Wikipedia:Reference desk/Archives/Science/2006 September 20

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September 20

Health Care Supply in Canada 12 years ago and today

Hello,

Thank you to anyone willing to help me out.

I'm looking for the number of medical school seats in canada in 1994, and the number available now. Does anyone have that information or a lead on where I can look for that information?

A most sincere thank you,

Matthew LR

Some information is available from Statistics Canada; for instance, they report 265 graduates in 2003 with earned doctorates (and a further 270 at "other graduate level") from "health, parks, recreation and fitness" programs, which includes medical residency programs. I think it's fair to assume most of these are med school; how many people get a doctorate in push-ups or camping? Multiply this by the length of medical school (6 years?) and it's a good back-of-the-envelope estimate. Their ESIS program may have more information, or could help with the historic info. This article might also be a good place to search. --ByeByeBaby 15:23, 21 September 2006 (UTC)

Breast removal

If I cut off a girl's breasts, what will happen to her? What will she look like? (Yes, I know she's not going to be able to breast feed, but are there any other negative effects?) --Bowlhover 04:19, 20 September 2006 (UTC)

See Mastectomy. --Allen 04:21, 20 September 2006 (UTC)

Massive blood lost (defined as over a liter) seemed to be ignored. — [Mac Davis](talk) (SUPERDESK|Help me improve)04:37, 20 September 2006 (UTC)

Surgery should only be done with the informed consent of the patient, and only by those medically qualified, using all applicable standards of sterile technique and anesthesia. And what would happen to you if she cut off your breasts?Edison 05:05, 20 September 2006 (UTC)

What about the Amazon warrior women? Or is that a myth?--Light current 05:39, 20 September 2006 (UTC)

Yes, I believe that is a myth, that Amazon women removed one breast to improve their ability to pull back an archer's bow. The existence of the Amazons may even be a myth, although there does seem to be some supporting historical and genealogical evidence. StuRat 13:01, 20 September 2006 (UTC)

That particular part of the myth is particularly hard to believe. It would take enormous breasts to interfere with archery at all, and in those rare instances they could be bandaged. Durova 13:31, 20 September 2006 (UTC)

Please discuss this question with your therapist. Please. 69.142.89.10 08:07, 20 September 2006 (UTC)

Im not a doctor (obviously?) but I would have thoght that the poor girl could bleed to death!--Light current 21:59, 20 September 2006 (UTC)

Your name isnt Shylock is it?--Light current 15:59, 20 September 2006 (UTC)

How did you know my name? --Bowlhover 04:01, 21 September 2006 (UTC)

Well...when I asked the question, I was thinking of torture rather than surgery. The Lord's Resistance Army loves to mutilate people, and I wonder what happened to the girls they abducted. --Bowlhover

She will look a lot like Agatha of Sicily a.k.a. Saint Agatha.

Atlant 01:14, 21 September 2006 (UTC)

about non watson and crick base pairing

it is known about watson and crick base pairing in DNA molecules but are there any other non watson and crick base pairing in DNA molecule please give me some informations on it.

it is quite common in RNA. not sure about in native DNA, but it can obviusly occur in DNA-like molecules containing unnatural bases. Xcomradex 07:20, 20 September 2006 (UTC)

See base pair, and follow the links in the 'See also' section. TenOfAllTrades(talk) 12:44, 20 September 2006 (UTC)

Attached to the normal base pairs, you might find DNA methylation, acetylation, or other epigenetic information. —Pengo ^{talk · contribs} 14:56, 20 September 2006 (UTC) (my RfA)

Can you prove existance of colors if you can only see B/W?

I was wondering on the subject on how the design of our human sensors and brain affects our understanding of the universe. Related to this I came up with this abstract question and would like ask the world for input:

If I have nothing but a black & white television, is it possible to prove the existence of color transmission? -- Let's say I suspect that there is a television transmitter sending out in full color somewhere, could I prove its existence using only my B/W television?

Thanks,213.199.128.152 09:14, 20 September 2006 (UTC)Jonas Sig

No, not with a b/w television. Reception in colour requires a very different technology. That was a very practical question. The abstract question you hinted at in the title would be a more interesting one.--Shantavira 09:28, 20 September 2006 (UTC)

To answer the abstract question, yes, a color blind person can prove the existence of color, by looking at a spectral analysis of various colors. That is, they can see that different frequencies are produced by different light sources. Now, they might have no idea how these frequency differences are perceived by those with normal vision, but they would certainly know that colors (frequency differences in light) do exist. StuRat 12:02, 20 September 2006 (UTC)

Color does not exists. It's a sensory fiction created by the biological system known as the eye and the brain. Just ask yourself this question: if no living creatures have eyes, does color exists? 210.49.155.134 12:14, 20 September 2006 (UTC)

The universe does not exist. It's a fiction created by information processing systems. Just ask yourself this question: if no living creatures exist, does anyting exist? --Lambiam^Talk 17:02, 20 September 2006 (UTC)

This is as much a question of philosophy as it is of science. With the television example, no, a B/W television can’t prove the existence of color transmission. However, televisions aren’t such a good analogy for eyes.

Firstly, we have to look at how color is seen. Color is the result of different waves lengths of light. Our eyes has cells which can respond to certain specific wave lengths. Information from many, many cells which respond to certain wave lengths are passed into our brain, where the brain puts together the information and tells our conscience mind what ‘color’ something is.

Now, if we defined color as being the different wave lengths of light, than the existence of color can be proven to a color blind person, as explained by StuRat.

However, if we define color as being the perception of color. So that it is an illusion created by our brain (based on the information received from the eyes) for our conscience mind, then color is completely meaningless for a color blind person. And it would be impossible to prove this perception to be color blind person, since color would be a creation of how the mind interprates sensory information.

In biology, color is defined in terms of the wave lengths of light – so yes, scientifically, ‘color’ can be ‘proved’ to a blind person. And yes, even if no living creatures have eyes, color would still exist because light still has different wave lengths.

But in some schools of thought – people will say that yes, science explains to us what color is in terms of light, but people define what color is. And if color cannot be perceived, then it is not color.

A good question to consider is, do you believe 'ultraviolet' exists? What does it take to prove ultraviolet rays exist to you? After all, ultraviolet refers to light of certain wavelengths. Just like the way “green” refers to light of certain wavelengths. But...is ultraviolet a color too then? you are blind to ultraviolet rays like the way a blind person is blind to the difference between different colors, what would you accept as a proof for the existence of ultraviolet? Yaksha 12:50, 20 September 2006 (UTC)

The claim ":However, if we define color as being the perception of color. So that it is an illusion created by our brain (based on the information received from the eyes) for our conscience mind, then color is completely meaningless for a color blind person. And it would be impossible to prove this perception to be color blind person, since color would be a creation of how the mind interprates sensory information." is somewhat dubious. As for most subjective phenomena, detection of prior basis for the phemonema can be ascertained by double-blind subject categorizations. Or, in less obscure language, one can perform a sequence of experiments on so called "color sighted" people (equiv., "psychic") where the subject is required to identify which of several objects is most similar to the "colored" object. Persistent correct classification, especially across a large selection of "color sighted" people, especially if the experimental design were sufficient and the probability of the sequence of same answers were unlikely to occur by chance, would be a mechanism of the proof of the existence of "color" to a skeptical "achromatic" person.

