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... for the condition of feeling a sharp and astringent sensation in the back of one's mouth and up to the inner ear parts when eating strawberries? --hydnjotalk02:17, 3 March 2007 (UTC)[reply]
You may be suffering from a mild allergy, causing your throat to swell. This might produce a tingling sensation. Allergies to berries are very common. 128.12.131.6203:35, 3 March 2007 (UTC)[reply]
You may be right, 128.12.131.62, but, as far as I know, I have no allergies and yet I'm very familiar with the sensation described by hydnjo. Could it be connected to the parotid glands overproducing saliva or such? It only happens to me when I haven't eaten anything for a while. I tried googling it, but only found diseases and allergies, not the everyday phenomenon. ---Sluzzelintalk03:56, 3 March 2007 (UTC)[reply]
At first I thought it was an obscure sensation relegated to only a chosen few but as I began to question others, it seems to be not so obscure; my wife Heidi has it as does one of my children. So, if it's prevalent (or somewhat common), why doesn't it have a name or whatever? Any help would be appreciated. --hydnjotalk04:05, 3 March 2007 (UTC)[reply]
I'm not sure, but I think I may experience a similar sensation to you. I don't believe it has ever happened with me and strawberries; the kicker for me is some sort of grapefruit, and it's completely unrelated to the strong aftertaste punch. It kind of reminds me of a chill, but somehow more electric and there doesn't seem to be any connection to my spine or nerves as a "chill" would. Could this be the same sensation? I'm also curious as to what it is. 222.158.163.24509:53, 4 March 2007 (UTC)[reply]
I am trying to help a student with a problem that has me stumped.
An electron is accelerated through an electron gun. The potential difference between the two plates (as shown below) is 4000V. Given the mass (9.1 x 10-31kg) and charge (-1.6 x 10-19C) of the electron, calculate its velocity. The diagram looks roughly thus:
+| |-
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------------> path of electron
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This is outside of what I feel comfortable with, but just off the top of my head, would the formulas in capacitor help? 0.5 QV looks promising...then, maybe equate that with KE since mass is known. --HappyCamper07:11, 3 March 2007 (UTC)[reply]
Trick is to think just in terms of energy - the energy gained by the electron depends only on the potential difference between the plates. Now the acceleration of the electron will depend on the potential gradient which does depend on the distance between the plates - but you are not asked to find any details of the motion of the electron as it travels between the plates - you are only asked for its final velocity. Gandalf6111:09, 3 March 2007 (UTC)[reply]
Atoms charged the same will repel each other, so it would create an extra outward force. It would probably expand the surface area, but also increase the Gibbs free energy (by increasing pressure). These might cancel out, but I wouldn't assume so. --h2g2bob21:20, 3 March 2007 (UTC)[reply]
Hi, I am just another curios reader of science and technoloy. I was reading about invisibility yesterday and I read some really interesting facts about metamaterials and about left handed reflection and retro refllection. But the working of metamaterials and how to create an invisibility cloak is still not known to me. I found the explanation in other sites too complicated. Can we create simple meta materials in a normal school physics lab? If so, how? i went to the following site and found their explanation too tough to comprehend. Could somebody please tell me how invisibility works please?
