I am not a physicist.

But... does the rate at which gravitational waves travel set an upper limit to the "speed" of a ship propelled with Alcubierre drive?

Or does it present a relativistic trick (ie. I got to Alpha Centauri in 4 months, but everyone I ever knew is old or dead)?

An explanation in layman's terms would be much appreciated.


No, they don't disprove it. However the Alcubierre metric, which underlies the warp drive stuff, requires something people refer to as 'exotic matter' which in this case means matter with negative energy density. Such matter violates many assumptions, and would normally be considered not to be possible (indeed my memory of Alcubierre's original paper is that he said more-or-less this).

One of the reasons people assume that such matter is not possible is that if it were then very bad things follow, such as causality violation (ie being able to travel into your own past) and, really, the collapse of most of physics. [The following is opinion, not answer.] Of course, other groups of people want it to be possible either because they want warp drives to be possible and do not understand the consequences of them, or because they do understand the consequences and are happy with them.

  • $\begingroup$ You make it sound like the discovery of such a material would actually cause bad things to result. $\endgroup$ – Neil Apr 14 '16 at 13:02
  • $\begingroup$ @Neil I think it would, yes, or rather I think (and this is opinion) that such a thing is not remotely possible in a universe anything like ours $\endgroup$ – tfb Apr 14 '16 at 14:27
  • $\begingroup$ I think it is more likely the latter. The common idea put on tv that you could go back in time and create a contradiction like killing your own mother is likely not much different than conceptualizing what would happen if we created a four-sided triangle. Though if such a material existed, then it also wouldn't have any of the properties that would violate causality, simply put IMHO. If that means it isn't "exotic material", then it means exotic material doesn't exist. $\endgroup$ – Neil Apr 18 '16 at 8:47

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