In fact, this is how achromats perceive color perception in others. They recognize that there is an objective reality to the attribute "orange" (say) that color sighted people persistently apply to specific objects, even though the achromat doesn't perceive any distinction between that object and the "green" object everyone's currently fawning over... -- Fuzzyeric 16:18, 21 September 2006 (UTC)

Perhaps not a very satisfying answer, but if you were to filter the colour signal to show only the red, then only the blue, then only the green, you could see each layer of the colour image on your black and white set. This answer, of course, doesn't look at the perception side of colour. However, we seem to believe bees can see ultraviolet colours even if we have no concept of what that perception may be like (or even if bees "perceive" anything, or if they're some sort of automata). Science is pretty shakey on the subject of consciousness and qualia. All we can do in that department is infer along the lines of "my brain looks like this when I see pink, so if that fish over there has a similar brain pattern when it sees pink, then we must be on the same wavelength." (no pun intended) —Pengo ^{talk · contribs} 15:05, 20 September 2006 (UTC) (my RfA)

Perceived colors do not map monotonically to the spectral wavelength of electromagnetic energy. Metameres are colors perceived identically, but having different physical bases. Many colors, defined by hue and saturation, are in the interior of the CIE color space, and can be created by mixtures of 2 or more spectral colors. These combinations are infinite in number. Also, color perception is influenced by prior exposure of the observer's eye. Stare at a color for say 30 seconds, and you will perceive its complementary color in an afterimage. Repeat the experiment, and after staring at a color, stare at the complementary color, and you will perceive a supersaturated color, more vivid than the pure spectral wavelength pruduces. Add a surround of the original viewed color, and the perceived color becomes even more vivid. Perceptual psychologists have techniques of convergant and discriminant validation to investigate the validity of sensation and perception experiences. They can determine that the same observer reports the same physical stimulus with the same label "red" and applies different color labels to different physical stimuli, and that different observers apply the same labels. They can systematically map stimuli to responses.Edison 17:00, 20 September 2006 (UTC)

I'm surprised that nobody has mentioned the fact that colorblind people do not see in black-and-white. The reason why they are colorblind is simply that the part of their vision system that would normally differenciate the colors doesn't function properly. As hinted above, most colorblind people can look at samples of colors that are considered to be of the same intensity (i.e. brightness/darkness) but of different colors, and clearly see that they are different colors. They would not have the ability, though, to determine which colors they represent, only that they are both of a similar intensity. To actually see something in black and white would involve a much more complex visual system, though would obviously be of no benefit. A friend of mine became mostly colorblind as he got older (and may eventually go completely blind), and he describes his vision now as a mess of indecipherable colors and images, as he progressively loses the ability to interpret the input coming from his eyes.  freshofftheufoΓΛĿЌ  01:31, 21 September 2006 (UTC)

There is a rare form of colourblindness where the vision becomes completely achromatic. In this case people do see in just black and white. The condition is usually from birth, but in one case a painter lost his vision, and for sometime couldn't even bring himself to eat anything ordinarily colourful (like a banana) because it was too odd and disturbing to eat a gray fruit. He also lost his ability to even imagine colour, although he rememebered it existing. The case was described in an Oliver Sacks book, Island of the Colourblind.—Pengo ^{talk · contribs} 15:03, 21 September 2006 (UTC)

Surface area of a pin

Hii my physics teacher asked me how to calculate the surface area of a pin, how the heck could u do that!!

Take a close look at it, is it a series of cylinders and cones ? If so, draw a diagram, then take measurements and do calcs for those primitives, being sure not to count areas twice where the primitives meet. Here is one possible way to model it (not drawn to scale):

+---+
|   +---------------------+ 
|   |                     |   >
|   +---------------------+ 
+---+
 CYL1       CYLINDER2      CONE

Accurately measuring the diameter could be tricky, you might need a vernier micrometer for that. StuRat 11:29, 20 September 2006 (UTC)

I hope it's not a safety pin () but more like a standard pin. The task can be split in three parts: (Step 1) deciding on an appropriate geometric model for your pin (for example the one suggested above by StuRat); (Step 2) estimating the parameters of that model (lengths, diameters, ...), preferably by taking measurements; (Step 3) doing the actual calculation using formulas for the surface areas of various geometric shapes. For step 1, stick to shapes for which you have a formula (see the article on surface area and various articles on shapes). You could go for a standard pin with a spherical head. I'd include a picture in the written report. Since the assignment is about calculation, I would not go overboard in doing the measurements with ultra-high precision. --Lambiam^Talk 14:20, 20 September 2006 (UTC)

Physics professors often give students questions like this to teach them how to do back-of-the-envelope calculations. My professor once asked on a test how much water a person drinks in a year, and there is a famous story about a mathematician who calculated the number of piano tuners in Chicago. Here's an article about these types of calculations: http://en.wikipedia.org/wiki/Back_of_the_envelope Gary 18:22, 20 September 2006 (UTC)

Fermi problem is another name of these, as Enrico Fermi was well known for them (he's apparently the one behind the piano tuner question—a physicist, not a mathematician). --Fastfission 23:49, 20 September 2006 (UTC)

I wonder if the answer is to find the volume first (easy - just drop lots of pins in a small measuring cup with water), and then to measure the pin length, divide the volume by it - that would give you the area of the cylinder's cross-section. That would give you the radius, and you are done. All of this assumes cylindrical shape, of course. --Ornil 20:58, 21 September 2006 (UTC)

Far too experimental: Paint the pin and a test unit area. Remove each mass of paint by solvent extraction. Weigh each mass of paint. Assert that the surface area is the ratio of the masses. For improved precision, dilute the paint first.

Far too hot: Heat the pin to a biggish temperature, like 1 kK. Measure the total thermal radiation of the pin. (Proportional to surface area minus small correction factors for self-visibility.)

Variant: coat the pin with a thin layer of fluorescent or phosphorescent paint. Also coat a test area. Measure the total fluorescent/phosphorescent emission of the pin (when excited) and compare to that of the test area.

Far too difficult: Heat the pin to a biggish temperature, like 1 kK. Insert into a well stirred quenching liquid. Measure the temperature profile for the liquid. Melt the pin into a sphere. Repeat the experiment. The repetition allows you to directly calculate the heat transfer coefficient between the pin and the fluid. Consquently, you may calculate the area of contact in the first experiment.

