The mew movie Tenet shows plenty of eye-candy action and charismatic characters, though it didn’t really make me care much emotionally about its characters or their problems. The movie did, however, scratch my big physics idea itch. So I’m going to talk a bit about the movie’s key physics premise. I’ll give spoilers; you are warned.
So I don’t think the kind of reversal in time happening in Tenet is the same as the time reversal that we do in physics. It’s more like: every object has it’s personal timeline. Usually the personal timeline is aligned with the external timeline. But some objects can go through something like a time-travel box and then have its personal timeline go in the opposite direction to the external timeline. So it’s like a standard time travel story but where one doesn’t go to the past instantaneously but has to traverse all duration in between.
So this means that in every object’s personal timeline entropy continues increase, and there’s a clear sense of what’s personally past and personally future. Whereas time-reversal as done in physics would instead lead to an older person becoming younger and younger. But that’s not what happens here.
It is not cool to put spoiler (I assume) right into article title - it is very new movie, not everyone had a chance to see it, and now thanks to my RSS reader (not even my choice to open the article yet) I know there is some time reversal issue in it...
Could it make more sense if the time reversed copies had to make it to a machine again "before too long"? The first reversal constrains the universe to have a time forward and approximately time reversed copy of the machine's contents when it is switched on, and the second reversal similarly ensures a reversed and forward copy of machine 2's contents exist when it is switched on, with a memory extending back to the interaction with the first machine. If the interval is short enough, it might be more likely for the same copy to persist between machine activations than for two copies to spontaneously form (though I worry that the "short interval" might be very short indeed).
So I don’t think the kind of reversal in time happening in Tenet is the same as the time reversal that we do in physics. It’s more like: every object has it’s personal timeline. Usually the personal timeline is aligned with the external timeline. But some objects can go through something like a time-travel box and then have its personal timeline go in the opposite direction to the external timeline. So it’s like a standard time travel story but where one doesn’t go to the past instantaneously but has to traverse all duration in between.
So this means that in every object’s personal timeline entropy continues increase, and there’s a clear sense of what’s personally past and personally future. Whereas time-reversal as done in physics would instead lead to an older person becoming younger and younger. But that’s not what happens here.
Could you really have heard about Tenet but not hear that it has something to do with time travel?
It is not cool to put spoiler (I assume) right into article title - it is very new movie, not everyone had a chance to see it, and now thanks to my RSS reader (not even my choice to open the article yet) I know there is some time reversal issue in it...
Could it make more sense if the time reversed copies had to make it to a machine again "before too long"? The first reversal constrains the universe to have a time forward and approximately time reversed copy of the machine's contents when it is switched on, and the second reversal similarly ensures a reversed and forward copy of machine 2's contents exist when it is switched on, with a memory extending back to the interaction with the first machine. If the interval is short enough, it might be more likely for the same copy to persist between machine activations than for two copies to spontaneously form (though I worry that the "short interval" might be very short indeed).