Wikipedia:Reference desk/Archives/Science/2009 July 12

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< July 11 << Jun | July | Aug >> July 13 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 12[edit]

What are these structures?[edit]

Gasometer in East London.jpg

Can anybody please tell me what these circular structures are? Thanks ItchyHoover (talk) 00:56, 12 July 2009 (UTC)

If you use the Google 'street view' camera - it's obvious that they are Gas holders. Large cylindrical tanks which rise within a circular frame when filled with gas - and whose weight pressing down on that gas ensures that there is sufficient pressure to push it through the local pipework to people's homes and businesses. SteveBaker (talk) 01:14, 12 July 2009 (UTC)
The photo at right is an almost identical Gas holder from West Ham. SteveBaker (talk) 01:40, 12 July 2009 (UTC)

Life span of the Voyager Golden Record[edit]

In the Article on the Voyager Golden Record there is a bit in the Appearances in fiction section that reads:

  • "In the speculative nonfiction series Life After People it is said that, after a million years of travel in interstellar space, the Voyager probes will be so heavily damaged from micro meteor impacts that the disks will become unreadable."

Because there is no mention of this beyond the fiction section i wanted to know if there was any truth to that statement.--SelfQ (talk) 01:25, 12 July 2009 (UTC)

The probes are so far from the sun now (well outside the Kuiper belt) that the amount of debris is almost zero - the odds are extremely good that these records will last for well over a million years. SteveBaker (talk) 01:54, 12 July 2009 (UTC)
On a related note, how are the disks packaged? It seems to me that the most likely scenario for an alien civilization to get the disks is if the Voyager actually collides with an inhabited planet (therefore, a planet with a breathable atmosphere), with all the consequences that this entails. And you can't very well read a bunch of disks if they've burned up during reentry, can you? (talk) 03:19, 12 July 2009 (UTC)
The discs are packaged in a protective cover, shown here. Micrometeorites would have to penetrate this cover to damage the actual recording medium. Nimur (talk) 03:38, 12 July 2009 (UTC)
It could enter the atmosphere of some alien planet and be burned up. The last meteor to enter the Earth's atmosphere might have been a space probe from some wonderful planet, complete with examples of their music, poetry, and science, that would have enriched our lives. But another scenario is that 100,000 years from now, Voyager is detected by radar and telescopes of another world, and a robot space tug takes it to their scientists for analysis. They play the record, look at the pictures and marvel that there were once such people as us, though we be tribal killer apes who may destroy our race. See also the Star Trek Next Generation episode wherein Picard is the particular target of such a probe from a vanished race and is forever changed as a result. See The Inner Light (Star Trek: The Next Generation) (took some searching to find it). Edison (talk) 03:40, 12 July 2009 (UTC)
Not within the next million years. Neither Voyager probe is aimed towards any particular star - and the odds of just happening to fly close enough to one are astronomically small. There is no possible way they could enter the atmosphere of a planet within that short an amount of time. Also, the Voyager probes will run out of power in about 15 years from now - beyond that, they would pretty much be indistinguishable from a rock as far as alien telescope users would be concerned...but since the closest they're coming to a star in the next 100,000 years is 1.6 lightyears - it's really not likely (and probably outright impossible) for an alien telescope to spot them by chance. The universe is a VERY big place and these are incredibly TINY probes. They'll most likely still be heading off in a more or less straight line without noticable deterioration for a few billion years...they'll probably outlast us, and our planet. SteveBaker (talk) 04:02, 12 July 2009 (UTC)
A more advanced civilization might note its approach. It might cross the path of one of their spaceships. By the way. did you read the article about the Startrek episode, which had the topic of a civilization ending out a probe so someone somewhere would remember them? Edison (talk) 04:52, 12 July 2009 (UTC)
I find it interesting that SteveBaker pretty much rules out the likelyhood of an alien civilization finding either Voyager probe. I never realized that you were that well versed in future alien technologies.  ;-) Dismas|(talk) 05:32, 12 July 2009 (UTC)
You don't have to understand their technologies - you only have to consider the fundamental limitations imposed by the laws of physics and statistics. If you take Dragons Flight's number (below) of 1-10 billion years to get within 60 astronomical units of another star - then consider the likelyhood of detecting something about 2 meters across and weighing 750kg at a distance of 60AU when it's in a totally unexpected (indeed random) position and moving in a random direction. At that kind of distance, the amount of light it would reflect will be truly negligable - it's nuclear power plant will have long ago run down - so it certainly won't be emitting radiation or heat or light or radiowaves of it's own. At 700kg you aren't likely to be able to detect any gravitational disturbance due to it's mass. What conceivable technology could spot it? The extreme limits of our ability to observe objects out that far is to detect Kuiper belt objects down to maybe 100km in diameter! Voyager (at around 2m in diameter) is going to be more than two billion times dimmer! The probability of an alien detector being hit by even one photon reflected by Voyager is quite negligable - so the detector would have to be tracking it for a long time, accumulating these occasional stray photons from it - but since it's coming from a random direction and at a random speed - the probability of the alien detector happening to track it by pure chance is essentially zero. Even if they did happen to pick up some tiny amount of reflected light from it - aside from it's somewhat unusual metallic composition - it's going to be utterly indistinguishable from any other tiny Kuiper-belt type of object - of which there are trillions and trillions to choose from. Why would they bother to investigate this one? Everything says that this craft would be quite impossible to detect with any halfway credible probability. If a similar alien craft entered our solar system - and even if it came close enough to graze our atmosphere - we'd never notice it. If it actually entered out atmosphere - it would burn up before we could tell what it was. There is literally no way for us to detect an alien craft that size. SteveBaker (talk) 15:06, 12 July 2009 (UTC)
A random object travelling through space ought to intersect a star system (within 60 AU) about once every 1-10 billion years. Incidentally, that number suggests the sun may have had a relatively close approach by some other star at some point in its 4.5 Gyr lifespan. It will take Voyager a long time to find another star merely by chance. Dragons flight (talk) 10:34, 12 July 2009 (UTC)

