Question about antimatter creation

[Guardsman Bass]

Suppose you wanted to create a heavier antimatter atom than anti-hydrogen, such as anti-nickel or even anti-iron. Could you only do that by creating anti-hydrogen in the lab, then slamming those together to create anti-helium, then repeat over and over again until you finally got to anti-iron? Or could you create iron anti-protons using iron nuclei in a particle accelerator?

[Simon_Jester]

"Iron antiprotons" is a meaningless term; there's no 'iron-like' feature of the antiprotons that come out of a pair of colliding nuclei that makes them 'remember' what kind of element those nuclei were.

So yes, you'd basically have to repeatedly fuse anti-atoms or artificially increase their mass by bombarding the anti-atoms with anti-alpha particles, antiprotons, or antineutrons, much as we create the transuranic elements by bombarding them with alpha particles.

[Guardsman Bass]

Sorry, that was poorly phrased. I should have said, "Would you have to slam antimatter nuclei together to fuse repeatedly until you got nuclei that, when combined with positrons, would create anti-iron? Or could you simply use heavier nuclei in your accelerators to create heavier antimatter nuclei?"

In any case, it's as I suspected. I was trying to think of how you could ultimately come up with "anti-iron", and wonder if you could create it directly as opposed to creating anti-hydrogen and then trying to make it more massive by colliding it with other particles. It all sounds incredibly difficult to do.

[Eternal_Freedom]

Why would you even want anti-Iron in the first place? I can tell you one way to make anti-Iron. Take about 3E32 kg (150 solar masses) worth of anti-Hydrogen, compact it into an anti-star and wait the million or so years for the anti-star to live it's life and the explode in a supernova. Search the remnants and find all the anti-Iron and anti-Nickel that will get thrown out. SN1987a threw out something like ten solar masses worth of Iron-56 and Nickel-56 IIRC.

Ok, it's not practical for us humans, but again, why do you want anti-Iron? What useful purpose woudl it serve?

[ryacko]

This is a semi-related question:

Why isn't there any antimatter galaxies in the universe? Do any concentrations of antimatter exist?
Why is "normal" matter so common?

[Eternal_Freedom]

This is a semi-related question:

Why isn't there any antimatter galaxies in the universe? Do any concentrations of antimatter exist?
Why is "normal" matter so common?

The last explanation I heard was that matter and anti-matter were created almost but not quite evenly in the big bang. For some reason matter was slightly more prevalent and when the inevitable annihilation occurred some matter was left over.

I don't like that explanation much, it sounds like a reach to me. THe most likely explanation for the no observed antimatter concentrations is that we just can't see them, either because they are dark/cold/emit anti-photons/other freaky shit or they are outside our light cone.

[bilateralrope]

Lets say another galaxy is purely made up of anti-matter. How could we tell ?

[starslayer]

I don't like that explanation much, it sounds like a reach to me. The most likely explanation for the no observed antimatter concentrations is that we just can't see them, either because they are dark/cold/emit anti-photons/other freaky shit or they are outside our light cone.

That explanation is on physically solid ground. It comes at least partially from symmetry breaking in particle physics, although that alone doesn't quite get us there.

Maybe a more observationally compelling reason why we don't think anti-galaxies are out there is because we don't see the the gamma rays from where the matter/antimatter regions meet. Antimatter has positive mass, so gravity affects it just the same way it does matter, and there's no real physical reason they should have been segregated. There's also no physical reason the antimatter wouldn't have collapsed to form anti-stars (so antimatter-dominated regions wouldn't be cold/dark), and photons are their own antiparticle.

Lets say another galaxy is purely made up of anti-matter. How could we tell ?

The only way would be to look for matter/antimatter annihilation at the boundary layer separating the antimatter-dominated region from the matter-dominated one, as I alluded to above. We unfortunately can't take advantage of antimatter's reversed charges in this instance.

[Eternal_Freedom]

I don't like that explanation much, it sounds like a reach to me. The most likely explanation for the no observed antimatter concentrations is that we just can't see them, either because they are dark/cold/emit anti-photons/other freaky shit or they are outside our light cone.

That explanation is on physically solid ground. It comes at least partially from symmetry breaking in particle physics, although that alone doesn't quite get us there.

Maybe a more observationally compelling reason why we don't think anti-galaxies are out there is because we don't see the the gamma rays from where the matter/antimatter regions meet. Antimatter has positive mass, so gravity affects it just the same way it does matter, and there's no real physical reason they should have been segregated. There's also no physical reason the antimatter wouldn't have collapsed to form anti-stars (so antimatter-dominated regions wouldn't be cold/dark), and photons are their own antiparticle.

I know, it's just the explanation just seems...too easy, even if it is plausible. I can see the thought process easily enough:

1. Matter and antimatter should be created equally
2. We don't see antimatter in any reasonable quantity in nature
3. Something got rid of the antimatter
4. Matter/antimatter annihilated
5. But why are we still here? Must have been more matter than antimatter.

Like I said, it's plausible, but it's another of those strange facts that morons like to use to say there must be a creator which probably explains my aversion to it.

