air drag, the coin will accelerate towards the center of the earth, overshoot and decelerate all the way to the oposite pole where it will poke it head (or tail) up and start falling again back to the original position. If you further assume a uniform density earth, the coin will be observed to follow a simple harmonic motion. --Dauto (talk) 22:29, 9 October 2011 (UTC)

(Edit conflict) If conditions were absolutely perfect, also assume there is a vacuum in the hole, the coin should accelerate to the centre of the earth. Whereupon reach the centre, it should undergo dampened occilation, before coming to a rest levitating at the centre of mass. Although conditions aren't perfect, which is to say that there is a variety of possible outcomes of how the experiment would fail. Like the centre of mass for the Earth does not remain in the same position over time, due to random fluctuations in density. Plasmic Physics (talk) 22:32, 9 October 2011 (UTC)

If you are assuming a vacuum, what causes the dampening? If the hole is full of air, then the coin will quickly reach terminal velocity, which for a coin is about 65 mph (according to Mythbusters). As it gets closer to the centre of the Earth, gravity will reduce (see shell theorem) and the density of the air will increase. That means the terminal velocity will reduce until it reaches zero at the centre. I'm not sure if the coin would slow down fast enough to avoid overshooting, but I wouldn't expect it to overshoot by much. --Tango (talk) 23:36, 9 October 2011 (UTC)

Dampening is caused is caused by a loss of momentum. Kinetic energy of the coin is converted to gravitational potential energy and as it overshoots the centre of mass. It is the same reason why a rubber ball bounces lower on each rebound. Plasmic Physics (talk) 00:02, 10 October 2011 (UTC)

Dampening occurs with your rubber ball due to inelastic collisions. Without losses to air resistance (or eddy currents) the gravity train acts more like a (magical) perfectly elastic superball which would keep on bouncing for ever. -- 49.230.105.185 (talk) 00:30, 10 October 2011 (UTC)

Other factors might cause dampening to occur: electromagnetically-induced currents in the surrounding material, transfer of gravitational momentum, vacuum energy pressures, etc. ~AH1 ^(discuss!) 01:08, 10 October 2011 (UTC)

Why would the air density increase? Tonywalton ^Talk 00:03, 10 October 2011 (UTC)

The immense gravity at that depth would squeeze any air to a very high pressure, and additionally heat it to above the boiling point of water, unless a near-vacuum is created. ~AH1 ^(discuss!) 01:08, 10 October 2011 (UTC)

Immense pressures, yes, but note that the greatest gravity occurs at the surface. -- 49.230.105.185 (talk) 01:38, 10 October 2011 (UTC)

(E.C.) Air pressure varies with elevation. The radius of the earth is significantly greater than the height of the substantial atmosphere, so it would seem that the air deep in the tunnel should liquify, but the critical point of nitrogen is 3.3978 MPa or only 34 bar (with T_cr = 126.19 K). With atmospheric pressure increasing by 0.5 bar in the last 6 km above sea level, 34 bar would be reached well before a depth of 34 bar * 0.5 bar / 6 km = 408 km (with the effect of the ever increasing heavier layers of air overhead greatly overwhelming the slight decrease in gravitation acceleration). From there on down the nitrogen would be a supercritical fluid. -- 49.230.105.185 (talk) 01:31, 10 October 2011 (UTC)

You might find the Gravity train article interesting. Tonywalton ^Talk 22:34, 9 October 2011 (UTC)

That article is missing an important piece of information: the maximum gravitational acceleration (it is different when the accelerated object is inside another object of mass that is exerting the gravity) assuming an infinite terminal velocity. For humans, determine whether an average body can survive the acceleration. ~AH1 ^(discuss!) 01:08, 10 October 2011 (UTC)

I'm not sure what you are implying here, AH1, but per the shell theorem (and square / cube considerations), the maximum gravitational acceleration will occur at the surface, and will decrease linearly to zero at the center. -- 49.230.105.185 (talk) 04:49, 10 October 2011 (UTC)

what would happen if i threw my mother-in-law in the hole? =D — Preceding unsigned comment added by 203.112.82.1 (talk) 23:51, 9 October 2011 (UTC)

You are describing a "gravity train" scenario. However, heat and atmospheric pressure/liquidity considerations are important. ~AH1 ^(discuss!) 01:08, 10 October 2011 (UTC)

In case there is air in that tunnel, the immense heat and pressures would likely slow down the coin as it spun around its own axis in the air, and very quickly vaporize. If vacuum engineering and other considerations fail to anticipate the launched object (or person!) arriving short of the surface target, retrieving the launchee may be a problem.