On the other hand, destruction of the disks might not be such a bad thing for us. Consider the inevitable consequences that have occurred on earth every time a culture encounters a vastly more advanced culture, and perhaps the person who characterized that Voyager message as the "single most reckless act in the history of our species" has a point... alteripse (talk) 19:04, 12 July 2009 (UTC)

When we get near-lightspeed spacecraft, we should probably think about going to retrieve it. Googlemeister (talk) 16:35, 13 July 2009 (UTC)
Assuming we would have the faintest clue about where to look for it, which we won't... (talk) 00:58, 14 July 2009 (UTC)
Assuming that the records weren't lost in the meantime, we'd be able to extrapolate its flightpath wouldn't we? Objects travelling in space tend to continue on in a straight line unless influenced by a large gravitational field (which we'd be able to allow for in the calculations), don't they? I think that it's far more likely that Voyager will end up on display in the National Air and Space Museum than in the hands of an alien race... --Kurt Shaped Box (talk) 01:11, 14 July 2009 (UTC)
True, but this assumes that we'd know all the grav fields that the Voyager will encounter along the way, which we don't! (talk) 01:37, 14 July 2009 (UTC)
And besides, if there's two or more grav fields acting on the Voyager at the same time, what we got now is a three-body problem, which is much harder to solve (impossible in some cases). (talk) 01:40, 14 July 2009 (UTC)
And yet another difficulty with extrapolating the flight path: Even for the grav fields that we do know about for certain, in many cases it's almost impossible to obtain an absolutely exact value for their strength, so what we got instead are approximate values with a certain margin of error. Likewise, the Voyager's flight path (therefore its position and direction / velocity) is only known with a certain margin of error (let's say a couple hundred miles for position, a few minutes of arc for direction, and a couple km/s for airspeed). Over time, these errors in flight path will build up (especially since the Voyager's exact flight path influences how close it passes to a given grav field and therefore how much it's deflected), so after a century or two, the uncertainty in the Voyager's position will be so big that we'd have to search a HUGE area! Keeping all this in mind, the search for the Voyager will be MUCH harder even than looking for a tiny airstrip on a tiny desert island in the middle of the South Pacific, especially since islands usually remain in the same place at all times. (talk) 08:01, 14 July 2009 (UTC)
She did not have radar though. We could. On earth, an AEGIS radar can see a small aircraft at 300+ miles, but it is limited by the curvature of the earth. Googlemeister (talk) 19:21, 14 July 2009 (UTC)
You'd still have to get to within 300 miles of the Voyager, which is still harder than looking for an island in the South Pacific. (talk) 01:16, 15 July 2009 (UTC)

So basically, it would be impossible as well for a Message in a bottle to be [read by someone eventually]? If someone wanted a space probe to be found, they could (if their technology were advanced enough) install a very long duration stored energy source and a transponder which would respond to radio signals with a detectable emission, or a beacon which would start operating when it got within plausible detection range of a target starsystem. Edison (talk) 19:24, 14 July 2009 (UTC)
Not the case with Voyager, though, since (as Steve pointed out) it doesn't have such a beacon / transponder. And remember, the only way one can find a message in a bottle is through a chance encounter with a ship (spaceship in this case) or through it washing up on some shore (in the case of the Voyager, that would be a planetary collision, which, as I previously said, would cause it to burn up along with all the disks it carries). (talk) 00:41, 15 July 2009 (UTC)

Watch our ancestors get a ticket for littering. Googlemeister (talk) 19:57, 15 July 2009 (UTC)

Love reading questions like this; the experts theorise of the answer with the best intentions with laws of physics; it is like saying we know how the universe works <TOTAL CRAP> explain the laws of physics for a super massive black hole DOH they dont apply; who is to say the alien networks out there dont have vast nets acting like collectors of information BEEP voyager goes through one o look alien tech lets take a look; who is to say there is a image being portrayed by aliens using sophisticated tech so we think we can see the big bang; <<<<<YES i know amazing but who is to say it isnt truth! if you can imagine it then a civilisation 3 million years older than ours can probs do it just because we cant does not mean they cant; of course with laws of physics and great distances and space is so big it is inconcievable from our prospetive that voyager may bump into a alien race just happened to be sitting on the shoulder of some gas cloud; I like the idea of we are starting to make things like invisability cloaks :) 3 milion year old race wounder what there cloaking technology would be like? wounder if they could be on mars and cloaked sending false images of mars back through our own technology! Yes i guess a bit of a fantasist i am but never rule anything out.Chromagnum (talk) 05:20, 18 July 2009 (UTC)

Hey Chromagnum -- how much $$$ for an "invisability cloak"? I'd love to buy one! LOL! (talk) 05:41, 18 July 2009 (UTC)

At present it is still in the early stages of production and can only be produced by bending light around objects- this is done on a very small scale; it will be some years untill a commercial viable one would be used as no doubt the military applications for such technology will come first. However this will change over time and will be able to used for all sorts of diffrent things. Start saving as if it becomes a viable tool in our life time i imagine it wont be cheap [1]Chromagnum (talk) 06:07, 19 July 2009 (UTC)


Congenital insensitivity to pain suggests that the sensation of pain can essentially be isolated from other sensations (with the exceptions of temperature). Does this have any analgesic applications? Is their any method of pain management (obviously one dealing with intense chronic pain) that attempts to "sear" the nerves responsible for pain?

