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A CPT symmetry and antimatter gravity in general relativity

  1. Jul 31, 2016 #1
    CPT symmetry and antimatter gravity in general relativity
    M. Villata

    Published 28 March 2011 • Europhysics Letters Association
    EPL (Europhysics Letters), Volume 94, Number 2
    Abstract
    The gravitational behavior of antimatter is still unknown. While we may be confident that antimatter is self-attractive, the interaction between matter and antimatter might be either attractive or repulsive. We investigate this issue on theoretical grounds. Starting from the CPT invariance of physical laws, we transform matter into antimatter in the equations of both electrodynamics and gravitation. In the former case, the result is the well-known change of sign of the electric charge. In the latter, we find that the gravitational interaction between matter and antimatter is a mutual repulsion, i.e. antigravity appears as a prediction of general relativity when CPT is applied. This result supports cosmological models attempting to explain the Universe accelerated expansion in terms of a matter-antimatter repulsive interaction.


    is this well motivated and plausible? what would be the implications if the above theory is correct?
    how would this impact SM, SUSY, GUT string theory, LQG etc if the above is correct.
    one prediction is that antimatter would fall up around matter, which can be verified by experiment

    there would be no necessary reason to have a SM baryogenesis, since there could be entire galaxies made of anti-matter equal in amount to matter, but repelled by it. dark energy could also be explained as repulsion of galaxies that are equally matter and antimatter.


    a spin-2 quantum field which gives a graviton is always attractive, never repulsive. so if the above theory is correct, it would seem to imply QG theories based on a spin-2 field are incorrect.

    the no hair theorem may be violated and a black hole made from a star that collapsed of antimatter may repel a black hole of a collapsed matter star.
     
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  3. Aug 1, 2016 #2

    mfb

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    99% of the mass of everyday objects comes from QCD binding energy which is neither matter nor antimatter. If you want to fit them into that scheme, you would have to assign them to 50% matter and 50% antimatter or something like that. Either way, if this 99% part would not contribute, or cancel, different elements (with a different fraction of mass coming from binding energy) would feel different accelerations, an effect that would have been noted long ago.

    There is no direct test of antibaryons falling down yet, but having them falling up is a really exotic approach that needs a lot of explanations why the equivalence principle works so well.
     
  4. Aug 1, 2016 #3

    if gr is extended with cpt, does the conclusion follow?
     
  5. Aug 1, 2016 #4

    mfb

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    Which conclusion?

    Gravity should be locally CPT invariant, globally the lack of a global time coordinate should not allow to consider such a symmetry.
     
  6. Aug 1, 2016 #5
    this


    "Starting from the CPT invariance of physical laws, we transform matter into antimatter in the equations of both electrodynamics and gravitation. In the former case, the result is the well-known change of sign of the electric charge. In the latter, we find that the gravitational interaction between matter and antimatter is a mutual repulsion, i.e. antigravity appears as a prediction of general relativity when CPT is applied."
     
  7. Aug 1, 2016 #6

    mfb

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    arXiv version

    What he does looks odd. Anyway, the conclusion violates GR and it is in disagreement with experiments.

    Also, what happens to black holes? They don't have a matter/antimatter difference, do they attract matter or antimatter? What happens to mesons, which are neither matter nor antimatter? What about electrons, are they matter or antimatter, and why?
     
  8. Aug 1, 2016 #7
    when you say violates experiments, are there experiments that prove antimatter falls down? and on observation that could explain is matter antimatter asymmetry and dark energy. if half the galaxies are antimatter and repel matter galaxies like milky way no need to baryogenesis
     
  9. Aug 1, 2016 #8

    mfb

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    Indirectly, as normal matter is 99% energy that does not fit clearly to "matter"/"antimatter" categories. See above.

    Repulsive antimatter would still leave the question what separated antimatter and matter in the first place - the gravitational influence of individual particles is way too small.
     
  10. Aug 1, 2016 #9

    ohwilleke

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    I would be very surprised if anti-matter and matter interacted differently via gravity. Among other things, this should have been discernible in the behavior of mesons and anti-neutrinos in Earth's gravitational field if it were true.
     
  11. Aug 1, 2016 #10
    did u read the paper? anything wrong with his theory?
     
  12. Aug 1, 2016 #11

    ohwilleke

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    Wikipedia has a nice review of the literature on the issue of whether anti-matter is identical to ordinary matter or repels ordinary matter with an equal an opposite force.

    https://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter

    In particular, it says this with regard to CPT:
    citing M.J.T.F. Cabbolet Elementary Process Theory: a formal axiomatic system with a potential application as a foundational framework for physics underlying gravitational repulsion of matter and antimatter, Annalen der Physik 522(10), 699-738 (2010).
     
  13. Aug 1, 2016 #12
    https://arxiv.org/pdf/1103.4937v1.pdf

    in the paper V is arguing that GR extended with CPT, it is the PT in CPT, namely antimatter as time going backwards, is what causes it to be repulsive to ordinary matter. antimatter lives in a T inverted spacetime

    in this new GR+CPT, gravitational charge does NOT equal mass but his new equation, where antimatter = -1, which is not negative mass but CPT where T is inverted for antimatter. pAGE5
     
  14. Aug 1, 2016 #13
    i think the idea is not that an individual electron would repel an individual positron gravitationally moments after the big bang, but that among baryonic matter, half of all baryonic matter in the entire universe is matter which would repel the other half antimatter gravitationally, as it would be electrically neutral, after big bang. and half the galaxies are antimatter which repel galaxies made of matter, which would give effects similar to dark energy. no need for baryogenesis in the SM.
     
