From what I have read gravitational waves cannot travel faster than the speed of light. And since gravitational waves are part of the fabric of space, wouldn't that disprove the idea behind an Alcubierre Drive?

An Alcubierre Drive tries to create negative mass in front of it and positive mass behind it. Since the negative mass is dependent upon some form of anti/dark matter this idea is already out of reach. However, what if you can, instead, create gravitational waves in front and behind an object (IE have the crest behind the object and trough in front of it) wouldn't that be the same concept as the below Alcubierre Drive? Thinking about it further, the two are different, because the area with negative mass will want to be filled in with some mass, and if you can keep creating negative mass in front of the object it will stay in motion. Now, change the idea to a wave - would you be able to 'ride' that wave?

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Does it prove that you can warp the fabric of space to eventually accelerate an object beyond the speed of light? Or, since gravitational waves propagate at the speed of light does that mean we can at least travel at light-speed? If so, how can you prove/disprove that?

Or does the detection of gravitational waves have no bearing on the possibility for humans to travel faster than the speed of light?

Another question would be - is it possible to artificially create gravitational waves to drive said object? What could be a possible method for doing so?


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    $\begingroup$ I feel as if this question could be improved by focusing the content a bit. It would also help to explain how you view the link between gravitational waves and the Alcubierre drive. $\endgroup$ – zephyr Sep 15 '16 at 15:24
  • $\begingroup$ @zephyr added some context - let me know if you have other questions and I can elaborate further. $\endgroup$ – Adjit Sep 15 '16 at 15:45
  • $\begingroup$ As for an artificial method of creation, no means exist currently, and are not likely to exist in the near future. Pulsating bodies with high intensity gravitational fields are generally the sources of such waves. We have neither of them withing our reach. $\endgroup$ – Lelouch Sep 15 '16 at 18:02
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    $\begingroup$ Based on my limited, layman's understanding of both, the fact that we can detect gravitational waves has absolutely no bearing on FTL travel. Per the LIGO web page, we would not have the ability to generate gravity waves; I get the impression that the Alcubierre drive would result in a different signal than regular gravity waves, but don't quote me on that. $\endgroup$ – John Bode Sep 15 '16 at 19:01

No, it does not. Gravity waves can't travel faster than the speed of light in the "direct" path, they will always appear to us as if that is the speed they are traveling. However, if space was stretched away from the source, it would take longer for them to get there, but they still would appear to be traveling at the same speed.

Bottom line, nothing has changed as regards to FTL travel as a result of gravity wave detection.


Both gravitational waves and the existence of the Alcubierre metric are predictions of Einstein's theory of general relativity (GR).

GR is strongly supported by a great deal of experimental evidence. In particular, gravitational waves were observed indirectly in 1974 through observations of the Hulse-Taylor binary pulsar, and GR's predictions about gravitational waves were verified in quantitative detail then. What is new within the last year or so is the direct detection of gravitational waves, but there hadn't been any doubt about their existence for decades.

Observations can never prove a scientific theory. They can disprove it, or they can fail to disprove it. When we accumulate enough observations that fail to disprove a theory, we start to believe that the theory is right, within its realm of applicability. This is what has happened with GR. Direct detection of gravitational waves has little effect on whether we believe GR is valid.

The Alcubierre metric is a solution to the equations of GR (the Einstein field equations), so additional confirmation of GR is additional confirmation that the Alcubierre metric is mathematically valid.

In any case, it's wrong/naive to think of the Alcubierre metric as a recipe for building a faster-than-light (FTL) spaceship, even in theory. You can't build one without exotic matter, which probably doesn't exist. It's probably unstable due to quantum effects. You can't get in or out of the drive region, which can't be turned on or off.

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    $\begingroup$ "You can't get in or out of the drive region, which can't be turned on or off." Not technically true. It can't be turned on or off from the inside, and you can't enter or exit while the bubble is in place, but the bubble could theoretically be engineered to diminish (or "turn off") within a certain amount of time. $\endgroup$ – called2voyage Sep 16 '16 at 16:48
  • $\begingroup$ @called2voyage: Interesting if true. But that physics.SE answer doesn't cite any references for its claims. $\endgroup$ – Ben Crowell Sep 16 '16 at 16:54
  • $\begingroup$ True, but I'm assured enough in Stan Liou's expertise to not dismiss what he's saying immediately. It would be nice to have links to references which discuss that issue. $\endgroup$ – called2voyage Sep 16 '16 at 16:55
  • $\begingroup$ Or a more complete sketch of the argument, using the machinery of GR. $\endgroup$ – Ben Crowell Sep 16 '16 at 17:17

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