Alfonse Stompanato (talk) 04:00, 12 July 2009 (UTC)

Well, there are many methods that temporarily block the nerves responsible for pain: some of the ones that you're likely to be familiar with are painkiller shots to numb your jaw before a dental procedure such as a dental filling or (if you got really bad teeth) a root canal; or (if you're a woman who's had kids), an epidural block to reduce the pain of childbirth. As for permanently "searing" or deactivating the nerves responsible for pain, I haven't the foggiest. (talk) 04:23, 12 July 2009 (UTC)

Well, there's radio frequency nerve ablation that's been used for chronic pain, but the problem is that nociceptive nerve fibers coexist with those of other perceptions - they don't exist in isolation - so you can lose sensation as well as the pain. - Nunh-huh 04:38, 12 July 2009 (UTC)

About time dilation[edit]

Sorry to ask frequently asked things. But I have two. The first is: I know if two observers start from the same inertial frame, accelerating and decelerating alike in opossite direction, experience the same time of inertial motion, and comes back to where they started, time dilation for both is the same (because everything is symmetrical). But while both are in inertial motion, each observe the other's time delay, and to compensate for that, the time for each (not the other) must delay during acceleration.(I don't think gravitaional time dilation quickens the other's time.) But the other's time does not delay the same amount? If it delays, special relativistic time dilation is not compensated. The second is: In the same situation, but changing only the duration of inertial motion for both, total special relativistic time dilation increases. What compensates for the adittional special relativistic time dilation? Gravitational time dilation has "vertical" distance h in the formula to calculate the gravitational time dilation. I'm not sure, but acceleration at differently distant point (even if the acceleraion is the same) causes different time dilation? And that equals the difference of special relativistic time dilations? Like sushi (talk) 04:38, 12 July 2009 (UTC)

You seem confused. There is no need to include gravitational effects in any of your examples since there is no gravity present. Acceleration is equivalent to a gravitational field only locally which is not the case here since there are two observers with an arbitrarily long space-like distance between them in your examples. When your observer accelerates it jumps from one reference frame into a different reference frame with a different set of simultaneaties. It is even possible that a distant event that was considered already past before the accelaration becomes a future distant event after the accelaration. No gravitational doppler shift (a better term than time dilation) can do that. Dauto (talk) 05:11, 12 July 2009 (UTC)
"Acceleration is equivalent to a gravitational field only locally" and we are dealing with "observers with an arbitrarily long space-like distance"? But if the motion of both are symmetrical,they would return to the point they started, and at the time they have just returned to the point they started and to the same reference frame, the traces of both are fully in the light cone of both. So everything is not "spacelike" at the time?
Like sushi (talk) 06:18, 12 July 2009 (UTC)
You are saying that the other is out of the light cone when the acceleration takes place? That is impossible (at least for an observer to see, because the skirt of light cone expands faster than the speed "the other" is observed to recede).
Like sushi (talk) 06:48, 12 July 2009 (UTC)
Or you are saying that the observer can not see the other's acceleration?
Like sushi (talk) 06:52, 12 July 2009 (UTC)
I forgot to write this, I am assuming that the two observers start from the same point.
Like sushi (talk) 07:25, 12 July 2009 (UTC)
I think what you're saying is this: if two people travel in a perfectly symmetrical way then when they meet again the elapsed time must have been the same for both (by symmetry). But that's inconsistent with each one seeing the other's clock run slower. The answer is that they don't see the other's clock run slower, they see it run sometimes slower and sometimes faster, with the average speed over the whole trip being the same as their own. The observed speed of the clock is determined by the Doppler shift factor, , not by the time dilation factor, . The latter is rarely relevant in physically meaningful situations. -- BenRG (talk) 08:59, 12 July 2009 (UTC)
Thank you. The formula you wrote is a variant of one in Velocity-addition formula#Doppler Shift##Relativistic Doppler Shift? I haven't known that. The observers do not always see time to delay. Thank you again!
Like sushi (talk) 10:18, 12 July 2009 (UTC)
Well, I have thought about it, and using the formula , there is still time dilation observed in the case each recedes and approaches with the same speed, because observed time dilations are reciprocal to each other, adding them does not (at least always) result in no dilation.
Like sushi (talk) 10:42, 12 July 2009 (UTC)
No, this is not time dilation, time dilation and time hastening (should I say?) both occur and total time in this case is hastened.
Like sushi (talk) 11:32, 12 July 2009 (UTC)
This isn't usually called time dilation (or time hastening). The effect actually called time dilation is something more abstract involving distributed networks of synchronized clocks. The total time (i.e. number of ticks) is not hastened, it's identical for both travelers (both in reality and "as observed" by each one). It's complicated to work this out explicitly. For one thing, the Doppler shift formula depends on the velocity of the emitter when the light is emitted relative to the velocity of the receiver when the light is received. Since those times are different for light going in the opposite direction, there's no simple relationship between the Doppler shifts seen by the two travelers.
Look at relativistic Doppler shift for the formula. The one I gave, , is only for motion in a straight line. For the general case it's more complicated. -- BenRG (talk) 11:29, 13 July 2009 (UTC)
Thak you. I don't know if I understand it, but I am taking it this way. Ignoring acceleration, the trace of both observers are a rhombus, and thinking about "the velocity of the emitter when the light is emitted relative to the velocity of the receiver when the light is received", the time during which one observes the other receding is full one way, but because there is time during which one observes the other to move in the same direction, the time during which one observes the other approaching is less than full one way. While receding, the other's time is observed to run slower, and while approaching, the other's time is observed to run faster, but because "the time during which the other's time run slower" is more than "the time during which the other's time run slower", both multipied is the same?
Like sushi (talk) 02:13, 14 July 2009 (UTC)
I tried calculation.
When the distance at which both swicth from receding to approaching is l, the time observed to pass during recesion and aproach seem to be both
and the time during which one observe the other to recede and approach added seems to be
Am I doing wrong?
Like sushi (talk) 04:42, 14 July 2009 (UTC)
Something to keep in mind is that observations can't happen instantaneously. Information is limited by the speed of light. So when A observes B, A is not seeing what B is doing right now. There is a delay of t = d/c where d is the distance between them.
In the case of the rhombus, from A's reference frame in the first part of the trip: A is stationary for a length of time t. Before B turns, B is moving away at speed v, and is experiencing time at a slower rate due to time dilation, so B travels for time before turning and goes a distance of vt' away from A. After B turns, B is stationary and sits for time t. After A turns, A is moving toward B at speed v and experiences time at a slower rate, therefore traveling for a time t' before meeting B. In this reference frame the point where B turns is after the point where A turns. When A turns and assumes a new reference frame, there is a Lorentz transformation of space time, and so the point where B turns moves. In A's new frame for the second part of the trip: A was moving away from B for a time of t' until turning and is now stationary for a length of time t. B was stationary for time t until turning, and after turning B moves toward A at a speed of v, and experiences time at a slower rate due to time dilation. B again travels for t' time and then reaches A. In this reference frame, B turned before A did. This is what Dauto was talking about. Immediately before A turns, the point where B turns is in the future, but immediately after A turns, the same point has shifted into the past. You can check yourself that the Lorentz transformation for increasing velocity by v in the x direction shifts the point (t'-t, vt', 0, 0) to (t-t', vt', 0, 0). B has the exactly symmetric experience. This is how both people can experience time at a faster rate in their own reference frame and still meet up after traveling for what they each perceive to be the same amount of time. This is different from what person A observes B doing, since observations of B are facilitated by light traveling from B to A, which is I think what BenRG is talking about. Rckrone (talk) 21:10, 15 July 2009 (UTC)
Thank you. I drew pictures and I think I understand what you say. So for an observer, not only the other's time delays, but also the time of himself during different inertial motion is different, and the time of the other once was delaying becomes not delayed when he assumes the same velocity as of the other at the time.
Then what happens if the receding and approaching speeds are different? (I think symmetry is still preserved)
Like sushi (talk) 05:44, 16 July 2009 (UTC)
Yeah, that's right.
Instead of thinking of events in space and time and using time dilation and length contraction to figure out how things change when we switch to a different reference frame and making sure that everything works out, I find it's a lot easier to think of events as points in Minkowski space M. In a particular reference frame, our usual space and time coordinates form a basis of M that's orthonormal according to the Minkowski inner product, but there are many orthonormal bases that we can use, each corresponding to a different inertial reference frame. The Lorentz transformations are exactly the transformations between different orthonormal bases, in other words they're the trasformations that preserve the inner product (modding out by the transformations that reverse time or flip space). This can be checked. Time dilation and length contraction (as well as relativistic energy and momentum, and the relationship between EM forces) follow naturally from this construction. Minkowski space, Lorentz transformation and related articles helped me understand special relativity much better than I did when it was just a bunch of mysterious formulas that miraculously worked out, so I highly recommend them. Rckrone (talk) 19:00, 16 July 2009 (UTC)
Thank you. I will try it.
Like sushi (talk) 10:23, 17 July 2009 (UTC)

