The problem with the "spacetime" theory is that space is NOTHING, which is infinite in distance, and there is no such thing as an entity called "time". "Time" is only our description of what is happening compared with something else that is happening, i.e. the clock's hands indicate one hour has passed for each 1/24 rotation of the Earth. Therefore, since "time" itself as an entity does not exist, it cannot be slowed or speeded up, which throws the theory of time dilation, or "time travel" out the window. The theory of "time" slowing down when nearing the speed of light is bogus. If a nuclear powered satellite's clock seems to change it's "rate of time", it's because the rate of nuclear fusion or fission changes when put into a weaker or stronger gravitational field, not because "time" itself has changed. It's the same as if I mix 5 minute epoxy at 70 degrees, it takes 5 minutes to cure, however, if I mix it at 35 degrees it will take 8 minutes to cure, time has not changed, only the conditions have changed.
So the "space-time continuum" is BS, only something from science fiction. The equation E=MC2 CANNOT be valid, because there is no way to quantify the speed of light to put it into the equation, other than by using numbers created by man's selection of units, i.e. "miles per second", "kilometers per second", and so on, which will give different numbers for the same velocity. The speed of light has NOTHING to do with energy and mass.