# Antimatter-matter equality questions **URL:** https://boards.straightdope.com/t/antimatter-matter-equality-questions/1020917 **Category:** Factual Questions **Tags:** science-math **Created:** [July 16, 2025, 1:50pm UTC](https://boards.straightdope.com/t/antimatter-matter-equality-questions/1020917 "2025-07-16T13:50:37Z") **Posts on this page:** 1 **Showing post:** 4
### Author: ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta) #### Post date: [July 16, 2025, 11:25pm UTC](https://boards.straightdope.com/t/antimatter-matter-equality-questions/1020917/4 "2025-07-16T23:25:05Z")
> [@Mijin](#): > > when all (?) particle transformations are symmetric with respect to matter and antimatter. The transformations aren’t purely symmetric, but the asymmetries seen so far are not anywhere near large enough to generate what is observed cosmologically. > [@Mijin](#): > > Some, like Sabine Hossenfelder (on one of her better days) say… You’d have to cite a specific rant of hers for me to comment further here about what she might be click-baiting about. > [@Mijin](#): > > And can we rule out that matter and antimatter were just not mixed? So there are two huge volumes with a bunch of explosions between the two outside of our visible range? Or can we already rule that out from what we see in the CMB? Some past discussion [here](https://boards.straightdope.com/t/would-an-object-made-of-antimatter-reflect-light/697236/22) and [here](https://boards.straightdope.com/t/how-does-gravity-react-with-anti-matter/778983). I’ll pull out some primary points: **Annihilation products.** The boundaries between matter and antimatter regions are not completely devoid of material and should show evidence of matter-antimatter annihilation. Such annihilation products are not seen, and based on the distributions of matter in the universe and constraints on matter densities in the intergalactic medium, current data is sufficient to exclude the presence of matter/antimatter boundaries in the observable universe. **Cosmic rays.** Our little pocket of space is bombarded by cosmic rays. These come from numerous processes at solar system, galactic, and intergalactic scales. Most of these cosmic rays are boring things like electrons and protons, but antimatter can also appear. Barring new physics, this antimatter comes from collisions of ordinary cosmic rays with other regular matter in the universe or in violent processes like supernovae and gamma ray bursts. The more complicated the antimatter gets, though, the harder it is to make using mundane physics. Antiprotons? Not that hard to make. Antideuterons? Sure. Antihelium-3? Pretty rare. Antihelium-4? Very rare. Experiments look for unexplained excesses of these light anti-nuclei, as evidence perhaps of large pockets of antimatter out there. **Early universe dynamics.** If you try to separate matter and antimatter into distinct regions, you need a mechanism to do that. There is a great corpus of cosmological data that gives insight into the dynamics of (anti)matter in the early universe. Cosmic microwave background radiation, large-scale structure (_e.g._, superclusters, [filaments](https://en.wikipedia.org/wiki/Galaxy_filament)), and more have well-measured and _highly detailed_ patterns that match exceeding well what is expected if the random, entropic processes in the early universe, together with the structure-forming influence of gravity, proceeded as we understand them. In other words, there is no evidence that anything other than normal large-scale dynamics was present. One specific conclusion is that, if there were antimatter domains, they would have to still be comingled with matter domains at least until a time well after “recombination” (the birth of the CMB photons), and they would be quite noticeable then. **Baryon/photon ratio and abundances of light elements.** These closely related quantities, measurable through cosmological observations, point to two key conclusions: there is a massive deficit of baryons relative to photons in the universe, indicating significant early (anti)baryon annihilation, and there was not “late”-time antimatter present to mess up the balance of primordial light elements, for which observations match expectations quite well. > [@Mijin](#): > > Others present the theory that for every billion or so antimatter particles, there would be 1 billion + 1 matter particles, and everything we see comes from that slight imbalance. Where did this specific number come from? It is essentially the baryon-to-photon ratio mentioned above, which connects to your intuition that the energy doesn’t disappear even if the baryons mostly annihilate away. But to be sure: while that’s a fairly direct line to the numerical imbalance, the imbalance is consistent with a host of observations. > [@Hari\_Seldon](#): > > The article goes on to say that these asymetries are not enough to solve the problem. And in this experiment, the matter decays _faster_ than the antimatter, which is the wrong direction. Still they will go on looking for other asymmetries. The LHCb result did not find a new source of matter-antimatter asymmetry. Rather, they observed the already predicted effect for the first time in these specific particles. It’s an experimental tour de force, but the “not enough to solve the problem” part is the exact same “not enough” as before (_i.e._, it’s the known asymmetry that stems from how quarks see the so-called “weak” force.) The next place to keep your eyes peeled for new information is likely the neutrino sector, wherein a matter-antimatter asymmetry could be present in a relatively large amount but just hasn’t been measured yet. In turn, this asymmetry could connect to the early universe given how neutrino masses might be generated. Current and near-term experiments are looking for this potential _new_ source of matter-antimatter asymmetry. --- _[View the full topic](https://boards.straightdope.com/t/antimatter-matter-equality-questions/1020917)._