You can't go faster than the speed of light, and so you can't go back in time. This answer is no cop-out. According the laws of physics as we know them, there's just no way to go faster than the speed of light. At best you can get really close to the speed of light. The faster you travel, the slower time will pass for you relative to someone standing still and the more squashed you'll look relative to that stationary observer. Unless you are a photon and don't have any mass, you are stuck travelling slower than the speed of light for your entire life.
Happy learning,