Can We Identify Anti-Matter Galaxies?

[Aspchizo]

As far as I know, matter and anti-matter are only different in charge and spin. Therefore a star undergoing fusion reactions with anti-matter should give off the same light spectrum we see with fusion reactions in a star comprised of matter, so it would show the same absorption lines.

Would we be able to tell the difference between light that comes from a star/galaxy that is made of anti-matter as opposed to one that is made of matter?

 

[cwilkins]

I don't think you can distinguish the two through emission spectra. However, I believe the decay of positrons--either by interaction with normal matter or by some other means--has a unique gamma ray signature. So, you'd probably have to see a collision between the star and some other large normal matter object to be able to tell.

 

[Drakkith]

By the visible light emitted itself, no. However we would see the gamma ray emissions from the annihilation of normal matter with this antimatter, as all of space is filled with a low density gas of hydrogen, protons, electrons, etc. The border of this normal gas with the antimatter galaxy would give off radiation we should be able to easily see.

 

[Chronos]

There could be subtle clues hidden in the spectrum of an antimatter star, but, we don't have enough antimatter to play with to know yet. Although, if such a star or galaxy happened to come into contact with normal matter, it would be fairly obvious. There would be high energy gamma ray emissions that would at frequencies characteristic of matter - antimatter annihilations.

 

[Bandersnatch]

By the visible light emitted itself, no. However we would see the gamma ray emissions from the annihilation of normal matter with this antimatter, as all of space is filled with a low density gas of hydrogen, protons, electrons, etc. The border of this normal gas with the antimatter galaxy would give off radiation we should be able to easily see.

I remember reading a book of some obscure Polish author, with highly misguided ideas about what a big bang is etc., in which he argued that an antimatter star/galaxy would not be detectable as you've described, due to an effect similar to what happens when you pour water on a hot plate. An isolating boundary forms that keeps the bulk of the water drop from touching the plate. Similarly, he argued that a boundary would form where interstellar hydrogen/antihydrogen came in contact, preventing the annihilation reactions from generating enough energy to be detectable.
I can not for the love of me remember the guy's name or the book's title, nor can I repeat his calculations to see whether the energy emitted from the boundary would be high enough to notice. Still, the idea itself seems sensible.

 

[Vanadium 50]

Drakkith's argument is correct, out to a few hundred million parsecs. Beyond that, the diffuse x-ray background makes such detection impossible.

 

[Drakkith]

I remember reading a book of some obscure Polish author, with highly misguided ideas about what a big bang is etc., in which he argued that an antimatter star/galaxy would not be detectable as you've described, due to an effect similar to what happens when you pour water on a hot plate. An isolating boundary forms that keeps the bulk of the water drop from touching the plate. Similarly, he argued that a boundary would form where interstellar hydrogen/antihydrogen came in contact, preventing the annihilation reactions from generating enough energy to be detectable.
I can not for the love of me remember the guy's name or the book's title, nor can I repeat his calculations to see whether the energy emitted from the boundary would be high enough to notice. Still, the idea itself seems sensible.

But a boundary of what? If it's matter or antimatter then there is no actual boundary, and if it's the gamma rays themselves, then I think we'd see them. Plus I don't think gamma rays react very strongly with interstellar gas since the density is so low. But I'm not sure.

 

[Bandersnatch]

The idea was that in the area where two clouds of matter and anti-matter dust collide, the initial annihilation produces enough radiation pressure to push the remaining particles of dust away from the region of annihilation, slowing down the reaction to an undetectable ratio and producing a de facto boundary separating regular matter from anit-matter.

Just to be clear on that, I'm not endorsing the idea in general, and indeed I have no credentials to be able to say anything substantial about it. But this particular objection you've raised seemed not so difficult to circumvent.

 

[Drakkith]

The idea was that in the area where two clouds of matter and anti-matter dust collide, the initial annihilation produces enough radiation pressure to push the remaining particles of dust away from the region of annihilation, slowing down the reaction to an undetectable ratio and producing a de facto boundary separating regular matter from anit-matter.

Just to be clear on that, I'm not endorsing the idea in general, and indeed I have no credentials to be able to say anything substantial about it. But this particular objection you've raised seemed not so difficult to circumvent.