Dumb sheep[edit]

What is Natalie Angier talking about 44 minutes into this 1995 Charlie Rose interview when she apparently states that the encephalaization quotient for sheep is the "highest of any mammal"? There is NO WAYYY we didn't know the EQ of sheep in the mid 90's, which, so far as I can see is nowhere near the largest of any mammal. So what is she talking about? —Preceding unsigned comment added by (talk) 09:29, 12 July 2009 (UTC)

Well there is a lot of bullshit out there. However, I listened from 41:00 to 47:00 and she didn't come anywhere close to mentioning sheep or encephalization quotient.--Shantavira|feed me 10:59, 12 July 2009 (UTC)

Oops sorry here's the right link: ......anyone? —Preceding unsigned comment added by (talk) 04:30, 13 July 2009 (UTC)
Well, she also says that without dung beetles "we wouldn't have a planet", so I'd take her pronouncements with a grain of salt. Anyway, page 243 of Macphail, E. "Brain and Intelligence in Vertebrates". Clarendon Press, 1982 lists the following EQs:
Man           7.44
Dolphin       5.31
Chimpanzee    2.49
Rhesus-Monkey 2.09
Elephant      1.87
Whale         1.76
Dog           1.17
Cat           1.00
Horse         0.86
Sheep         0.81
Mouse         0.50
Rat           0.40
Rabbit        0.40
I looked in the book she was hawking and saw the sheep EQ assertion, but there wasn't any citation for it, or even a notes section. --Sean 15:05, 13 July 2009 (UTC)
It's of note, in that list, that the sheep certainly is the dumbest of the large mammals listed. (Obviously "large" is somewhat subjective but mouse/rat/rabbit aren't large by any definition.) That being said, being just slightly "dumber" than a horse ain't too bad. Not like being as dumb as a rabbit, which even in causal acquaintances are pretty dumb. -- (talk) 20:51, 13 July 2009 (UTC)

Trading agro products[edit]

Is there a Board of Trading where all agro products are traded? So far, I only found the more important like coffee, rice and such stuff. --Quest09 (talk) 11:08, 12 July 2009 (UTC)

OR Some (most?) vegetables don't get traded by boards of trading because they are grown on contract. I.e. depending on company rules/contract terms, a company like Green Giant will give the farmer the seeds, the fertilizer and if required pesticides (or issue rules for "organic" produce) and will come pick up the harvest with their trucks right from the field. They'll process and package the produce in their facilities and deliver to their distributors. Smaller non-contract producers will sometimes make contracts directly with local supermarkets. Restaurants and small markets pick up produce at local Farmer's markets sometimes. (talk) 20:48, 12 July 2009 (UTC)
Check out List of traded commodities which has a list of commodities and the location where they are traded.--SPhilbrickT 23:00, 12 July 2009 (UTC)
This is list is clearly incomplete. Frozen orange is not there, frozen butter is not there. The question still remains: are there other products like dried garlic, apple juice or the two in the last sentence so uncommon that no trading board would trade them? I understand that lettuce, strawberries or even tuna can not be easily traded by a board, but many other precisely defined product should be traded in a trading board. Just compare it with the small caps that are traded at stock markets. How small must a market be to be excluded from a trading board? --Quest09 (talk) 10:19, 13 July 2009 (UTC)
Plse. feel free to expand the article with well sourced material. Your question wasn't really a Science question to begin with and you might have had more luck on the Humanities desk. (There's some discussion on creating a business desk because "humanities" don't really come to mind there.) I don't really see a necessity for things to be traded by a board. FWIW the following links might help Onion Futures Act, [2], [3], [4], [5] probably not a good article reference, but for information check out commodities trading sites e.g. [6] -- (talk) 17:10, 13 July 2009 (UTC)
I can't really comment on the reasons, but I think organized market trading is more of the exception than the rule for ag products. Feedstuffs, for example, seem to be bought and sold through individual contracts, even through they are fairly standard and traded in large quantities. (I'm not 100% sure about this. I know it is the case for animal byproducts, but not as sure about others). ike9898 (talk) 19:23, 13 July 2009 (UTC)

