First, there is absolutely no evidence that time travel is possible, if you are referring to the freedom to move into your relative future or past.Secondly, as objects approach the speed of light, they begin to experience noticeable increases in kinetic energy (simplified in non-relatvistic physics to E = 1/2 m v^2), which is measured by others outside of that object's reference frame as an increase in mass, as others have noted. The equation E = m c^2 talks about how much total energy any object with mass has WHEN IT IS AT REST in its environment. It has NOTHING to do with its movements relative to the speed of light.Now, as any one rest frame accelerates away from another rest frame, time begins to move at different rates between the two. The one accelerating, for instance, a spaceship, still experiences normal time and mass INSIDE the environment, but to anyone outside that environment (still on earth, for example), the time inside the spaceship seems to drag out, so that one second on earth is faster than one second on the spaceship.The people/machines/animals on the spaceship still experience normal time flow while in the spaceship, so time appears to pass normally, while thousands, or, if they are moving close to the speed of light, millions of years will pass on earth.If a spaceship were to travel from Earth to Andromeda galaxy at 85% of the speed of light, the astronauts would experience about 28 years to get there, but the earth would experience over 2 billion years.Now, taking this to the extreme of travelling at the speed of light, time outside the environment stands still. If you could travel at the speed of light, you would still experience time as you normally do, but the rest of the universe would appear to be standing still.Now, is faster-than-light travel possible? Not by normal means. There are theories about compressing space gravitationally to allow a ship to pass thru the space that has been compressed faster than the light that was IN that space when it was compressed, but this is still way beyond testing. We need to learn to create gravity, and we are still a LONG way from that point.In short, travelling at the speed of light is not physically possible if you have mass. If you have mass, you can always go faster towards the speed of light, but your mass appears to increase to observers outside your environment, and this means you would need to overcome the inertia to move faster. At the speed of light, any massed object has infinite mass, requiring infinite energy to get there. As you move closer to the speed of light, time for the REST of the universe appears to slow down, but your time still proceeds as normal.