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The point of an Alcubierre drive is that there aren't any reference frames that are moving FTL. There's cases where spacetime itself is stretching FTL but we k
by monocasa 4y ago
The point of an Alcubierre drive is that there aren't any reference frames that are moving FTL. There's cases where spacetime itself is stretching FTL but we know that's possible because we can already see that in the expansion of the universe. Pretty much all of the galaxies outside of the local group are going to slowly fade away from our perspective because of the stretching of space crossing FTL.
- at_a_remove 4y agoThis is wrong. The method of travel is irrelevant. Visit here https://en.wikipedia.org/wiki/Alcubierre_drive#Causality_violation_and_semiclassical_instability https://en.wikipedia.org/wiki/Alcubierre_drive#Causality_vio... and, after that, read further down to the section: "Alcubierre briefly discusses some of these issues in a series of lecture slides posted online,[44] where he writes: 'beware: in relativity, any method to travel faster than light can in principle be used to travel back in time (a time machine)'." Draw your light cones. Finish the diagram. Any FTL gives CTC, so long as your propulsion method allows for you to steer, or stop and build one that goes in any other direction.
- monocasa 4y agoI mean, we don't know what he said when those slides were up, but in context with the other slide cited, it seems to be a rejection of the base point. What that slide says is true. But the whole point of the drive is that you aren't traveling FTL from the viewpoint of GR. It's no different than traveling through a wormhole for the purpose of this discussion; it's that you dynamically create a shorter path and don't exceed the speed of light along that shorter path.