Wikipedia:Reference desk/Archives/Science/2008 January 10
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Communicating Faster than Light Using a Rotating Rod
A thought experiment: suppose you created a perfectly stiff rod or fiber of some material that stretched from Earth's orbit out to Pluto. An astronaut on the Earth end turns the end of the rod back and forth in a kind of Morse code. Given that the material is perfectly stiff the astronaut's friend at Pluto should see his end of the rod rotate simultaneously and data is transmitted faster than light. What am I missing here? —Preceding unsigned comment added by Sslam (talk • contribs) 00:26, 10 January 2008 (UTC)
- The fact that you can't create such a rod -- no material is perfectly rigid. When you move one end, the other end does not respond immediately; it has to wait for the signal to be transmitted along its constituent atoms. That signal is transmitted by means of emitted and reabsorbed virtual field quanta, which travel at the speed of light, so at most your signal can travel at the speed of light. In practice it will be much slower (at most the speed of sound in the chosen material). --Trovatore (talk) 00:39, 10 January 2008 (UTC)
- Also Earth and Pluto do not remain equidistant. Plus we have all those other planets et al in the way. Cool idea however. Lanfear's Bane | t 12:37, 10 January 2008 (UTC)
- This ought to be on the Reference Desk FAQ; it gets asked at least every six months or so. The fundamental problem with communication by rigid object is that what we perceive as "rigidity" is really an electromagnetic effect: atoms and molecules interact by means of the electron shells of the atoms and molecules. As such, this interaction is just as constrained by the speed-of-light as any other interaction. This means that a perfectly rigid object can't be constructed and that even mechanical motions won't propagate faster than light.
- Rigidity is a practical concern and could be partially ignored here (there is a relativistic upper bound on rigidity, but you could accelerate slowly enough to avoid it, methinks). Rotating the rod such that the ends reach the speed of light would require an infinite ammount of energy, and so it would be impossible. Someguy1221 (talk) 19:42, 10 January 2008 (UTC)
Something removed from Wikipedia article, List of common misconceptions
BTW, I won't say that there aren't other "misconceptions" on the page that may not be totally accurate (or flat out wrong), but I found this to be rather unbelievable. I've removed it until further notice.
- That all objects, irrespective of their masses, fall at the same rate in a vacuum (i.e. ignoring air resistance) is only true for masses small in comparison with the mass of the Earth. The effect of gravity depends on the sum of all masses involved, and not just on the mass of the heaviest object. In other words, a hammer dropped from a tower has a greater mass than a pebble dropped from the same tower, which means that the Earth moves towards the hammer faster than it moves towards the pebble and, relative to the surface of the Earth, the hammer will be very slightly faster. If both objects are dropped in the same place at the same time, this will not apply. Nor would it apply if the unused object was left at the base of the tower (since it would then effectively add its mass to the mass of the earth).
If the concept that (all objects, irrespective of their masses fall at the same rate in a vacuum) is false, I don't believe this argument is convincing. If I was more familiar with physics, I think I could rewrite this to make more sense if it is indeed true. But I have significant doubts. And this article I'm working on is supposed to be about common misconceptions (and I add that can be easily proved to be misconceptions). BTW, I also started a conversation at Talk:List of common misconceptions#What is this?!? (Physics Gravity problem)
Thank you for your time.
- The Newtonian gravity formula dictates that if you increase either of the object's mass, F will increase. But, , does the increase in F offset the increased mass? --antilivedT | C | G 05:10, 10 January 2008 (UTC)
- If there is a kernel of truth hidden within this "misconception" then I think it might be as follows. Suppose we take an object with the same mass as the Earth - say a neutronium asteroid - and drop it from some height above the Earth's surface (and, to keep things simple, let's say that the height is small compared to the Earth's radius). Then in an inertial frame of reference the asteroid will accelerate towards the Earth with an acceleration of g. However, the Earth will also accelerate towards the asteroid with an acceleration of g (by symmetry, or by Newton III). Therefore to an observer standing on the surface of the Earth underneath the asteroid (which is not an intertial frame of reference), the asteroid will appear to fall towards them with an acceleration of 2g. This hypothetical and suicidal observer will have to have a firm grip on the Earth, because the gravitational pull of the asteroid on them is much greater than mg (they are much closer to the centre of mass of the asteroid than to the centre of mass of the Earth) - and the Earth will probably be ripped apart by tidal forces anyway - so remember that no consequential damages can be sought against Wikipedia if you try this at home. But I agree that the statement that "all objects fall at the same rate in vacuum" is not really a misconception - at most, it is an oversimplification. Gandalf61 (talk) 10:53, 10 January 2008 (UTC)
Not sure where to post this question ... but I am thinking here in Science, as it deals with photography. I have noticed recently that people use a rather "cool" effect which makes their photos look almost like the negative in film. For example, your light/white face would appear dark/black ... and your dark/black hair would appear light/white. Is there a name for that type of photography or photo? It's hard to explain in words what I mean ... but perhaps someone knows what I am referring to. Thanks. (Joseph A. Spadaro (talk) 06:34, 10 January 2008 (UTC))
- Modern image-editing software allows all sorts of interetsing transformations. The one the originalquestion may be referring to is to take the luminence (lightness) channel of the image and invert it while leaving the chromanence (color/hue) channel the same.