A question - in the case of a magnetically-levitated train, would any effects occur upon interaction with the Earth's polar magnet, and even considering a non-magnetic vacuum train: how does one ensure that the projectile does not hit the side of the tube, whatever material it is constructed of, and instantly vaporize? ~AH1 ^(discuss!) 01:08, 10 October 2011 (UTC)

Dampening is occuring to momentum being converted to waste heat. Work is done on the coin to draw it towards the centre of mass. As we all know, no thermodynamic process is perfect. Plasmic Physics (talk) 01:43, 10 October 2011 (UTC)

The whole atmosphere will be sucked into that tunnel. The pressure as a function of height is given by:

$P(x)=P(0)\exp \left(-{\frac {mMG}{2kTR^{3}}}x^{2}\right)$

where M is the mass of the Earth, m the average mass of an air molecule and R is the radius of the Earth. This is assuming constant temperature and validity of the ideal gas law. It follows from this that the total mass of air in the tunnel is given by:

$M_{t}={\sqrt {\frac {2\pi mR^{3}}{MGkT}}}\exp \left({\frac {mMG}{2kTR}}\right)P_{\text{at}}A_{t}$

where $P_{\text{at}}$ is the atmospheric pressure at the surface and $A_{t}$ is the cross sectional area of the tunnel. The total mass of the atmosphere times g equals the atmospheric pressure times 4 pi R^2. Before we build the tunnel, the atmospheric pressure is 1 bar, and that gives a total mass of about

$M_{\text{at}}=5.28*10^{18}{\text{ kg}}$

Then after the tunnel is completed, air will flow into the tunnel until the above formula for $M_{t}$ becomes consistent with an atmospheric pressure of $(M_{\text{at}}-M_{t})g/(4\pi R^{2})$ For a cross section of 1 m^2, this leads to an atmospheric pressure of about 10^(-151) bar. Count Iblis (talk) 04:12, 10 October 2011 (UTC)

Neither of your assumptions (isothermal and ideal gas law) seem reasonable to me. Dauto (talk) 04:39, 10 October 2011 (UTC)

They're not wrong by 150 orders of magnitude, though. You need to take into account what happens to all the matter you remove in order to create the hole, though - that will have the same volume as the air that replaces it. If you place it all on the surface, it will expand now it isn't under pressure and will take up quite a lot of space. I'm not quite sure what that would do to the atmospheric pressure, though. --Tango (talk) 11:37, 10 October 2011 (UTC)

Actually it is, once the pressure reaches the point that gas liquifies you aren't going to increase the density more than about 10 times beyond that. At that density less than 1 millionth of the atmosphere will actually fit in your 1 m^2 tunnel. Dragons flight (talk) 18:46, 10 October 2011 (UTC)

In any case, the coin should melt or even vaporize since the earth's core is thousands of degrees. Googlemeister (talk) 13:18, 10 October 2011 (UTC)

Well obviously the evacuated tunnel of unobtanium is cryogenically cooled. Dragons flight (talk) 18:35, 10 October 2011 (UTC)

October 10

Lightning and auroras

Hi. I'd like to know more about the interaction of upper-atmospheric lightning and tropospheric-origin electrical discharges, including elves, sprites, jets, gamma-ray flashes and antimatter generation events, with the lower-ionospheric geomagnetic aurora activity, which can extend down to 35 km altitude. In particular, are there any effects of interaction, which could be rare since strong thunderstorms and auroras are differentiated by latitude, but do effects occur that either change the atmospheric composition or channel energy from the Earth's geomagnetic field and solar wind, including its ionizing radiation and magnetic anomalies, down to the Earth's surface through lightning discharge or other phenomena, including plasma radiation? Please also link to any relevant scientific journal articles, and in particular the information found in Schumann resonances may be relevant. Thanks. ~AH1 ^(discuss!) 00:46, 10 October 2011 (UTC)

Please correct me if I've missed your point, but are you asking for scientific information about how elves and sprites effect the weather and the aurora borealis? Beeblebrox (talk) 20:18, 10 October 2011 (UTC) Never mind, it appears these terms are actually used by science to describe u-a lightning events. How silly of them. Beeblebrox (talk) 20:20, 10 October 2011 (UTC)

