[Dr. Octogonopus]

The way I understand it, it's technically possible to travel backwards in time. It would just take immense amounts of energy, more than can be created from all the earthly materials. But, it is impossible to travel forwards, because it does not exist yet. So, in a way, if you had perfected cryogenics, you could put yourself in cryo, hope you get revived, and eventually go back into your proper timeframe. But it would be waaay more trouble than it's worth.