Kierkegaard said once, “Life is understood backwards, but it must be lived forwards.” No time traveling for Kierkegaard, obviously. Clearly, these scientists say the same thing. As far as I can tell, they aren’t ruling time travel out theoretically, but rather practically, suggesting that the technology required to do it would be so advanced that we couldn’t even conceive of what it would look like.
What these scientists would say about the theoretical worry about paradox is another issue that they don’t bring up. It’s a good thing, too, because otherwise us philosophers would be left with no pressing concrete live problems to solve.
The situation that makes time travel difficult is obvious.
1. You go back into time to Jan 1, 1900.
2. Before you left, there were X number of people on the planet on that day.
3. When you arrive, there are X + 1 people.
4. Thus, on Jan 1, 1900, there are X and X + 1 number of people.
But that’s not possible, because that would engender a contradiction (something would be the case and not be the case at the same time). Of course, there are other possibilities:
A. When you “go back” you don’t really go back to your time line. You are in another parallel universe in which you were ‘always scheduled to arrive’ and so there’s no contradiction. But that’s not “time travel” in the sense that people want it. They want to go back to their time line. I don’t want to meet some amazingly similar version of my wife, say, I want to meet my wife when she’s a child.
B. You can go back to your own time line because contradictions can exist. I don’t know how to handle that one.
C. Time travel is bogus, but it makes for good stuff on the sci-fi channel.
Which one is right?
(by the way, the DeLorean time machine is so much cooler than any of the other versions that have been kicked around in science fiction)