Why do men and women exist? (evolutionary biology)[edit]

This might seem like a simple question, but I still can't figure out the answer. Evolution of sexual reproduction gives some plausible reasons for the development of sexual reproduction, in the sense of reproduction requiring more than one individual. But why are we and many other species not hermaphrodites (like Earthworms and plants)? After all, this seems like an advantage to me: a hermaphrodite can reproduce both as a male and as a female, thus increasing its reproduction chances. --filip (talk) 11:21, 12 July 2009 (UTC)

An earthworm has been around for a long time. It hasn't evolved much. This is one of the reasons for it. Having two sexes increases the chances for evolution and diversity. Rkr1991 (talk) 11:33, 12 July 2009 (UTC)
Expanding a little on Rkr1991, some creatures (eg aphids) will even reproduce by parthenogenesis at times when food is plentiful, making an immediate supply of identical creatures to consume the food. Later they will reproduce sexually to increase their diversity. Hermaphrodites will turn into female to take advantage of good conditions, as one male is enough to impregnate many females. This type of arrangement is suitable where quantity of population is needed for species survival. I all these cases the young are produced and left to their own devices.
In higher animals, much of survival depends on the (few) young being well cared for and educated, over long periods of time. This makes a variably large number of females a disadvantage, over a fixed smaller number having the permanently female characteristics needed for the nurturing of the young. In other words, we don't come in two sexes to be able to conceive more young, but to be able to nurture to maturity the few young that we do conceive. - KoolerStill (talk) 12:19, 12 July 2009 (UTC)
The benefit of not being hermaphrodites is that there are adaptations in the two sexes that make child rearing more efficient. For example, if we were hermaphrodites, we'd all have to have all of the baby-making apparatus - mammaries, womb, fallopian tubes, extra-large hips, monthly periods, etc. Since human children cannot be abandoned to fend for themselves at birth (as is the case with the offspring of hermaphroditic species) - it takes a minimum of two individuals to care for the child - one to stay home and look after it - the other to hunt the mammoth for supper. The one who is hunting the mammoth is more a more efficient hunter because he doesn't have to carry around all of that baby-rearing stuff. Of course, in reality - the split came a very long time ago when some hermaphroditic ancestor of all non-hermaphroditic animals evolved to have two different sexual morphologies - we would really have to ask the question as to why the change was most beneficial for THAT creature - which is tricky because it's unlikely that we know precisely when that happened and why. SteveBaker (talk) 14:31, 12 July 2009 (UTC)
Steve, that explanation applies to very few species, so clearly is not the explanation. It also smacks of 'Man, the mighty hunter' anthropology, which surely was discredited years ago because it doesn't really make sense? (talk) 18:28, 12 July 2009 (UTC)
Agreed. Steves explanation, especially the part about having a womb and boobs making someone a less efficient hunter is a pile of steaming bs.
bs or not (ok bs) - 2 sexual organisms tend to be(are) higher up the food chain - thus a grain of truth
There is some sort of link here - (talk) 21:35, 12 July 2009 (UTC)

The latest explanation, for which there is some recent experimental evidence involving sexy & unsexy snails (actually sexually and asexually reproducing) is that the main benefit of sexual reproduction is parasite protection because a greater genetic variety of individuals is generated with each generation. Far more individual variation is provided by recombination of chromosomes than by single codon mutations. alteripse (talk) 18:58, 12 July 2009 (UTC)

That explains the point of sexual reproduction, which the OP already said he understands, but I don't see how it relates to the actual question: what's the point of some snails (or humans) having only male reproductive organs and some having only female reproductive organs? —JAOTC 19:33, 12 July 2009 (UTC)
You are correct, I misunderstood the question. I suspect it has to do with the expense of maintaining parallel or bipotential reproductive systems not being worth it. There are a few vertebrates, like the wrasse that have capability to change sex if environmental circumstances make it advantageous. alteripse (talk) 20:17, 12 July 2009 (UTC)
Men and women exist because the far more primitive organism(s) from which we evolved found pressures to reproduce sexually. It was advantageous for some earlier link in the chain of life forms that led to us to reproduce sexually. It doesn't make sense to ask why we didn't switch back to asexual reproduction. (I realize the OP didn't ask this question.) The possibilities of the configurations both physical and behavioral of life-forms is bewildering. Why don't we have antennae? Why don't we possess the ability for echolocation? Bus stop (talk) 20:44, 12 July 2009 (UTC)

The primary function of sexual reproduction is to generate new combinations of alleles of the genes of two organisms. In hermaphroditically generated offspring, all the genes come from the same animal, so you don't get novel combinations. Looie496 (talk) 21:56, 12 July 2009 (UTC)

No. Hermaphrodites, even those that are technically able to, avoid copulating with themselves, so generally the genes will still come from two different animals. Again, this question was specifically not about sexual vs. asexual reproduction. —JAOTC 11:57, 13 July 2009 (UTC)
Because it takes a long time to rear the young, there is no point having 99% of the population being able to turn female and HAVE young all at once. They will then have to remain female for the ages it takes to rear the young, including the ability to feed them, which is a substantially bigger change than just changing the reproductive organs short-term. Food supply for the large number of young (and supporting mothers) would become a big problem, with very few food providers not engaged in rearing offspring. All the hermaphrodites just produce some eggs and go their merry way as whatever sex they then turn into. Having the majority of the population do this in good times increases the numbers, and therefore their survival chances as a species while lowering the chances as individuals -- which you can't afford with young that have years of work invested in their nurturing. Higher animals go for quality rather than quantity. - KoolerStill (talk) 18:33, 13 July 2009 (UTC)
But many, many, many animals that do not rear their young have roughly 50/50 male/female ratios, without being hermaphrodites. Again, you are offering (some)higher-animal-specific explanations for something that evolved much earlier, and neglect the species (for example, some garden birds) in which both parents share the child-rearing and feeding, and... it just really doesn't answer the question. It's just the usual 60's explanation of why contemporary gender roles were natural and part of our basic nature. It assumes that the usual situation in 'primitive' cultures and higher animals is for the male to provide most of the food for the children and female. (talk) 21:50, 13 July 2009 (UTC)