Far too phishy: Offer to give the makers of the pin some money if they'll tell you the surface area of the pin. -- Fuzzyeric 02:37, 22 September 2006 (UTC)

Piano tuners

How many pianos? How many people want em tuned? How many can afford it? So how many tuners can that business support? Is that the logic?--Light current 23:52, 20 September 2006 (UTC)

Pretty much. As I recall, it required estimates on things like the population of Chicago, the average size of a household, the proportion of households with a piano, the frequency with which pianos are tuned, and the number of pianos the tuner can tune in a year. Put them together, you get your answer. Confusing Manifestation 03:31, 21 September 2006 (UTC)

What kind of bug is this?

I found a bug. Is it identifiable? It was captured in New England, not too far from the coast, if that helps. grendel|khan 12:23, 20 September 2006 (UTC)

Looks a lot like a western conifer seed bug (Leptoglossus Occidentalis) [1][2]. Weregerbil 14:26, 20 September 2006 (UTC)

As both you and the random university entomologist that I emailed concur, I shall be fixin' that image to illustrate the article. Thanks! grendel|khan 18:11, 20 September 2006 (UTC)

Energy when cycling

Yesterday I was cycling along a route I normally run, when I started wondering - why is cycling easier than running? You're going faster, and carrying more weight (moving the bike frame as well as yourself), but using the same legs and cardiovascular system to generate the energy - so surely you should get tired more quickly. Yet it feels easier. Obviously there's some energy not-loss, in that your energy is just going into moving forwards, wheras running also uses energy to push upwards with every step, but is that all the difference? Or is cycling more efficient/am I just imagining the difference in tiredness? Our article on Cycling didn't seem to cover the energy input. --Mnemeson 13:10, 20 September 2006 (UTC)

As long as you don't ride up an incline, the weight of the bike is not directly relevant to the amount of work needed. You have to counter the force of friction and of the deformation of the tubes, which is higher for a heavier bike, but still small if the bike is in good condition. On the other hand, when walking on a strictly horizontal plane, various body parts also have an up-and-down motion component, which does involve work, and this gets stronger with a running gait. Going up a steep incline, walking is easier than running or cycling (at least for me). --Lambiam^Talk 13:32, 20 September 2006 (UTC)

(edit conflict) :Walking requires constant lifting and lowering (or bobbing) of the body to swing the legs. THats where the energy goes in walking (on the flat)--Light current 13:35, 20 September 2006 (UTC)

This is precisely why Ug invented the wheel (which was followed by a rather crazy epoch until someone else invented the brake).--Shantavira 14:56, 20 September 2006 (UTC)

Yeah but it took him a while to realise it should be round. The square wheel he first invented still required extra energy. We still have some of those original wheels on out local buses. 8-)--Light current 15:16, 20 September 2006 (UTC)

Which reminds me of a B.C. cartoon in which we are in the waiting room of the patent examiner's office. Through a window we see carts with square wheels go by in the streets; in the room someone is sitting with a model cart on his lap that has triangular wheels. As the proud inventor explains to his neighbour: "It eliminates one bump."  --Lambiam^Talk 16:49, 20 September 2006 (UTC)

Square wheel production continues today but they are used mostly on shopping carts. I believe there was a Scientific American article in the 1960's looking at the efficiency of bicycling versus running or walking, which showed the calories burned by mile to be way lower for the cycle. For one thing, you are not having to move your center of mass up and down with every step like running.Edison 17:04, 20 September 2006 (UTC)

Hasn't it anything to do with the fact that a bicycle preserves forward momentum much better than walking does? That is, when you're walking, you have to constantly add energy to have the same velocity, and that energy-cost is much lower on a bike. More energy can be directed towards acceleration instead, thus you go faster. Oskar 23:05, 20 September 2006 (UTC)

Mind you, the equilateral curved polygon gives a smooth ride if you use it as a roller.--Light current 17:34, 20 September 2006 (UTC)

Do you mean the Reuleaux triangle? (It sounds like something Inspector Clouseau might say.) While having a constant height in all orientations, its centre does bob up and down a bit – if I remember correctly by something like 7%. --Lambiam^Talk 00:47, 21 September 2006 (UTC)

Well yes! Or anything similar with more 'sides'--Light current 02:16, 22 September 2006 (UTC)

Cycling is the most efficient form of transport. More effcieint than walking or a car (taking into account energy used by the car of course). I think the scientific term for the energy conservation mechanism found in a moving bicycling is called "rolling along". —Pengo ^{talk · contribs} 00:46, 21 September 2006 (UTC) (my RfA)

Thanks for the answers, you guys :) --Mnemeson 01:38, 22 September 2006 (UTC)

Glycemic response

After doing much research on Glycemic index at WP and other sites, a question seems to emerge. Is there any way for a person who suffers from exaggerated insulin response but is otherwise healthy to improve their response to normal foods, aside from reducing glycemic load in meals? --Jmeden2000 14:40, 20 September 2006 (UTC)

I believe many small meals instead of a few big meals helps to distribute the load on the pancreas more evenly. StuRat 15:26, 20 September 2006 (UTC)

As always, get your nutritional info from a registered dietitian and your medical advice from a doctor , nurse, or diabetes educator. Now what do you mean by "exaggerated insulin response?" Are you diabetic? How do you know your body has an abnormal insulin production after a meal? Do you have hypoglycemia, diagnosed by yourself or a doctor, and how was it diagnosed? Anyone can buy a glucose meter for $30 or so at a drugstore and do a finger-stick to test blood sugar premeal, say an hour after, and 2 hours after, etc. Never use someone else's meter or lancets, since hepatitis and other illnesses have been spread thereby. Edison 17:13, 20 September 2006 (UTC)

I am otherwise healthy (according to my doctor) but I experience lethargy after eating a meal of high GI foods, typical of a blood sugar swing. It isn't health threatening but it's disruptive to my work, so I am trying to learn more about it to know if I need to change my diet, behavior, or both so that I can perform better. --Jmeden2000 19:38, 20 September 2006 (UTC)

The lethargy is healthy and normal, the bodies response to the sugar you are eating in the meal. Xcomradex 21:43, 20 September 2006 (UTC)

If its just the high GI foods that wipe you out, why not stick largely to low GI foods then? Mattopaedia 09:44, 21 September 2006 (UTC)

So see above. Buy a Freestyle Flash meter or similar, and test your fasting glucose (premeal) the after the meal 1 hour, 1.5 hours, 2 hours, 2.5 hours, etc up to say four to six hours after eating, and you and the doc will know more than you do now. Edison 14:37, 21 September 2006 (UTC)

a question about seed

Answered

can u tell me what sort of plant has the biggest seed and where they r found?

thanx ~spike

A coconut ? StuRat 15:30, 20 September 2006 (UTC)

The words biggest seed are a really good google search term. See Coco de mer. Weregerbil 15:40, 20 September 2006 (UTC)

ANSWERED -> Capacitance Time Delay Circuit

What formula should be used to solve the following ?

An open circuit exists with a 500 kOhm resistor and 35 microfarad capacitor in series with a 30 volt battery. Once the switch is closed and the circuit is energized, how long until the circuit will acquire 63.2% of it's final charge ?