Modified HIV-based cancer vaccine

Can someone please explain in laymans' terms how http://www.msnbc.msn.com/id/44090512/ns/health-cancer/t/new-leukemia-treatment-exceeds-wildest-expectations/ works? Why do the modified white blood cells start killing cancer? Are they trained to produce 3-BrPA when they taste cancer cells? 208.54.38.211 (talk) 02:57, 10 October 2011 (UTC)

White blood cells are a key component of the immune system, which recognize foreign cells and begin the process of their destruction. So when you have a cold or other infection due to some bacteria or other invader, the WBCs attack. One problem with cancer is that cancer is in many ways our own cells, so our own immune system does not recognize it as a foreign threat--if our immune system turns against our own cells, we are in serious trouble (see Autoimmune disease)! So a scientific advance is to train some WBCs (in particular, T cells) to recognize the cancer cells as foreign but distinguish them from non-cancerous cells.

In addition, WBCs only live for a few days. That's not a problem usually, because our bone marrow constantly produces new ones (in part adapting/responding to novel foreign invaders that may be detected). But special WBCs produced in a lab would not by regenerated because the marrow itself (in the body) was not altered to produce more of them--the body only contains as many as were injected for as long as that batch lives. Another scientific advance here was to make the anti-cancer WBCs able to replicate after being injected. DMacks (talk) 09:21, 10 October 2011 (UTC)

Actually, they don't kill cancer - they kill B cells of any kind. Chronic hypogammaglobulinemia is a side effect. For people within weeks of death, this is a tremendous advance, but it is a drastic treatment. Wnt (talk) 13:16, 10 October 2011 (UTC)

By B cells do you mean B-lymphocytes? I like the idea of merely training the white blood cells to produce anti-cancer agents around cancer cells instead of treating them as foreign (although if that could happen too, all the better.) Ad astra. 69.171.160.57 (talk) 15:53, 10 October 2011 (UTC)

Human Sensitivity to IR

Generally, I think, human beings are not sensitive to Infrared rays. Is it possible that some disease or deformation or DNA defect can make a human being sensitive to infrared rays.  Jon Ascton  (talk) 03:51, 10 October 2011 (UTC)

The receptivity of the human eye is actually a bell curve (three of them, actually), and a very tiny portion of the thin part of the bell curve is actually in the spectrum we call "infrared". this person found that by wearing goggles that completely blocked out the visible light, and then went out into bright sunlight, he could see a little bit of infrared. APL (talk) 04:18, 10 October 2011 (UTC)

That would have been near-IR, though. Not the kind of IR used in thermal-imaging. If the OP wants that kind of IR, then it's pretty much impossible - you would have too much interference from the IR the eye itself is emitting (although, I suppose there's no fundamental reason the eye couldn't be cooled to below usual skin temperature - it would require some pretty major evolutionary changes, though). Radio telescopes have the same problem - they need to be cryogenically cooled in order to avoid emitting too much radition in the part of the radio spectrum that they are trying to observe. --Tango (talk) 11:41, 10 October 2011 (UTC)

The only animals that can "see" in the infrared range, as far as I know, are certain types of snakes, and they use a special sensory system called a pit organ to do it, not their eyes. There are a variety of biophysical issues that make it nearly impossible for an eye-like mechanism to function well in that frequency range. Looie496 (talk) 15:36, 10 October 2011 (UTC)

I'm not sure the OP meant "seeing IR" when he said "being sensitive to IR." He could be thinking about something like light allergy, but against heat. Quest09 (talk) 15:46, 10 October 2011 (UTC)

Hold a warm object close to your lips. Can you feel the heat (infra red radiation)?--92.28.77.67 (talk) 16:04, 10 October 2011 (UTC)

Yes, but feeling is not "being sensitive." "Being sensitive" for me is being harmed/annoyed when in contact. Quest09 (talk) 16:55, 10 October 2011 (UTC)

The OP didn't say 'being sensitive', they said 'a human (being) sensitive to infrared rays'. Nil Einne (talk) 18:27, 10 October 2011 (UTC)

Thanks all. To be precise : when we press a button on a TV's remote control it emits IR from it's IR LED at front. That's invisible to human eye i.e. both the source of IR (LED) or any surface reflecting it. Is there any special biological defect that can make a man see it ?  Jon Ascton  (talk) 00:51, 11 October 2011 (UTC)

No (and, if they could, I wouldn't call that a "defect"). StuRat (talk) 01:36, 11 October 2011 (UTC)

How a Latino could not be a Caucasien?

