So the conclusion of the thought experiment is that upon returning to earth, the traveler has aged only slightly, while his friends and family are much older. Why is it not the other way around - the traveler is older and the people on Earth have barely aged?
I understand that if someone is traveling away from Earth at a very high speed, time will slow down for the traveler relative to the people on earth. However, why is it not the other way around? If there is no universal reference frame, could this situation not also be thought of as the traveler...
If a particle is moving with kinetic energy T(x) in a potential field of energy V(x), why is the total energy E(x) = T(x) - V(x), i.e. why is potential energy negative?
The way I have seen it explained is that the potential energy is less than if the particle was an infinite distance from the...