Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Matter Vs. Antimatter-They have reversed charge, but sadly not reverse gravity.

  1. Jan 30, 2013 #1
    "Antimatter gravity could explain Universe's expansion:"
    http://phys.org/news/2011-04-antimatter-gr...-expansion.html [Broken]

    "Anti-matter atoms to address anti-gravity question:"
    http://www.bbc.co.uk/news/science-environment-16756457

    Image Source (before editing):
    http://www.atlas.ch/angels-demons/3.html [Broken]


    Any thoughts on this subject ?
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jan 30, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Your first and last link look broken.
    I think you mean the Dirac equation. In General Relativity, gravity is linked to energy, and antiparticles have a positive energy - they should fall down.

    The positronium experiment looks interesting, but I think it will take 1-2 years until we get results. The same is true for the antihydrogen experiments.
     
  4. Jan 30, 2013 #3
    Ahh, I apologize for the link issues.

    "Antimatter gravity could explain Universe's expansion:"
    http://phys.org/news/2011-04-antimatter-gravity-universe-expansion.html

    "Anti-matter atoms to address anti-gravity question:"
    http://www.bbc.co.uk/news/science-environment-16756457

    https://www.facebook.com/photo.php?....313338668752549.73826.313312622088487&type=1

    Yes this topic does or is talking about the Dirac equation,

    " From Quarks to Quasars(facebook page)
    Question: If antimatter was predicted via the negative time solutions of Einstein's equations, shouldn't it also have both reverse gravity and reversed charge?

    Asked By: John Martin

    They have reversed charge, but sadly not reverse gravity.

    Let's get the record straight. Antimatter was not predicted by Einstein's equations, but by the famous Dirac equation. But a minor error, so let's move on. "

    and thanks for your response,
    I appreciate this.
     
  5. Jan 30, 2013 #4
    @mfb you say antiparticles have positive energy but then does something have negative energy , because how come energy be negative? I just wanted to clear things up by asking this.
     
  6. Jan 30, 2013 #5

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    No particle has a negative energy.
    You can get a negative energy density, this is related to the Casimir effect.
     
  7. Jan 31, 2013 #6
    A description of negative energy electron in dirac sea is used.The positrons which are an absence of the negative energy states are considered real and having positive energy.
    Casimir effect is related to vacuum point zero energy which is just first infinity of quantum electrodynamics but it is just subtracted away as it is supposed that only differences will matter.but this zero point electromagnetic field has other consequences as well.
     
  8. Jan 31, 2013 #7

    Bill_K

    User Avatar
    Science Advisor

    Must we discuss the Dirac sea again? :frown: Dirac proposed his hole theory in 1933. It was refuted by Heisenberg in 1934, and Dirac himself quickly abandoned it. Nevertheless here we are 80 years later...

    Despite its obvious shortcomings, hole theory seemed at least somewhat plausible in the framework of first quantization, when people still thought of the Dirac ψ as a wavefunction analogous to the Schrodinger ψ, all of whose solutions represented realizable states.

    But in second quantization, ψ becomes an operator which creates particles and destroys antiparticles, and physical states form a Hilbert space in which negative energy states simply do not appear.

    Next you will tell me that antiparticles move backwards in time.
     
    Last edited: Jan 31, 2013
  9. Jan 31, 2013 #8
    no,I will not tell you anything this time.Somethings like topology of aharnov bohm effects are explained using the sea of fermions at someplaces which just makes thing easier,if not correct entirely.
     
  10. Jan 31, 2013 #9

    Bill_K

    User Avatar
    Science Advisor

    andrien, Sorry, I'm not trying to be tough on you, but the misinterpretation of antiparticles has been a recurrent issue.
    You may be thinking of this paper, in which a measurement of the Aharonov-Bohm effect relies on the electron tunneling between two electrodes. The Fermi sea encountered in condensed matter, where the particle states are filled up to some Fermi energy, is a different thing entirely. The hole states in such a case are quasiparticles, not antiparticles.
     
  11. Feb 1, 2013 #10
    http://www.nat.vu.nl/~mulders/QFT-0.pdf
    actually I was talking about the above page 41.Also you cut my statement in half at middle.The structure of vacuum with zero point energy can be explained using a sea of particles which will alter the structure of vacuum.One more thing can you cite me a reference where Dirac has abandoned this sea interpretation himself in single particle dirac theory.thanks.
     