Hi clever people, please excuse my poor English, I'm French. Recently in the TV-serie "BONES" they find 2 corpses and the gifted Dr Brennan says "One is a Latino the other one is a Caucasian". I thought that Caucasian in American means something as White or European to indicate the difference with "Negro" or "Asian" and so on. And so for me Spaniards are obviously white, european Caucasians.

Question : What is this thing that I don't understand? Latinos have Spaniards ancestors, why not including them among the Caucasians? Thanks a lot for reading. Joël Deshaies-Rheims-France---85.170.172.37 (talk) 10:14, 10 October 2011 (UTC)

There is certainly some confusion regarding the term Latino: sometime it depicts a culture (Latin-American) and others it depicts a phenotype (native Indians of Latin-American and its descendents). Quest09 (talk) 10:29, 10 October 2011 (UTC)

Africans, brought to the Americas, and currently from Central/South America are referred to as Latino. They are not of Spaniard/European descent. To complicate it further, whites, from the same area, are referred to as Latino. The native people, from the same area, are referred to as Latino. Pretty much, anyone from Central/South America is considered Latino. In U.S. Government forms, Latino/Not Latino is asked separately from Race. So, you can be White Latino, Black Latino, or even Asian Latino. -- kainaw™ 12:37, 10 October 2011 (UTC)

Race is a peculiar concept. I've read that the term "Hispanic" was coined by the United States Office of Management and Budget in 1978, [16] with "Latino" becoming popular shortly afterward - before then, curiously enough, according to the article it was used by people of certain politics to express affinity between Mexicans and French who were involved there. How "Latino" excludes Latium, I don't know; Italians are right out. In practice I think the term largely means people with a family history of speaking Spanish. What's funny is that white x black = black, and anything x "Hispanic" = "Hispanic" - unsurprisingly there are continually "news reports" that Hispanics are the "fastest growing minority" taking over the country. It is amazing how much weight can be placed on imagination and semantics. Wnt (talk) 13:30, 10 October 2011 (UTC)

I'm from Brazil and consider my self Latino, but not Hispanic. I've met some Italians that felt the same way. Dauto (talk) 14:46, 10 October 2011 (UTC)

Latino means actually from 'Latin(o)-America' in most cases. That would exclude people like Italians and such. If it means from from the Latium, it would include Italians. The word is simply ambiguous. Quest09 (talk) 15:51, 10 October 2011 (UTC)

In a context of forensic anthropology, "race" is usually just a way to say, "here's what an average person in this culture would think about this person." That's really all. So if I were to find a skeleton with certain facial characteristics, I'd be able to say, "oh, this looks more or less like someone who has a lot of their ancestry derived from people who lived on this continent." A shorthand of which is to say, "black" or "white" or "Asian" or "Latino" or what have you. From a strictly taxonomical point of view, this is a very problematic statement. But from the perspective of, "can we match this skeleton up to a number of possible missing people?", it's very useful. This is, anyway, what I gleaned from talking with a number of forensic anthropologists awhile back. So if I heard a forensic anthropologist in the United States say "this skull looks Latino," I'd assume, "this person looks like they have ancestry that was from South America, which is probably some form of European-Indian mix." If they said they were just "Caucasian," I'd assume they meant, broadly, "a very European looking skull." The skull would tell you exactly zero about what languages they spoke, what holidays they practiced, etc., obviously. I've of course no knowledge of what was necessarily meant by a fictional television show. --Mr.98 (talk) 16:53, 10 October 2011 (UTC)

hydrogen peroxide

Does the regular 3% peroxide kill fungal spores such as ringworm spores? — Preceding unsigned comment added by 66.209.177.15 (talk) 10:18, 10 October 2011 (UTC)

Lots of studies - but they are of using high concentrations of H2O2 at elevated temperatures. Anecdotal for the 3% stuff. Collect (talk) 13:05, 10 October 2011 (UTC)

Timing of natural death

What makes a species have a typical life-span? I know that telomeres limits the number of years that humans can live, but are they present in any living creature? And are there other mechanisms to guarantee that a living being will die? Quest09 (talk) 10:24, 10 October 2011 (UTC)

We have an article on ageing in which some theories about the ageing process are explained. For the biology aspect of the question: Telomere actally talks about animal telomeres at some point. Generally speaking: If it has chromosomes (but not a Nucleoid) then it probably has telomeres. --Abracus (talk) 11:15, 10 October 2011 (UTC)

The relationship of the Hayflick limit to aging and death is still not very clear btw. It's also only part of the different "wear and tear" and "programmed death" theories and combinations thereof on the causes of aging (in this case DNA damage).

