Wikipedia:Reference desk/Archives/Science/2008 January 26

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January 26

Time Travel

So say you are in the year 2100 and time travel is possible. You get in the machine (assuming that's how it will work) and come back to the present-day. Which would happen first? The future changes because you aren't there or the future changes because you affected (even minute things can change) it in the past (present-day)? This is ponderous for me but maybe not so much the science-savvy folks around here. Thanks, schyler (talk) 01:08, 26 January 2008 (UTC)

We have a quite extensive article on Time travel. Now strictly speaking, we can't actually say what would happen as the laws of physics make no explicit permission for time travel, and are often argued to prohibit it. Of course, you can always make physical predictions if you make assumptions for all those things we don't know, and one of my favorite ones (although I disagree with it) is found here. In my own personal opinion, if you displaced a person through time, even if paradoxes are assumed a non-issue, the perturbations you induce on history would be utterly catastrophic in the long term (just look at Half-Life 2!). I base this opinion mostly on the chance of a particular sperm making it into the egg, and I presume that such simple things as bumping into a guy on the street could significantly alter that. Maybe I'm wrong, though, but a difficult thing to experiment on. Someguy1221 (talk) 01:28, 26 January 2008 (UTC)

Thanks. I guess since it isn't possible there is no answer. I DO have a time machine in my room here. It only goes forward at regular speed though. It's basically a cardboard box that has the words time machine written on it. schyler (talk) 01:46, 26 January 2008 (UTC)

Really? My more advanced model reads Tim Mashin. Confusing Manifestation(Say hi!) 06:46, 26 January 2008 (UTC)

The entire concept of "changing history" with time travel comes up a lot. There are two things to consider when thinking about time travel into the past. I am going to try to condense these rather complicated topics as much as possible. You can find much more detailed information by searching for related topics on the Internet.

First, if time is continuous and there is a future, no time machine will be built that people can use to travel into our time or our future. This is based on the fact that there is no time machine available now that can do it. If one was to be invented in the future, the inventor would be popular because he or she invented a time machine. Eventually, the technology would become public and someone would travel back to a time before the time machine's invention and "invent" it to steal the popularity. Then, someone would travel to a time before that and invent it. With billions of people in the world, there will always be someone at some point in time that will travel back to an earlier time and invent time travel. Eventually, someone will travel back to 2007 and invent time travel. Since that hasn't happened, either time is not continuous (meaning the future/past doesn't exist for us) or a time machine that can travel to the present time will not be invented in the future.

Second, time is not necessarily continuous. We may exist in the present and only in the present. We remember the past, but if we travel back a day or more, we will not find our past selfs. Something entirely different will be there. We can change the past universe without having any effect on our universe. It is like jumping out of a car on the highway and landing in a car behind it. What you do in the car behind it doesn't affect the car you came from.

It is possible that neither of the previous concepts are true at all, but they both get rid of the time travel paradox issue. -- kainaw™ 12:05, 26 January 2008 (UTC)

Nothing would happen since time travel isn't possible, not even theoretically. Time doesn't exist per say, as in, a place you can go to. Time merely defines the speed at which stuff happens. Once they happened they are done, they no longer 'exist' someplace in the past. (I would edit the wormhole section of the article to correct obvious errors, but I have no sources, so it would just be reverted. Basically: moving one end of the wormhole would do one of two things: it would move the other end, so nothing useful would happen. Or it would be pointless - only mass experiences time dilation, a wormhole is not mass, it is a rift in spacetime, it would experience no dilation.)

