srm@pyuxnn.UUCP (10/04/83)
I'm driving down the NJ Turnpike at the speed of light. I turn on my headlights. Does anything happen? (I was just wondering.)
CSvax:Pucc-H:ab3@pur-ee.UUCP (10/05/83)
From: srm@pyuxnn
I'm driving down the NJ Turnpike at the speed of light.
I turn on my headlights.
Does anything happen?
(I was just wondering.)
1. If you are driving at 99.9999% of C, then the
headlight beam propagates away from you at C.
2. If you are driving at C, then you have transgressed
the {known, well-understood, apparent -- pick one} laws
of the universe and you will be stopped by the next
traffic cop, who will of course catch you by riding a
tachyon-constituted motorcycle.
Darth Wombatstudent@nmtvax.UUCP (10/07/83)
>From Micheal Ellis: >Now wait... going the speed of light is not in violation of any law of >physics I know! To my knowledge, your clock slows down as you approach the >speed of light, and completely stops should that speed ever be attained. >That means that you can never `do anything' at C -- you are `frozen' as >long as you continue to travel this speed. Therefore, you cannot turn on >your headlights while traveling at C. > >To actually accelerate to C would, of course, require dumping mass-energy >as you accelerated, until your `rest mass' becomes zero, since it takes an >infinite amount of energy to accelerate a positive `rest mass' to C. Your >car and headlights, as well as you yourself, would have to transform >themselves into some pretty elusive stuff, `weighing' nothing in your >coordinate system (who needs to, since you can't do anything there >anyway!). Einstein's theory of relativity states that in an inertial frame all observers will see the same thing. An inertial frame is a little hard to understand but it is basically a frame of reference where all of Newton's Laws are observed to be followed. Thus the Earth's surface is not an inertial frame since gravity bends objects into parabolas not straight lines as seen from an observer. When in an inertial frame the observer notices time chugging along at 3 X 10 exp 8 meters per second. That is correct Einstein (and those who talk about relativity) measure time in meters. A person can do anything he wishes, including turning on the headlights. To accelerate up to NEAR c the objects rest mass approches infinity not zero. This is because of Newton's Second Law of F = dp/dt or more commonly F= ma. The second version does not hold for high velocities since the mass is now a function of velocity in m = m sub naught / ( 1 - beta sup 2 ) sup 1/2 where beta is the fraction of your velocity over the velocity of light. For those of you who are still confused I suggust reading "Spacetime Physics" by Taylor and Wheeler. Sincerely; Greg Hennessy; ..ucbvax!unmvax!nmtvax!student
Shinbrot.WBST@PARC-MAXC.ARPA@sri-unix.UUCP (10/10/83)
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ellis@flairvax.UUCP (Michael Ellis) (10/12/83)
Hope this doesn't become tedious to advanced physics people, but I'd really like to know how things appear from a C-velocity reference frame. From my previous article... >... you can never `do anything' at C -- you are `frozen' as long as you >continue to travel this speed. Therefore, you cannot turn on your >headlights while traveling at C. {nb. we're discussing hypothetical zero rest mass people, clocks, headlights} to which, unless I misunderstood, Greg Hennessy replied: >(in an inertial frame traveling at C..) A person can do anything he wishes, >including turning on the headlights. Now wait a second. To my understanding, any positive time interval in a C-velocity reference frame corresponds to an infinite amount of time in ALL sub-C reference frames. To the extent that an infinite amount of time in the `universe' has meaning at all, Greg Hennessy's remarks seem correct. Seems to me, if you were in a C-velocity frame: o If a positive amount of time passed (as measured your clock), the first thing you'd encounter would be, uh, maybe the end of the universe. This would occur instantaneously. I won't even try to speculate where or when you would be if you and your clock kept going after that... o If precisely zero units of time passed (again, by your clock), but your velocity were subsequently (according to someone else's clock) slowed to less than C, you could have traveled to ANYWHERE in the universe. It is in this sense that I meant you can't `do anything' (except move in a `frozen' state) in a C-velocity reference frame. Comments, flames welcome. I'd really like to know if this is correct. And does experimental physics show that time does not pass for photons? It always struck me as strange that they were something, yet had no mass. -michael -ps to Darth Wombat: I wasn't trying to pick at your response as much as I was trying to determine how things `appear' to a photon. Sorry. -pps Whether this article is correct or not, we still haven't determined what things `look like' from a C-velocity frame. I heard somewhere as your velocity increases toward C, the visual area in the direction of motion `appears to expand'; does this imply that at C the point at your direction of motion expands to fill your entire visual field?
nazgul@apollo.UUCP (Kee Hinckley) (10/12/83)
I'd like to add a complication to all of this. It was stated that an object could
not attain the speed of light (unless it had no rest mass) for reasons that I won't repeat.
It seems to me however, that part of the concept is that it would take more energy than
you can carry (alternativly the idea is that your mass becomes infinite, in which case
this question is moot).
Framework: Lets hypothesize a light-sail ship. One side is totally transparent to
light and massed objects, the other is completely resistant. Presumably the force of
light upon this vehicle will cause it to accelerate.
Query: Can this ship reach the speed of light? (Why/Why not?)
-keemwe@astrovax.UUCP (10/13/83)
First, about experimental evidence: We know to high accuracy (about 1 part in 10 to the 34th power I think) that the photon has no rest mass. Special Relativity then indicates that it travels at the speed of light. Of course, we have no independent measure of the speed of light, having only "photon beams" to play with. (yes, I know about gravitational waves, and as soon as we find one, we can worry about its speed: also if your hard core then a neutrino is also massless, but they're so sneaky its hard to get velocities anywhere near as accurately as for light) If you believe SR, which is considered well grounded in experiment, then you are forced to the conclusion that proper time does not pass in a frame moving with speed c. It therefore seems to be a particularly uninteresting frame to be in (unless of course you're massless, in which case you can't exist in any other frame). I'm not sure if field of view has any meaning in a frame where time does not pass, but you have the right limiting case: the direct forward direction fills your field of view. As you are traveling at c however, nothing comes at you. This field of view is discovered as you run into things in your path. I also don't think that the infinite blueshift ahead of infinite redshift behind has any meaning. Speed c really is a limiting special case.
gwyn@brl-vld@sri-unix.UUCP (10/14/83)
From: Doug Gwyn (VLD/VMB) <gwyn@brl-vld> You can't possibly be driving down the NJ turnpike at the speed of light. This puzzle (without the turnpike) was one of the things that got Einstein started on working out the special theory of relativity.
gwyn@brl-vld@sri-unix.UUCP (10/14/83)
From: Doug Gwyn (VLD/VMB) <gwyn@brl-vld> Were you to "dump" your rest mass at an exponentially decreasing rate, it would all be gone by the time you reached the speed of light - perhaps; but then this process takes infinitely long in your reference frame, you must realize.
gwyn@brl-vld@sri-unix.UUCP (10/14/83)
From: Doug Gwyn (VLD/VMB) <gwyn@brl-vld> I don't think that Einstein actually believed that one would see himself in a mirror if he were travelling at the speed of light.
Shinbrot.WBST@PARC-MAXC.ARPA@sri-unix.UUCP (10/18/83)
n sort out the mess above is that not only will the spaceship gain in mass indefinitely as it is accelerated, but the time for which the force is applied will become shorter and shorter. So the spaceship cannot reach c whatever the means of propulsion. - Troy