“There can never be a clock at the center of the Universe to which everyone can set their watches. Your entire life can be the blink of an eye to an alien who leaves Earth traveling close to the speed of light, then returns an hour later to find that you have been dead for centuries.” UniversePhysicsAliensSpecial Relativity Book:The Physics Book: From the Big Bang to Quantum Resurrection, 250 Milestones in the History of Physics Source: The Physics Book: From the Big Bang to Quantum Resurrection, 250 Milestones in the History of Physics
“But this result [that light would travel faster towards a moving observer] comes into conflict with the principle of relativity [the laws of physics are the same for all observers]", Einstein added. "For, like every other general law of nature, the law of the transmission of light must, according to the principle of relativity, be the same when the railway carriage is the reference body as it is when the enbamkment is the refernece body". [...] There should be no experiment you can do, including measuring the speed of light, to distinguish which inertial frame of refence is "at rest" and which is moving at a constant velocity.” PhysicsSpecial Relativity Book:Einstein: His Life and Universe Source: Einstein: His Life and Universe