Now, if you are simply looking for a plausible idea, my favorite is the multi worlds theory - every time you travel to the past you travel to a copy of the world. You can change whatever you like - it won't affect you, since you are from the other copy. Ariel. (talk) 08:13, 28 January 2008 (UTC)

Time travel has been discussed both by science fiction writers such as Robert Heinlein decades ago and by present day physicists. I agree with Ariel and those who posit a multitude of parallel universes, such that every thing which COULD happen, DOES happen as the multiverses diverge. So if I built a basement time machine and travelled back to April 30, 1900 and put several warning flares on the railroad tracks near Vaughn, Mississippi, to give Casey Jones ample and unmistakable warning that a train was on the tracks ahead, thus preventing his famous fatal train wreck, that universe would diverge from this one, and there would not be the popular songs, cartoon, or TV show about him, and if someone created a Wikipedia article about how he was a railroad engineer who had a long career, retired, and died at an advanced age of emphysema. it would doubtless be deleted as failing the notability requirement. But who knows: he might have affected other aspects of history in the remainder of his life. The people in the non-trainwreck universe would not know that there had been a change. If I went back to Clear Lake, Iowa on February 3, 1959 and prevented Buddy Holly, the Big Bopper and Richie Valens getting in the light plane that killed them, then the song The Day the Music Died would not have been written, or would have been about something else, but that universe would not remark on the fact. If someone has already diddled in our own history, causing the esarly deaths of Amelia Earhart, Glenn Miller, and Anton Cermak before their time, and preventing the capture of General Douglas MacArthur by the Japanese in 1942, or preventing the the death of John F. Kennedy when a Japanese destroyer ran over his PT boat in 1943, we would have no way of knowing that our universe had been altered. There are many points in history where a slight influence could have vastly altered history, and we would have no way of knowing. The very worst time travel fiction is that which posits a unique history and some force or "time police" which prevent history from being changed. In one such unimaginative work a man tried to shoot Hitler in 1938, but the air "solidified" and the bullets fell to the ground a foot from the gun. Edison (talk) 02:37, 31 January 2008 (UTC)

I must point out that time travel IS possible. You can go forward in time by approaching the speed of light. Time for you, slows down, and you can travel forward in time as long as you want and be perfectly fine. There's nothing in physics that prevents this, although it is beyond our technological level. However, we don't know if it is possible to go back in time. Black holes may be a method to do this, but evidence is inconclusive. 64.236.121.129 (talk) 17:15, 1 February 2008 (UTC)

MMR Vaccine

My child is highly allergic I understand that a MMR vaccine might be available that is not grown on "chich embryo cell cluture". My pediatrician cannot recall where or when he saw this information. Can you provide this info? Thank you, <email removed> —Preceding unsigned comment added by 24.251.164.241 (talk) 02:01, 26 January 2008 (UTC)

Hello. As far as I am aware, there is not MMR vaccine that is guaranteed free of egg protein or gelatin. Its actually gelatin hypersensitivity that causes most of the anaphylactic reactions to MMR, not egg protein. Its generally thought that the tiny amounts of egg protein are not sufficient to induce a reaction. For example, in a study of 1227 egg-allergic patients who received the MMR vaccine, only two had any symptoms suggesting an allergic reaction, and they were from the same case report, whereas in better studies no patient reacted. These combined data indicate that 99% of children who are allergic to egg can safely receive the vaccine.

That said, there is a measles-rubella combination vaccine called MoRu-Viraten that "is free of avian proteins and antibiotics, posing no risk to children with allergies to these substances." Obviously this would offer no protection against mumps, though. I don't think there is a egg-free single mumps vaccine either. Whether MoRu-Viraten is licensed for use in your locale, and whether this is appropriate for your child, we cannot say of course. You should discuss the issue further with your doctor. By the way I removed your email address for your protection from spam. Rockpocket 07:50, 26 January 2008 (UTC)

Producer Gas through fixed bed coal gasification

What is the difference between Coal Tar and Tarry residue ? Nagarajan11 —Preceding unsigned comment added by Nagarajan11 (talk • contribs) 07:06, 26 January 2008 (UTC)

In this context they are probably the same. Though 'tarry residue' could refer to anything. Coal tar is more specific.87.102.89.223 (talk) 18:21, 26 January 2008 (UTC)

Coal tar is the tarry residue produced from coal.87.102.89.223 (talk) 18:23, 26 January 2008 (UTC)

What kind of bird is this?

