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Negative Mass repels Gravity?

  1. Nov 26, 2011 #1
    Michio Kaku mentions in his TV series "Physics of the Impossible" about negative mass being able to repel gravity. I haven't heard much about this before.

    How would the negative mass affects the geodesic in spacetime manifold? Perhaps by causing negative curvature of spacetime? Would this actually make object float without propulsion but merely maintaining or stabilizing the negative mass?
     
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  3. Nov 26, 2011 #2

    Bill_K

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    "Beam me up, Scotty." You haven't heard much about negative mass, stglyde, because it doesn't exist. They don't call the program "Physics of the Impossible" for nothing. Kaku has discovered how much money can be made by talking about fantasy physics as if it were real. There's apparently a big audience for this. If you want to learn about physics, TV is not the place to do it.
     
  4. Nov 26, 2011 #3
    No. Kaku didn't invent the term. It's just an uncommon term that is even mentioned in peer reviewed journal:

    http://rmp.aps.org/abstract/RMP/v29/i3/p423_1

    Anyway. Wiki mentioned it as:

    http://en.wikipedia.org/wiki/Negative_mass

    "In theoretical physics, negative mass is a hypothetical concept of matter whose mass is of opposite sign to the mass of the normal matter. Such matter would violate one or more energy conditions and show some strange properties such as being repelled rather than attracted by gravity. It is used in certain speculative theories, such as on the construction of wormholes. The closest known real representative of such exotic matter is a region of pseudo-negative pressure density produced by the Casimir effect."
     
  5. Nov 26, 2011 #4

    phinds

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    +1 on that !
     
  6. Nov 26, 2011 #5

    D H

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    +2 on that!

    I am getting to despise those kinds of TV shows. A good measure of the non-scientific nature of the spoutings of Kaku/Greene/pick your poison spout is to look at the traffic on this site. It spikes. We have to clean up after their mess.
     
  7. Nov 26, 2011 #6

    atyy

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    OK, am not a Kaku fan (at least his pop sci personality, some of his technical books have been quite helpful for me) and have never seen Greene, but is it possible to find a good question in the nonsense?

    Eg. Are Barcelo and Visser justified in claiming the null energy condition "moribund"?
     
  8. Nov 26, 2011 #7

    PAllen

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    Violation of the energy conditions is not at all the same as negative mass. It's been a little while since I looked at the paper you reference (I had a thread about it here, to discuss alternatives to energy conditions), but I don't recall negative mass in any of their motivations for the limitations of energy conditions.
     
  9. Nov 26, 2011 #8

    atyy

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    What then is negative mass?
     
  10. Nov 26, 2011 #9
    I see nothing wrong in having questions about negative mass, which is not a priory excluded by GR. Also I do not see any point in slandering Kaku or Greene.

    Frankly I do not understand the arrogant attitude of some of those who have the label "science advisor" on this forum.
     
  11. Nov 26, 2011 #10

    atyy

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    One reason I thought "negative mass" could be a handwavy reference to an energy condition violation is eg. Thorne refers to exotic material in a wormhole having negative energy density, says that energy is mass, and this negative mass defocusses light beams http://books.google.com/books?id=GzlrW6kytdoC&dq=thorne+worm&source=gbs_navlinks_s p488.

    I'm sure he'll take our "slander" as a compliment! He writes technical books too which are sane, sane, sane. I'm sure this is his stage personality! Reminds me of :biggrin:
     
    Last edited by a moderator: Sep 25, 2014
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