We recently received an interesting question:
I have an interesting idea that could in theory break the famous law that states nothing can travel faster than the speed of light. More specifically, a method of communicating that could instantly travel across space. Suppose a really long pole similar to the space elevator made out of carbon nanotubes could be constructed in space. Suppose this pole was one light year long. Assuming that all this was possible and ignoring all the orbits and gravity from everything near it. Couldn’t you push and pull this pole to create coherent binary code that would be expressed instantly at the other end? I am very sceptical about this idea as I know nothing can break the light speed barrier. What am I missing here?
Thanks all, keep up the good work.
Paul Manchester, UK
Thanks for the question
Your proposal sounds plausible and I remember thinking along similar lines a while back. It just seems to make such good sense that pushing on one end of a pole instantly moves the other end, no matter what its length is.
Can you think of anything in your experience that would lead you to the opposite conclusion?
Unfortunately, common experience is often of little help when discussing such over-the-top scenarios.
As you may have guessed..pushing on one end of a pole (even a nanotube pole) would unfortunately not cause the opposite end to move in any way that would permit instantaneous or even incredibly fast communication.
The bottom line is that because the pole is so long and atoms cannot influence each other instantaneously, the push would necessarily propagate along its length at a sub-light speed that can’t be overcome.
In fact, the push would necessarily propagate at the speed that sound travels within the material the pole is made of. The speed is determined by the elasticity and density of the pole.
Sure, if you had an infinitely rigid pole (…ahem) you might have something but Relativity limits the potential rigidity of any object in such a way that the speed of sound could never exceed the speed of light.