Right now, it doesn't work - there have been some half-assed attempts to do something along the general lines of invisibility - but the best minds have worked on it and don't yet have an answer. I would guess that over the next ten years we might have some success in producing an outfit you could wear that would provide limited invisibility when viewed from a particular direction - but a gadget that would produce invisibility from all possible directions is a lot further off than that - if it's possible at all. SteveBaker16:14, 3 March 2007 (UTC)[reply]
I read somewhere that it may be possible to create an 'invisibility suit' woven from densely-packed optic fibre. The incoming light from the back is transferred around the wearer's body through the fibre optic cables to the front and vice versa. It'd certainly be a feat of engineering to make it convincing and effective though. Then again, 100% invisibility may not be necessary anyway - just enough to break up the human shape against a complex background and cause confusion would probably be as much 'invisibility' as most humans would require (say, in a combat situation). I mean, the Predators weren't 100% invisible, were they? ;) --Kurt Shaped Box19:15, 3 March 2007 (UTC)[reply]
That's why I made the caveat about when viewed from a particular direction. You could (in principle) use a dense bundle of optical fibres to capture light shining on a person's back - and route it around to their front. In order to do that, you'd need some kind of lense to capture and distribute light over the whole area of the body - then scrunch it down into narrower fibres and distribute it on the other side - but maybe we could believe that. But now consider what happens if you are looking from the person from 45 degrees off to one side. If the fibres capture the light from a wide angle and distribute it out through a wide angle then the image you'd see would contain light that came from directly behind the 'invisible' person - which would be off to your side when you are looking at them from 45 degrees to their front. So that would just give them an overall diffuse glow without providing enough detail of what's behind them to make them invisible. So you'd need the fibres to grab light from just one narrow angle and distribute it out through one narrow angle. But then at each teeny-tiny location on the persons exterior, you'd need thousands of fibres capturing light from different angles. The impossibility of doing that in any reasonable way is what makes me thing that this simple approach won't work. There have actually been some experiments with people attempting this kind of thing - although they tend to use a camera to capture the light and some kind of LED display to display it. A guy called Susumu Tachi has demonstrated a suite with 'retro-reflective' properties that can be made to vanish into the background by projecting the background image onto the front of it. It's not exactly impressive though: [1]. To make these things really work, you need realtime interactive holograms - which are a long way off yet (at least as a practical matter. SteveBaker23:40, 3 March 2007 (UTC)[reply]
There are no veins in the neck that will cause unconsciousness if occluded (at least not for a pretty long time). The brain is fed mostly by the internal carotid artery, a branch from the common carotid; and vertebral artery, though there are many anastomoses. The common carotid is accompanied by the vagus nerve, which may also cause unconsciousness if stimulated manually. Blocking blood flow to the brain can cause ischemic brain damage, traumatic brain damage including hematoma, stroke, thromboembolus, and death. These arteries and nerves are located in the... cervical region. tucker/rekcut17:36, 3 March 2007 (UTC)[reply]
In judo class we learned certain techniques for occluding blood flow through arteries in the neck which quickly led to unconsciousness. It only takes seconds. Edison07:16, 4 March 2007 (UTC)[reply]
is it posible to ionise air using a laser ? if it is what kind of laser would it require , would it be expensive and could it be used to help propagate an electric arc along its path? —The preceding unsigned comment was added by 216.113.99.56 (talk) 14:10, 3 March 2007 (UTC).[reply]
Yes, it's possible. Laser-induced breakdown is usually an unwanted side effect in certain industrial applications. You need very high laser powers; see this page for a bit more detail. I suppose it could in principle be used to start an electric arc, though I'm not sure how much distance you could get it to cover. TenOfAllTrades(talk) 19:14, 3 March 2007 (UTC)[reply]
I love this diagram from the USGS, but I can't find a higher resolution, colour version of it. (I can find a higher resolution 1-bit black+white version, or a smaller colour verison, but nothing better than this one). Anyone? —Pengo14:16, 3 March 2007 (UTC)[reply]
The graphical style makes me think it's from an older print publication, perhaps from as early as the 1960's. I suggest you write to Kathie Watson and ask her -- there's a chance that, once you know the name of the publication, you can order a copy or otherwise track one down. —Steve Summit (talk) 15:17, 3 March 2007 (UTC)[reply]
If you don't mind it being a little grainy there are programs that can upscale images quite a bit without noticeable distortion, although there is a bit of pixelation if you blow it up too much. If I were too pick a less extreme resolution it could be blown up without as much grain. --VectorPotentialTalk15:23, 4 March 2007 (UTC)[reply]
That's pretty useless, at least the way you've done it. There are programs that can scale up images in ways that at least mostly avoid the pixelation effects, leading to a perceived, if not actual, higher resolution. (One I've personally used is Shortcut S-Spline, but apparently there are others such as Genuine Fractals.) However, even those programs can't really add detail that isn't there in the original. —Ilmari Karonen (talk) 01:02, 5 March 2007 (UTC)[reply]
Yes, all it's done is increase the filesize by 27× from 104 KB to 2.89 MB. Much of the detail in the image (either version) is washed out, which you cannot retrieve this way. —Pengo23:01, 5 March 2007 (UTC)[reply]
Electricity, electromagnetism, evolution, the Hall effect, the Edison effect, or relativity were fine discoveries, but were of little immediate use. For useful discoveries, I would look to the germ theory of disease by Pasteur, which immediately led to lower morbidity and mortality in surgery, the discovery of X-rays which was immediately put to use treating persons with broken bones or imbedded bullets, or the discovery of insulin which was immediately put to work saving the lives of Type 1 diabetics, or the discovery of antibiotics, which was soon used to save the lives of persons with infections during World War 2. Edison07:12, 4 March 2007 (UTC)[reply]
What about whatever it was that persuaded people to then try to find out even more about the world
Maybe it was the toilet. Think about all the lives that were saving from living seperated from our crap
environmentally friendly of disposal of dildoes (dildos?)..