I took a picture of a bird at an exhibit of raptors and other birds of prey. Unfortunately, I don't have any record of the kind of bird it is. What did I take a picture of? (The exhibit was in eastern Connecticut, but I don't think the birds were all indigenous to the region.) grendel|khan 07:08, 26 January 2008 (UTC)

Looks a lot like one of my favourite birds - the Kestrel. Grutness...wha? 07:54, 26 January 2008 (UTC)

My favourite bird - the Great Black-backed Gull can easily defeat your favourite bird in combat. I've seen it happen a couple of times now. The GBBGs don't much like Kestrels hovering in the sky over their nesting areas. --Kurt Shaped Box (talk) 18:12, 26 January 2008 (UTC)

I don't suppose you can identify which species it is? I like to tag things as specifically as possible. grendel|khan 18:44, 26 January 2008 (UTC)

Assuming it is a bird native to North America, it is a Merlin of the Prairie subspecies. Merlins are a type of falcon, similar to Kestrels, but slightly larger.--Eriastrum (talk) 19:59, 26 January 2008 (UTC)

I don't think so. You can see a trace of russet that seems to be the color of its back, making it a juvenile American Kestrel (Falco sparverius) if it's a native bird. --Milkbreath (talk) 15:56, 30 January 2008 (UTC)

I'm afraid that I have to disagree with you Milkbreath. American Kestrels (male, female, and immature) always have strong face markings. Grutness's Grendel's photo has pale grayish head with no mustache markings of any kind. You are right about the touch of russet, so perhaps this is the Common Kestrel of Europe, Falco tinnunculus. --Eriastrum (talk) 21:26, 30 January 2008 (UTC)

Do we want experiment pages?

Does wikipedia want pages for experiments, such as the spouting can, or ball and hoop, or are they considered non-notable? Thanks --Dvorak (wtkwhite) ^(Talk) 10:45, 26 January 2008 (UTC)

If you can find references that denote notability, then it is notable. The big problem with notability is that many articles make no attempt to show notability. If you can find references to claim notability, then editors can discuss the merits of the topic on the article's talk page. -- kainaw™ 11:55, 26 January 2008 (UTC)

I believe that many pages of wikipedia should actually be in wikionary, wikibooks or wikiversity. I don't understand why some people are so pushy to include everything into wikipedia. It would be much easier to navigate all these sites if different kinds of information were on the appropriate place. Mr.K. (talk) 14:41, 26 January 2008 (UTC)

I find it much harder to navigate across several sites - put it all in one place works best for me. DuncanHill (talk) 17:42, 26 January 2008 (UTC)

Bright object in the sky last night...

I saw a bright object in the sky last night, no it wasnt a UFO, I am just interested if there was anything signifcantly astronomical happening last night? I live in South East England and the night sky was partiuarly clear. It didnt move all night, so no it wasnt a plane. Thanks RobertsZ (talk) 12:49, 26 January 2008 (UTC)

I know that the planet Venus can been seen from Earth, see this. I might also haven been a satellite. They can often be seen orbiting from Earth, but you'd have to check your time and location. Try this and this to see if you can match one to your location. Think outside the box 14:45, 26 January 2008 (UTC)

Mars and Jupiter are both visible in the night sky at present. (I think Venus doesn't rise during the hours of darkness at present) If you know your constellations, well, Orion, Mars is 'above' Orion at about midnight. Across to the left a fair way the other bright 'star' is Jupiter. I'm sure there are technical terms for these directions but hey, I think you'll see what I'm pointing at! If you want to know a little more try [1], sign up, and have a look around Richard Avery (talk) 16:37, 26 January 2008 (UTC)

Ahhh, i didnt look at the stars around the bright object, i just thought 'oh thats bright' and didnt think much more of it, untill reading earlier this morning about that asteroid passing close to the earth(loads of paranoid hype). I guess its probably a planet then? If so will it be equally visible tonight? I will look in more detail and see where it is in relation to other selestial points. Thanks for the replies so far RobertsZ (talk) 16:47, 26 January 2008 (UTC)

Mars is very bright right now and is visible in the east after sunset and high in the sky later at night. It is slightly yellowish or reddish. Venus is also very bright right now, but is visible only low in the east just before sunrise. Jupiter is not too far from Venus, but not as bright. An asteroid would probably not be easily visible until just before it hits us. So I hope you didn't see an asteroid.!--Eriastrum (talk) 19:53, 26 January 2008 (UTC)

