Suppose you are inside a closed box which is moving with a constant speed with no acceleration whatsoever. You cannot see outside the box. If you are given all the instruments you need, what experiment could you perform to ascertain that you are, in fact, in motion?
This was a question asked in an interview for admission to a pure sciences research university.
The only thing I was able to think of was maybe if we somehow converted the mass of some object into energy it would be slightly more than what we would expect from $E=mc^2$ since it also has kinetic energy.
Is this even remotely correct? Does it even have an answer or was it simply a trick question?