And yes, excluding gradual senescence and death by predation, diseases, etc. in organisms with negligible senescence, there are other mechanisms that ensure death. Semelparous organisms, for example, like octopuses and most salmon, die because they become completely consumed in ensuring reproductive success in a single event. The rapid senescence and death that follows is hormonal, the body actually tells itself to stop living (phenoptosis). In some species the body of the mother becomes the first meal of the offspring. In Stegodyphus lineatus, for example, the mother actually willingly lets herself be killed for food by her spiderlings. Also see Parent–offspring conflict.

Others die due to mechanical reasons. Weddell seals will eventually die when they lose their teeth, because they can't anymore maintain the breathing holes in Antarctic ice needed for access to water for food, and the surface for air and rest. Grazing mammals will also assuredly die when their teeth are eventually all worn out. Mayflies (which are also semelparous) will die because they do not have the means to feed themselves as adults (aphagy), etc.

In addition to Abracus' link, also see Evolution of ageing and this excellent site: http://www.senescence.info/ .-- Obsidi♠n Soul 13:47, 10 October 2011 (UTC)

Animal sadness

Apart from humans do other animals experience sadness. --86.45.146.152 (talk) 14:49, 10 October 2011 (UTC)

Yes, Jaak Panksepp has done a great deal of research on this topic. In animals sadness is most commonly referred to as separation distress (we ought to have an article about it) -- Panksepp calls it PANIC but that is widely felt to be a bad choice of terminology. There is also an animal emotion that you might call "despair", known as learned helplessness -- animals that experience bad things repeatedly without any way of controlling them eventually stop struggling and become apathetic. Learned helplessness is thought by many psychologists to be the animal version of human depression. There is a lot more to say about this topic -- Panksepp's textbook Affective Neuroscience covers it in depth. Looie496 (talk) 15:22, 10 October 2011 (UTC)

We do, its on separation anxiety in dogs. CS Miller (talk) 19:55, 10 October 2011 (UTC)

See Animal emotion for an overview. Richard Avery (talk) 15:27, 10 October 2011 (UTC)

(e/c) Also see Animal psychopathology#Depression and Stereotypy#In animals which also discuss anhedonia in animals subjected to stressful conditions, the equivalent of human despair.-- Obsidi♠n Soul 15:29, 10 October 2011 (UTC)

How do bats avoid bees and wasps?

Do bats eat bees? If not, how do they avoid they avoid them at night? Because bats come out at sunset and bees return to the hive at sunset, do bats perform culling of bee colonies? 69.171.160.57 (talk) 16:00, 10 October 2011 (UTC)

Bees return to the hive well before bats go out feeding. There are bats that are up during the day, but they eat fruit. Unless the bee is huge and looks like a big lemon, the daytime bats won't have any interest in it. -- kainaw™ 16:18, 10 October 2011 (UTC)

They both compete for nectar. I can't imagine an animal with the intelligence of a mouse wouldn't be able to figure out how to bite the head off a bee without getting stung, and then steal its nectar. 69.171.160.57 (talk) 16:45, 10 October 2011 (UTC)

That seems like an awful lot of work for not very much nectar. Anyway, this guy (best source of this I could find) says it's unlikely, mostly for the reasons given above. --Mr.98 (talk) 16:57, 10 October 2011 (UTC)

And no, they do not compete for nectar. There's a wide range of specifically nocturnal blooming flowers for nectarivorous bats (which are most emphatically not insectivorous, though they may be frugivorous esp. in Old World megabats) and moths alike. Plants that actually rely on them, rather than hymenopterans, for pollination.-- Obsidi♠n Soul 17:14, 10 October 2011 (UTC)

Oops. Strike that. It seems that nectar-feeding phyllostomid microbats do eat insects on the side. -- Obsidi♠n Soul 17:23, 10 October 2011 (UTC)

Hm... and megabats as well. Interesting. Though theirs is more opportunistic as they do not possess echolocation (with the exception of Rousettus aegyptiacus) and thus can't snatch insects from midair like microbats do. When they do eat insects though, it's for the protein, not for the nectar.