hi,
I' having a big clear out of my room and, like all good global citizens, am trying to reduce what i send to landfill. Anyway, i've come to a stumbling block with my dildo collection. Aside from not knowing the plural form, i think my dildo phase may have passed so want to chuck them. is there anyway they can avoid landfill or will the planet just have to be another thing that they screw? help much appreciated!
87.194.21.17715:04, 3 March 2007 (UTC)[reply]
assuming that this is ligitimate, you have two types of "waste" to dispose of: plastics and batterys. Separate the plastics from the batteries and dispose each based on local directives. But this is NOT the proper solution from an environmental perspective:Yyou should recycle them. you are past this phase, but many others are not. Therefore, you should try hard to pass these devices on to others, After cleansing them. If you fail to do this, you are contributiong to destruction of the environment exactly to the extent that the "others" are purchasing new "equipment." So, if you do not know others who will use eh devicec, the most enironmetally acceptable approach is to place the devices on e-bay. -Arch dude07:20, 4 March 2007 (UTC)[reply]
Cheers guys- most helpful! i think ebay might be the answer (although, someone who buys a second hand dildo.......). anyway, check out ebay.co.uk in the near future! (p.s. i'm loving quiver of dildos!)
As a means to explore artificial human intelligence I developed a computer program which could reduce multiple state equations to minimum form. In very short order I realized that I would need a much bigger computer for more than only a few states and variables due to the resulting exponential increase of the chart for the method I was using. One of the major problems I was having was in trying to locate other multiple state logical equation reduction researchers who may have known about or who had themselves created less resource consuming methods or that perhaps ran the method I was using on the fly. However, I never found anyone. Now with the Internet and the capability offered by the Wikipedia in particular I was wondering if there might still be someone interested in this field since reduction of only a minimal number of variables and states has proved to provide results similar if not identical or superior to humans. Nocternal17:20, 3 March 2007 (UTC)[reply]
Can you give us a bit more detail on how the resources are currently consumed ? Do you mean memory, disk space, or CPU time ? Can you describe the data structure you are using and their size ? StuRat20:53, 3 March 2007 (UTC)[reply]
Essentially the method creates a table consisting of every possible combination of variable and state contained within the terms of the logical equation being submitted for reduction. The method proceeds through the table marking the terms in the equation and then eliminating irrelevant and higher level combinations until the reduction is complete. The difficulty being that the amount of memory required to create every possible combination grows exponentially with the number of variables and states of which the terms of the equation are composed. Its been awhile but my margin notes indicate table size to be: T=(x^n)*((x^n)-1) where x is the number of states and n the number of variables.
