A Ku Indeed!

Time Travel Ruled Out!

Posted in philosophy by Chris on January 20, 2008

delorean.jpgKierkegaard 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)

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  1. eyeingtenure said, on January 20, 2008 at 8:12 pm

    I choose A.

    By going back in time, you create an alternate time line. From then on, even if you somehow do not interact with anyone or cause anything else to change, any movement forward in time would be in that newly created timeline.

    However, if you do not interact with anyone in that timeline, you can be sure that the events occur exactly as they did in your original timeline.

    Here’s a question: would it be it possible to return to one’s original timeline?

  2. Adam said, on January 21, 2008 at 9:14 am

    Time travel is definitely possible, as most of us have no problem traveling forward in time. It’s just the back part that seems hard. I tend to think that while it’s possible (and probably happens all the time… heh…) for particles to go back in time, it won’t be technologically possible for quite some time (if ever) for persons to travel backwards in time. As it stands now, trying to travel backwards would probably kill us off.

    But really the little paradox argument relies on a view of time (moments?) that makes them eternal containers of a set amount of events. I’m thinking that backwards time travel could be made more plausible by thinking of moments as individual four-dimensional coordinates. Then just as no one has any problem with their being two people in your house, then three people in your house, there would be no problem with having X people at t1 and later X+1 people at t1. It’s not a contradiction because right now there *are* X people there at coordinates (x12,y24,z6,t1), but when the time traveler visits it is only true that there *were* X people there. Now, there are X+1 at (x12,y24,z6,t1). Granted, I’ve just pushed time back into another dimension, but something like that has to be true. If calling it time doesn’t make sense, call it shmime or something.

    Thus the paradox really gets going by conflating subjective experience of time with the objective facts about time. I get dizzy trying to think of it all subjectively, but objectively it seems to make sense.

    Off to the Aristotelian Society!

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