I think it's a valid argument IF the radiation pressure is high enough AND not enough gets through for us to see. Since I don't know how to find either of those out then I cannot say anything more.

 

[Aspchizo]

So the answer is, as far as we know thus far, there would be no difference in the emmision spectrum. However we could expect to see specific high energy gamma rays from annihilation of matter and anti-matter particles, unless there is a mechanism we do not yet fully understand like one Bandersnatch suggests.

Thanks for the replies. I was just curious, because physicists appear to me to be quite sure that the universe is mostly matter. Yet it makes much more sense for their to be equal amounts of both, a symmetry between the two. Not that the universe always makes sense! Just thought I would explore the possibility.

 

[Drakkith]

Thanks for the replies. I was just curious, because physicists appear to me to be quite sure that the universe is mostly matter. Yet it makes much more sense for their to be equal amounts of both, a symmetry between the two. Not that the universe always makes sense! Just thought I would explore the possibility.

It's important to realize that if there had been equal amounts of matter and antimatter in the very early universe, right after particle creation stopped, it would all have annihilated, leaving practically nothing to form galaxies, stars, and planets.

 

[Bandersnatch]

Yeah, that mechanism I mentioned, supposing for the moment that it's plausible, is hardly enough to support the idea of coexistence of matter and antimatter in our universe.
For one, as Drakkith mentioned, there's a question of how could possibly the two types of particles separate from the primordial soup without annihilating and go on to form large scale structures.
And even if you consider only the now of the universe, for the sake of the argument, that mechanism would only work if everything was close to static. If the two stars/galaxies just sat there calmly forever never getting too close to each other.
Any sort of galactic collision, or a supernova ejecting gas into the interstellar medium, or one star wandering close by another, would trigger violent annihilation. And since these interactions occur all the time, everywhere, with no observable signatures of annihilation, we might just as well discard the hypothesis.

 

[Aspchizo]

It's important to realize that if there had been equal amounts of matter and antimatter in the very early universe, right after particle creation stopped, it would all have annihilated, leaving practically nothing to form galaxies, stars, and planets.

Yeah, that mechanism I mentioned, supposing for the moment that it's plausible, is hardly enough to support the idea of coexistence of matter and antimatter in our universe.
For one, as Drakkith mentioned, there's a question of how could possibly the two types of particles separate from the primordial soup without annihilating and go on to form large scale structures.
And even if you consider only the now of the universe, for the sake of the argument, that mechanism would only work if everything was close to static. If the two stars/galaxies just sat there calmly forever never getting too close to each other.
Any sort of galactic collision, or a supernova ejecting gas into the interstellar medium, or one star wandering close by another, would trigger violent annihilation. And since these interactions occur all the time, everywhere, with no observable signatures of annihilation, we might just as well discard the hypothesis.

I don't think that can be said with certainty that it would have been impossible for such a thing to happen but I do agree the chances seem slim.

 

[Drakkith]

I don't think that can be said with certainty that it would have been impossible for such a thing to happen but I do agree the chances seem slim.

It's not impossible, and I would indeed expect a very very small percentage of particles to not have annihilated by sheer chance, but the amount of normal matter we see far exceeds what we would expect to see without something like CP violation occurring. Even with current CP violation added in, the amount of matter seen in the universe is far in excess of what it can explain. It only accounts for about one galaxies worth of matter, so we are obviously missing something.

 

[Aspchizo]

I saw an experiment where they were trying to determine if Antimatter fell down or up in a gravitational field. They don't have results yet. It got me thinking, we say matter and antimatter have opposite values for everything except mass. What if the mass is somehow different? negative mass or something. What if that causes a different form of curvature in spacetime, and that pushes matter and anti-matter galaxies apart? preventing annihilation from occurring at the borders.

Just a thought.

 

[PAllen]

Author of anti-galaxies theory

I believe the scientist Bandersnatch is referring to is Hannes Alfven. His book was:

Worlds-Antiworlds: Antimatter in Cosmology (1966)

See: http://en.wikipedia.org/wiki/Hannes_Alfvén

I was quite intrigued with his theories in high school (circa 1970).

