A new theory says that antimatter could exist in the voids between galaxy clusters

[n2doc]

n exciting new theory says that antimatter could exist in the voids between galaxy clusters and superclusters and that some kind of repulsive gravity –- antigravity –- is pushing the Universe apart. The new theory is a direct challenge to the accepted theory for the Universe expanding at an accelerating rate: the presence of an unidentified X Factor labeled "dark energy," although several other possibilities have been proposed.

As a new study shows, general relativity predicts that the gravitational interaction between matter and antimatter is mutually repulsive, and could potentially explain the observed expansion of the Universe without the need for positing an elusive dark energy.

Ever since antimatter was discovered in 1932, scientists have been investigating whether its gravitational behavior is attractive –- like normal matter –- or repulsive. Most physicists think that the gravitational behavior of antimatter should always be attractive, as it is for matter. However, the question of whether the gravitational interaction between matter and antimatter is attractive or repulsive has not been answered until now.

In the new study, Massimo Villata of the Osservatorio Astronomico di Torino (Observatory of Turin) in Pino Torinese, Italy, has shown that the current formulation of general relativity predicts that matter and antimatter are both self-attractive, yet matter and antimatter mutually repel each other. But unlike previous antigravity proposals –- such as the idea that antimatter is gravitationally self-repulsive –- Villata’s proposal does not require changes to well-established theories.

more
http://www.dailygalaxy.com/my_weblog/2011/04/antigravity-trumps-dark-energy-for-the-accelerated-expansion-of-the-universe.html#more

[qazplm]

1. if matter and antimatter were self attractive to each other

but mutually repulsive, why wouldn't we have whole galaxies of matter, and whole galaxies of antimatter and thus see a pattern of matter/antimatter galaxies attracting each other and those same galaxies repelling their opposites?

Why would the lumped antimatter not form stars and galaxies just like the lumped matter?

[On the Road]

3. That Was Actually a Theory

proposed in the book "Worlds-Anitworlds: Antimatter in Cosmology" by Swedish cosmologist Hannes Aflven in the late 60s. He also showed that if this were the case, it would be difficult or impossible to observe the difference from afar.

[HysteryDiagnosis]

4. Alfven's bio at Los Alamos

Hannes Alfvén (1908-1995)

http://public.lanl.gov/alp/plasma/people/alfven.html

[qazplm]

9. but with this "theory"

of M/AM galaxies repelling each other you actually should be able to observe the difference from afar. You wouldn't be able to tell which galaxies were which, but you'd be able to see some galaxies moving away from others and toward others, and you'd probably be able to find at least one galactic pair that were moving away from each other in a manner suggesting this theory were true.

I think it unlikely that whole clumps of AM are sitting out there in voids without creating galaxies, and we see no evidence of whole galaxies pushing away from each other. The other poster gave another reason against this theory.

[On the Road]

14. I Don't Necessarily Subscribe to His Theory, Either

For one thing, he used it to present a steady-state alternative to the Big Bang. I may have been reasonable in the 1960s, but I don't it squares with more recent observations.

But as far as contiguous galaxies repelling each other, Alfven believed that areas of the universe where antimatter was predominant would self-segregate and form barriers with area of normal matter. This is because at the boundaries, there would be a region of collisions in which, eg, electrons and positrons would collide and which would generate a slightly repellent force. He compared it to a drop of water on a hot skillet which is protected from immediate evaporation by a layer of steam on the bottom.

So the effects might be discernible, but they might not stand out unless you were looking for them.

[qazplm]

17. I'd think a galatic sized

or even small group sized interaction between electrons and positrons would be noticeable even if you weren't looking for them.

Wouldn't there be a constant energy signature? Sure, each interaction is small, but combined, I'd guess it would be humongous.

I'd also guess that in at least some places it would still be in the "Segregating" phase where things had not quite settled down to just electrons and positrons. Those would stand out like a giant beacon.

[On the Road]

19. I Don't Know Enough to Judge

Alfven's argument was first that antimatter creates the same mix of particles (photons, etc) as ordinary matter, so that an antimatter galaxy would look exactly like any other galaxy.