Also I'm wondering why a lot of sources say megabats are "all diurnal". The vast majority aren't. Out here flying foxes (which are unmistakably huge bats with characteristic slow wingbeats) do not come out until twilight which makes them crepuscular.-- Obsidi♠n Soul 17:46, 10 October 2011 (UTC)

Setting aside the relative rarity of nocturnal bees and wasps that might sting a bat, there is evidence that some bats are able to distinguish between different insects based on their wing beat frequency. Perhaps their target selection is good enough to avoid certain insects. See the theory and the practice. Impressive as that is, oddly on several occasions bats have crashed into me as I've walked through my garden at night. It's quite a complicated space and they have to patrol using complicated looping flight paths but it's almost as if they don't bother to update the large, slow moving objects in their model of a space very often. I guess tree trunks rarely move. Sean.hoyland - talk 18:09, 10 October 2011 (UTC)

I found a paper with percentages of insects found in bat diets. It seems they do eat bees and wasps. There's also an anecdote here of a small bat that attempted to catch a tarantula hawk (genus Pepsis, large diurnal wasps about ~2in), and the squabble that ensued.-- Obsidi♠n Soul 19:34, 10 October 2011 (UTC)

About satellite communication

What is the amplifier used in satellite communication. — Preceding unsigned comment added by 117.231.103.93 (talk) 16:19, 10 October 2011 (UTC)

An operational amplifier. 67.6.175.132 (talk) 23:34, 10 October 2011 (UTC)

Push-ups and the "funny bone" nerve

So I'm curious, what action could cause the funny bone nerve to get pinched while one is doing push-ups? I notice sometimes that when I am doing push-ups, I feel a slight pinching sensation on the nerve (or sometimes a bit closer to the area above the left side of the end my forearm's bone (I forget its name)). So what is the action during a push-up that would cause this? Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Tishrei 5772 16:41, 10 October 2011 (UTC)

Please see Ulnar nerve entrapment. 67.6.175.132 (talk) 23:37, 10 October 2011 (UTC)

Oy vey, this will be fun to tell my doctor about.... Sir William Matthew Flinders Petrie | ^{Say Shalom!} 13 Tishrei 5772 00:05, 11 October 2011 (UTC)

Drunkeness

Obviously humans get drunk on ethanol and from my personal observations, other mammals such as dogs and pigs do as well, but I was wondering if other animals had similar effects? Specifically, I am interested in flying animals, birds and insects, but would also like to know about fish and amphibians. Obviously they have different physiology, but perhaps the effects of ethanol are applicable to a very large range of creatures? Googlemeister (talk) 19:37, 10 October 2011 (UTC)

When I lived in southern California, there was a problem one summer with birds getting drunk off fermented berries along the highway and flying into buildings. So, that implies that birds get drunk. -- kainaw™ 19:52, 10 October 2011 (UTC)

Googling "birds drunk fermented berries" turns up a lot of information on the topic. -- kainaw™ 19:55, 10 October 2011 (UTC)

I don't know if they get drunk first but a 1% ethanol solution by mass is enough to kill fish and crustaceans within 24 hours. Dragons flight (talk) 20:03, 10 October 2011 (UTC)

I would think that in creatures with less complicated digestive systems the amount that would get them drunk and the amount that would kill them would be about the same. I certainly wouldn't recommend trying to get a turtle or an ant drunk. Beeblebrox (talk) 20:27, 10 October 2011 (UTC)

Sap-feeding beetles actually love ethanol as it is a primary indicator that resin in trees are ripe for feeding. Beer in pans are commonly used as baits when collecting them. It seems fruit flies can also inhale alcohol vapor as food and can definitely get wasted. LOL. So can bees. Tropical fruit eating bats, however, seem to have evolved alcohol tolerance as a necessity, as a large part of their diet may include fermenting fruits.-- Obsidi♠n Soul 21:38, 10 October 2011 (UTC)

Etymology of gestures, difference between intented and unintended gestures, and animals

Woman making the loser gesture

Is there some kind of Etymology research for gestures? Like: are there contemporary gestures of which the original -literal- meaning is lost but which would be easy to grasp for people in the Middle Ages? For instance, the gesture for loser is today clearly related to the letter L as is Air quotes to actual quotes. Maybe in 500 years or so, everyone forgot about that original meaning but is still using these gestures in a (possibly changed) meaning. Nod (gesture) has some unsourced explanation (babies nodding when they want milk), and shrugging had a (doubted and removed) explanation.

Slightly related, is there an "official" difference between gestures like "I'm sad", "I'm angry" or "I'm thinking really hard about this" which can be used on purpose but are expressed unintended as well by 4 year-olds when they are sad or angry, and on the other hand the "cultural gestures" one has to learn (like nodding)?