         /SWITCH   R=500 kOhm   C=35uF
+-------/  --------/\/\/\-------| |----+
|                                      |
|                 |   |                |
|             - | | | | +              |
+---------------| | | |----------------+
                | | | |
                  |   |
                 30 volts

This is a homework problem, although not mine, but somebody I'm helping. Also, I want the formula, not the answer. (However, if you want to give the answer, I won't object too strongly.) :-) StuRat 15:38, 20 September 2006 (UTC)

THe formula for voltage across the capacitor is Vc= 30* [1-exp(-t/RC)]. The figure of 63.2% is a special one as you may see from the equation and the cap charges to this level in a time that is known as one time constant which is equal to RC (ie t=RC). Because [1-1/e]= 0.632.--Light current 15:50, 20 September 2006 (UTC)

Answer 17.5sec--Light current 15:54, 20 September 2006 (UTC)

Thanks...glad to see you have interests other than going to find a man in a bar. :-) StuRat 19:04, 20 September 2006 (UTC)

Welcome! I have many interests, but I must still be a sad person to be spending so much time here. 8-))--Light current 19:11, 20 September 2006 (UTC)

Did you try RC circuit (which needs a bit of a reorganization...)? :p —AySz88\^-^ 17:04, 20 September 2006 (UTC)

A Question Of Bread

In the UK/Netherlands, the cheapest bread money can buy is 28p/€0.39. Is this bread nutritionally inferoir to bread of two or three times the price? --Username132 (talk) 15:43, 20 September 2006 (UTC)

I wouldnt eat that stuff. It wont be wholemeal or anything for that price.--Light current 15:56, 20 September 2006 (UTC)

Sounds like conjecture to me. What do you propose it's made of? --Username132 (talk) 16:18, 20 September 2006 (UTC)

Flour--Light current 16:24, 20 September 2006 (UTC)

We have always referred to cheap fluffy white bread as "balloon bread" and buy whole wheat instead. "Wheat bread" is a misleading advertising trick term, since balloon bread is made of wheat. The whole grain is supposed to have some nutritional value, but at least it is higher in fiber. Still, cheap white bread will keep body and soul together and if money is tight, something is to be said for the most grams of complex carbohydrate per unit cost. Bakery outlet stores sell all kinds ofday old bread for a small fraction of the grocery store cost, and most bread is day old by the time it is consumeed anyway.Edison 17:18, 20 September 2006 (UTC)

Is a $20000 car 100 times worse than a $2000000 car? Is a $100 dollar pair of jeans half the quality of a $200 pair?

I would guess that the more expensive bread would advertise that it uses better raw ingrediants, 'organic' ingrediants, ...etc. But whether this makes the more expensive bread nutritionally better, no one really knows. Personally, i wouldn't ever buy the cheapest food - because when it's that cheap, it's target customers are really poor people, which means the quality probably is worse. but at the same time, i wouldnt' bother to buy the more expensive food, because when it's that expensive, it's just fancy-ness.

I should also point out that more expensive food is something nutritionally worse. Here, the most expensive breads are the ones that tastes the best...which also happens to be the ones with the most preservatives and oil. Yaksha 07:54, 21 September 2006 (UTC)

The bread I buy (Allinson wholemeal) is rather expensive if you look at the price per bread. But I don't. I look at the price per weight. The bread may cost twice as much as average bread (75 eurocents per half bread), but it also weighs twice as much, so will (ceterus paribus) have twice the nutritional value. I consider most breads to be 'gebakken lucht' ('baked air' - it seems that is English too). Also, I prefer my bread to stay in one piece when I smear pâté on it. :) DirkvdM 08:30, 21 September 2006 (UTC)

Well other then nutrional value, there are also things like taste, freshness, longevity, amount of presevatives etc, slice size and a number of other factors that will vary. BTW, here in NZ someone came out with a bread in a paper bag that tasted real nice but was also real expensive. We stopped buying it after a loaf got mold several days before the expiry date Nil Einne 23:52, 27 September 2006 (UTC)

Water window ph4 - ph 9

Water window or de:Wasserfenster from pH 4 bis 9, we need help on the discussion here [[3]], The pH of wastewater leaving manufacturing plants and wastewater purification plants, as well as potable water from municipal drinking water plants, must be within a specific pH "window" as set forth by local, state or federal regulatory agencies. This value is typically between 5 and 9 pH, but can vary from area to area. source, :[[4]].

The question: is it a term used in the field or should the article be removed? reg. Mion 16:55, 20 September 2006 (UTC)

I have not heard of this term before, but it seems logical enough.--Alex 13:04, 21 September 2006 (UTC)

Micrometeorites and radiation

Assuming the Apollo missions did go to the moon, how did the astronauts survive the intense radiation and the numerous fast moving micrometeorites? --Light current 17:38, 20 September 2006 (UTC)

There weren't as many as you think, that's all. If there was too much radiation or even one small rock the system would have crashed. — [Mac Davis](talk) (SUPERDESK|Help me improve)17:44, 20 September 2006 (UTC)

They had micrometeorite shields. It looks like gold foil and is held away from the spacecraft surface. When micrometeorites hit it, they turn to plasma and expand. Only a wide region of gas will impact the spacecraft surface, rather than a tiny dense grain of rock. I believe the gold color is heat-reflecting metal, not necessary for the meteor shield effect (but they make the shields double as a thermal protection layer. --Wjbeaty 02:31, 28 September 2006 (UTC)

How many small holes were there in, say, the lunar lander module? And why didnt these particles that caused them puncture the spacesuits?[5]

Radiation dangers are here [6]--Light current 17:48, 20 September 2006 (UTC)

Your links answer your question. The Apollo missions were short. Note that the "from space" example (not the lab example) is a 1mm "crater" after 6 years of exposure, and the Apollo missions spent around a week outside of the Earth's magnetic field. — Lomn 18:17, 20 September 2006 (UTC)

Yes the Apollo astronauts were incredibly lucky:

• not to have been hit by micrometoeries of any damaging size
• not to have been out and about during a solar flare
• not to have got more of a dose (a life times worth wasnt it?) of radiation than they did.

However this points up the difficulties of long spaceflight: something that seems to have been forgotten by the general pubic most of whom think that holidays on the moon are just around the corner. 8-(--Light current 18:28, 20 September 2006 (UTC)

Well, "incredibly" is not really the right word. That implies that particularly adverse odds were withstood, which really wasn't the case. The vast majority of the time, damaging micrometeorite collisions do not occur. The vast majority of the time, solar flares are not present in a particular region of space. And the radiation dosage taken was something like two or three years' worth, fully expected and not life-threatening. Are you correct that something like a Mars mission carries more inherent risk? Sure. But engineers are also aware of that, and can take measures unnecessary during the Apollo era. If you want to talk about "lucky", though, your radiation dangers link also answers this: takeoffs and landings compromised the bulk of the mission risk. — Lomn 18:50, 20 September 2006 (UTC)

You can see solar flares coming, and predict them accurately enough, there are no serious radiaton risks, the link you gave, expressed that a 2 year trip would reach NASA imposed limits, these are usually well below levels you can become affected by. As they dont what to risk even an outside chance, so the odds are even if you recieve a lifetimes worth of radiation, deemed as safe for an astronaut, you'll till be fine. And also that the magnetosphere is a lot bigger than you might have thought. Philc _T^E_C^I 18:55, 20 September 2006 (UTC)

I agree the magnetosphere is the primary protection mechanism against radiation and charged particles, near the earth. But it doesnt extend as far as Mars. Does Mars have a magnetic field? Also a quote from the ref.