  15. Aug 1, 2016 #14
    if neutrinos are majorana fermions they would be their own antiparticle.
     
  16. Aug 1, 2016 #15

    mfb

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    Those galaxies would not form in the first place. There is no mechanism that would separate matter and antimatter. The universe doesn't start with "here is matter, and antimatter is over there".

    A questionable approach (see @ohwilleke), that does not agree with experiments at all (see 99% matter is not from quark masses) and has problems to explain the observed baryon asymmetry. Uh, well...
     
  17. Aug 1, 2016 #16

    i don't necessarily have all the answers to your objections, but is the reasoning in that paper sound? does his conclusion follow from his premises?

    obviously if experiments showed antiatoms fell up, then the binding energy in a proton made of anti-quarks does not alter the fact that anti-quarks create an inverted spacetime that is opposite in effect to quarks in a proton. and perhaps the big bang model can be modified to take into effect gravitational repulsive effects of antimatter should experiments show that is the case.

    there are several research groups i.e Alpha

    http://newscenter.lbl.gov/2013/04/30/antimatter-up-down/

    Does Antimatter Fall Up or Down?
    The atoms that make up ordinary matter fall down, so do antimatter atoms fall up? Do they experience gravity the same way as ordinary atoms, or is there such a thing as antigravity?

    These questions have long intrigued physicists, says Joel Fajans of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), because “in the unlikely event that antimatter falls upwards, we’d have to fundamentally revise our view of physics and rethink how the universe works.”

    So far, all the evidence that gravity is the same for matter and antimatter is indirect, so Fajans and his colleague Jonathan Wurtele, both staff scientists with Berkeley Lab’s Accelerator and Fusion Research Division and professors of physics at the University of California at Berkeley – as well as leading members of CERN’s international ALPHA experiment – decided to use their ongoing antihydrogen research to tackle the question directly. If gravity’s interaction with anti-atoms is unexpectedly strong, they realized, the anomaly would be noticeable in ALPHA’s existing data on 434 anti-atoms.

    The first results, which measured the ratio of antihydrogen’s unknown gravitational mass to its known inertial mass, did not settle the matter. Far from it. If an antihydrogen atom falls downward, its gravitational mass is no more than 110 times greater than its inertial mass. If it falls upward, its gravitational mass is at most 65 times greater.

    What the results do show is that measuring antimatter gravity is possible, using an experimental method that points toward much greater precision in future. They describe their technique in the April 30, 2013 edition of Nature Communications.

    How to measure a falling anti-atom

    ALPHA creates antihydrogen atoms by uniting single antiprotons with single positrons (antielectrons), holding them in a strong magnetic trap. When the magnets are turned off, the anti-atoms soon touch the ordinary matter of the trap’s walls and annihilate in flashes of energy, pinpointing when and where they hit. In principle, if the experimenters knew an anti-atom’s precise location and velocity when the trap is turned off, all they’d have to do is measure how long it takes to fall to the wall.

    ALPHA’s magnetic fields don’t turn off instantly, however; almost 30-thousandths of a second pass before the fields decay to near zero. Meanwhile flashes occur all over the trap walls at times and places that depend on the anti-atoms’ detailed but unknown initial locations, velocities, and energies.



    Wurtele says, “Late-escaping particles have very low energy, so gravity’s influence is more apparent on them. But there were very few late escaping anti-atoms; only 23 of the 434 escaped after the field had been turned off for 20-thousandths of a second.”
     
  18. Aug 1, 2016 #17

    ohwilleke

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    After reading the paper, I don't think that the reasoning is sound. If you reverse PT, then you are getting the properties of anti-matter from the perspective of anti-matter moving backward in time. Gravity has mutual attraction when bodies are moving forward in time. If you "rewind the videotape" to demonstrate its behavior for particles viewed as moving backward in time, then, yes, it is mutually repulsive. But, this feature is true of both matter and antimatter viewed as moving backward in time. So, the reasoning is unsound.
     
  19. Aug 1, 2016 #18
    antimatter is equivalent to matter going back in time, not antimatter going back in time.
     
  20. Aug 1, 2016 #19

    ohwilleke

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    But viewed that way you have to think of antimatter from a backward looking perspective. The antimatter is moving backward and from that perspective is mutually repulsive. The matter is moving forward and from that perspective is mutually attractive. There is no contradiction. If one treats all particles as moving forward in time, which is how we observe them, then gravity is attractive.
     
  21. Aug 1, 2016 #20
    ultimately experiments on anti-hydrogens are in the works, ie ALPHA.
    physicists who work on ALPHA do consider the real possibility anti-hydrogen will fall up, and have described how they plan to produce, trap, slow down and then study anti-hydrogen effects.

    suppose anti-hydrogens fall up at -G, and this is confirmed under review and by other experiments.

    How would you modify GR to explain anti-matter falling up?
     
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