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I've read a bit on Harold White's recent work. (A paper on Nasa's site) I haven't been able to find any comments by people claiming to know anything about the physics involved. Is this really serious? From a blog post (first link in this question):

"But interesting things have developed since the original Alcubierre paper. Running quickly through what White told the Houston audience, Chris van Den Broeck was able to reduce the energy costs of a warp drive significantly and other theorists have continued to drop the numbers. White’s team has been examining ways to continue that progression, but what is eye-catching is that he is working on a laboratory experiment to “perturb spacetime by one part in ten million” using an instrument called the White-Juday Warp Field Interferometer to create the minute spacetime disruption. "

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Irrepspective of the amount of negative mass matter required, it's still a fact that these schemes require negative mass matter to work, and negative mass matter is not known to exist. And there are still problems with faster than light travel that you would have to resolve--in particular, that a solution like this would enable you to construct a time machine, and then you'd have to have a way of resolving all of the time travel paradoxes we know and love.

Full disclosure: I am also a former student of Richard Matzner, FWIW. I have never discussed this matter with him.

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    $\begingroup$ Exactly! Even if we needed only 1 particle of negative mass matter we are can't do FTL since negative mass has never been observed. Any comment on how he is going to do the lab prototype? $\endgroup$
    – FrankH
    Commented Sep 23, 2012 at 20:30
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    $\begingroup$ I'm interested in the lab experiment too. Is it just creating the positive mass part to show the geometry works as it should? $\endgroup$
    – JollyJoker
    Commented Sep 24, 2012 at 12:08
  • $\begingroup$ Okay, maybe I'm lacking a bit of knowledge to be asking this but: How would an Alcubierre drive, by nature, create a time machine? It's my understanding that the space-time inside the bubble would remain unchanged (congruous with space-time outside the bubble) and therefore no time travel would actually take place. While it would present some interesting options to observe past events, I don't see how it would allow the traveler to influence them. Or, are you saying that a feasible Alcubierre drive would not create a time machine in itself, but would enable spin-off technologies that could? $\endgroup$
    – Iszi
    Commented Sep 24, 2012 at 20:24
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    $\begingroup$ @Iszi: it's just special relativity. The region with the curvature can be made arbitrarily small, so we can consider only special relativity. In this case, consider an observer moving at some superluminal speed. This will be a spacelike line in the enveloping spacetime. Then, you can find a timelike direction that is exactly perpendicular to this spacelike direction, which is interpretable as an observer moving relative to your initial "still" frame. This observer will say that time stops for our superluminal observer. $\endgroup$
    – Zo the Relativist
    Commented Nov 27, 2012 at 18:16
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    $\begingroup$ Any additional acceleration will cause them to say that the superluminal observer's future points toward their past. If you don't believe me, do the lorentz transforms yourself. $\endgroup$
    – Zo the Relativist
    Commented Nov 27, 2012 at 18:18
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It doesn't require negative mass but negative vacuum energy density, which presumably he is generating using the Casimir effect.

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A relatively new summary from Harold White: WARP FIELD PHYSICS

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  • $\begingroup$ Republishing recipes for perpetual motion machines also didn't do much for their adoption as energy sources. Sorry for being a little bit of a killjoy. The most one can learn about nature from this "research" is in which ways the mathematics of general relativity is deficient. $\endgroup$
    – FlatterMann
    Commented Jan 20 at 0:31

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