So I asked him. "First of all" he said "When a guy has the possibility to go back in time, he would not go to work and raise a familily - he'd go back over and over again to bang Rachel McAdams' brains out. I'd be more like 'Groundhog Day'".
For your information, "Groundhog Day" is a movie from 1993, where Bill Murray is forced to relive the same day over and over again. Which isn't too bad a deal, according to my boyfriend, unless you want to get any work done. Because you can't take anything back except your own memories. Even your body is reinstated - since death also doesn't apply. It's a perfect way to attain immortality.
But that wasn't his only criticism. What happened to his former self when he jumped back? He didn't have to move in the cupboard first so he can exit later on. That was the plot of the movie "Primer" from 2004. You'd activate the device, your former self would crawl out a short while later, and you'd enter the box in a few hours. No paradoxes there. The box was there when you got out and you would in fact end your existence when you got in.
"Even 'Back to the Future' does better!" he exclaimed. Which seems to be true, since he used this clip to explain the phenomena to me:
It seems you create a new time line when you jump back. That is, a time line where you already exist. It's like taking another, parallel track on the railway, which seems the same, but is vastly different from the original one. And that is where "Back to the Future" goes wrong. Time travel is very personal. When Biff jumps back, he creates a new time line of his own. The time line of the others would remain unaffected.
But worst of all is, you can never get back to the original one. Obviously, when you jump back in time, for the observer on the current time line you simply cease to exist. Which makes sense, since you already changed the original one by being there twice. Or even not at all.
Whatever you do on this new time line, it won't make any difference, because you're an alien body which is not supposed to be there. You can kill your grandfather if you want. You're already there - you won't disappear. There just will never be a second you. You're even not forced to jump back in time to make things "right". Things are not right to begin with.
You can save President Kennedy on the new time line if you want. He will still die on the original one. And if you're not happy with the results, you can go back again (creating another time line) and talk yourself out of it. Again, things may appear to be the same, but they aren't, since there now two (or even three - depending on when you were born) of you there.
It's like you made a correction to a painting and then reverted to the original by painting over it again. That's three layers of paint instead of one. That's how queer loops like "Looper" or "Terminator" may come to be.
"The best book on time travel is 'The Man Who Folded Himself'" he said "It contains some funny loop itself, but it realistically shows how a man may live his life when he can time travel". I read the book and I can tell you it is good. Without it, I would never have been able to write this post.
In the end, the man ends up being old and rich, surrounded by copies of himself of various ages. But although he can jump forwards and backwards in time he still ages - and dies. That's an advantage of the "About Time" method: you will never die - unless you're caught in an violent accident. When you feel your time is near, you seek out the nearest cupboard and jump back somewhere in your youth. Who's stopping you.
BTW, jumping forward in time is no problem because you don't need to change time lines. It's like they've frozen you and waken you up much later. If we had the technology, we could do that right now. You simply don't exist in the meanwhile.
However, the moment you jump back the same rules apply - although the world would seem much more consistent to you, because there would be no "other" you - that is: if you jumped backward just after the moment you jumped forward. Whatever you remember is rather moot, because you still changed the time line. The future would be just as open as it was before.
The interesting question is: if your second "you" jumped forward, would he reappear on the split time line? Probably yes, because when the time line was split, everything was duplicated. Including any pending transactions. Not appearing would probably lead to an inconsistency.
I found the whole discussion rather entertaining. Not only did I learn a lot about time travel (if there is such a thing) I also learned how differently men and women would react if such a possibility would arise.
I wasn't surprised how the main character used this special gift - entertaining the relationships with his friends and family - but my boyfriend seemed to see it as a kind of toy he could play with - like getting everything he ever dreamed of, girls, riches. "In real life, you only get one take" he said "I could do things over and over again until I got it right".
In the end, I'm happy he can't. And so is Rachel McAdams, I guess.