If you had a filament that was made of a single molecule that was several light years long, could you deliver instant messages to the other end of it by tugging on one end? If not, why?
Whether it’s one molecule or a conglomerate of molecules, it’s held together by “springy forces” and has a stiffness and there is a maximum speed of a physical impulse passing though it. The maximum speed of this physical impulse is far less than the speed of light in a vacuum. A single molecule may be stiffer than steel, but it won’t be stiff enough to transmit a motion anywhere near c.
See Is response faster than light?. In that thread I calculated that it would take around 385,000 years for an impulse to travel along a steel rod reaching from here to the closest star, a distance that light travels in four-something years.
At the risk of starting yet another “speed of gravity” post, I still have an unanswered question: if gravity has no detectable finite propagation time, than in theory couldn’t someone light years away simply swing a mass on the end of a pole, and a sufficiently sensitive gravity meter detect the shift instantly?
Badtz Maru – As JonF said, because each atom/molecule of the filament must pull on the next, there is a speed limit. You would need a perfectly rigid object (no jokes please!)…which does not exist.
Lumpy – gravity is thought to also travel at the speed of light. (sorry - I missed the previous speed of gravity thread)
We have darned good reason to believe that the propagation time of gravity is not detectable because we haven’t yet figured out how to build an instrument to detect it. We also have darned good reasons to believe that, when the propagation speed of gravity is measured, it’ll come out dead-on at “c”. Of course, people want to run the experiments anyway, because it’d be so freakin’ fascinating if it doesn’t come out dead-on at “c”, so they’re working on it. E.g. LIGO
Today the answer is no, just faintly possibly subject to future revision … don’t hold your breath.
In theory, yes, this could be done (though not instantaneously, as mentioned above), but in practice, we don’t have instruments sensative enough to pull it off, yet. LIGO might be able to do the trick, and LISA definitely will, if she ever gets the funding to get off the ground.