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I have been curious for many years how all of the anti-matter in the universe disappeared. I just read another article that indicates this is an active area of research. I often read descriptions of the early universe that follow a common progression: universe begins as a dense 1” wide point, space is created, inflation occurs, elements occur as universe expands and cools. So my questions are: 1. Why is there no mention of anti-matter in these early steps? 2. Wouldn’t we expect it to exist as soon as elements condensed? 3. If it did exist, and if it was annihilated through a succession of reactions, wouldn’t that process deserve a footnote in the description of the process? 4. How long would it take to convert all of the matter/anti-matter into matter? 5. How many reactions would be required to perform the conversion? It seems we are missing an important step in the process the early universe followed. I understand that scientists don’t like to speculate, but this seems like a good time to. I have asked my friend Joel about this, but he said we don't know. Can’t we at least acknowledge the elephant in the room? Thanks.
Question Date: 2018-04-02
Answer 1:

This is one of the great unanswered questions in physics - I guarantee you whoever answers this one is going to get the Nobel prize. We know of no process that can create matter without also creating equal amounts of antimatter, and vice-versa. Likewise we know of no way to destroy matter that do not require the destruction of an equal amount of antimatter, or vice-versa.

The problem is that, while physicists acknowledge that this problem exists, none of the hypotheses that have been proposed to explain it make any predictions that we can test, and as a result we have no way of knowing which, of any, of these explanations are even partially correct. In science, problems like this get ignored not because they aren't there, but because they're unanswerable with our given capabilities, so we scientists instead focus our efforts on those questions that we can answer. Also, while this is a big problem in physics, I can think of other elephants in the room that are even bigger than this one (the natures of dark matter and energy leap to mind).

From what I can tell, there are two leading possibilities for why the matter-antimatter asymmetry might exist. These are (1) there is some process that we have never observed that creates matter but not antimatter or that destroys antimatter but not matter, and (2) there are regions of the universe that are dominated by antimatter instead of matter, and some force that separated the matter and antimatter into these respective domains. Both of these must involve processes that are unlike anything we have ever seen before, either in the laboratory or in nature, so it is difficult to imagine what kind of observation or experiment would be needed to test them.

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