  12. Feb 1, 2013 #11

    Bill_K

    User Avatar
    Science Advisor

    Obviously some references will get it right and some will still get it wrong. Anyway, on p31 he says,
    Apparently he considers the Dirac Sea a proposal that was later done properly by second quantization. (The "implementation" on p61 turns out to be anticommutators.)

    On the page you referenced, p41, he points out that the Aharonov-Bohm effect is a "manifestation of a nontrivial vacuum [for electromagnetism] ala the Dirac sea for fermions." We all agree that the vacuum state is "nontrivial", but I see no relationship between the two cases. :confused:
    Contrast the treatments given in the early and later editions of "Principles of Quantum Mechanics".
     
  13. Feb 1, 2013 #12
    I do not want to continue this discussion but a last question is what do you think about the reason for being a non-trivial vacuum.It is amusing to note that klein nishina formula was first derived using the interpretation that all negative energy states are completely unfilled but it still gives the correct answer.
     
  14. Feb 1, 2013 #13

    Bill_K

    User Avatar
    Science Advisor

    Well, that's an interesting point! According to the description in The Oskar Klein Memorial Lectures (vol 2 p 105) they did things quite differently:
     
  15. Feb 1, 2013 #14
    Interesting.
     
  16. Feb 1, 2013 #15
    Antimatter has positive inertial mass and positive "energy mass", so by the Equivalence Principle, it must therefore have positive gravitational mass.

    "Energy mass"? From a particle's pair-production threshold being twice its rest mass.

    Inertial mass? Going from particle to antiparticle has the same charge-to-mass ratio but with opposite sign.

    There's also the question of such matter/antimatter-dependent gravity would work out for different sorts of particle. A particle that is its own antiparticle would produce zero gravity, and interactions between persistent particles would also produce zero gravity. Thus, binding energy would produce zero gravity.

    So there would be a composition difference in the gravitational force. From nuclear binding energy, it would be about 10-3 between (say) water and iron (Nuclear binding energy). Small, but detectable. Differences in internal structure between protons and neutrons will also contribute.

    [1207.2442] Torsion-balance tests of the weak equivalence principle reports on comparisons of beryllium, titanium, aluminum, and platinum.

    Observed accelerations for Be-Al and Be-Ti are <~ 10-15 m/s2

    That's about 10-13 for Earth and Sun effects, and 10-5 for dark-matter effects. That's well under 10-3, so one can rule out that theory.
     
  17. Feb 2, 2013 #16

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    QCD binding energy within the nucleons would be even worse - as 99% of the mass of a proton comes from that. If gravitational force from nucleons would come from valence quarks only, the proton would have a mass of just ~20 electrons, and a neutron would fall much quicker than a proton. I think that effect would be visible just by dropping lead and (frozen) hydrogen and watching.
     
  18. Feb 2, 2013 #17
    That would be correct if the quarks were nonrelativistic, but the sizes of the nucleons are much less than the Compton wavelengths of the up and down quarks, making those quarks very relativistic. In fact, from nucleon sizes, one finds that each valence quark has a few hundred MeV of mass each, adding up to much of the mass of a nucleon.
     
  19. Feb 3, 2013 #18

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    The energy of valence quarks is significant, but that is true for the energy of virtual quarks as well. And if we consider energy (from relativistic quarks) as relevant for gravity, we have the regular GR (gravity acting on energy) anyway.
    Anyway... if antimatter (including virtual antiquarks) would fall upwards in some way, this should have been noted in precision experiments with protons, neutrons and electrons.
     
  20. Feb 11, 2014 #19
    Anti-matter and gravity

    Is there any evidence about the response of anti-matter to gravitational fields?
     
  21. Feb 18, 2014 #20
    Book of A. Zee "Quantum Field Theory in a Nutshell, Second Edition" page-36:

    It is difficult to overstate the importance (not to speak of the beauty) of what we have
    learned: The exchange of a spin 0 particle produces an attractive force, of a spin 1 particle
    a repulsive force, and of a spin 2 particle an attractive force, realized in the hadronic strong
    interaction, the electromagnetic interaction, and the gravitational interaction, respectively.

    In my opinion, antimatter also exchange spin-2 graviton, thus they attractive, too.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Matter Vs. Antimatter-They have reversed charge, but sadly not reverse gravity.
  1. Matter vs antimatter (Replies: 22)

  2. Antimatter vs Matter (Replies: 3)

Loading...