Last question, do animals have these "cultural gestures"? Has someone ever tried to learn a chimp to strike his belly to signal hunger? (instead of pushing the "Hunger" button) Joepnl (talk) 20:02, 10 October 2011 (UTC)

Don't know of any comprehensive research, but the origin of flipping the bird is discussed in the article. Turns out it has quite a long history. Beeblebrox (talk) 20:07, 10 October 2011 (UTC)

Animals communicate with gestures. Most don't have hands and use their body. There are thousands of examples of animal gestures from mating gestures to "get the hell away" gestures. -- kainaw™ 20:10, 10 October 2011 (UTC)

See Gesture#Neurology as well. Beeblebrox (talk) 20:11, 10 October 2011 (UTC)

Some animals can learn very complicated gestures. See e.g. Koko, who has been taught over 1,000 arbitrary gestures (which happen to be American Sign Language, but to Koko they are arbitrary). See also Great ape language. --Mr.98 (talk) 20:15, 10 October 2011 (UTC)

@Beeblebrox, Flipping the bird makes me wonder what it has to do with a bird, but that is precisely the kind of etymology I wanted, and I wonder if there's more like it. Thanks. @Kainaw I know animals use gestures, but I wonder if there are examples of groups of gorillas that have a sign for "Watch out for the crocodile" that other groups don't know. Koko proves that learning them works, but are gorillas also teaching them? The "non-cultural" gestures like "get the hell away" are hard wired evolutionary gestures I think. A peacock probably doesn't know he's making a gesture when he's raising his tail. (I know of a gesture like it that a lot of males along many different species don't need to learn) Joepnl (talk) 20:45, 10 October 2011 (UTC)

As a sidebar, isn't that woman in the picture giving the sign backwards? Falconus^{p t c} 21:21, 10 October 2011 (UTC)

Only a loser does it that way - OR, someone taking a picture in the mirror. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:09, 10 October 2011 (UTC)

Woodpecker facts I've been told - true or false?

Things that I've heard people say about woodpeckers - true or false?

1. If a woodpecker didn't shut its eyes when drilling, its eyeballs would fall out?

2. If a woodpecker's tail feathers are removed, it knocks itself unconscious as soon as it tries to drill (because it can't brace itself against the wood properly)?

3. Woodpeckers more than a couple of years old suffer from near-constant headaches and neck pain?

Some of these sound possible, but I've had a look at the woodpecker article, but these points are not specifically addressed. Thanks. --95.150.167.67 (talk) 20:20, 10 October 2011 (UTC)

2 seems to be true somewhat. The tailfeathers are used as support. Removing them probably won't affect their drilling ability though and won't knock them unconscious, but it would certainly have a large effect on their ability to climb trees. Wrynecks do not have stiff tailfeathers, but can still drill on vertical tree trunks by clinging to them with their legs. 1 is true. The eyes are fit particularly snugly to prevent trauma during drilling. The nictating membranes ("eyelids") are slid shut over the eyes just before impact and helps protect them from flying debris as well as restrain them somewhat. The brains are also fit snugly, small, located above the bill, and protected by shock-absorbing mechanisms in the jaw, which in turn makes 3 false. But then again, woodpeckers can't exactly come up to you and tell you they've got a headache. :P -- Obsidi♠n Soul 21:15, 10 October 2011 (UTC)

I asked one about various myths, and all he had to say was, "Ha-ha-ha-HAAA-ha!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:04, 10 October 2011 (UTC)

Dude. You taught him that laugh. And at least he's not teeing puttytats.-- Obsidi♠n Soul 22:27, 10 October 2011 (UTC)

Drop impact absorbtion

So I'm not sure I'm phrasing this right, but I hope you guys will get the right idea about it. I am wondering, I have purchased both an Otterbox Defender for a BlackBerry Bold 9900 and a Commuter type for a 9700. Now these guys are built differently in which layer is where. The 9700 has the silicone skin against the phone and the hard plastic on top of that. The 9900 one is reversed with the hard plastic on the inside and the silicone skin on the outside (forget about the hard plastic holster and the fact that the whole thing together is a tank). So here is my question. Which design is better for absorbing the energy from an impact? Silicone inside and plastic outside or plastic inside and silicone outside? The plastic is some kind of Polycarbonate btw, but that doesn't mean much to me (by which I mean I don't much about it). Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Tishrei 5772 20:29, 10 October 2011 (UTC)

It is impossible to answer this question without details of the structural composition of each design. 67.6.168.177 (talk) 22:01, 10 October 2011 (UTC)

