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Physicists create 'negative mass'?

  1. Apr 18, 2017 #1
    Now this sounds interesting! Is this really "negative mass" or is that marketing spin? Thoughts?

    Paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.155301
  2. jcsd
  3. Apr 18, 2017 #2
    Always a catch... dang it. Still interesting though!
  4. Apr 18, 2017 #3


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    I covered a news report on this yesterday:


    Note that this is the effective mass. The whole concept of "negative effective mass" isn't new. Those of us who took intro Solid State Physics classes have seen these due to the way effective mass is defined.

    What is new here is that they detected this in a superfluid system. But considering that there is now a smooth connection between BE condensate and BCS system (thanks to the work of the late Deborah Jin), it is not unexpected that one can have a dispersion in a BE condensate that can produce such negative mass.

  5. Apr 18, 2017 #4


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    So no Hoverboards, just yet.
  6. Apr 18, 2017 #5
    I don't know, but I'm interested in anything like negative mass that can help me lose weight.
  7. Apr 18, 2017 #6
    That means that a force between this fluid an object with a corresponding positive mass would accelerate both in the same direction. I'm sceptical until I see such an experiment.
  8. Apr 18, 2017 #7
    "Negative mass"? Makes no sense to me, but then neither does quantum mechanics.
  9. Apr 18, 2017 #8


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    An air bubble is water has negative mass. One can easily renormalize the mass so that the water surrounding it has zero mass. This is no different than what is done in QFT, resulting in positive holes in semiconductors.

    One must pay attention to the background information here. These are many-body effects, the same effect that gives electrons in solids an effective mass that can be hundred of times more than the bare mass! In other words, such effects are already extremely common in the modern electronics that you are currently using!

  10. Apr 18, 2017 #9
    Does it behave exactly like "negative mass"? Or is the term just for news?

    You can't make hoverboards with it, can you? because If Newton's gravitational law still holds, Then it would accelerate downward as any positive mass object.

    Interestingly, What would happen if you place two identical objects with the same magnitude of mass but with opposite signs in space. They will just keep accelerating forever(Newtonian). It won't violate conservation of energy or momentum. I think my mind has just gone Kaboom. Can't you use that to reach nearby stars faster?
  11. Apr 18, 2017 #10
    Negative effective mass, yes?
  12. Apr 18, 2017 #11
    Wonder if models of the early universe could utilise this physics re inflation?
  13. Apr 18, 2017 #12


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    "Effective" is the third word in the PRL abstract: "A negative effective mass..."
    Anyone want to find the first appearance of the word "effective" in the phys.org piece?

    Just sayin'....
  14. Apr 19, 2017 #13
    Could this negative mass have anything to do with dark energy? Or the vacuum temperature considerable above of absolute zero is already an indicative that it's not the case?
  15. Apr 21, 2017 #14
    <Moderator note: moved from separate thread>

    So I have a question about negative mass:

    does the equation "k=1/2mv^2 " still apply to negative mass? If it did, does that equal to negative energy? If it does not lead to negative energy, does that mean absolute value bars need to be added to the equation?

    I'm using "k=1/2mv^2" for an example, of course my question apply to all energy equations that use mass.
    Last edited by a moderator: Apr 21, 2017
  16. Apr 21, 2017 #15
    In classical physics, yes.

  17. Apr 21, 2017 #16


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    When i saw the news article i wondered how conservation of momentum worked out? For example if you push something away from you and it accelerates towards you then to maintain conservation of momentum don't you also have to accelerate towards the object? Its as if the negative mass of the object somehow gives you negative mass as well?
  18. Apr 24, 2017 #17


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    There are two kinds of momentum, "true" momentum and effective momentum, the latter one being also called "crystal momentum" for the more specific case of particles moving in a crystal.
    E.g. for an electron moving in a crystal, the effective mass can be negative as upon acceleration, the electron is reflected more strongly from the crystal lattice. While the effective momentum may also be negative, the total momentum is conserved, as momentum is transferred to and carried by the crystal.
  19. Apr 25, 2017 #18


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  20. Apr 29, 2017 #19
    So are we talking alcubieere drive or no? Us trekies get excited when we hear negative mass....
  21. Apr 29, 2017 #20


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    Not even close. Sorry.
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