Virtual memory [or disk space] was not available [for microcomputers] in 1978 so disk space was not used as it would be now. CPU time was not a factor purse except for the additional time to process a larger chart. Modern Internet based distributed programming would most likely increase the number of variables and states but a limit would still be reached quickly due to the exponential requirements of the chart. Nocternal00:31, 4 March 2007 (UTC)[reply]
OK, what type of variable is the table composed of ? Integers ? What values do you have in mind for X and N ? Is it really necessary to keep the entire table in memory at a time, or could most of it be written to disk and only accessed as needed ? StuRat01:40, 4 March 2007 (UTC)[reply]
As I recall the original binary version was written using a string array since it was the only way to handle non-existent or non-relevant states which were therefore represented by a blank space (neither zero or one being valid, i.e., not used or not necessary in the reduced equation.) [One spin-off project was the fabrication of a three state reduction processor chip using this technique but as I recall cost became the issue.] In fact it was the use of a string array that led to the discovery that the method could be applied to multiple state equations as well by simply using two ASCII characters to represent variables with multiple states respectively. (Actually the binary version used upper and lower case letters to represent binary variables and their states while lower case letters followed by integer string characters were used to represent variables and their multiple states.) Most operating systems now provide built in virtual memory such that any table larger than internal memory is partly stored on disk no different than an oversized document in say Microsoft Word or Excel. Nocternal02:40, 4 March 2007 (UTC)[reply]
Distributed programming offers the greatest potential for processing a mammoth table such as would be required to reduce to minimum form a multiple state equation even limited to only a reasonably few number of variables and states; where: x=e^(ln[1/2+1/2*(1+4*T)^1/2]/n), and n=ln[1/2+1/2*(1+4*T)^1/2]/ln[x]. Nocternal02:46, 4 March 2007 (UTC)[reply]
I still need to know what the final numeric values are for X and N, to know what size of T you're talking about. Certainly using an efficient storage method is important, too. If you use one character to represent one of three states (yes, no, and unknown), out of the 256 states it can hold, that's quite inefficient. It takes some time to write the current memory out to paging space and fill the memory back up with another chunk. This isn't a problem in some cases, say if the memory is used sequentially, but can be a real CPU time issue in other cases. If the memory is accessed at random, for example, then it will constantly be necessary to swap memory. Thus, the program needs to be written in a way to limit this swapping, or the CPU time becomes absurdly large. Also, depending on the operating system, it may not have access to the entire hard disk for use as virtual memory. This is because the software hasn't kept pace with hard drive expansion. For example, the indexing scheme may not allow access to the entire hard disk. Also, under Windows 98, at least, you can only specify a single disk partition for virtual memory. Under Linux, you need to create specific Linux swap partitions and mount them to the system. What's your OS and current virtual memory settings ? StuRat12:19, 4 March 2007 (UTC)[reply]
Is the data in the table 'coherent' in any way - is it (for example) mostly full of zeroes - or do long stretches of the array fill up with identical values? Sparse matrix techniques or run-length encoding or perhaps even delta encoding could produce drastic size reductions if that is the case. SteveBaker01:54, 4 March 2007 (UTC)[reply]
Unfortunately each value in the array is unique and not subject to that form of direct size reduction. If the operating system uses such forms of compression then that might be a different story and the only way the application program might take advantage of that. For storage, as with other compression methods, yes. For processing, as with other compression methods, no. Nocternal02:47, 4 March 2007 (UTC)[reply]
Here is a scheme you could use to encode 4 variables, with 3 possible states each, into a standard 8-bit character:
Bit 1 (unknown flag for variable A)
Bit 2 (value of variable A, if known)
Bit 3 (unknown flag for variable B)
Bit 4 (value of variable B, if known)
Bit 5 (unknown flag for variable C)
Bit 6 (value of variable C, if known)
Bit 7 (unknown flag for variable D)
Bit 8 (value of variable D, if known)
This is 50-100% efficient, since, if none of the variables are known, the even bits are not needed. Another issue is the index size. If each variable can have a non-contiguous location in memory/on disk, then each needs to have it's own memory location index, which could easily be larger than the actual data. This is normally handled automatically by the run-time system, but still needs to be considered. For example, if you had 100 gigabytes (800 gigabits) you wanted to use for the actual data, and each bit can be non-contiguous, this would require 39 bits of index to record the memory offset for each bit of data. Thus, only 2.5% of the memory/disk space is taken up by actual data, with the rest for indexing. If you can specify that the entire table in-memory/on-disk used for virtual memory is contiguous, then this indexing can be skipped, and the location offset of each array element simply becomes the array element number times two, with the unknown flag for that variable being directly before that. This would require programming in a language that supports direct memory access, like C, and you would also need to have a large chunk of contiguous disk space available without any bad sectors. Alternatively, some more efficient way for dealing with a small number of bad sectors could be devised. StuRat13:03, 4 March 2007 (UTC)[reply]
Thanks StuRat for this suggestion and your time and hard work behind it.
Lets consider using this scheme for chart creation and data storage so as to facilitate retaining the current logical equation reduction method and using it to process equations on the fly.
Such a scheme requires 2 bits for a binary stated variable and would require 9 bits for a multiple stated variable with 256 states, etc. Since it embodies the basic requirement for knowing whether a variable is living or not lets consider using this scheme to record any number of states for any variable. We can name this scheme the StuRat Number of States payload or the SNS payload for short and make it part of a logical equation reduction data protocol.
