theoretically, E=mc^2 does not gove you a formula for time travel. Theory of Relativity (General and Special) requires 4-vectors and tensors and only from their mathematics can one "theorize about time travel" In addition, matter and energy can be converted to and fro. An example of this process is pair production and annihilation. In production, light , near the presence of an atom can produce an electron positron pair. On the other hand, annihilation involves the production of 2 photons from an electron and positron pair. Also, theoretically, there are particles which travels faster than light. These particles are called tachyons.
Theoretically speaking, Time travel is both possible and impossible, using Einstein Theory of Relativity, E=mc2.
It is possible, because time slows down when speed approaches the speed of light, and if faster than light speed is achieved, we can travel backwards in time. Only one future time travel is possible, and that what's we're doing now.
It is impossible, since mass is converted to energy as it approaches the speed of light. This is irreversible. Matter can be converted to energy almost instantaneously, but converting energy to matter is a different story altogether. If an object achieved light speed, it has become light energy. Converting it back into matter will require "devolving" it, and that is a complicated process I can't even try to explain (nakalimutan ko na kung papaano, but it's still in my head somewhere).
Also, with those things considered, NOTHING travels faster than light.
Except probably, the speed of thought. (Think you're in Andromeda and you're there).
In addition to time travel, scientists (that's us!) are probing the idea of a multiverse. These multiverses exists simultaneously and can be found beyond the Hubble Dimension of our Universe.
By the way, these things are ourely theoretical. no concrete evidence of these things exists (Well, except for E=mc^2 probably, which is the way our Sun produces its energy).
Just to enlighten you guys...