If it was moving rather than stationary, it could well have been a satellite flare from an iridium satellite, or could even have been the International Space Station, which is easily seen making its slow graceful passes across the sky. Grutness...wha? 19:57, 26 January 2008 (UTC)

Ah skip that - I didn't notice that you said it didn't move. Grutness...wha? 19:58, 26 January 2008 (UTC)

Well it wasnt moving noticably, it may have progressed across the sky slowly, how quickly do objects orbiting the Earth move? (I will have a look outside in a minute, see if its there again) RobertsZ (talk) 20:19, 26 January 2008 (UTC)

Nope, it isnt there tonight, but I cant see any stars either, I guess there is too much light pollution at the moment, no one has gone to bed, there isnt much cloud cover, look like i will be late night staregazing . RobertsZ (talk) 20:24, 26 January 2008 (UTC)

They're slow but move noticeably, about the speed of a distant aircraft. Grutness...wha? 20:34, 26 January 2008 (UTC)

Most satellites are in one of two types of orbit. One is low Earth orbit, which is used because it's the cheapest to achieve has the shortest communication distances. LEO satellites make a complete orbit around the Earth in under 2 hours, so if you see them from a particular place, they will move noticeably in a few minutes, like a distant airplane. The Iridium satellites are of this type.

The second type is a geostationary orbit, or Clarke orbit, which is used because, when seen from the ground, the satellite remains in a fixed location at all times, day and night — which allows communications (TV, telephone, etc.) to be received by an antenna that does not move. I'm not sure if there are any satellites in Clarke orbit that can be seen from the ground, but there certainly aren't any that are seen as bright objects. It's too far away.

Planets, on the other hand, rise and set in the same manner as the Sun, the Moon, and the (non-circumpolar) stars. Which is to say, they move in an arc from a point on the eastern horizon to a point on the western horizon, such that a north-south line bisects the angle between the two points. Because all the planets' orbits are in similar planes, they all follow more or less the same path in the sky that the Sun does from sunrise to sunset. Their positions change all the time — that's why they're called planets — but not so much that you'd notice from one night to the next, unless you compared the position of the planet with another nearby object.

Mercury and Venus have orbits inside the Earth's orbit, so they always stay fairly near the Sun. If you see something in the sky "all night", then it's not Venus. (Incidentally, Venus is bright enough to see in the daytime sky, if you know where to look, at times when it's not too near the Sun.)

For the other planets, the Earth's orbit is inside theirs, which means they can appear at any position along the Sun's path. Currently Mars is fairly near its opposition, the time when it is directly oppposite the Sun and also closest to Earth. Jupiter, on the other hand, is in almost the opposite direction. (In fact, Venus and Jupiter should be visibly close together just before sunrise now -- I haven't checked this myself -- and moving closer together in the sky. On the morning of February 1st they will be less than a degree apart, before they start moving apart again.)

Conclusion: either you saw a star, or you saw Mars. Since you noticed it, it's probably something that isn't there all the time, and therefore Mars. It should indeed be visible on subsequent nights.

--Anonymous, 22:20 UTC, January 26, 2008 (links edited later).

I think we can safely assume that there is currently no geostationary satellite visible to the naked eye. The ISS - the brightest satellite (except Iridium flares) - is visible at magnitude 0 at 1000 km distance and 50% illumination according to Heavens-Above. That makes magnitude 7 at a geostationary distance and 100% illumination. Icek (talk) 00:14, 27 January 2008 (UTC)

Hmm... with the "maximum brightness" from Hevanes-Above I get magnitude 5.3 at geostationary distance instead (it seems like 50% illuminated means 11% illuminated) - but the ISS is way larger than any current geostationary satellite - the data for e. g. Genesis I says that it's about 5 magnitudes dimmer than the ISS. Icek (talk) 00:24, 27 January 2008 (UTC)

Isn't that the satellite that lost power and is closing in on earth for the end of feb ? Mion (talk) 07:59, 27 January 2008 (UTC)

No, Genesis I is a satellite of Bigelow Aerospace. The satellite that "lost power" is a US spy satellite. I don't have detailed information about what happened to that spy satellite or even what its orbit is (but I haven't searched the internet for that information so far), but apparently they have lost control of it - either it would have crashed anyway, but in a controlled way, or they lowered the perigee for better observations and planned to raise it again, but now they cannot (air resistance decelerates the satellite so that it eventually deorbits - see orbital decay for details). Icek (talk) 13:26, 28 January 2008 (UTC)

Setting toaster timer: stand by...

