Could you expand on “you don’t need to hugely stretch general relativity for closed timelike curves to become possible”? After all, the only thing keeping everyone from flying off of the planet is a minus sign in different equations relating to gravity, but we don’t worry about that as a risk. Are the changes to general relativity similar to that, or more like “relativity allows it but it has some huge barrier that we can’t currently surpass”?
It’s been a while since I looked into it, but my impression was something like “general relativity allows it if you use some sort of exotic matter in a way that isn’t clearly possible but isn’t clearly crazy”. I could imagine that intelligent agents could create such conditions even if nature can’t. The Internet Encyclopedia of Philosophy has a decent overview of time travel in general relativity.
Could you expand on “you don’t need to hugely stretch general relativity for closed timelike curves to become possible”? After all, the only thing keeping everyone from flying off of the planet is a minus sign in different equations relating to gravity, but we don’t worry about that as a risk. Are the changes to general relativity similar to that, or more like “relativity allows it but it has some huge barrier that we can’t currently surpass”?
It’s been a while since I looked into it, but my impression was something like “general relativity allows it if you use some sort of exotic matter in a way that isn’t clearly possible but isn’t clearly crazy”. I could imagine that intelligent agents could create such conditions even if nature can’t. The Internet Encyclopedia of Philosophy has a decent overview of time travel in general relativity.