That time-traveling universe is interesting. Physics question: Is it at all possible, never mind how likely, that our own universe contains closed timelike curves? What about closed timelike curves that we can feasibly exploit?
Is it at all possible, never mind how likely, that our own universe contains closed timelike curves?
Very very very unlikely. Hawking once wrote a paper called Chronology protection conjecture, arguing that any time loop would self-destruct before forming. Even if they existed, it’s not like you can travel them to do things. There is no entering or exiting the loop. Everything in the groundhog day has been there forever and will be there forever. Because there is no difference between “first time through the loop” and “n-th time through the loop”. This is all predicated on classical general relativity. Quantum gravity may change things. But no one knows anything about quantum gravity.
Thanks for the info. Hmm. What do you mean by “There is no entering or exiting the loop?” Could the loop be big enough to contain us already?
I’m not concerned about traveling backwards in time to change the past; I just want to travel backwards in time. In fact, I hope that I wouldn’t be able to change the past. Consistency of that sort can be massively exploited.
Could the loop be big enough to contain us already?
Note the reversibility issue. After a complete loop, you end up in exactly the same state as you started with. All the dissipated energy and information must somehow return. Unless you are willing to wait for the Poincare recurrence, this is not very likely to happen. And in this case the wait time is so large as to be practically infinite.
If we are in a time loop we won’t be trying to escape it, but rather exploit it.
For example: Suppose I find out that the entire local universe-bubble is in a time loop, and there is a way to build a spaceship that will survive the big crunch in time for the next big bang. Or something like that.
Well, I go to my backyard and start digging, and sure enough I find a spaceship complete with cryo-chambers. I get in, wait till the end of the universe, and then after the big bang starts again I get out and seed the Earth with life. I go on to create a wonderful civilization that keeps to the shadows and avoids contact with “mainstream” humanity until, say, the year 2016. In the year 2014 of course, my doppelganger finds the machine I buried in his backyard...
I’m not saying this scenario is plausible, just that it is an example of exploiting time travel despite never breaking the loop. Or am I misunderstanding how this works?
As long as every loop is identical to every other loop, why not. I don’t know if you would call it “exploit”, since, classically, your actions are predefined (and already happened infinitely many times), and quantum-mechanically, they are determined up to a chance (or, equivalently, every outcome happens in one of the Everett branches).
That time-traveling universe is interesting. Physics question: Is it at all possible, never mind how likely, that our own universe contains closed timelike curves? What about closed timelike curves that we can feasibly exploit?
Very very very unlikely. Hawking once wrote a paper called Chronology protection conjecture, arguing that any time loop would self-destruct before forming. Even if they existed, it’s not like you can travel them to do things. There is no entering or exiting the loop. Everything in the groundhog day has been there forever and will be there forever. Because there is no difference between “first time through the loop” and “n-th time through the loop”. This is all predicated on classical general relativity. Quantum gravity may change things. But no one knows anything about quantum gravity.
Thanks for the info. Hmm. What do you mean by “There is no entering or exiting the loop?” Could the loop be big enough to contain us already?
I’m not concerned about traveling backwards in time to change the past; I just want to travel backwards in time. In fact, I hope that I wouldn’t be able to change the past. Consistency of that sort can be massively exploited.
Note the reversibility issue. After a complete loop, you end up in exactly the same state as you started with. All the dissipated energy and information must somehow return. Unless you are willing to wait for the Poincare recurrence, this is not very likely to happen. And in this case the wait time is so large as to be practically infinite.
If we are in a time loop we won’t be trying to escape it, but rather exploit it.
For example: Suppose I find out that the entire local universe-bubble is in a time loop, and there is a way to build a spaceship that will survive the big crunch in time for the next big bang. Or something like that.
Well, I go to my backyard and start digging, and sure enough I find a spaceship complete with cryo-chambers. I get in, wait till the end of the universe, and then after the big bang starts again I get out and seed the Earth with life. I go on to create a wonderful civilization that keeps to the shadows and avoids contact with “mainstream” humanity until, say, the year 2016. In the year 2014 of course, my doppelganger finds the machine I buried in his backyard...
I’m not saying this scenario is plausible, just that it is an example of exploiting time travel despite never breaking the loop. Or am I misunderstanding how this works?
As long as every loop is identical to every other loop, why not. I don’t know if you would call it “exploit”, since, classically, your actions are predefined (and already happened infinitely many times), and quantum-mechanically, they are determined up to a chance (or, equivalently, every outcome happens in one of the Everett branches).