If the toaster is set to low, I put my bread in, initiate the toasting sequence and then raise the toasting level, is the toasting timer reset to the longer period? What if the toasting sequence is nearing completion (say, 90%) and then I reset the timer to 50% of the initial toasting magnitude; will the total toasting equal 140%? ----Seans Potato Business 13:09, 26 January 2008 (UTC)

That depends entirely on the construction of your toaster. I think old-fashioned toasters work with a bimetal mechanical spring/catch mechanism. They should actually toast until a certain temperature has been reached (at the spring, not necessarily at the toast). But for modern electronically controlled toasters, everything goes. --Stephan Schulz (talk) 14:20, 26 January 2008 (UTC)

This is a surprisingly deep question. Stephan is right; every toaster is different. And even if we knew how your toaster was constructed, it would be very easy for our RDesque armchair speculation to come up with an entirely wrong answer. So if you really care about this question: experiment! See how long the toaster toasts at various settings, without switching settings in mid-stream. See if it makes a difference whether there's bread in the toaster or not. See if it makes a difference whether the toaster is hot or cold -- I've found that the second piece of toast toasted at the same setting often comes out differently than the first one. Finally, with that preliminary data in hand, begin performing experiments where you vary the setting partway through the toasting cycle, as in your original question.

Keep good notes. Develop hypotheses -- educated guesses -- about what will happen, and refine your experiments to test those hypotheses. Develop theories about how the toaster works, and see if your experiments can confirm or refute those theories. This could end up being an excellent educational application of the scientific method. —Steve Summit (talk) 15:36, 26 January 2008 (UTC)

I've wondered about this too. I think the simplest clock that would be used (and thus also the most likely) is a capacitor resistor circuit, or a digital clock circuit. The toast is done when the capacitor is charged (or discharged). So changing the dial is changing the variable resistor, and will affect the future speed at which the capacitor charges, but will not affect how much it charged so far. A digital clock circuit would act much the same way - moving the resistor changes how fast the clock runs down. But it would not affect how much it ran down so far. Ariel. (talk) 08:27, 28 January 2008 (UTC)

cheap scientific tools

I am searching for cheap scientific tools that can be used within a high-school environment. Something under $1,000, perhaps some tool that can analyse small things (like crystals and the like). PC is provided, if the tool need to be connected to one.

Can you recommend some? Mr.K. (talk) 14:57, 26 January 2008 (UTC)

I'm not sure exactly what sort of equipment you're looking for, but American Science and Surplus often has good deals on lab equipment. APL (talk) 20:03, 26 January 2008 (UTC)

The American Science and Surplus is surely in the right direction. Mr.K. (talk) 20:40, 26 January 2008 (UTC)

Dammit, why do they have to be American? Anything similar in Britain? DuncanHill (talk) 12:34, 27 January 2008 (UTC)

You can probably get all the junk off ebay. ----Seans Potato Business 17:09, 29 January 2008 (UTC)

Are RGY and RYB monitors possible?

http://en.wikipedia.org/wiki/Color_wheel

In my learning about color perception I've come across the opponent process theory of color which posits 3 color channels: red-green, blue-yellow, and luminance.

I understand that computer monitors represent color by varying amounts of Red, Green, and Blue (RGB) for each pixel. Since we have a blue-yellow color channel, would it be possible to create a Red, Green and Yellow (RGY) computer monitor?

following this same logic, would a Red, Yellow, and Blue (RYB) monitor be possible as well?

Thank you!

