Physics Emergency: Two Trains Moving Away at 51% Light Speed

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SUMMARY

The discussion centers on the relativistic effects of two trains moving away from each other at 51% the speed of light (0.51c). It clarifies that, according to the relativistic velocity addition formula, one train will not appear to be traveling at 102% the speed of light, but rather at approximately 80.946% the speed of light (0.80946c) as measured from the other train's frame. The importance of specifying the reference frame when discussing velocities in relativity is emphasized, ensuring clarity in communication.

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Okay, I made a statement in another forum completely unrelated to physics and I believe it to be wrong even though I made the statement in good faith. (Which is to say, I THOUGHT I knew what I was talking about.)

So please, if you can, bail me out.

Two trains are moving away from each other, both traveling at 51% the speed of light. In one train, viewing the other, would it appear to be traveling at 102% the speed of light?

Okay, that's it! Any help will be greatly appreciated!
 
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Rico Bamchug said:
Okay, I made a statement in another forum completely unrelated to physics and I believe it to be wrong even though I made the statement in good faith. (Which is to say, I THOUGHT I knew what I was talking about.)

So please, if you can, bail me out.

Two trains are moving away from each other, both traveling at 51% the speed of light. In one train, viewing the other, would it appear to be traveling at 102% the speed of light?
Nope, you have to use the relativistic velocity addition formula here--in one train's frame, the other train will be moving at (0.51c + 0.51c)/(1 + 0.51^2) = 0.80946c, i.e. 80.946% the speed of light.
 
Awesome! And thank you Jesse!
 
Whenever you talk about this kind of problem, it helps to always add "as measured ..." When you say a train is moving at 0.51c, state relative to what or measured relative to what. That helps keep things straight.
 

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In an inertial frame of reference (IFR), there are two fixed points, A and B, which share an entangled state $$ \frac{1}{\sqrt{2}}(|0>_A|1>_B+|1>_A|0>_B) $$ At point A, a measurement is made. The state then collapses to $$ |a>_A|b>_B, \{a,b\}=\{0,1\} $$ We assume that A has the state ##|a>_A## and B has ##|b>_B## simultaneously, i.e., when their synchronized clocks both read time T However, in other inertial frames, due to the relativity of simultaneity, the moment when B has ##|b>_B##...
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