"A big solar event during one of those missions could have been catastrophic," said Cary Zeitlin, a radiation expert at the National Space Biomedical Research Institute at Baylor College of Medicine in Houston. "The risk was known. They gambled a bit." My bolding --Light current 19:03, 20 September 2006 (UTC)

My point is that such a statement is analogous to "A wreck while driving from coast-to-coast could be catastrophic. The risk is known. Truck drivers gamble a bit." And yet most truck drivers complete their routes without incident. It's not that the risk does or doesn't exist; it's placing said risk into proper context. — Lomn 19:30, 20 September 2006 (UTC)

Alternately, the apples-to-oranges comparisons need to be stopped. The topic originated with Apollo, and references such as the gambling above refer to Apollo, but you're referring to Mars. Nobody is claiming that the Apollo approach is suitable for Mars, or that it is being considered for such. — Lomn 19:33, 20 September 2006 (UTC)

OK. The points Im making here are:

• Travel to the moon was very risky (because of possible meteorite damage).Astronauts WERE v.lucky!
• safe travel beyond the earths near environs (and its protective magnetosphere) is going to be a lot more difficult than most people think.

People think that because we've managed to get to the moon, all problems are minor, and its just a slightly longer journey to Mars. Any spacecraft for this sort of trip is going to need some pretty good (and massive) shielding against radiation and meteorites. It's probable that the only way of doing this is to build the spacecraft in earth orbit, as we would never be able to launch it all in one go!--Light current 20:49, 20 September 2006 (UTC)

I'm still going to have to disagree with your assessment of relative meteorite risk. There has never been a significant meteorite impact on a manned spacecraft and, as far as I know, no such impact on an unmanned telemetry-capable craft either, and that's with 40-plus years of manned flight (much of it continuous due to space stations). Empirical data , therefore, suggests that the chance of catastrophic event on a week-long Apollo mission is pretty low. For that matter, there's probably a greater chance of incident in near-Earth orbit due to all the man-made junk floating around than in cislunar or interplanetary space. More spacecraft have been lost due to collision damage from their own debris than from that of extraplanetary origin. — Lomn 21:41, 20 September 2006 (UTC)

That is very interesting! I m sure I saw a TV programme illustrating the high micro meteorite risks.--Light current 21:52, 20 September 2006 (UTC)

You are correct in thinking that the lack of adequate protection from radiation does pose a significant complication for long-term habitation beyond the Earth's viscinity. For this reason some proposed lunar or martian settlements comprise metal habitats sent from earth that are buried in the regolith, the local material providing the bulk of the radiation shield. This page shows estimated radiation on the surface of Mars, which vary between 10 and 20 rems (about half the dosage one would get in the ISS and 2 or 3 times what you'd get on Earth [7]). And that's unshielded doseage (what you'd get if you lived ontop of Olympus Mons wearing a polkadot bikini for a year). Explorers on mars would get a lot less in practice, because a) they'd be at lower altitudes for some of the time (depending on the mission profile and base location) b) they'd be in some kind of suit which would afford some protection c) they'd only be outdoors for a few hours a day, and would spend the rest of the time in the rad-shielded hab watching Battlestar Galactica and d) they'd probably (at least in the forseeable missions) be there only a month or two. Explorers would likely receive more radiation during the long flight to and from Mars than on its surface. This is one argument for running trips to Mars via a chunky permanent station in the Hohmann transfer orbit; each individual mission to and from Mars wouldn't have to spend energy accelerating and decelerating a heavy radshield - they'd just accelerate and decelerate themselves (and their supplies, spacecraft etc.). Higher exposure incidents (particularly for solar flares) call for chunkier mars-habs and a beefier Hohman station, and you'd just no go outside during a solar storm. Per radiation poisoning, doses in the ranges you might expect to be achieveable (say ~5 rems a year for a 2 or 3 year mission) are probably going to elevate the astronauts' cancer risks (and you can bet they'll be closely monitored for the rest of their lives) and its certainly much more than is permitted for occupational exposure, but it's still below the threshhold for proximate health problems. -- Finlay McWalter | Talk 23:13, 20 September 2006 (UTC)

About the impact danger, what realy astounds me is that one spacecraft (which one was that again?) flew through Saturns rings and survived.

Spacecrafts for manned Mars missions are designed with a 'radiation free' room that astronauts can survive in during a passing solar flare. The big problem is their functioning depends on weight (eg lead) to stop the radiation, and that is precisely something one wants to keep down when sending a spacecraft. Another problem is that weightlessness for more than a year will cause weakening of the muscles, which will make the trip pointless if it means the astronauts can't do any work in the week or so they get before they return. Unless they stay until the Earth and Mars are in the right positions again and return a year or so later, but then they'd need a whole support system set up on Mars first.

That said, what's the point in manned Mars missions anyway? For above reasons they would cost loads more than sending robots (no life support needed and and more expendable, so crafts don't have to be as full proof). Sending, say, ten robots for the same price would give us much more info. I suppose democracy gets in the way here (give the people instead of the scientists what they want), especially in the US, where people were made to believe that the USSR's landings on the Moon 'didn't count' because they weren't manned missions, so the US government could claim that the US had won the race to the Moon (which was also presented as 'the big goal', which was also a load of bull - sorry about the rant :) ). DirkvdM 08:54, 21 September 2006 (UTC)

Em momentum transfer

I read somewhere that there is a drive that can cause momentum transfer in air molecules to produce propulsion useing micro-waves. Its called an EM drive i think, not like in the biefeld -brown effect where the air molecules are ionised and collide with air molecules.

Proplusion with momentum transfer in air molecules needs a starting force, what kind of Em waves can create a momentum transfer with air molecules? Are there more than one type and what kind of frequency is needed.

Robin

See EmDrive, and the caveats therein. -- Finlay McWalter | Talk 22:22, 20 September 2006 (UTC)

uuuuuuuuuum that didnt anwer my question, i asked if EM waves can cause moemtum transfer in air molecules, this says nothing about that. its just about the EM drive but it sounds quite different from how i heard it described in another article. but the question still stands.

