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Alcubierre drive has trouble with quantum effects

  1. Dec 27, 2009 #1

    bcrowell

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    A recent paper says that Alcubierre's warp drive probably won't work due to quantum effects:

    http://www.technologyreview.com/blog/arxiv/23292/ -- nontechnical summary

    http://arxiv.org/abs/0904.0141 -- paper

    Speaking as a non-specialist, it seems hard to tell which predictions about the interface between QM and GR to take seriously and which ones not to take seriously. Some, like Hawking radiation, seem fairly secure. Hawking radiation has been studied thoroughly over a long period of time, and the reasons behind it seem relatively model-independent.

    On the other hand, semiclassical gravity makes some predictions that seem relatively shaky, as far as I can tell as an outsider looking in, and without having mastered the techniques of the field. For instance, there's a claim that quantum-mechanical effects can strongly affect the process of formation of black holes, even causing the collapse to halt under certain conditions: http://arxiv.org/abs/0909.4157
     
    Last edited: Dec 27, 2009
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  3. Dec 27, 2009 #2

    marcus

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    We already have a thread discussing this. I reported the same article and Tech Review item in April 2009:
    https://www.physicsforums.com/showthread.php?t=305091

    It looks sound. Alcubierre's goose is probably cooked. May even be overdone. :biggrin:

    About what really happens at the (supposed) classical black hole singularity, you cited just one of many recent papers which explore what might happen in the bh pit, when quantum effects are factored in.
    There is a lot of work in progress. We just need to keep an open mind and wait.

    As quantum gravity BH papers appear, they usually get spotted and added to the QG bibliography in Beyond forum. That is a separate question. I'd say forget Alcubierre but keep an eye out for the next few QG papers on BH.
     
    Last edited: Dec 27, 2009
  4. Dec 27, 2009 #3

    atyy

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    The paper from Visser and colleagues is motivated as follows. Is Lorentz invariance fundamental? Maybe not (no working models, but several very interesting lines of pursuit from Volovik, Visser, Xiao-Gang Wen, and Horava). However, if Lorentz invariance is not fundamental and black holes exist, we can have a perpetual motion machine (I think this is Ted Jacobson's result). So maybe black holes don't exist.

    However, there is mention of "black holes" in the literature about Horava gravity. A footnote in http://arxiv.org/abs/0905.4480 says "Due to the lack of Lorentz invariance in UV, the very meaning of the horizons and Hawking temperature would be changed from the conventional ones. The light cones would differ for different wavelengths and so different particles with different dispersion relations would see different Hawking temperature TH and entropies, the Hawking spectrum would not be thermal. But from the recovered Lorentz invariance in IR (with = 1), the usual meaning of the horizons and T as the Hawking temperature would be “emerged” for long wavelengths. The calculation and meaning of the temperature should be understood in this context."
     
  5. Dec 27, 2009 #4

    bcrowell

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    Ah, thanks for pointing that out. I feel silly. Arxiv blog is giving a retrospective of 2009, but I didn't realize that, thought this was a new article.
     
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