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Registered Member #1951
Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105
cool, i thought the pole wouldn't fit, but i now know that simultaneous is not a constant. but why does the last door ( for the runner) close faster then the first one. hmmm
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Maybe someone can answer this one for me...
You have a hollow cylinder with a detonation switch at the bottom. A solid piston fits into the cylinder, but is too short to hit the switch by a few centimeters. A lip at the end of the piston prevents it from slipping past this point. Now, take the piston out and get it heading straight for the cylinder close to a velocity close to the speed of light. From the perspective of someone next to the cylinder, the piston contracts in length allow its axis of motion and will be too short to hit the switch when it enters the cylinder. From some riding with the piston, the cylinder appears shorter and the piston will hit the bottom despite having a lip on the end.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It doesn't matter, the energy of the explosives is negligible compared to the kinetic energy of the piston.
I would say that when the lip on the piston hits the end of the cylinder, it'll decelerate from its relativistic velocity. As it slows down, one of the observers will see the piston get longer until it almost but not quite hits the switch, the other will see the cylinder get longer and the switch retreat away from getting hit at the last moment.
The paradox, like the pole and barn one, is really about which frame of reference is appropriate for analysing the collision when two relativistic objects smash into each other. Intuitively I would say whichever frame makes the conservation of mass-energy work out.
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The pole and barn paradox