Mark465 (talk) 15:09, 26 January 2008 (UTC)

Marcus Cowgill

You could produce such a monitor with any combination of colors as primaries and whatever combination of colors you choose some colors the human eye can see will be unrepresentable. But some combinations of primaries can cover a much larger part of the human eyes visual range than others. A correctly chosen red green and blue are about the best we can do with three primaries. In particular with your red yellow and blue system it would be impossible to mix white. Plugwash (talk) 15:21, 26 January 2008 (UTC)

See color space. Mixing colors only gives you a limited number of colors. Picking the wrong colors means you won't be able to represent certain colors. Don't confuse the physiology of color processing with the physics of color mixing—they're not the same thing. --24.147.69.31 (talk) 16:34, 26 January 2008 (UTC)

Returning to the original question, sure, you could design the signalling between the video generator and the monitor to use any number of different encodings. RGB came to dominance simply because it was a direct representation of what was actually happening at the electron guns of the cathode ray tube and the phosphor dots on the screen so it made for the simplest electronic circuits back in the days when this stuff was done with stone knives and bearskins. But note that component video typically used in home video uses a different encoding: YPbPr. You might also enjoy our article about gamut.

Atlant (talk) 17:38, 26 January 2008 (UTC)

You can easily determine the gamut of colors reproducible with given primaries by looking at Image:CIExy1931.svg. Simply form a triangle with the three primaries as vertices. You can recreate the color with those primaries if and only if it is inside the triangle. So we see that RGB is a good choice because that triangle covers most possible colors. RGY is an awful choice because that triangle is very narrow, almost degenerate. It is impossible to create blue or white from red, green, and yellow. RYB is not so bad, but you still can't get most shades of green. —Keenan Pepper 19:06, 26 January 2008 (UTC)

What Keenan said. I recommend David Madore's writing about Colors. – b_jonas —Preceding comment was added at 08:48, 28 January 2008 (UTC)

Highest village in Tibet

What is the village with the highest altitude in Tibet? Most sources give different information, and there doesn't seem to be any note of it on Wikipedia (besides the altitudes in individual village articles). - Super Sam ^{ultra quick reply} 16:55, 26 January 2008 (UTC)

It's impossible to answer that sort of question, unless you define how many dwellings constitute a village, how close together they would have to be, etc. Also most people living at high altitude do so on a seasonal basis, so would you include yurts and tents? Even then, Tibetan society is much more loosely structured than the Chinese would have us believe. I wouldn't trust any statistics supplied by Chinese sources.--Shantavira|^{feed me} 09:03, 27 January 2008 (UTC)

Sykeds ?

I was watching a gardening show and they talked about planting "sykeds", an endangered tree similar to palm trees. They didn't spell it for me and I've never heard the term before, so have no idea how it's spelled. What is the correct spelling and do we have an article on them ? StuRat (talk) 18:29, 26 January 2008 (UTC)

I believe you may be referring to cycads. grendel|khan 18:42, 26 January 2008 (UTC)

Yes, that's it. Thanks, StuRat (talk) 19:33, 26 January 2008 (UTC)

Reason for lack of sense of time - i.e.: thinking it's years ago?

I read the articles on time and sense of time and understand a little better, but still, my great-aunt had a stroke a while back and for a while as she recovered she would swear it was 1955; yet she knew her daughter (who would have been maybe a 5-year-old adoptee then) and others. I'm thinking that some part of her mind had been blocked (she's better now), a part that had registered what year it was. Is that accurate? Also, another oddity which I've heard is related to Asperger's Syndrome in some people is that they will think this without any impairment such as a stroke; not often, but they might think they're in antoher time; is this accurate? Is it because of the eidetic memory and how they recall things with all the sights, sounds, and everything so specifically? Or, don't those with AS really have this happen?Somebody or his brother (talk) 21:18, 26 January 2008 (UTC)

Ribot's Law and retrograde amnesia may be of some interest. Serious cases can have people believe they are living in the past, but general dementia or psychological regression might also be involved. MilesAgain (talk) 20:01, 27 January 2008 (UTC)

Thanks; sounds like just dementia, as just her placement of the date was faulty and she knew her daughter was her daughter, rather than thinking her daughter should be about 5 years old, whereas in retrograde amnesia everything shifts back to that date, if I'm understandingit right. —Preceding unsigned comment added by DTF955 (talk • contribs) 21:27, 28 January 2008 (UTC)

pyro

im making my own pyro vidos have any ideas? —Preceding unsigned comment added by 76.14.124.175 (talk) 21:42, 26 January 2008 (UTC)

Buy life insurance?