[Lord of the Abyss]

I know, it's just the explanation just seems...too easy, even if it is plausible. I can see the thought process easily enough:

1. Matter and antimatter should be created equally
2. We don't see antimatter in any reasonable quantity in nature
3. Something got rid of the antimatter
4. Matter/antimatter annihilated
5. But why are we still here? Must have been more matter than antimatter.

Oh, it's not really that "easy". The question of why matter/antimatter production wouldn't be equal is an unsolved one; there's various theories but they don't really know for sure how it happened.

[Arthur_Tuxedo]

Of course, if you believe inflation theory then the actual universe could be so much bigger than the observable one that 50% of the whole universe could very well be comprised of antimatter without us ever seeing gamma rays from any of the boundaries because the observable universe could represent only a portion of a 100% matter region.

[Guardsman Bass]

Why would you even want anti-Iron in the first place? I can tell you one way to make anti-Iron. Take about 3E32 kg (150 solar masses) worth of anti-Hydrogen, compact it into an anti-star and wait the million or so years for the anti-star to live it's life and the explode in a supernova. Search the remnants and find all the anti-Iron and anti-Nickel that will get thrown out. SN1987a threw out something like ten solar masses worth of Iron-56 and Nickel-56 IIRC.

Ok, it's not practical for us humans, but again, why do you want anti-Iron? What useful purpose woudl it serve?

I remember someone proposed containing anti-hydrogen fuel in a tank made of anti-iron in a debate a long while back here, and I got curious after the topic of using antimatter as fuel came up in the comments for a recent article at the Atlantic. The idea would be that the anti-iron tank would be easier to manipulate with magnetism.

[Zixinus]

Doesn't matter-antimatter annihilation create a specific wavelength of gamma radiation?

[Ariphaos]

Positron-electron annihilation does. Sometimes. Nucleon-nucleon much less so, IIRC (I linked the paper on this forum somewhere) a minimum of 56% of the energy gets radiated as neutrinos and predictability goes only down from such an idealized reaction.

[Terralthra]

I don't like that explanation much, it sounds like a reach to me. The most likely explanation for the no observed antimatter concentrations is that we just can't see them, either because they are dark/cold/emit anti-photons/other freaky shit or they are outside our light cone.

That explanation is on physically solid ground. It comes at least partially from symmetry breaking in particle physics, although that alone doesn't quite get us there.

Maybe a more observationally compelling reason why we don't think anti-galaxies are out there is because we don't see the the gamma rays from where the matter/antimatter regions meet. Antimatter has positive mass, so gravity affects it just the same way it does matter, and there's no real physical reason they should have been segregated. There's also no physical reason the antimatter wouldn't have collapsed to form anti-stars (so antimatter-dominated regions wouldn't be cold/dark), and photons are their own antiparticle.

Isn't it up for debate whether the gravitational effects of antimatter are truly identical to matter? CPT predicts that antimatter will attract other antimatter in the same way matter attracts matter, but whether that carries over to matter/antimatter gravitational interaction is unclear. As far as I know, no experiment has been able to detect gravitational force from antimatter due to sensitivity of the small amounts of antimatter created. It would appear to be equally likely that there is a positive/negative-type interaction between the two, thus while you could have, so to speak, anti-stars and anti-planets and anti-nebulae, they would repulse normal matter gravitationally, neatly explaining why we don't see evidence of antimatter stellar phenomena - they behave just like normal matter phenomena until and unless they interact, which they wouldn't on any large scale due to gravitic repulsion.

[LaCroix]

Since photons are their own antiparticle, wouldn't it possible that 50% of the known galaxies are in fact anti-material ones, but we won't know due to lack of interaction with matter?

[Terralthra]

Since photons are their own antiparticle, wouldn't it possible that 50% of the known galaxies are in fact anti-material ones, but we won't know due to lack of interaction with matter?

Yes, assuming non-interaction. It would seem improbable that there's no interaction unless there's something keeping matter and antimatter stellar phenomena apart. A repulsive gravitational interaction between matter and antimatter would be one explanation.

[starslayer]

Isn't it up for debate whether the gravitational effects of antimatter are truly identical to matter? CPT predicts that antimatter will attract other antimatter in the same way matter attracts matter, but whether that carries over to matter/antimatter gravitational interaction is unclear. As far as I know, no experiment has been able to detect gravitational force from antimatter due to sensitivity of the small amounts of antimatter created. It would appear to be equally likely that there is a positive/negative-type interaction between the two, thus while you could have, so to speak, anti-stars and anti-planets and anti-nebulae, they would repulse normal matter gravitationally, neatly explaining why we don't see evidence of antimatter stellar phenomena - they behave just like normal matter phenomena until and unless they interact, which they wouldn't on any large scale due to gravitic repulsion.

This kind of thing runs right into the equivalence principle. It is known, for example, that magnetic fields affect antimatter exactly as if the only difference between it and regular matter is its electric charge. Since the only other difference between matter and antimatter is its spin (applying the CPT operator to a particle transforms it into its antiparticle and flips the spin state), this means that the inertial mass of matter and antimatter is identical. By the equivalence principle, this also means that the gravitational masses of antimatter and normal matter are identical. If antimatter and matter mass acted as different gravitational charges, this would break the equivalence principle and tear down GR with it. Quantum gravity may still do this in whatever form it takes, and it will certainly destroy GR on small scales, but I doubt a wholesale violation of the equivalence principle will end up coming out of it.

