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Esquire.J
2008-Dec-21, 10:38 PM
A slightly annoying question perhaps but i would like peoples take on it...

lets say we had some kind of timing device... as accurate as an atomic clock. The device can be read from two ends. These ends are attached to each other by an extremely long rope/wire/connection... whatever. The two 'ends' are linked mechanically and will always read the same time. Now if i sit here with my 'end' ticking away and send my friend with the other 'end' in a space ship that travels close to the speed of light around the earth a few times (its a real long wire) what happens to the readings? In theory they should read different times but if they are mechanically linked would they simply become out of synch and break? or would they still read the same time? would the person on the ground see his clock speed up?

hhEb09'1
2008-Dec-22, 12:16 AM
Welcome back, Esquire.J

I've moved your question from the Always travel through time at the speed of light? (http://www.bautforum.com/against-mainstream/82364-always-travel-through-time-speed-light.html)thread to its own thread, where it might get more visibility.

tdvance
2008-Dec-22, 12:48 AM
"The two 'ends' are linked mechanically and will always read the same time. "

that's part of the problem--every signal travels at the speed of light or less. That includes motion of a "long rigid pole"--which is not truly rigid, since it is made up of atoms--push the atoms at one end, it takes time for the atoms at the far end to respond. In fact, the speed of the push is the speed of sound in the material of the object.

If it doesn't break, it might bend--the longer a rod, the more flexible it becomes no matter how rigid the material (there's a video out there of the Tacoma bridge--you can see how, I guess it's concrete in that case, becomes flexible if long enough).

John Jaksich
2008-Dec-22, 01:02 AM
In my interpretation, if there is a clock at rest --- then its time would differ from a clock in motion (near the speed of c) whereas -- the mechanical or rope-like connection would undergo Lorentz contraction to a degree ( a gradient-type of contraction ) that is proportional to its length from the clock of motion. I hope I am not reading into it incorrectly.

Jens
2008-Dec-22, 01:29 AM
These ends are attached to each other by an extremely long rope/wire/connection... whatever.

As tdvance pointed out, this is the problem. It cannot happen. In fact, there is no such thing as a "mechanical connection" in the way that you are trying to hypothesize. Things might seem solid to us, but they are not. They are just masses of atoms linked together by forces, and so a "solid" is not really solid. So in this universe, nothing is actually linked directly to anything else.

John Jaksich
2008-Dec-22, 01:51 AM
Jens and tdvance


Without intending to rile you --- I find this to be a very good thought experiment--- I believe that applying Lorentz's rules of length contraction and time dilation can correctly solve the problem. This problem is not an engineering problem per se; as so much as, an exercise in math physics --- with relativity and quantum mechanics thrown in to distract from the problem at hand. This can be taken to be an "action at a distance" problem. If anything it can serve as an example...

Jens
2008-Dec-22, 02:07 AM
The problem is, though, that I was going to add something else: if such a contraption were possible, then we would be living in a universe where relativity is not true. But if you want to use it to explore math, then feel free to explore it.

blueshift
2008-Dec-22, 02:51 AM
Your experiment is interesting and has come up before. But your need to look closer at your experiment. It is equivalent to a pendulum and the two ends of a pendulum are not as rest with respect to one another. The pivot is at rest with respect to earth while all the points on the swing is not so they (the two clocks or any others you add to the long rod) are not in a special relativistic reference frame. One clock is in an inertial reference frame (the pivot) and the other is not.

DrRocket
2008-Dec-22, 03:40 AM
"The two 'ends' are linked mechanically and will always read the same time. "

that's part of the problem--every signal travels at the speed of light or less. That includes motion of a "long rigid pole"--which is not truly rigid, since it is made up of atoms--push the atoms at one end, it takes time for the atoms at the far end to respond. In fact, the speed of the push is the speed of sound in the material of the object.

If it doesn't break, it might bend--the longer a rod, the more flexible it becomes no matter how rigid the material (there's a video out there of the Tacoma bridge--you can see how, I guess it's concrete in that case, becomes flexible if long enough).

Right. Special relativity prohibits the existence of rigid bodies. The physics of atoms and the resulting elasticity of real materials is consistent with that prohibition, but the prohibition also results from just the implications of relativity without necessity of the atomic explanation.

Re: Tacoma bridge. That movie is incredible. I showed that to a differential equations class once, as an example of the power of resonance. What is amazing is the amount of deformation of that concrete road bed before it comes apart.

mugaliens
2008-Dec-22, 11:25 AM
In fact, the speed of the push is the speed of sound in the material of the object.

For accelerations only. For a constantly rotating pole, this is not true.