Robin

your question is unclear. if you are asking can EM fields cause air to move, then yes, eg. rotational spectroscopy or microwave. Xcomradex 23:35, 20 September 2006 (UTC)

Thank you , yes i was asking if EM waves or fields can move air, and it looks like the answer is yes. Robin

A photon has momentum and will transfer some or all of its momentum to an atom if it interacts with that atom. So the answer is yes. EM waves can "move" air molecules. 202.168.50.40 00:17, 21 September 2006 (UTC)

Another way to say that is that light makes air hotter, and therefore moves it, due to the definition of heat. — [Mac Davis](talk) (SUPERDESK|Help me improve)05:22, 21 September 2006 (UTC)

It's not just heat; if a beam of light interacts with air, the air (or perhaps its container) will be propelled in the direction of the beam as well as heated. Heat is molecular kinetic energy with an average momentum of 0; it is possible to heat something without moving it, and to move it without heating it. A beam of light will do both because photons are more efficient at carrying energy (to be precise, their ratio of non-rest (or "kinetic") energy to momentum is greater) than all massive particles. This means that after all the momentum is transferred, there's still some energy left over that can't accelerate anything, so it heats it instead. (In reality, of course, not all of the beam will be absorbed, and new radiation will be being emitted all the time.) Hope this helps. --Tardis 18:15, 21 September 2006 (UTC)

Excitation of the vibrotational spectrum of air molecules doesn't make them move (translate), it makes them vibrate or rotate, and therefore get hotter. Translational motion of molecules has less energy than these modes. (Diatmoic nitrogen gas with 0.1 eV of translational energy is moving ~800 m/s, which is about 5-times the mean free velocity of air molecules.) Compton scattering and Raman scattering are common forms of inelastic scattering of light. Compton scattering doesn't apply to neutral atoms. Raman scattering has a typical efficiency of 10^-7 * 10^-3 (interaction probability, momentum transfer fractions, respectively) although there are nonlinear effects at high intensity that can make this a bit higher. Nevertheless, moving air by this method is an extremely inefficient method (watts in, nanowatts out). -- Fuzzyeric 19:26, 21 September 2006 (UTC)

Basic Law of Electrostatics

What is a simple way to expain thislaw to a 3rd grade student?

Are you talking about Coulomb's law? If so, I would say that, if two objects have opposite charge, they attract just like gravity, but with amount of charge, rather than mass, determining how strongly they attract. And if two objects have the same charge, they repel, just like gravity in reverse. Now if the student wants more detail about inverse-square laws in general, take a look at Inverse-square law, especially the diagram at the top. The idea of radiating flux lines can be useful to understanding why force decreases with distance the way it does. --Allen 23:32, 20 September 2006 (UTC)

Human evolution

Now and then I hear people (very credible people) say that since the rise of agriculture and civiliazation, human evolution has essentially stopped. Is this really true? I mean, we're getting taller, we're getting older, we're getting smarter all the time. I find it hard to believe that all of these things are simply results of an advancing society with better dietary conditions and so forth. Is that all it is? How about a more concrete example: the lactose-tolerance gene. That is a fairly recent genetic improvement that has spread across the world from northern europe. Isn't that a textbook example of evolution?

However, I am not a doctor, nor a scientist, so it's very possible (probable even) that I've got it all backwards. Can someone explain what exactly has changed during the last few millenias that would supposedly stop the mechanisms of evolution for humans? Oskar 23:00, 20 September 2006 (UTC)

Spread of genes isnt really evolution, possibly an example of evolution in progress. But any changes that have taken place on a timescale shorter than at least several hundred thousand years are not going to be evolution really, so any differences between us and cavemen, are purely due to conditions, diet, social stuff, etc. Philc _T^E_C^I 23:03, 20 September 2006 (UTC)

I thought that micro-evolution (ie spread of individual genes) and macro-evolution (major changes in species) was the same thing in modern evolutionary biology. That is, a genetic change that passes natural selection in a race is evolution, no matter how small the improvement. Is that not accurate? Oskar 23:09, 20 September 2006 (UTC)

Evolution is not stopping. Some of the natural selective pressures have been taken away, such as the need for good eyesight. That in and of itself changes the frequency of certain alleles. If you think of evolution as some progression towards bigger and better things, that's not what evolution is and may be part of the problem. InvictaHOG 23:07, 20 September 2006 (UTC)

This is what I'm thinking! So what are the arguments for of these people that claim that evolution has stopped? I mean, unless they're not figments of my imagination. I seem to recall the argument that since we are no longer isolated in small tribes, but in much larger communes, that any big evolutionary change will be quickly diluted and disappear. The evolutionary incubator, so to speak, has gone away. I may be imagining that too (damn those imaginary scientists!), but that is what I've heard people say. Is it all a misunderstanding on my part? Oskar 23:14, 20 September 2006 (UTC)

Well, without strong differential reproduction pressures you're not going to deviate terribly far from the mean, to use a statistical analogy. But "diluted" is the wrong metaphor to use (it is not actually a melting pot) and "disappear" is probably wrong (in fact the biggest evolutionary change of modern society is that many genetic combinations which would otherwise be more likely to disappear can be accomodated for). If you mean, "we'll never be able to see the same change take over the entirety or even the majority of the species very quickly," that's true, but that isn't really different from any species with a large, stable population ("big" changes usually occur with things like founder's effect and in other small populations). There are shifts in allele frequencies, of course (there have to be, if you are reproducing) but you're not going to get radical changes in them unless there are reproduction pressures which favor one against another. --Fastfission 23:43, 20 September 2006 (UTC)

(EC) There is a common equivocation between evolution-as-getting-better and evolution-as-change. When biologists talk about evolution, they mean simply change in gene frequencies among certain populations. Since Europeans/North Americans are reproducing at slower rates than members of other nationalities, I feel confident that gene frequencies amongst human populations are changing, perhaps very rapidly (by geological standards). Before humans were capable of radically modifying their environment, change in gene frequencies often corresponded to humans becoming more adapted to their environment. This usually resulted in what we would call improvements, like better immune systems, etc. So, in early human evolution both evolution-as-getting-better and evolution-as-change where occurring together. Now however, our bodies are undergoing evolution-as-change, but not perhaps evolution-as-getting better. In fact, there may be some reason to think our bodies are getting worse because people who otherwise might have died out are now able to reproduce. --best, kevin [kzollman][talk] 23:20, 20 September 2006 (UTC)

"I find it hard to believe that all of these things are simply results of an advancing society with better dietary conditions and so forth. Is that all it is?" As for getting taller, older, smarter, pretty much. All three of those things correlate directly with things like diet, medicine, public health, education, and luxury. Now whether there are not also smaller long-term gains across the population — it would be a very subtle effect, if it was one, because evolution works sloow. Evolution works on the scales of hundreds of thousands of years — improved diet, medicine, public health, education, and luxury are only what? Two hundred years old, max? And these changes are what, a hundred or so years old? Almost definitely an environmental issue. (But the question of "are humans evolving?" is a totally different one from that one.) --Fastfission 23:37, 20 September 2006 (UTC)