Since photons are their own antiparticle, wouldn't it possible that 50% of the known galaxies are in fact anti-material ones, but we won't know due to lack of interaction with matter?

Ninja'd, but what the hell:

Again, there'd be a boundary region where matter and antimatter interacted, and we'd see gamma rays coming from this boundary. You might propose that there's no appreciable gamma flux because the boundary region is just too rarefied, but I don't think this washes according to my general feel for the density of the universe and structure formation. Since we know dark matter permeates the universe, and it only weakly interacts with itself or anything else, there should be at least some filaments where matter and antimatter mingle with sufficient density to produce a detectable gamma ray flux. It would probably show up as a resolved source in the Fermi LAT, and maybe unresolved in some other detector.

[Ariphaos]

If a field star or even a field dwarf galaxy in say, the Bootes void was made of antimatter, would we actually be able to notice with current detectors? Especially since its surroundings would be even more rarefied than normal, with most of the annihilation occurring shortly at the Big Bang itself.

[amigocabal]

I don't like that explanation much, it sounds like a reach to me. The most likely explanation for the no observed antimatter concentrations is that we just can't see them, either because they are dark/cold/emit anti-photons/other freaky shit or they are outside our light cone.

That explanation is on physically solid ground. It comes at least partially from symmetry breaking in particle physics, although that alone doesn't quite get us there.

Maybe a more observationally compelling reason why we don't think anti-galaxies are out there is because we don't see the the gamma rays from where the matter/antimatter regions meet. Antimatter has positive mass, so gravity affects it just the same way it does matter, and there's no real physical reason they should have been segregated. There's also no physical reason the antimatter wouldn't have collapsed to form anti-stars (so antimatter-dominated regions wouldn't be cold/dark), and photons are their own antiparticle.

Lets say another galaxy is purely made up of anti-matter. How could we tell ?

The only way would be to look for matter/antimatter annihilation at the boundary layer separating the antimatter-dominated region from the matter-dominated one, as I alluded to above. We unfortunately can't take advantage of antimatter's reversed charges in this instance.

How many annihilation events would there be in such a boundary region? If I remember correctly, galaxies are actually pretty much thin. The only attractive force between matter and anti-matter on a large scale would be gravity. If, for example, Proxima Centauri were replaced with an anti-matter star of equivalent mass, the anti-matter star will be nowhere close to annihilating Earth or our own sun, and we would have no fucking clue that Proxima Centauri was replaced by an anti-matter star (unless anti-hydrogen has a different spectral pattern than regular hydrogen.)

[Simon_Jester]

No, we'd get a spike in annihilation events and detectable gamma rays. Sure, there's only one hydrogen atom per cubic centimeter of vacuum for the antistar to collide with, but there are a LOT of cubic centimeters of vacuum out there, and it hits a lot of them.

[Jerry the Vampire]

Personally I think that if there were galaxies entirely made of Antimatter we would have detected them. For example via lots of matter being annihilated.

[amigocabal]

Personally I think that if there were galaxies entirely made of Antimatter we would have detected them. For example via lots of matter being annihilated.

If there is an antimatter galaxy out there, where in that galaxy would there be matter to annihilate? Would not almost all of the matter in those galaxies have been annihilated billions of years ago?
(I am assuming arguendo that the Universe started with the same amount of matter and antimatter, the distribution was uneven, and the expansion of the Universe keeps the antimatter regions apart from the matter regions.)

It would seem improbable that there's no interaction unless there's something keeping matter and antimatter stellar phenomena apart. A repulsive gravitational interaction between matter and antimatter would be one explanation.

Would not the expansion of the Universe be sufficient?

[Terralthra]

Personally I think that if there were galaxies entirely made of Antimatter we would have detected them. For example via lots of matter being annihilated.

If there is an antimatter galaxy out there, where in that galaxy would there be matter to annihilate? Would not almost all of the matter in those galaxies have been annihilated billions of years ago?
(I am assuming arguendo that the Universe started with the same amount of matter and antimatter, the distribution was uneven, and the expansion of the Universe keeps the antimatter regions apart from the matter regions.)

And since there'd be some billions of years away, we'd still be detecting the annihilation energy, if true. Speed of light is the speed of light.

It would seem improbable that there's no interaction unless there's something keeping matter and antimatter stellar phenomena apart. A repulsive gravitational interaction between matter and antimatter would be one explanation.

Would not the expansion of the Universe be sufficient?

It's not sufficient to prevent matter and matter from interacting gravitationally, since we rather obviously exist, so no.

[Jerry the Vampire]

The collisions don't have to be within the galaxy.

The idea is we live in a matter universe because in the beginning there was a million and one particles of matter to a million particles of Anti Matter (not exactly but ya know) The matter and antimatter annihilated each other leaving us with a matter filled Universe.