cavediver
From the persepctive of GR, this cannot happen. Space-time is a fixed, non-dynamical 4d space of events. There is simply no mechanism for events to be changed.
I was recently reading Brian Greenes book The Fabric of the Cosmos and in it he was making the point about how ,though difficult, time travel to the past is not in violation of physics. He stated that the way spacetime is structured should make situations such as killing your parents an impossible task and it struck me as odd that time travel according to him should not violate any physical laws.
The reason I find this difficult is because I fail to see how the law of mass energy conservation can be maintained if a person of given mass leaves the spacetime "now" that he presently occupies and travels back in time to a past spacetime. Would the universe not now be deficient in total mass energy in his "now" time frame and overbalanced in the past? Or is the total mass energy of the universe not constant and subject to alteration?
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