I just said that the hard one was made of polycarbonate and the soft of silicone, so you know their composition. :p Of course, I guess I could link the specs so you can see their dimensions and such. Defender and Commuter Technical specs are at the bottom. However, I am asking which way absorbs better generally speaking? Hard over soft or soft over hard? Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Tishrei 5772 23:21, 10 October 2011 (UTC)

Sorry, those are the same link. But without detailed blueprints of the phones and the cases both, I am not going to be able to give you a good answer, and neither is anyone else. These kinds of designs are almost always perfected by potentially destructive actual use testing (throwing them against the floor) so even if you gave us all the blueprints and we had the time to run them in simulators, the answer might still be wrong. 67.6.175.132 (talk) 23:51, 10 October 2011 (UTC)

(edit conflict)Well, I'm not sure how readily available blueprints for either are I'm afraid. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Tishrei 5772 23:58, 10 October 2011 (UTC)

I would think the soft material on the outside would work better, because otherwise the hard material may fracture when it hits the floor (or the floor may dent or crack). Perhaps a soft-hard-soft arrangement might be even better. StuRat (talk) 23:55, 10 October 2011 (UTC)

Depends on how thick they make it. I mean the Defender is pretty damn big already and very thick. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 12 Tishrei 5772 23:58, 10 October 2011 (UTC)

Thicker and harder isn't always better (well, in some cases it is :-) ). Time to pull out and ancient Chinese proverb: "In the gentle breeze, the willow bends, while the mighty oak stands firm. In the powerful wind, the willow bends even more, and thus survives, while the mighty oak stands firm until it breaks. So, which is the stronger, then, the willow or the mighty oak ?" StuRat (talk) 00:07, 11 October 2011 (UTC)

Yes, all other things being equal, placing padding on the outside instead of the inside will change the damage the assembly will do to what it is dropped on at the expense of easier abrasion, and the advantage of less likely case cracking. 67.6.175.132 (talk) 02:31, 11 October 2011 (UTC)

time travel

first of all, i dont have any deep knowledge about physics. Im just wondering, if relativity says going faster that light is going backwards in time, and nothing can go faster than light, that just means the theory is saying that we cannot go back in time, is this right? if its right, then why do we still believe in time travel? — Preceding unsigned comment added by 203.112.82.1 (talk) 22:13, 10 October 2011 (UTC)

I'm not sure scientists actually "believe" in it. Fiction writers certainly do, as it makes for entertaining stories. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:18, 10 October 2011 (UTC)

Scientists don't currently believe that going back in time is possible given our current understanding of physics. Going forward in time, even at different rates, is allowable (and actually achievable). As for why the idea exists outside of science, it is because it is an interesting idea, and allows for the creation of interesting plots, paradoxes, and other Cool Things™. But that's got nothing to do with whether the physics is real or not. --Mr.98 (talk) 22:37, 10 October 2011 (UTC)

i guess my question really is, does theory of relativity implies that going back in time is impossible?

Time travel says "Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime, or specific types of motion in space, might allow time travel into the past". It's still one of the unsolved problems in physics. Clarityfiend (talk) 22:55, 10 October 2011 (UTC)

actually achievable*?wow, can you tell me more about it. — Preceding unsigned comment added by 203.112.82.128 (talk) 22:59, 10 October 2011 (UTC)

If you have magical powers to create any spacetime you want, then it is certainly true that there are solutions to general relativity that involve things appearing to travel into the past. However, it is unclear if there are any such solutions that are actually achievable given that one is starting with a nearly flat spacetime such as the one we live in. You tend to run into problems that need infinite energy, negative mass, or other things unknown to science. So while someone with Godlike powers might be able to open a bridge from the future to the past (e.g. a type of wormhole), it is unclear if any physically achievable configuration of mass or energy would allow that to actually happen in our universe. And the logical difficulties with causality violation seem so severe, that many people argue that it must be impossible to travel into the past. Dragons flight (talk) 23:08, 10 October 2011 (UTC)

I would go further than that and say that opening a wormhole to the past would change the past, which means that it's not really the past, just some kind of copy of what had been the past here in the present. So it would be like making a copy of what happened, and storing it in a transporter buffer and then materializing it and telling everyone, "hey look, it's the past!" The past itself would not change. It's like saying a historical reenactment is the real thing. A complete waste of time and effort for the non-fiction side of the aisle. 67.6.175.132 (talk) 23:43, 10 October 2011 (UTC)

October 11