I don't remember his dealing with the question of detecting these barriers between the two regions. Apparently he thought it was a diffuse low-level phenomenon that would be difficult to observe, but that was in the 60s.

I am assuming this theory is wrong BTW, but Alfven had an interesting way of looking at the universe. It probably had something to do with his interest in electricity and electromagnetism.

[Confusious]

8. Andromeda is coming toward us

???? :scared:

[girl gone mad]

2. His paper is here..

http://iopscience.iop.org/0295-5075/94/2/20001/fulltext/epl_94_2_20001.html

You can read it for free, but you have to register.

[andym]

10. Version of the paper is here too (no need to register)

http://arxiv.org/abs/1103.4937

[dimbear]

5. Cogitate this.........

"As a new study shows, general relativity predicts that the gravitational interaction between matter and antimatter is mutually repulsive........."

Uh uh.

Matter+antimatter=explosive release of energy. Thus both matter and antimatter are composed of the same thing, energy, which is positively attracted by gravity. The current state of the energy (compressed into matter or not) makes no difference.

That doesn't rule out the possible existence of another kind of matter made of negative energy. It does seem, however, that such matter would travel backwards in time.

[girl gone mad]

7. You are describing the Feynman-Stuckelberg interpretation of antimatter..

where from CPT symmetry, antiparticles are viewed as the corresponding particle moving backward in spacetime. It's actually not necessary to adopt this framework, but it can be helpful.

Here is a Feynman diagram for electron-positron annihilation which produces a quark-antiquark pair, with the arrow of time from left to right (the squiggly green line represents the carrier particle for the color force, a gluon):

[girl gone mad]

12. Just to be clear, the negative energy problem goes away.

Someone above indicated that this was a reason to discount the idea of gravitationally repulsive matter/antimatter interactions.

The equation for current density for an electron (charge -e) and momentum ( E, p⃗ ) is:

jμ ( −e ) = −2e |N|2 pμ = −2e |N|2 ( E, p⃗ )

The equation for current density for a positron (charge +e) and momentum ( E, p⃗ ) is:

jμ (+e ) = +2e |N| 2 pμ = −2e |N|2 ( −E, −p⃗ )

Therefore, we can see that the positive energy solution for a positron is the same as the negative energy solution for an electron.

This is not another kind of matter made of negative energy, it's just a negative energy electron (antimatter) traveling backward in time. The problem of negative energy states was also solved prior to Feynman-Stuckelberg in another way by Dirac.

So, no, this is not a reason to throw out the new theory.

eta: my equations keep turning into smilies. I think I fixed it.

[dimbear]

13. It seems to me I offered a cogent reason that general relativity does not support the OP.

It's not cricket to drag in any quantum mechanics. That's not relevant. General relativity says mass and energy behave the same in fields. Antimatter has positive energy, so it has positive mass equivalent, so it is gravitationally attractive within the framework of general relativity.

That's all I'm asserting.

[girl gone mad]

15. It's relativistic, too.

I guess Dirac doesn't get much credit for it, but he did unify quantum mechanics and special relativity here, and accurately predicted the existence of antimatter.

There are some different ways of extending the Dirac matrices to curved spacetime, for example using a local Minkowski frame:

http://xxx.lanl.gov/abs/hep-th/0411016

Theorists still have problems nailing it all the way down, but it's not a good reason to completely throw it out.

I was in a lecture with Roger Penrose where he stated that he thinks quantum will "go away" eventually. I used to feel that way, too, but I don't know anymore so his recent certainty surprised me. It sounds like you would agree with him.

Thanks for giving me something to think about this weekend. I didn't mean to offend you. I agree that your point was cogent.

[dimbear]

16. You're quite correct, Dirac tied in the special theory.

But General Relativity and quantum mechanics probably can never be reconciled. One of them has to be wrong.

And no offense taken, we're just talking physics here. :)

[qazplm]

18. depends on what you mean by wrong

wrong as in, just completely off, or wrong as in close but not quite.

Because I doubt it's the former. Odds are both are slightly off.

[DetlefK]

6. Take a look at the comment section: Looks like there are books to be sold.

[laconicsax]

11. I guess the OP should read, "A new book says..."