- I think you may be thinking of infrared photography, where the image does look almost a reversal of black & white, where in actual fact it's picking up a different wavelength of light. -- MacAddct 1984 (talk • contribs) 15:47, 10 January 2008 (UTC)
- Yeah, solarization is probably what he means. It's one of those filters that got overused and misused with the advent of digital image editing, but doing it in a dark room with real prints is fun, cool, and can lead to a lot of surprising things. Man Ray's early work with it is awesome. --184.108.40.206 (talk) 19:29, 11 January 2008 (UTC)
- Ah, that is most definitely a straight negative image, as suggested by MrRedact with it's colors reversed as well. If you were to stare at one spot long enough and then look to a blank white space, you could get an afterimage of what the "true colors" were. -- MacAddct 1984 (talk • contribs) 20:37, 12 January 2008 (UTC)
- That's all that it is ... a negative? How can the entire photo be black and white (really, grays) with just that small patch of purple? The purple seems odd ... in the negative image, why wouldn't the purple flowers just be some shade of gray like everything else is in the photo? Why are the flowers any different? Thanks. (Joseph A. Spadaro (talk) 21:14, 12 January 2008 (UTC))
Drugs named after places
A while ago, an internal medicine doc asked me to name three drugs named (generic name, that is) after geographic locations -- I didn't have a clue. He rattled them off so quickly that I only caught one of them, warfarin (which might be a stretch since I'm doubtful that the Wisconsin Alumni Research Foundation is technically a place). It's completely trivial, but I've been trying to figure out the other two (or more) for a while. Any ideas? Thanks, David Iberri (talk) 19:05, 10 January 2008 (UTC)
Thanks for the replies. I forgot to mention that I'm looking for generic drug names, not trade names or street/colloquial names. Nystatin works, but not the others. --David Iberri (talk) 18:59, 11 January 2008 (UTC)
Gulls and countershading?
With reference to the penguin question above - is the white below, grey/black on the wings/back plumage seen on (most) adult gulls also an example of countershading? --Kurt Shaped Box (talk) 22:30, 10 January 2008 (UTC)
- Yes, the wing plumage has the effect of countershading. Though many species of gull undergo quite remarkable morphological colour changes with age and season, suggesting that there could be additional reasons beyond camouflage. Rockpocket 00:23, 11 January 2008 (UTC)
- Agreed. Some of the larger gulls do not attain their full adult plumage until (at least) four years of age - and they're predominantly brown for the first two. Large gulls, however are more than capable of defending themselves against the majority of things that would attempt to eat them on a regular basis (okay, so they're not going to have much of a chance against a seal, shark or killer whale coming at them from below the water - but who would?), so perhaps their colouration is less important to their survival than it is in the smaller gull species. I have noticed that Black-headed Gulls are mostly countershaded upon fledging, for what it's worth. --Kurt Shaped Box (talk) 00:51, 11 January 2008 (UTC)
I have a friend that drives a 1994 Ford Escort that has a broken speedometer. Instead of showing the real speed it oscillates about 10-15 MPH above and below what the indication should be. She told me that her uncle said that the problem was that one of the fans that runs the speedometer is broken. That is when I immediately questioned such a diagnosis, since I know how speedometers work and it certainly isn't with fans. She believes this man's word so I let it go. However, every time I rode in the car I observed the speedometer and saw that it didn't rise up when driving against the wind (as it would if the silly "fan" theory was correct), nor did it suddenly dive when she drove behind the slipstream of, say, a large semi-truck. I told her this observation, calling her uncle's explanation "bullshit". That is when her brother cut in and said that this man is an "engineer", and that he has "patents". I was about to say that "Tesla had patents too, but I don't think he was an expert on cars", but I let it drop - seeing as I respect her brother as a very intelligent person. My question is: am I right about the Escort's speedometer having nothing to do with fans? And if I am, is there any easy way to fix this problem? Chris16447 (talk) 23:22, 10 January 2008 (UTC)
- If you can get at one end of the cable that runs from the transmission to the dashboard, pump WD-40 into it until it runs out the other end. Problem fixed. (You should be hearing a zizzing noise, and you should be able to affect the reading by kicking the cable where it comes through the firewall as you drive.) Tesla was a decent repair tech, by the way, from the stories I've heard—a rare confluence of talents that catapults him into genius territory in my book. Kooky, though. --Milkbreath (talk) 00:03, 11 January 2008 (UTC)
- This is a pretty common Ford problem, FYI. Our mechanic blamed it on the cable and lubricated the cable, but that didn't fix our example. It was always accompanied by sound effects and I believe the problem was actually the rotary magnet out of position and bumping the alumin[i]um cup that drives the speedo needle or some foreign material that had gotten into the gap between those two.