Why not hermaphrodism instead of gonochorism? Both strategies can work, but in many instances hermaphrodism is subject to specialization by individuals, leading to gonochorism. Suppose there are many available partners around, and an individual happened to fail to develop the eggs it was carrying but instead used the energy of egg development and nurturing for inseminating others. In many cases it could be much more successful in spreading its genes into the next generation than the typical hermaphroditic individual, who would inseminate fewer times due to the higher resources needed to develop eggs, lay them, and perhaps care for young. In such situations, it would be common for insemination specialists to evolve, and from this the species could easily establish them as a requisite male sex distinct from the egg carrying individuals. -R. S. Shaw (talk) 04:00, 14 July 2009 (UTC)

And keep in mind that this works both ways: the individual that develops the eggs would not have to spend energy for insemination of other individuals, so would be more successful in bringing forth her progeny. FWiW (talk) 08:09, 14 July 2009 (UTC)

Plz help me quickly(some science related questions)[edit]

1>Which Filter is used for passing ONLY HIGH frequency a: LADDER B. crystal

2>If water is heated from 0degree to 10 degree effect on volume a: increase steadily b: remain same c: decrease steadily

3>if we dig EARTH FROM North to South pole and a stone is dropped in it then efffect on its velocity a :increase continously b: First increase and become Zero in center c. It Will Start Oscillate

4>Radiation pattern of loop antenna a: cardioid b. semicircular c. circle d. none

5>plural of "DIBIYA"IN HINDI  ?

6>RADDISH is a a: modified root b: bulb c; stem —Preceding unsigned comment added by Swapnendu (talkcontribs) 11:36, 12 July 2009 (UTC)

Pardon me if I am mistaken, but this looks like homework. The Reference Desk does not do your homework. You can try reading the relevant articles or consult your textbooks. If you still have doubts in understanding any particular concept, we would be happy to help. Cheers. Rkr1991 (talk) 12:01, 12 July 2009 (UTC)
I also thought "homework" but I wonder what sort of class would ask questions that diverse. Anyway, coincidentally if there was a hole from north pole to south, or any other line through the centre of the Earth, and all air was evacuated from the hole, it would take 42 minutes to traverse the passage (42, of course, being the meaning of life, the universe and everything). Anyway, velocity of a falling object is due to acceleration due to gravity. At the start of the drop the stone would have the whole world ahead of it - the whole world has quite a bit of gravity. By half way, it'd have half the world ahead and half behind - so would be pulled equally in both directions. As it approached the other end of the tunnel, it would have more and more of the world behind it, pulling it back. Repeat. -- (talk) 12:10, 12 July 2009 (UTC)
oh and...
1. A high pass filter passes high frequencies. <- If it's homework, check your text book. Radio filters can be made with crystals, but also look a little like a ladder.
2. Hotter gasses or liquids have greater volume. Water is a liquid.
4. See loop antenna
5. Sorry, try the language ref desk.
6. See Raddish, root, bulb and stem
-- (talk) 12:15, 12 July 2009 (UTC)
Actually for number 2, the volume would increase, then decrease. Water reaches its maximum density at 4°C, which is why water expands when frozen. Chaosandwalls (talk) 13:49, 12 July 2009 (UTC)
This does sound an awful lot like homework - but much nicer answer to Q3 (which is a very complicated question unless there are a LOT of caveats) is that the air pressure in the hole increases the deeper you go - and quite a long time before you reach the center of the earth, the pressure would be sufficiently high to liquify the air - hence your rock will fall for a very long time (because it'll reach terminal velocity quite quickly) then make a very, very distant "splash" sound and then slowly sink to the center of the earth. If there is a vacuum throughout your tunnel then 203's answer above is good enough. For 203's benefit, the reason the hole has to go from North pole to South pole is because coriolis forces on the rock would cause it to hit the sides of the tunnel on the way down if it were drilled in any other it's NOT true that just any old hole would do! SteveBaker (talk) 14:21, 12 July 2009 (UTC)
I believe 42 is the answer to a couple of other interesting questions as well, which I vaguely seem to remember. I think it is half the time period of an infinitely ling pendulum, and something to do with waves which I can't remember.. And Steve, don't forget that these are just ideal imaginary textbook problems, so we should approach it without thinking too broadly...Rkr1991 (talk) 15:18, 12 July 2009 (UTC)
Perhaps you are thinking of the angle of the bow waves formed by a ship - irrespective of shape or speed through the water - which is 42 degrees. SteveBaker (talk) 16:13, 12 July 2009 (UTC)
If you have a source for that, you may want to add it to 42 (number). Deor (talk) 16:16, 12 July 2009 (UTC)
also number of faces on a football Truncated rhombic triacontahedron - thus football is not the meaning of life... (talk) 19:50, 12 July 2009 (UTC)
#2: water DEcreases in volume from 0C->4C then increases;
#3: time-of-passage through a straight tunnel from ANY 2 points through the (spherical, homogeneous, frictionless, etc.) Earth is the same! How cool is that?
Saintrain (talk) 01:39, 17 July 2009 (UTC)

General all-over soreness and tenderness when ill[edit]

I appear to be coming down with some nasty virus, and it has me curious. Nearly every time I get sick, I always get a very unpleasant feeling of general weakness, tenderness and soreness all over my body. It makes me want to curl up in bed and not move. Every tactile sensation, particularly unexpected ones, has a note of unpleasantness that it doesn't normally have. What is the cause of this general "unwellness" symptom? Note: I don't want a diagnosis, that's what I'll go to the doctor for. I'm just curious about the actual mechanism behind the symptom. Maelin (Talk | Contribs) 11:46, 12 July 2009 (UTC)

I have the idea that it comes from interferons and other cytokines. Exactly how they do it I have no idea. I seem to recall that this is considered to be adaptive because it keeps you from running off after mammoths while you're sick. --Trovatore (talk) 11:55, 12 July 2009 (UTC)
Our most relevant articles seem to be Malaise and Sickness behavior, which may lead you to more information. Trovatore's response appears to be borne out by Hyperalgesia#Causes. Deor (talk) 14:37, 12 July 2009 (UTC)
Malaise is my favorite symptom ever; it sounds like some sort of jungle fever. If you call up your boss and tell him your doctor says you have malaise, I can bet that boss is going to let you stay home. :-D -RunningOnBrains(talk page) 22:45, 12 July 2009 (UTC)

What mechanisms trigger vasodilation?[edit]

I've been researching a minor affliction I suffer from which I think is cholinergic pruritus (but note that this is not a request for medical advice!). Assuming it is that, is the following an accurate description?:

I get too hot (or embarassed etc.) > ... > ... > Histamine is released as a vasodilator > This also makes C fibers fire which causes the itch sensation (H1 antagonists such as Loratadine are very effective preventatives.)