I too like the idea of using contiguous memory to hold data since it can greatly simplify an addressing scheme so lets do this by wrapping the SNS payload in a layer which contains the variable number or name. We can then combine these as terms in our equation and wrap them in layers as well. The data which makes up the chart can be organized in the same way. Then its only a matter of putting a distributed program to work by submitting various work units made up of logical equation reduction data packets to a number of the programs for processing. Nocternal16:58, 4 March 2007 (UTC)[reply]
Note that while it would indeed take 9 bits to represent 256 possible states with an "unknown flag", it would only take 8 bits to represent 255 states, if you just designate 00000000 as meaning that the state is unknown. StuRat19:50, 5 March 2007 (UTC)[reply]
Unfortunately 8 bits (0-0000000 - a "disregard flag" plus 7 bits) already has the preallocated meaning of 0000000 (7 bits/128 states) not being part of the final equation. However, I'm quite satified with this scheme as to it memory saving capability over using string variables and its ability to serve as the core payload in a logical equation reduction data packet protocol. Next step is to write a distributed processing program based on the current methodology that will use this protocol and allow a single equation to worked on by many resources. I'l first have to come up to speed on the details of how the current methodology works. Its been a long, long , long time since I was tinkering around inside the engine! Nocternal22:52, 5 March 2007 (UTC)[reply]
If the propagation of a gravtational field is not instantaneous and probably not faster than light (has any experiment yet been devised to try and measure this speed), then how would the vast delays - 100,000 years to traverse our galaxy - affect the dynamics of the evolution of galaxies? Paul venter18:42, 3 March 2007 (UTC)[reply]
Well, I'm definitely no expert in this area - but since nobody else has rushed in with a great answer, I would speculate that because gravity is more or less a side-effect of significant amounts of matter accruing, that the slow motion of the matter (compared to the speed of light at least) would mean that the shape of the gravity field would not lag behind the location of the matter to any important degree. Perhaps more importantly, remember that when you are outside of a body (even a loosely connected one like a dust cloud or a galaxy), the gravity acts exactly as if all of the mass was located at the 'center of gravity'. So if dust and gas is merely falling or coalescing into the center of some body like a star or a star cluster, the gravity field outside of that forming body will be just the same as it will finally be after it's finished coalescing. Well - that's my best shot. It's possible that I'm wildly wrong. Let's see if anyone can correct me. SteveBaker00:33, 4 March 2007 (UTC)[reply]
The most important aspect of how galaxies evolve is the radial gravitational potential, and, to first approximation, that's pretty constant, since you don't get stuff rapidly zooming in and out changing that radial profile - instead it goes round and round. It can make a small difference to the dynamics where matter is conentrated locally - spiral arms, for example - but I doubt the effect will be dominant above everything else that's going on. Since most speeds are far slower than the speed of light, and the distances involved are vast, most motion would still be relatively small when compared to the propagation time for gravity. i.e. two massive concentrations of matter might be a long way away, but they probably won't be moving too fast relative to one another and will only cover a bare fraction of the distance between them, when compared to c, so the effect will be small.
People and goverments are not happy that there is every summer more and more algae in the Baltic Sea. It looks bad and it makes some beaches unswimmable, and it makes some species not to like environment. But I don't understand why no one seems to be happy that it removes carbon dioxide and fights against global warming. What is your opinion, is Baltic Sea algae more good or bad? 193.65.112.5118:56, 3 March 2007 (UTC)[reply]
It sounds like a NIMBY issue. That is, it may be good for the planet, but not for the local residents. There are many such issues, like the proposed nuclear waste dump at Yucca Mountain. StuRat20:41, 3 March 2007 (UTC)[reply]
The amount of carbon dioxide it's mopping up is probably trivial, and the cause is probably super-phosphate fertilizers from agriculture, and the algae probably isn't algae but blue-green algae aka Cyanobacteria, which would probably not naturally occur in such quantities in the area. I say probably because I know nothing about this actual case, so i'm just guessing —Pengo23:10, 5 March 2007 (UTC)[reply]
Why do doctors use silicon or saline rather than fat from another part of the body? Will the body absorb the fat if its moved from one place into the breasts? —The preceding unsigned comment was added by 76.167.136.84 (talk) 18:48, 3 March 2007 (UTC).[reply]
Would make the procedure more complicated then it would need to be, they'd need to start by surgically removing the fat, then they'd have to take time to manufacture a custom implant, and then another major surgery to implant them. Which would be two elective surgeries rather close together, which doesn't give the patient much time to recuperate--VectorPotentialTalk20:47, 3 March 2007 (UTC)[reply]
Not to mention that the woman would then have two breast-shaped depressions on some other part of her body. Hardly the fetching effect the woman would be hoping to achieve. 71.112.122.21400:54, 4 March 2007 (UTC)[reply]
Surgeons do use little lumps of fat from the thighs or abdomen to fill in the holes left when a pituitary tumor is removed, but to replace a removed cancerous breast would require a huge amount of fat. Edison07:05, 4 March 2007 (UTC)[reply]
Actually some doctors use liposuction to gather fat to place in the mammary region but there are some problems with it, the fat can crystallise renderring detection of tumours very problematic and some of it can be re-absorbed by the body resulting in asymmetric breasts. This procedure does not leave "two breast-shaped depressions on some other part of her body" since the fat is removed from varios regions, the liposuction should leave some minor scars though.
