
#1
Jan3013, 10:44 AM

P: 32

"Antimatter gravity could explain Universe's expansion:"
http://phys.org/news/201104antimat...expansion.html "Antimatter atoms to address antigravity question:" http://www.bbc.co.uk/news/scienceenvironment16756457 Image Source (before editing): http://www.atlas.ch/angelsdemons/3.html Any thoughts on this subject ? 



#2
Jan3013, 11:44 AM

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P: 10,854

Your first and last link look broken.
The positronium experiment looks interesting, but I think it will take 12 years until we get results. The same is true for the antihydrogen experiments. 



#3
Jan3013, 12:34 PM

P: 32

Ahh, I apologize for the link issues.
"Antimatter gravity could explain Universe's expansion:" http://phys.org/news/201104antimat...expansion.html "Antimatter atoms to address antigravity question:" http://www.bbc.co.uk/news/scienceenvironment16756457 https://www.facebook.com/photo.php?f...2088487&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. 



#4
Jan3013, 01:38 PM

P: 853

Matter Vs. AntimatterThey have reversed charge, but sadly not reverse gravity.
@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.




#5
Jan3013, 02:04 PM

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P: 10,854

No particle has a negative energy.
You can get a negative energy density, this is related to the Casimir effect. 



#6
Jan3113, 03:59 AM

P: 987

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. 



#7
Jan3113, 05:25 AM

Sci Advisor
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P: 3,861

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. 



#8
Jan3113, 07:25 AM

P: 987





#9
Jan3113, 08:54 AM

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P: 3,861

andrien, Sorry, I'm not trying to be tough on you, but the misinterpretation of antiparticles has been a recurrent issue.




#10
Feb113, 12:29 AM

P: 987

http://www.nat.vu.nl/~mulders/QFT0.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. 



#11
Feb113, 06:32 AM

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P: 3,861

On the page you referenced, p41, he points out that the AharonovBohm 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. 



#12
Feb113, 06:43 AM

P: 987

I do not want to continue this discussion but a last question is what do you think about the reason for being a nontrivial 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.




#13
Feb113, 10:08 AM

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P: 3,861





#14
Feb113, 10:22 AM

P: 32

Interesting.




#15
Feb113, 07:27 PM

P: 514

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 pairproduction threshold being twice its rest mass. Inertial mass? Going from particle to antiparticle has the same chargetomass ratio but with opposite sign. There's also the question of such matter/antimatterdependent 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] Torsionbalance tests of the weak equivalence principle reports on comparisons of beryllium, titanium, aluminum, and platinum. Observed accelerations for BeAl and BeTi are <~ 10^{15} m/s^{2} That's about 10^{13} for Earth and Sun effects, and 10^{5} for darkmatter effects. That's well under 10^{3}, so one can rule out that theory. 



#16
Feb213, 01:35 PM

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#17
Feb213, 11:19 PM

P: 514

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.




#18
Feb313, 06:00 AM

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P: 10,854

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. 


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