 

[Bandersnatch]

I believe the scientist Bandersnatch is referring to is Hannes Alfven. His book was:

Worlds-Antiworlds: Antimatter in Cosmology (1966)

See: http://en.wikipedia.org/wiki/Hannes_Alfvén

I was quite intrigued with his theories in high school (circa 1970).

Hey, that's the book! For some reason I thought the author was Polish.

If anybody wants to have a look at it, it's available from here:
http://archive.org/stream/WorldsAntiworlds/Alfven-WorldsAntiworlds#page/n0/mode/1up

 

[Ryuu]

It's important to realize that if there had been equal amounts of matter and antimatter in the very early universe, right after particle creation stopped, it would all have annihilated, leaving practically nothing to form galaxies, stars, and planets.

Yeah, that mechanism I mentioned, supposing for the moment that it's plausible, is hardly enough to support the idea of coexistence of matter and antimatter in our universe.
For one, as Drakkith mentioned, there's a question of how could possibly the two types of particles separate from the primordial soup without annihilating and go on to form large scale structures.
And even if you consider only the now of the universe, for the sake of the argument, that mechanism would only work if everything was close to static. If the two stars/galaxies just sat there calmly forever never getting too close to each other.
Any sort of galactic collision, or a supernova ejecting gas into the interstellar medium, or one star wandering close by another, would trigger violent annihilation. And since these interactions occur all the time, everywhere, with no observable signatures of annihilation, we might just as well discard the hypothesis.

The problem I see with the currently accepted theory is that matter is somehow “inherently superior" to antimatter, which violates CP. And the efforts to explain how it doesn’t violate CP seem convoluted and contrived.

I've often wondered about if the large scale voids, between galactic clusters as filaments and wall between the voids were sufficient to "hide" antimatter galaxies.

I think that at the beginning of the Big Bang, well after the force of gravity separated from the other 3, the primordial soup was still homogenous so there was nothing much for gravity to work upon. But the instant matter and antimatter began to react en mass, then the explosions would reduce the local density just for a moment, giving gravity the opportunity to pull the substance of the soup in all directions away from the point of the blast, leaving the sides of the bubbles to form what would become the galactic filaments and walls--which galaxies became to be made of matter and which were made of antimatter was perhaps something random chance decided on a more local level than across the entire universe.

Then, as the matter/antimatter annihilations continued, the visible mass of the universe might still reach the ~1% of the original substance that existed that we see today—it’s just that then we look at a faraway galaxy, we can’t tell if we’re looking matter or antimatter.

And the vast distances of the voids themselves would keep them separated, preventing interactions that we should otherwise detect.

 

[Mordred]

The voids between clusters are not empty of matter. The matter density may be low however their is still some matter in the voids. Including dark matter. So the voids cannot count as a seperation. Also there has been no detection of photon annihilations from sources of one filament to the next.

 

[hilbert2]

If we'd make the hypothesis that there is a repulsive gravitational interaction between matter and antimatter, we could explain how there could be galaxies consisting of antimatter without any noticable gamma radiation from annihilation events. The repulsive interaction would mostly keep matter and antimatter away from each other, and there would not be any significant collisions leading to annihilation. See http://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter .

There's actually an experiment underway in CERN that tests whether matter and antimatter have an attractive or repulsive gravitational interaction: http://home.web.cern.ch/about/updates/2013/04/alpha-novel-investigation-gravity-and-antimatter .

 

[Drakkith]

The problem I see with the currently accepted theory is that matter is somehow “inherently superior" to antimatter, which violates CP. And the efforts to explain how it doesn’t violate CP seem convoluted and contrived.

The accepted theory is based on real observations. Matter is, one way or another, "inherently superior" to antimatter when it comes to the big bang nucleosynthesis. As for CP violation, hasn't that been observed to actually happen?

I've often wondered about if the large scale voids, between galactic clusters as filaments and wall between the voids were sufficient to "hide" antimatter galaxies.

No. There's nothing there. That's why they are voids. Besides, how would a void hide anything? It's a void.

