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Is length contraction an optical illusion? Does object really shrink? Though measurements say yes, does it really happen? Or I have to say object is really measured to shrink?

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    Bell's spaceship problem is relevant here: http://en.wikipedia.org/wiki/Bell's_spaceship_paradox – Johannes Oct 15 '14 at 09:52
  • @Johannes: Bell's spaceship problem is manufactured and very sloppy one. The string connecting the spaceships must be treated as much a part of one of them, or both, as any other part. The rope is accelerating as much as everything else is. And the rope actually converts these two spaceships into one body. Does Relativity tell us anything about materials or methods of construction? How can we assume that welding or riveting is better than tying with a rope? Or the perhaps the "delicacy" of the rope has anything to do here ... ? – bright magus Oct 15 '14 at 10:21

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Or I have to say object is really measured to shrink?

That's the right answer.

Imagine a thought experiment. Let's say we are shooting another sequel of the Speed movie, 5 (I lost track :) ). So there is a bomb on the board of a spaceship, and a terrorist says you cannot slow down below the speed of 0.5c, because if a mechanism that involves a measuring stick shows the stick gets longer than a certain length, the bomb will explode.

So will the bomb blow off, if the spaceship does slow down below 0.5c?

Well, it depends ...

1) It will explode, if the measuring stick is located outside of the ship, in a reference frame from which the spaceship was measured to slow down below 0.5c.

2) But the bomb will never blow off, if the measuring stick is located on board of the spaceship. (Because locally length and time never change due to velocity, they are only measured to change from an outside frame of reference considered stationary.)

bright magus
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