Alan Boyle asks the question at Cosmic Log, how well does "Lost" treat time travel? And enlisting the aid of Caltech theoretical physicist and author of the book "From Eternity to Here," Sean Carroll, answers "not bad at all." Traversing the logical paradoxes in time travel is tricky business, but Lost manages it without losing touch with the underlying physics of it all. For example, if life is one grand exchange of energy for information, then as Carroll views it, going back in time to change the future violates one binding law.
The way Carroll sees it, the mysteries of time - including the permanence of the past, as well as predestination versus free will in the future - focus on the cosmic concept known as entropy. Entropy is generally defined as the progression from order to disorder, from useful energy to useless energy equilibrium, from an ice cube to a puddle of lukewarm water.
Our universe appears to moving irrevocably from a state of low entropy (the big bang) to high entropy (the Big Chill). That means the past has less entropy than the future ... and that, in turn, means you can't go back and change things. 'The way the laws of physics work, we're never going to experience anything going backward in time from our own point of view,' Carroll said.
Even for time travel, there are rules. Boyle:
Carroll's book isn't so much about the impossibility of time travel as it is about that bigger mystery of entropy. Why does the arrow of time fly in just one direction, and where did that arrow come from, anyway? Does it make sense to talk about what happened before the arrow flew?
Some physicists would say such questions can't be discussed in scientific terms. But Carroll isn't one of those physicists. After explaining in detail what we know about entropy and its relation to the arrow of time, he moves on to the more speculative side of the issue.
Wikipedia: Arrow of time