I think that at the beginning of the Big Bang, well after the force of gravity separated from the other 3, the primordial soup was still homogenous so there was nothing much for gravity to work upon. But the instant matter and antimatter began to react en mass, then the explosions would reduce the local density just for a moment, giving gravity the opportunity to pull the substance of the soup in all directions away from the point of the blast, leaving the sides of the bubbles to form what would become the galactic filaments and walls--which galaxies became to be made of matter and which were made of antimatter was perhaps something random chance decided on a more local level than across the entire universe.

Quantum fluctuations are believed to be the cause of the inhomogenous structure of the universe.

Then, as the matter/antimatter annihilations continued, the visible mass of the universe might still reach the ~1% of the original substance that existed that we see today—it’s just that then we look at a faraway galaxy, we can’t tell if we’re looking matter or antimatter.

The problem is that the intergalactic medium has particles in it, so if you have antimatter and normal matter galaxies, then you would have antimatter and normal matter making up the intergalactic medium, which should result in either the complete destruction of the medium thanks to annihilation events, among other things. This should be clearly visible as a large source of gamma rays in all directions, yet it is not seen at all.

If we'd make the hypothesis that there is a repulsive gravitational interaction between matter and antimatter, we could explain how there could be galaxies consisting of antimatter without any noticable gamma radiation from annihilation events. The repulsive interaction would mostly keep matter and antimatter away from each other, and there would not be any significant collisions leading to annihilation. See http://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter .

There's actually an experiment underway in CERN that tests whether matter and antimatter have an attractive or repulsive gravitational interaction: http://home.web.cern.ch/about/updates/2013/04/alpha-novel-investigation-gravity-and-antimatter .

The problem is that this would be very very obvious as normal matter galaxies near antimatter ones repel each other instead of attract. We simply do not see this.

 

[Chronos]

The putative force carrier for gravity, the graviton, is an integer spin boson, so it has no corresponding antiparticle - meaning it cannot be repulsive.

 

[Mordred]

The putative force carrier for gravity, the graviton, is an integer spin boson, so it has no corresponding antiparticle - meaning it cannot be repulsive.

is the prediction of the graviton being a massless spin 2 boson still considered likely?

 

[Chronos]

In field theory, it remains likely.

 

[Ryuu]

The accepted theory is based on real observations. Matter is, one way or another, "inherently superior" to antimatter when it comes to the big bang nucleosynthesis. As for CP violation, hasn't that been observed to actually happen?

I just looked at the wiki about CP. Some of it seems problematic. The experiments involving Co60, for instance, only exists for matter, as there're no samples of antimatter Co to work from. There is evidence of Neutral Kaons & B mesons to support some sort of violation, but it's unclear if they might simply highlight the differences between CPT and just plain CP as opposed to proving an inherent superiority of matter over antimatter.

As Q is fond of saying, "the jury's still out on this"

No. There's nothing there. That's why they are voids. Besides, how would a void hide anything? It's a void.

I hope you weren't thinking I meant "hide" in the litteral sense of a cloaking field--I thought I clearly made it understood as "hide" in the sense that there'd be no physical interation with galaxies on either side of the voids, thus "hide" the possibility that the light coming from the other side of a void might be from antimatter stars

Quantum fluctuations are believed to be the cause of the inhomogenous structure of the universe.

Since the radiation of the CMBR is after the combining of electrons with the Hydrogen/Helium nuclei, it's possible the flucuations are solely from the quantum fluctuations, but other factors can also be instrumental: sound waves and matter/antimatter annihilations being the principle ones, or a combination of all those.

The problem is that the intergalactic medium has particles in it, so if you have antimatter and normal matter galaxies, then you would have antimatter and normal matter making up the intergalactic medium, which should result in either the complete destruction of the medium thanks to annihilation events, among other things. This should be clearly visible as a large source of gamma rays in all directions, yet it is not seen at all.

But with the distances and low density of the gases involved, do we see any interactions from oposite sides of the voids?

The problem is that this would be very very obvious as normal matter galaxies near antimatter ones repel each other instead of attract. We simply do not see this.

The experiment Hilbert2 mentions would be a good way to test, but I'm not holding my breath that antimatter really does possesses antigravity--I'm willing to trust that perhaps CP is valid, but antigravity would require CPT to be true, and I don't think that's accurate.