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I watched this youtube video about anti-matter, which says we don't know "why the big bang produced more matter than anti-matter".

How do we know that more matter than anti-matter was produced in the big bang?

Wouldn't it be possible that equal amounts of both matter and anti-matter were produced, but not spread out uniformly, and that our observable universe is in an area where there happened to be more matter than anti-matter?

Zach
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Short answer, this is what we observe around us in the observable universe, and even on the largest scales, the universe is accepted to be homogenous and isotropic.

https://en.wikipedia.org/wiki/Cosmological_principle

This is assuming that the governing laws of physics are the same everywhere in the universe.

So if the amount of matter and anti-matter was originally equal then just turning into photons and back would still result in equal amounts of matter and anti-matter. To produce an excess of matter (as we see around us) requires some additional mechanism, and it is not know what that mechanism is. There are processes known that can produce an excess of matter over anti-matter (or vice versa) but these produce too small an excess to account for all the matter there is in the universe.

Matter vs. Antimatter shortly after Big Bang

That being said, it is possible that the universe is so big, that there are parts, where the laws are different from the ones we know, and the distribution of matter and antimatter is different from what we observe here.

Árpád Szendrei
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  • This answer appears to conflate 2 things - assuming that the universe is homogenous/isotropic and assuming the laws are universal, to skip past the possibility that the universe is homogenous and isotropic but the part of the universe that is observable happens to have a tiny non-zero matter/antimatter balance by chance (anthropomorphic principle.seems relevant too). So for me, it doesn't really answer the question in the OP, why that couldn't be the case. – Stilez Apr 05 '21 at 20:11