While evolution hasn't 'stopped', but there has been a change of perspective. The agricultural revolution was only a few thousand years ago, and the whole period of recorded history is compared to the entire stone age, at least hundreds of thousands of years, so in the very short historical period human biology seems to be 'standing still'. Also, humans have the power to alter their environment far more profoundly than any other species, and while this does not eliminate evolutionary pressure, it does mean that we respond by both biological evolution and cultural/technological evolution. Peter Grey 23:52, 20 September 2006 (UTC)

Agreed!--Light current 23:55, 20 September 2006 (UTC)

Also, evolution can never stop, it being the genetic change of an organism. As for the first sentance, "credible" does not always mean "correct." — [Mac Davis](talk) (SUPERDESK|Help me improve)05:25, 21 September 2006 (UTC)

I'm afraid I don't understand what you mean. Evolution is not usually about organisms, but about populations. Although statistically unlikely, it seems possible to me that a population could maintain gene frequencies over several generations, and thus not experience any evolution. Can you say more about what you meant? --best, kevin [kzollman][talk] 06:05, 21 September 2006 (UTC)

You might be interested in the concept of higher evolution (from which there is a link for more info), although it is only a stub.--Shantavira 06:28, 21 September 2006 (UTC)

"Now and then I hear people (very credible people) say that since the rise of agriculture and civiliazation, human evolution has essentially stopped. Is this really true?"<<<the rise of agriculture and civilization would have removed most evolutionary pressures from humans. If people are saying humans haven't evolved since agriculture and civilization, then they are quite right. Since agriculture and civilization where only about 10 thousand years ago at most, which is a blink of an eye in life history. In terms of evolution of species, not much happens in 10 thousand years, it's a very short period of time.

If the question was merely whether humans are still evolving...then it's quite a debated issue. Microevolution - so the change in gene frequency over generations, is certainly happening. But whether the human race in general is still changing is a question that doesn't really have an answer. Lots of hypothesis and beliefs, but there's never been any large scale research done.

And quite possibly there never will be, due to the contraversy it would bring, especially because most religions believe humans where made by god, and therefore we have never evolved and shouldn't be evolving. If the topic interests you, i recommend you try and get your hands on some old New Scientist magazines. Try public libraries or university libraries - it's one of the most popular science magazines. It had in the last year quite a few large article asking exactly your question - whether humans are still evolving - http://www.newscientist.com/channel/earth/mg18925422.700-editorial-are-we-still-evolving.html, http://www.newscientist.com/channel/being-human/mg18925421.300-are-we-still-evolving.html, http://www.newscientist.com/channel/being-human/mg18725174.600-human-brains-are-still-evolving.html.

And there's one article on brain size which is open for public view: http://www.newscientist.com/channel/being-human/dn7974-human-brains-enjoy-ongoing-evolution.html enjoy. Yaksha 07:38, 21 September 2006 (UTC)

Though it should be noted that New Scientist is not a terribly reputable science magazine, and has published some utter nonsense in recent years. --Fastfission 20:27, 21 September 2006 (UTC)

some. But it's pretty easy for general audience to read, and at least where i am, very easy to get hold of Yaksha 03:20, 22 September 2006 (UTC)

And is usually far better then most of the science stuff you get in papers and the like Nil Einne 23:47, 27 September 2006 (UTC)

Sound waves and momentum transfer

What is the difference between sound waves and other air molecule momentum transfers such as overpressure shockwaves, or just air pumps. why is some waves propagating by air molecule momentum transfer called sound and others are not. Would a vibratiing peice of metal causing air vibrations and levitating something be called acoustic levitation?

thanks

Sound is defined as what we can hear. Anything else is just compression waves! 8-| --Light current 23:59, 20 September 2006 (UTC)

i thought that what we couldnt hear was still souund, either ultra or infra sonic?

thanks

Sound is what sounds like sound to you--Light current 00:34, 21 September 2006 (UTC)

What I'm sure Light current means to say, is that "sound waves" are basically waves that happen to fall into the range of frequencies that are audible to humans. Since other animals such as dogs can hear much higher frequencies than humans, those waves can also be considered sound waves. If a piece of metal vibrates at a frequency within the range of human hearing, you will be able to hear it and thus it will make a sound. Of course high-frequency waves can be called ultrasound (not ultra-sonic or super-sonic, which is a speed as opposed to a frequency), and low-frequency sounds can be called infrasound (not infra-sonic), but in many cases it's not useful to think of vibration as merely types of sound.  freshofftheufoΓΛĿЌ  01:06, 21 September 2006 (UTC)

Just to correct. Ultrasonic and infrasonic refers to frequency of sound. While terms for speed are subsonic, supersonic and hypersonic implying speeds less than, greater than and more than five times the speeds of sound respectively.nids(♂) 10:53, 21 September 2006 (UTC)

Fundamantally there are three types of waves we know about (or believe we do): mechanical (this includes sound waves), electromagnetic and (we believe) gravitational. So in answer to your first question, there is not fundamental difference between the phenomena you asked about.

Acoustic levitation is acoustic levitation. The first order effect in acoustic levitation is parking a mass at a node of the acoustic field so that the field minimizes the work done on it. Displacing the mass away from the node causes a restoring force, similar to the force in the Casimir effect. The air molecules in acoustic levitation oscillate in position, but do not have a net collective displacement. A rock, thrown through the air, has a net collective displacement. A pump produces a net collective displacement, not positional oscillation. Consequently the mechanism whereby a pump lift an object by flinging air at it is different from the mechanism where an acoustic field can hold an object at a position of minimal energy. In the first case, momentum is transferred to the object to oppose gravity. In the second case, energy is transferred to the object to oppose its moving off the node. -- Fuzzyeric 19:34, 21 September 2006 (UTC)

Has anyone ever held a seagull?

Has anyone here ever held a seagull? What do they feel like? I see them sat around and they look like they're really warm, soft and fluffy.

Theyre aggressive and could peck your eyes out tho!--Light current 00:00, 21 September 2006 (UTC)

Especially the male ones. Oops, minus 20 points. Clarityfiend 00:29, 21 September 2006 (UTC)

Shit I forgot!--Light current 00:32, 21 September 2006 (UTC)

Assuming that we can generalize from parrots to seagulls, what you'll find is that the tactile impression you get from touching a bird varies a lot across the bird. The downy head and body feathers are soft and fluffy but the long wing flight feathers and tail feathers are stiff and make crackly noises not unlike crinkling very stiff paper. Also, birds vary in "cuddliness" depending on how they are raised. Our sun parakeet, adopted by us a few months ago, spends a lot of time snuggled up with my wife, often falling asleep inside her shirt! She (the parakeet!) also very often likes to be petted, to have her beak rubbed, or, occasionally, to be aggressively played with including flipping her over on her back and then letting her hang from your fingers.