So, firstly, is that right? Secondly, what happens in the dotted sections? How does thermoregulation work? What detects elevated temperature, what releases histamine (mast cells?) and how are signals sent between the two? Thirdly, what is it that makes me different from most people? Is it how much histamine is released, or how sensitive the nerves are to it, or something else?

My curiosity yearns for further insight so thank you very much for any information you can give on these mechanisms. ASmartKid (talk) 14:14, 12 July 2009 (UTC)

[From Terry0051] May I suggest some preliminaries -- like first taking a step back and having another look. Look at as many alternative explanations as you can find. It might not be the complicated thing you suspect. Common things happen most commonly. Skin is a temperamental and individual tissue/organ. For an otherwise healthy young person, traditional homespun measures to get you comfortable can often be all that is needed. Try various simple and safe measures. Beware of pharmaceutical (over)use. If still uncomfortable, get yourself along to a physician. Good luck. Terry0051 (talk) 21:07, 12 July 2009 (UTC)
Thanks for your concern but I'd love some info on the mechanisms, regardless of what I have. ASmartKid (talk) 16:33, 13 July 2009 (UTC)
Don't know, but the following articles might help Thermoregulation, Human homeostasis (stub), Homeostasis, Vasodilation. (talk) 17:24, 13 July 2009 (UTC)

Abdominal muscles[edit]

I have a feeling this question may well be rejected as medical advice but if it is, it was still worth trying. I'm currently working on my abs in hope of getting a sixpack and, after looking around online, the bicycle crunch seems to be the exercise of choice. Now I've been doing this for a while and have noticed it's getting easier and am looking for a way to make it more challenging, in the hope of causing more muscle development. Is there any suggested way of altering it? I've tried making my elbows meet my leg closer to the hip, rather than meeting at the knee as suggested, and this has definitely been tougher. I'm open to any suggested or even suggestions of different exercises to try. Thanks (talk) 15:19, 12 July 2009 (UTC)

According to the crunch article, “the difficulty of the crunch can be increased by lying on a declined bench and/or holding a weight on the chest or behind the head.” Red Act (talk) 16:11, 12 July 2009 (UTC)
Or attaching weights to your legs. Anyway, you'll only get a six pack if your fat is low enough.--Quest09 (talk) 18:57, 12 July 2009 (UTC)
Who needs a six-pack when you can have a whole keg... ;) no to drama 04:56, 13 July 2009 (UTC)
I'd imagine it's unlikely that the average person which achieve a six-pack merely through abdominal crunches. As mentioned above, you need to have sufficiently little fat for it to show. I got lucky in that I'm pretty skinny anyway, so exercises tend to work and I got one pretty easy (and as an unexpected byproduct of exercise). I recommend you just keep trying like you are, and if it doesn't work, combine it with another form of exercise which is more efficient at burning away fat (for example, running). As for altering it, or making it harder, the best way is to have weight added as suggested above. Remember though that the key point is reducing the fat levels around your stomach area sufficiently for a six-pack to show as it's pretty easy for fat to cover up the strongest of muscles. Regards, --—Cyclonenim | Chat  19:34, 12 July 2009 (UTC)

I have several body building friends who all have the preverbial six pack - they concentrate more on body fat ratio to ensure there awesomness; basicly i was told that you needed to do lots of CV(cardioa vascular) & FB (Fat burning Exersise) and your awesomness will show when you Body fat Ratio is at a sufficent level. If you wish to provide a work out that is the most challenging for yourself; Hanging Leg Rasises are deemed to be sufficently painfull a lot more so than abdominal crunches.Please see attached link to core muscle exersise were you will find the correct method for abdominal raises [7] However if this does not work; "you could and by no means am i telling you to do this" but you could take performance in enhancing substances to help with the fat loss/muscle growth. You could try something along the lines of this [8] all legal and used by AUZ swimming teamChromagnum (talk) 06:07, 28 July 2009 (UTC)

Video... thing to I.D[edit]

Not for the squeamish. Link. Online guesses include slime mould and tubifex worms. Neither seems quite right. To me, there's something wrong with the supposed scale in the vid; given the size of the supposed tunnel, you'd have to guess the large one here is about a foot high or thereabouts, but the water doesn't look right to me. Water doesn't miniaturize properly and the way this water behaves makes me think there's some trickery involved, like the tunnel is more like six inches high instead of six feet. Gross, anyway. Matt Deres (talk) 16:28, 12 July 2009 (UTC)

I agree it's probably a 6" sewer - with one of those remote cameras 'they' have (ie they = CIA hopefully.. help) (talk) 17:19, 12 July 2009 (UTC)
Apparently 6"CP = 6 inch clay pipe. (or concrete or cement )
also see;topic=12820.0 (talk) 17:28, 12 July 2009 (UTC)
or (talk) 17:31, 12 July 2009 (UTC) (talk) 17:34, 12 July 2009 (UTC)
Actually, it looks very much like a slime mold. I would be surprised if it were not one. There are hundreds of varieties of slime mould. This one seems likely to be a Dictyostelid or something similar. no to drama 17:50, 12 July 2009 (UTC)
I'm not disagreeing - but the thing is red - can a slime mold be red? also the things move quickly and appear to be 1" long - I wonder if there's a mixture of different things in there? (talk) 21:09, 12 July 2009 (UTC)
See also this discussion from a few days ago. (talk) 18:04, 12 July 2009 (UTC)
offtopic someone should tell the Church_of_the_Flying_Spaghetti_Monster - if they didn't already know... mmh I wonder [9] (talk) 19:07, 12 July 2009 (UTC)
Definitly a small pipe. Nowhere near 6 feet. But the...thing, appears to be sensitive to light, as it begins to squirm each time the camera (and consequently light) passess over them. It seems very much like a slime mould, but not exactly like any particular slime mould I've ever read about. Drew Smith What I've done 04:38, 18 July 2009 (UTC)


