Hypothetically lets say you were in Kurt Godel’s universe and time travel was possible. http://img96.imageshack.us/img96/4307/ti [Broken]... An image that may help explain what I’m saying Imagine going back in time to visit yourself 10 minutes ago. Just to made it easier to visualise lets imagine ten minutes ago you were down the shops, you walk back home, remember this bit you push a cup off the table what lands on the floor and then you go into your time machine to travel back in time 10 minutes to when you were still down the shops. Now on travelling back in time the energy that went from the cup into the floor goes back into the cup and the cup rises and goes back into the table. But the atoms that made up you ten minutes ago are still in status in the time machine, so they can’t go back down the shop for you to visit them. The atoms that made up you 10 minutes ago will not just appear this would create more mass in the universe and due to E=MC^2 there is more energy in the universe going again fundamental laws in physics.