Asri-unix.1092
net.space
utzoo!decvax!ucbvax!ARPAVAX:C70:sri-unix!ES@MIT-MC
Tue Mar 23 21:55:52 1982
Thought experiment in general relativity
     The whole question was improperly posed on account of the non-existence
of rigid bodies.  Suppose you observe a rigid body.  It has the property
that when pushed at one end, all parts of it start to move simultaneously.
However, to an observer moving relative to you, simultaneity is different,
and the body appears nonrigid.  Furthermore, a "rigid" body has an infinite
speed of sound.  To other observers, the speed of sound can be anywhere
down to but always greater than the speed of light.  To some observers
sound travels backward in time.