Physicist Sean Carroll explains why time travel isn’t likely (it has to do with entropy), and how Hollywood and fiction writers fail to get the science right:

Q. YOU WRITE THAT THE NATURE OF TIME IS SUCH THAT WE CAN’T GO BACKWARD.
A. It’s likely that we can’t do time travel. But we don’t know for sure. The arrow of time comes from the increase of entropy, meaning that the universe started out organized and gets messier as time goes on. Every way in which the past is different from the future can ultimately be traced to entropy. The fact that I remember the past and not the future can be traced to the fact that the past has lower entropy. I think I can make choices that affect the future, but that I can’t make choices that affect the past is also because of entropy. I can choose to have Italian food tonight, but I cannot choose to have not had it last night. But if I travel into the past, all that gets mixed up. My own personal future becomes part of the universe’s past. We’re not going to make logical sense of that. So the smart money would bet that it’s just not possible.
Q. THE CENTERPIECE OF THE RECENT MOVIE “BENJAMIN BUTTON” AND THE ABC TELEVISION SERIES “FLASH FORWARD” IS THE TIME TRAVEL. HOW DO YOU RATE THE SCIENCE OF THOSE ENTERTAINMENTS?
A. Well, the Benjamin Button character ages in reverse. In “Fast Forward” people glimpse the future. These are great story-telling devices.
But the writers can’t resist the temptation to bend the rules. If time travel were possible, you still wouldn’t be able to change the past — it’s already happened! Benjamin Button, he’s born old and his body grows younger. That can’t be true because being younger is a very specific state of high organization. A body accumulates various failures and signs of age because of the arrow of time. But this is fiction and real bodies all go from being young to old. I think the screenwriters of Benjamin Button blinked because they didn’t take their premise far enough. Though Benjamin Button’s body is born old and grows younger, his mind is born young and grows older. He remembers the past just like we do. His personality is that of a young person when he’s young, even though his body is that of an 80-year-old man. Reversing the mind’s arrow of time would be more dramatic than reversing the body’s arrow.

Isn’t “reversing the mind’s arrow of time” not a bad description of what happens with Alzheimer’s Disease?
Carroll also talks in the interview about how we screw up the teaching of physics to young people. Take a look. By the way, as I write this just before noon Eastern time, the comments function is down on this site. Beliefnet is aware of it; hang tight…