I watched Primer again the other day and it got me thinking. Some people say that the fact that there are no people visiting us from the future proves that time travel into the past never gets invented at all. But is that really proof?
Consider time travel as it is portrayed in Primer. How does it work? Supposing you wanted to travel back in time from Monday night to Monday morning (to make a killing day trading or something). You don’t simply hop into the machine Monday night and twist the Destination dial to 8 hours in the past. Doesn’t work that way. Here’s what you do:
- Wake up Monday morning and turn the time machine on. Do not get in it.
- Go sequester yourself in a hotel room or something and watch the stock market.
- Leave the hotel Monday evening. Go to the time machine, turn it off and climb inside as it is powering down.
- Emerge from the machine at the exact moment you powered it up–Monday morning. There are now two of you. Your other self is on his way to the hotel room, but you are now free to surf over to eTrade armed with your foreknowledge of the closing bell.
- Your hotel self gets into the time machine at 5 PM just as you did–and promptly disappears. Or rather, becomes you.
Supposing you built the time machine the day before these events, on Sunday. Could you ever use it to go back to Saturday? No. Because the machine would have had to exist on Saturday for you to climb out of it. It didn’t exist on Saturday, so you can’t possibly do that.
So perhaps the reason there are no time travelers visiting us from the future isn’t because time travel doesn’t get invented. It could just be because they can only travel as far back as the date of the invention.