It is known that, by the expansion of the universe, galaxies that are roughly 4200 megaparsecs away travel away from each other faster than c. A little thought experiment on this; 1- The equation for relativity suggests that results become unphysical. 2- Time would be stopping or going backwards. 3- Effects can be before the cause. 4- Mass of an object would become infinite Now, this would be disproving everything we know so far. And assuming we know things right, we can conclude; 1- When two galaxies move away from each other faster than c, they can no longer communicate with each other. Therefore this solves the arising problem that effect can be before cause. 2- For them to be unable to communicate with each other, even if an object travels back faster than c from one galaxy by any means, it can not reach the other galaxy. This would mean that once two galaxies are past the threshold they no longer are part of the same universe. (To explain simply) 3- Beyond the threshold the galaxy slowly becomes stationary and redshift and disappear from the other galaxies universe. --- Now after reading these points, i have one question. Since the galaxy is becoming stationary and redshifting from the other galaxies point of view. How does relativity explain what happens after enough time passes and a galaxy reaches to the coordinates that another galaxy has redshifted from its universe? Normally the galaxy A is no longer there, and no effect would be expected. But from galaxy Bs point of view that coordinate is the exit point of the galaxy A. And relativity suggests its mass would be infinite, its time would have stopped.