I've been reading around on bodybuilding sites and they talk about Insulin like Growth Factor 1. I also read the wikipedia article and still dont understand exactly what it would do for a bodybuilder and why they use it. Is it like growth hormone? What are its benefits?
Not being an expert on the field but being a bit of a weight lifter myself I can give the following comment. According to the article this growth hormone simulates muscle growth and has been used for therapies treating muscular dystrofy. So body builders most likely use it to increase muscle mass. —The preceding unsigned comment was added by PvT (talk • contribs) 13:32, 4 March 2007 (UTC).[reply]
I'm wondering how efficient the body is in absorbing the calories that are ingested? Since the calories of a food product are determined with a bomb calorimeter, it's not clear how much of it is actually absorbed. The nutrition article mentions some stuff, but is not clear on how efficient the body is in absorption. I have no basis for it, but I would believe a number in the 75-90% range, so your 100 calorie snack is really 75-90 calories absorbed. —The preceding unsigned comment was added by 75.42.129.102 (talk) 20:14, 3 March 2007 (UTC).[reply]
Well, it depends on how you define efficiency. For most energy uses, heat is considered to be a wasteful byproduct of inefficiency, but that same heat produced by the human metabolism can be either considered a useful product (when it's cold around you) or an absolute nuisance (when it's hot out). So, the efficiency might be much higher in winter, given those definitions. StuRat20:26, 3 March 2007 (UTC)[reply]
Then of course you have that Olestra oil which has a similar calorific value (as measured by a bomb calorimeter) as regular fats - but which is totally indigestible to humans. Several kinds of potato chips use it to make "low-calorie" snacks. In that case, the efficiency must be close to zero! What this shows is that there is certainly going to be a difference in absorption rates for different lipids and carbohydrates compared to the numbers that a calorimeter produces. How big those differences are - and whether they matter - is a question for which I have no answer. SteveBaker00:59, 4 March 2007 (UTC)[reply]
I can see why fish would need to swim in a certain orientation when near the surface or the ocean floor, but when far from either, why not swim upside-down or side-ways ? Is there any advantage to swimming in a certain orientation in a "weightless" environment ? StuRat20:21, 3 March 2007 (UTC)[reply]
Well, Stu, as you know an ocean is not really a weightless environment. Any part of the fish that is lighter than water (swim bladder or tissue rich in fat) exerts an upward net force, and any part of the fish that is heavier than water exerts a downward net force, hence the orientation. The particular heavier-than-water piece that fish use for up-down orientation is called otolith. That would not work in orbit though, or in any truly weightless environment. Cheers, Dr_Dima.
Fish that live relatively close to the surface often have lighter undersides and darker topsides as a form of protective camoflage. That would only work if they swam the same way up all the time. SteveBaker22:01, 3 March 2007 (UTC)[reply]
Oops. I re-read your question and it looks like what I said above wasn't really what you were asking. You are asking about an advantage of swimming in a certain orientation, not about how the fish "knows" which orientation it is in. IMHO, the preferred orientation is dictated by sensory organ positioning (most importantly, eyes) and by the shape of the mouth. Most non-bottom-dwelling fish prefer the "standard" orientation for these reasons, I think. Sharks often turn on their side for an attack, though. Best wishes, Dr_Dima.
