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RoS question
On Sep 3, 11:22*pm, Tom Roberts wrote in
sci.physics.relativity: Note also that "length contraction" is misnamed, and no object's length actually contracts, only MEASUREMENTS of length do so. But don't think it is purely measurements -- because the underlying effect is a geometric projection, it can have physical consequences (e.g. the kinematics of high-energy collisions and interactions). Tom Roberts Bravo, Honest Roberts! When your brothers Einsteinians teach that the 80m pole remains inside the 40m barn IN A COMPRESSED STATE, they mean just this: the pole is not contracted at all - the underlying effect is a geometrical projection with physical consequences: http://math.ucr.edu/home/baez/physic...barn_pole.html "These are the props. You own a barn, 40m long, with automatic doors at either end, that can be opened and closed simultaneously by a switch. You also have a pole, 80m long, which of course won't fit in the barn. Now someone takes the pole and tries to run (at nearly the speed of light) through the barn with the pole horizontal. Special Relativity (SR) says that a moving object is contracted in the direction of motion: this is called the Lorentz Contraction. So, if the pole is set in motion lengthwise, then it will contract in the reference frame of a stationary observer.....So, as the pole passes through the barn, there is an instant when it is completely within the barn. At that instant, you close both doors simultaneously, with your switch. Of course, you open them again pretty quickly, but at least momentarily you had the contracted pole shut up in your barn. The runner emerges from the far door unscathed.....If the doors are kept shut the rod will obviously smash into the barn door at one end. If the door withstands this the leading end of the rod will come to rest in the frame of reference of the stationary observer. There can be no such thing as a rigid rod in relativity so the trailing end will not stop immediately and the rod will be compressed beyond the amount it was Lorentz contracted. If it does not explode under the strain and it is sufficiently elastic it will come to rest and start to spring back to its natural shape but since it is too big for the barn the other end is now going to crash into the back door and the rod will be trapped IN A COMPRESSED STATE inside the barn." Pentcho Valev |
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