3 ms·

Highly unlikely. Unless wormholes are setup with strange restrictive configurations they allow sending messages back in time, without needing any new physics.

Highly unlikely. Unless wormholes are setup with strange restrictive configurations they allow sending messages back in time, without needing any new physics. Once you have a wormhole, if you use gravity to accelerate one of the ends away then bring it back near the other end, they will have a time difference, due to general relativity. If you bring them close enough, that time difference will be greater than it takes to travel between them in normal space, allowing you to travel to your own past. This video gives a quick explanation of the problem: https://www.youtube.com/watch?v=sUqxzH0652w&t=186s https://www.youtube.com/watch?v=sUqxzH0652w&t=186s

erikpukinskis 8y ago
Doesn’t that just put bounds on which wormholes are possible, rather than proving no wormhole is possible?
- akvadrako 8y ago
  It doesn't prove they are impossible, but what it shows is if they are possible, the universe is conspiratorial. Because it restricts your free will so you don't create time travel paradoxes.
- krapp 8y ago
  As the maxim says, "relativity, causality, or FTL... pick two." The bounds on which wormholes are possible are likely bounds which make the transmission of information (including matter) impossible, because we live in a universe in which relativity and causality exist, and cannot (as far as we know) be violated.
ben_w 8y ago
I’ve recently become dissatisfied with the two standard ways to make closed timelike curves. Gravity: that’s treating gravity like it doesn’t go through the wormhole. I expect it would. If it does, both sides are time dilated equally. Acceleration: what, exactly, are you accelerating? If it’s made of stuff, you time dilate the stuff. If it’s not made of stuff… can you even move it in any meaningful sense, or is that like trying to move a patch of curved space from here to the moon to create artificial gravity?
- akvadrako 8y ago
  You are accelerating the space which contains the wormhole. It doesn't matter if it's "stuff" or not.
  - ben_w 8y ago
    The patch of space is directly attached to the other end of the wormhole. GR assumes stacetime is differentiable, you just put a discontinuity in it somewhere inside the wormhole.

erikpukinskis 8y ago

Doesn’t that just put bounds on which wormholes are possible, rather than proving no wormhole is possible?

akvadrako 8y ago
It doesn't prove they are impossible, but what it shows is if they are possible, the universe is conspiratorial. Because it restricts your free will so you don't create time travel paradoxes.
krapp 8y ago
As the maxim says, "relativity, causality, or FTL... pick two." The bounds on which wormholes are possible are likely bounds which make the transmission of information (including matter) impossible, because we live in a universe in which relativity and causality exist, and cannot (as far as we know) be violated.

ben_w 8y ago

I’ve recently become dissatisfied with the two standard ways to make closed timelike curves. Gravity: that’s treating gravity like it doesn’t go through the wormhole. I expect it would. If it does, both sides are time dilated equally. Acceleration: what, exactly, are you accelerating? If it’s made of stuff, you time dilate the stuff. If it’s not made of stuff… can you even move it in any meaningful sense, or is that like trying to move a patch of curved space from here to the moon to create artificial gravity?

akvadrako 8y ago
You are accelerating the space which contains the wormhole. It doesn't matter if it's "stuff" or not.
- ben_w 8y ago
  The patch of space is directly attached to the other end of the wormhole. GR assumes stacetime is differentiable, you just put a discontinuity in it somewhere inside the wormhole.