I don't understand, why is it better to have your eyes on "top" and mouth on the "bottom" in a 3D medium ? StuRat23:04, 3 March 2007 (UTC)[reply]
There is the interesting case of flatfish such as the Sole/Flounder - which swim like ordinary fish when juveniles - but as they get towards maturity start to swim on their sides. That would seem on the face of it to fit with your theory that it doesn't matter - but whichever eye would end up beneath the fish moves around on to the top and the mouth moves around underneath. The 'top' side of the fish gets darker in colour and the underside gets lighter. But these are bottom-feeders so I guess they have an important reason to need that set of orientations. SteveBaker23:23, 3 March 2007 (UTC)[reply]
My best answer, though in someways unsatisfying, is phylogenetic inertia (roughly, stability of a species or resistance to evolutionary change). Simply put, there was possibly a first order appearance of a stable organism with eyes above mouth; so unless there is disadvantage to this first model, or an advantage to a new model, no change takes place. A bit vague I know, but it's all I can muster right now. --Cody.Pope08:24, 4 March 2007 (UTC)[reply]
That's a satisfactory explanation for me. Assuming a mutation allowing easy upside-down swimming in a single fish (i.e. if the eyes were in a different position, and/or the fins shifted), would the fish not need the ability to orient itself easily from both positions? Having all fish pointing in the same direction seems to eliminate additional orientation problems, or at least one level of complexity in the instict to orientate "upwards". 222.158.163.24509:29, 4 March 2007 (UTC)[reply]
Why are we assuming each fish must have a single orientation in which it swims ? The "phylogenetic inertia" seems wrong to me unless a specific mechanism can be found which favors the old way over the new way. Indeed, I would expect genetic drift to slowly change organisms in ways that don't matter. I can think of one mechanism for keeping fish swimming the same way, though. Once it was established that some fish would swim in one orientation (probably because of the advantage of swimming this way for bottom-feeders), then any fish which evolved from those would also tend to swim in the same orientation initially. Any fish which were different would be visually obvious, making them easier prey, especially if swimming in schools. Also, such behavior might trigger other fish of the species to "think" that "there's something wrong with that fish, don't reproduce with it". This seems somewhat less likely with the many fish which fertilize eggs externally, however. This theory presupposes that all fish are descendants of bottom-feeders, is this true ? StuRat11:20, 4 March 2007 (UTC)[reply]
I suppose it could be something like: Gravity makes small particles of food drift slowly downwards - so if your eyes are on top then you see the food coming from above and have time to open your mouth before it's fallen far enough to eat. If you habitually swam 'upside down' then you wouldn't see the food until it was too late to grab it. For predators (at least close to the surface), looking upwards allows you to see your prey sillouetted against the sunlight filtering down from above. If you look down on your prey then they can camoflage themselves against the dark water beneath much more easily. I don't think this works for all species - but if it mattered greatly for some ancestor of all modern fish and there was no particular preference for subsequently evolved descendents of that ancestor - then all fish would end up with their eyes above their mouths. It doesn't surprise me that fish have a preferred way of swimming because matters of directional control are much easier when you are stable in the water rather than rolling around all over the place - so if the only matter is which orientation you pick to be stable in - then 'eyes on top' has enough of an advantage. It doesn't take much of an advantage to make evolution drive the entire species in one direction. SteveBaker15:14, 4 March 2007 (UTC)[reply]
Other than in a fish tank, I don't think most food particles fall from the surface. Many fish eat krill or other fish, for example, which can move about in any direction. As for the camo, many fish are lighter on the bottom so they blend in with the lighter water on the surface, when viewed from below. Of course, this could just as well be reversed, and they could have light-colored backs and swim upside-down, right ? StuRat22:07, 5 March 2007 (UTC)[reply]
Fish anatomy, particularly with regards to fins and gills and protective colouration, evolved to make an exquisite swimming machine when in the classic orientation. Its not so different for human swimming. Freestyle swimming is often considered synonymous with front crawl, even though swimmer can use any style they want. Why? Because in terms of speed, economy, safety and awareness, that is the best swimming orientation. Rockpocket21:27, 4 March 2007 (UTC)[reply]
Also consider that when fish die they usually have a different orientation which might attract crabs or other sea creatures that look for fish that are dead. Maybe its just plain safer not to swim upside down or sideways and probably better for their love life. Nocternal01:30, 5 March 2007 (UTC)[reply]
Can the suject this picture that I took be identified? I like the picture, and I would like to see it in the appropriate article. (Forgot to sign!) Thegreenj20:33, 3 March 2007 (UTC)[reply]