Atlant 01:25, 21 September 2006 (UTC)

Baby gulls are cuddly. I've raised a couple of young'uns myself and they do love to be held and snuggle (they like the 'inside the shirt' thing too). When they grow, they stop liking it and become quite aloof. Gulls are not social preeners, you see - even mated pairs keep a respectful distance, aside from during the 'physical act of love' itself (much like some human couples, heh)... --Kurt Shaped Box 12:09, 21 September 2006 (UTC)

Mentioning the word or alluding to it: Minus 20 points! Sorry!--Light current 01:39, 21 September 2006 (UTC)

What's the in-joke? Mattopaedia 10:27, 21 September 2006 (UTC)

Start with the 4th question of Sept. 10, then switch to Miscellaneous and look at the 2nd question of the 17th. Clarityfiend 00:03, 22 September 2006 (UTC)

Well, believe it or not, I saw someone hold a seagull today. It literally just fell from the sky and landed on a busy street in the city. And old man went and lifted it away and sat it out of the way of the crowds. IT didn't seem to creat much of a fuss.

It was probably sick and/or dying. I once picked up an adult great black-backed gull with a broken wing and it fought like hell and was screeching and whining all the way as I wrapped it up in my coat and carried it home. --Kurt Shaped Box 20:22, 21 September 2006 (UTC)

"Do you think [the seagull had] a message on him like that dude in Con Air?"

Atlant 14:01, 22 September 2006 (UTC)

Calling The Future

Will this prove that time-travel is possible?

I create a message like:

"If time-travel exists, would a time-traveller email or call me on my mobile phone(insert number here) at (let's say a minute after the time I posted the message to stop fraudulent cases). I will not reply to the email or answer the phone."

I would need to keep the message on a medium that will last for many centuries or thousands of years. The internet would be ideal, as I can imagine the message would be constantly archived and backed-up for many many years.

So theoretically, if i put my email address or mobile number on the message I should be able to discover if time-travel is possible and only within a minute.

What would make the theory impractible?

ImbalancedZero 23:53, 20 September 2006 (UTC)

you assume the medium lasts forever, and that someone finds it, reads it and understands it and considers you important enough to answer. all big calls. Xcomradex 00:04, 21 September 2006 (UTC)

Has a future Wikipedian left a message on your talk page yet?

Seriously, that would rely on the people capable of time travelling finding your message, coming back in time to right after you left it, figuring out how to use a phone, and calling you on it. Either that, or else calling you from the future on a phone the waves from which could travel in time, and arrive in a form recognisable to current technology. In principle an interesting idea, but in practise I think there are too many obstacles. --Mnemeson 00:07, 21 September 2006 (UTC)

This is a message from the year 2262 to tell ImbalancedZero that time travel is possible. Thank you.

People have tried this sort of thing at least once; a few years ago someone held a big conference, inviting all future time-travelers to stop by. They did their best to publicize the invitation in as many permanent media as possible. Sorry I don't have a link for you; but if memory serves no time travelers showed up. Maybe next time. --Allen 00:15, 21 September 2006 (UTC)

The conference you mention is the Time Traveler Convention at MIT. No-one from the future turned up. Rockpocket 03:54, 21 September 2006 (UTC)

The trouble comes afterwards when you try to convince others that sentient beings from the future are contacting you. —Pengo ^{talk · contribs} 00:22, 21 September 2006 (UTC) (my RfA)

What you mean by 'sentient beings' earthling??--Light current 00:24, 21 September 2006 (UTC)

Presumably we'll have radiated or adapted into different species by the time the laws of physics have changed adequately for time travel to be possible. —Pengo ^{talk · contribs} 00:37, 21 September 2006 (UTC)

I guess the media wasn't so permanent Allen 8P --Agester 01:36, 21 September 2006 (UTC)

Can the future caller reverse the charges? Peter Grey 02:08, 21 September 2006 (UTC)

Ask yourself this - if you were a time-traveller, would you bother to reply to messages in the past? Imagine the chaos it would cause.

and also ask yourself this - if timetravelling became possible, it would no doubt be heavily regulated. That kind of technology is the kind of stuff they'd hole up in the military and the government, the public isn't even likely to know about it until a long time after...when adequet technology has been made to regulate time-travell. In which case...do you think people would really be allowed to contact the past whenever they want? And do you think the government would simply choose a random person in the past to contact?

Further more, there're a lot of theories about how time travel works. Some people will say if you can travel into the past, you can change it, contact people in the past. Other's will say it's impossible - travelling in the past will take you to a different past where you have always travelled to the past. Just think about all the time-travel paradoxes. Others will say it'll never be possible to travel into the past, even if you can time-travel, you can't change what's already happened. Which means if a time-traveller has never visited you, there never will be a time-traveller who can. For any RPGamers here, just think Final Fantasy 8 scenario when it comes to doing things in the past. Yaksha 07:47, 21 September 2006 (UTC)

Everything is used illicitly or illegally eventually. Everything. Strict rules, laws, regulations, oversight, and even social mores aren't foolproof, and they definitely aren't foolproof forever. Even if it took a million years for someone to get around the Timecops, they would still be able to go back in time to whatever year they wanted to. -- Plutortalkcontribs 12:10, 21 September 2006 (UTC)

I suppose. But if i was going into the past illegally, no way in hell would i show up at such a high-profile event claiming to be from the future.

And i wouldn't publically claim to be from the future at all. Maybe i'd contact some ancesters, or famous people in the past. But i wouldn't be so careless as to answer a random "hey time traveller contact me" message from a random person whom i didn't know. Yaksha 14:06, 21 September 2006 (UTC)

No law is foolproof but the law of physics. And it is this what stops the timetraveller from visiting us. —Pengo ^{talk · contribs} 15:06, 21 September 2006 (UTC)

It is still an open question among physicists whether time travel is possible. One interpretation that avoids the paradoxes is that when you travel to the past and say, prevent your own parents from meeting each other, you split off a separate universe, i.e. you stop the birth of the "you" in that universe, but that does not make you vanish, because you are from a different universe. Clarityfiend 16:46, 22 September 2006 (UTC)

Tell the time-traveller that a government minister with no known family has died and left his unclaimed millions in you bank and you will split the fortune if they impersonate his long-lost great-great-great-great nephew. They will/have not be/been able to resist leaving a message for you. Gandalf61 15:33, 21 September 2006 (UTC)

Actually, with inflation what it is, the Millions would No Doubt be worthless by the time they got the money Back to the Future. smurrayinchester^{(User), (Talk)} 17:41, 22 September 2006 (UTC)

Maybe you should tell the time-traveller you have some antique items instead of money? Since they would be worth more in the future, not less --Yaksha 02:01, 23 September 2006 (UTC)

It might help to first legally change your name to Sarah Connor. Peter Grey 12:17, 22 September 2006 (UTC)

Buy life insurance first, lots and lots of life insurance. Clarityfiend 16:46, 22 September 2006 (UTC)

Time travel is absolutely possible. I myself do it every day. Even as I write here, I find myself traveling forward through time at the rate of one second every second. Dipics 18:19, 22 September 2006 (UTC)