Atlant (talk) 22:00, 26 January 2008 (UTC)

Don't? Paragon12321 (talk) 23:10, 26 January 2008 (UTC)

I mean for the videos. like wat should i put in them? have any good pyro tricks? —Preceding unsigned comment added by 76.14.124.175 (talk) 04:10, 27 January 2008 (UTC)

For some ideas on what NOT to do take a look at the discussion on #Firing flare guns at people above. SpinningSpark 16:07, 27 January 2008 (UTC)

Do it in a video game. --f f r o t h 16:11, 27 January 2008 (UTC)

You don't think you're going about this rather backwards? Don't such videos usually get created when someone thinks of something or does something and says "Wow, that would make a great video."? You question strikes me like someone asking "I want to write a book, what should I write it about?" APL (talk) 23:58, 27 January 2008 (UTC)

Sitting too close to TV

Is it really harmful to sit "too close" to the television? Would the same thing apply to computer monitor screens, given differences between their use (difference also between CRT vs LCD?)? ----Seans Potato Business 22:10, 26 January 2008 (UTC)

[2] ----Seans Potato Business 22:59, 26 January 2008 (UTC)

In short, "no". I don't agree with some of the material used in the Straight Dope answer above. The thing to keep in mind (as SD mentions) is that sitting too close to the TV might lead to eye fatigue (which is usually a transitory problem relieved by switching off the boob tube and doing something else), but not to myopia, which is (largely) genetically determined. I only add the (largely) in there because some kinds of injury can mimic the effects. Matt Deres (talk) 20:11, 28 January 2008 (UTC)

Thermochemical tables

hello can you tell me where can i find on the internet some accessible thermochemical tables containing data such as enthropy and enthalpy of formation, of reaction?(on the page "thermochemical equation" there is a link to ΔH tables, but it doesn't work)

can you also tell me if it's possible, and how, to find Active Thermochemical Tables (ATcT) online?

thank you 82.60.0.232 (talk) 22:43, 26 January 2008 (UTC)

NIST Chemistry Webbook http://webbook.nist.gov/chemistry/ —Preceding unsigned comment added by Shniken1 (talk • contribs) 05:18, 27 January 2008 (UTC)

Malonic acid

Just how concentrated is it in apples? Could one get a useful yield from a bushel of apples, or would it be significantly (>50% higher yield) more useful to just preform a synthesis? Yamakiri ^T_C § 01-26-2008 • 23:11:37

I would not be so much worried about the content of it as I would be worried about how exactly one would extract it. For obvious reasons, it would be hard to chemically differentiate it from, say citric acid or malic acid or succinic acid. —Preceding unsigned comment added by 18.96.6.239 (talk) 02:10, 27 January 2008 (UTC)

RC Copter Problem

I got a Small RC Helicopter for Christmas from my friend (A knock-off of the Picoo Z). It worked fine out of the box after I adjusted the (electronic) trim. But on it's 3rd flight it started spinning uncontrollably in a counter-clockwise fashion. The tail rotor is spinning fine, and for the first 30 seconds of flight after charging the helicopter flies straight, only to go nuts every time I try to fly any time after wards. Does anyone have any idea how to fix this? I try adjusting the trim, but that doesn't work. I have no clue what to do now Chris16447 (talk) 23:29, 26 January 2008 (UTC)

• Two rotors on top, right? Make sure both of them are firmly seated on their axles (or whatever you call that part.) When mine crashes (or even lands a little hard), the bottom one ends up loose on its axis, and it just freely rotates rather than turning in a powered fashion, resulting in spin spin spin. --jpgordon^∇∆∇∆ 16:02, 27 January 2008 (UTC)