White Goodman wrote:Right.
Lightspeed is the universal speed limit and takes roughly 8 mins to travel from the Sun to the Earth.
If I could set up a rope between here and Sun (so 93 million miles long) and arrange it so it was just short of taut (and I mean infinitesimally short of that state) so that to pull it tight from the Earth end took 1 second and pulling it tight was distributed evenly along the rope.
Would someone at the Sun end feel the rope go tight immediately? If they do, aren't you sending a signal along the rope faster than the speed of light?
that would require the rope to be almost completely rigid. so basically a stick, and a bloody stiff one at that. in that case, yes, all the atoms of the object would move coherently and instantly.
however, a material of perfect rigidity does not exist and cannot exist, as this would mean that the speed of sound in that material would be infinite, hence faster than the speed of light, which creates some relativistic issues. but i digress...
tension propagates at the speed of sound in that medium, because the interaction between atoms is elastic and when you push the end of a stick what happens is that atoms push on the next ones and so on, taking some time.
basically, whenever you push a stick you compress it and it decompresses by moving the other end. a bit like an earthworm.