If the universe was dominated by antimatter instead of matter, would we physically notice?

Question

I read that antimatter and matter are identical aside from their opposite charge and quantum number. Of course, the mystery of why matter dominates in our universe is an active field of research. But from a purely physical standpoint, if our universe happened to be dominated by antimatter, would we even be aware?

Are there any physical limitations of antimatter vs matter in which certain processes we observe would not work in an antimatter universe?

I gather, if all matter in the universe were able to simultaneously change into their antimatter counterpart, that there would still just exist the same balance we observe in our regular universe since everything flips together.

But I also read an interesting point that neutrinos (which don't have charge) have antimatter twins which have opposite helicity (spin) direction, which may affect decay rate. Still though, would this even make a difference to what we observe in our everyday lives? Domination of matter aside, is there anything that restricts a universe comprised of antimatter?

Answer 1

Let's start with an assumption that we're also made of antimatter and that antimatter doesn't have some kind of anti-mass property as well. In that case, the answer would be a hard no, we would not really notice. The resulting reversals of charge, symmetry, chirality, and so on would be the common state of things, so would not be especially obvious. We might create matter in a lab. Of course, to an anti-matter person, posi-matter would be consider anti-matter from their point of view. The models as far as we know work the same for both matter and antimatter. In fact, the whole notion of "an electron is negatively charged" is kind of arbitrary - we could just as easily have called it positive, the key is that they repel like-charged particles and attract oppositely-charged ones.

If we assume that we're still made of matter (our solar system) with the the universe being antimatter, then yes, you would notice, because you would see a glow emanating from the boundary of our matter bubble where the solar system material annihilates with the surrounding region.

Let's assume that there really is nothing in interstellar space to annihilate with. Antimatter emits the same light as matter does (antihydrogen still has the same lyman series, and so on). In this case, you wouldn't notice. And since light is all we really get from elsewhere and we don't see boundaries where matter and antimatter regions contact and annihilate, clearly the universe isn't segregated in that manner.

Answer 2

Yes, this is detectable, but it requires accessibility to matter and antimatter to determine this.

Under Earth conditions it is easy. A charged anti-particle is deflected in a magnetic field in the opposite direction to the deflection of a normal charge.

In a pure antimatter world, on the other hand, this experiment is pointless, since the designation of the electric poles and the magnetic dipole is a pure convention.

Only if you take your own magnet from one world to the other and look at the deflection of the electron/positron is the difference visible. But before that, it is likely that the annihilation process will occur, and then it is already too late for experiments.

Answer 3

The cosmological models we have to model the observations of the universe and attempt to predict new data are mathematical and follow the logic of mathematics with the functional solutions of rigorous mathematics, simply adding extra postulates in order to pick up the physically relevant solutions. The units are part of these postulates.

The models are such that if we had labeled the electron with a plus sign then the positron would have a minus sign and all the other labels would follow. The same is true for what we call antimatter. Matter is postulated to start with the table of elementary particle physics in the standard model

All matter is hypothesized to emerge from these axiomatically postulate particles , and a corresponding table of antimatter particles such that when particle interacts with antiparticle all the quantum numbers shown in the table are zero.

Thus, by construction, we could have decided to use the antimatter table as describing matter and the models would mathematically work out the same.

As long as there is no experimental evidence to show a difference between particle reactions and the reversed antiparticle reaction the model will still say that the distinction between a matter universe and antimatter universe is just a definition.

(for example: An experimental evidence would be if one could find a proton proton interaction whose experimental distribution to specific matter particles would be statistically significant different from an antiproton antiproton interaction to the specific antimatter particles .)