Watching Top Gear, they mentioned a new Zonda car which is made of something like Cartanium or some other made up name, a combination of carbon fiber and titanium. The first mention of titanium and carbon makes me think of titanium carbide, which if my memory serves me correctly, is brittle and thus a big reason we don't extract titanium through the blast furnace. Anyone heard about this cartanium or similar name, and why it's so different to titanium carbide? Regards, --—Cyclonenim | Chat  19:26, 12 July 2009 (UTC)

titanium carbide could like any other brittle material be made in to fibes eg glass fibres, basalt fibres
Cartanium i suspect is a joke - ie car-tanium eg indestruc-tanium [10] , category:fictional materials etc. (talk) 19:38, 12 July 2009 (UTC)
Just a mention at Pagani Zonda#Zonda Cinque. I haven't found any clear description on the Web, but that's not surprising; I suppose Pagani wants to keep the details secret. Deor (talk) 20:01, 12 July 2009 (UTC)
I've no idea what exactly they do, though I wouldn't be suprised if it were something like this [11], though it could equally as likely be something else involving titanium and carbon... (I'd imagine that the price of a relatively new material would be just as effective as preventing copying as secrecy - I doubt they were trying to cut costs on the design :) (talk) 20:52, 12 July 2009 (UTC)
If it is TiC coated then the aim is to protect the fibre, - it seems that other strong metals are not as good see [12] (talk) 20:57, 12 July 2009 (UTC)
It would be easier to guess if it was known what part of the car was being made - other options exist - such as titanium metal with carbon, or titanium carbide fibre reinforcement, and carbon fibre with titanium carbide inside it eg [13] mentions brake discs. (talk) 21:03, 12 July 2009 (UTC)
If anyone is curious, the actual term used was "carbotanium". --Mark PEA (talk) 11:46, 13 July 2009 (UTC)
Ahh that's the one, thanks! Regards, --—Cyclonenim | Chat  14:34, 13 July 2009 (UTC)

Primate Relatedness[edit]

I know that the apes are the closest relatives to humans, with the Chimpanzee/Bonobo being the closest to humans out of the apes. I also know that Old World Monkeys are then the next closest in relatedness to humans after the apes, but which living species of Old World Monkey is closest in relatedness to apes, and thus humans? Hot floppy bread (talk) 21:00, 12 July 2009 (UTC)

Remember that the evolutionary tree spreads (sideways), and is not purely linear - so that the old world monkey closest to apes is not necessarily the closest to humans. (Though it probably will be having said all that) (talk) 21:07, 12 July 2009 (UTC)
Indeed that is something I should have taken into consideration. If there are two different species for ape/humans I suppose I'd be interested in what both of them are. I was thinking it may possibly be a species of Macaque seeing as some of them have not much of a tail, although I suppose that it is far more likely a result of paralell evolution between the macaques and apes rather than a direct linear evolution from macaque to ape.
It seems that the prevailing opinion is that the old world monkeys are a monophyletic group, that is, they all derive from a single common ancestor species. This would mean that they are all equidistant from humans in evolutionary terms. Looie496 (talk) 21:39, 12 July 2009 (UTC)

Interesting, thanks. So that obviously explains the relatedness in evolutionary terms, but presumably the genetic relatedness to humans would differ within the old world monkeys, considering the wealth of diversity found within the family? If this is the case, which species would genetically be the closest (if this is even known at all)? Hot floppy bread (talk) 21:53, 12 July 2009 (UTC)

Even if the genes of all were known I think you would be looking at different species sharing and lacking matching dna (with humans) to varying extents (not necessarily the same sets of genes) - possibly with no clear winner. eg which of "1235" and "1245" is closest to "12345". Maybe it would be best to ask in terms of characteristics. (talk) 22:05, 12 July 2009 (UTC)
Looking at characteristics leads to endless disputes with no principle way of resolving them. If you look at genes, and if you buy into the prevailing dogma that average rates of genetic change are constant over time, then the Law of large numbers applies: with thousands of genes to take into account, the differences between various species of monkeys and humans should all be the same to within a few percent. Looie496 (talk) 00:22, 13 July 2009 (UTC)
"The prevailing dogma that average rates of genetic change are constant over time" is neither a dogma, nor an assumption, nor true. It seems to be approximately true for certain types of non-coding DNA among closely related animals with similar generation lengths. --Stephan Schulz (talk) 12:05, 13 July 2009 (UTC)

Gametogenesis in Hermaphrodites (earthworms)[edit]

I understand earthworms, nematodes, and several other species reproduce sexually with both sperm and egg production. Since they are hermaphrodites, and they perform both oogenesis and spermatogenesis, I wonder how they split their chromosomes during meiosis. Do they have an X and a Y, or do they have some type of sex determining chromosome?

And how exactly do they form sperm and egg? I know during meiosis in humans, it is supposed to be only sperm or only egg, and the determining chromosome, the Y in males, is what leads to the formation of male sex organs. Do earthworms have specific karyotypes for male or female? XX or XY?

And how are male earthworms made? (A small percentage apparently have only male sex organs).

I ask this because I have learned about the XX and XY chromosomes, but I can't understand the concept of meiosis in hermaphrodites.

Any biologists please help.

--Screwball23 talk 22:11, 12 July 2009 (UTC)

The Sex-determination system article is a good place to start. It addresses some of your questions directly, and provides links for further reading. --Dr Dima (talk) 23:08, 12 July 2009 (UTC)