you have to have more matter than anti-matter for this to add up. but it shouldn't happen, by it's own admission. and so the truth is that it really doesn't add up. if the explosion was as explained, we should really have this universe of pure light. but, we don't. so, it can't be quite as explained.
this is a history of the universe, rather than of the cosmos. if we have many universes [not in the many-worlds sense, i mean many different universes], you open up the possibility that the universe is not closed - that there is a possible additional source of matter from outside the universe. i think that's the right answer. but don't expect me to explain it in too much detail.
discussions on the origins of the cosmos (or really on anything outside the universe we live in) are currently outside the realm of any sort of coherent thought.
http://www.youtube.com/watch?v=7KYTJ8tBoZ8
if you conceive of many universes [not parallel ones] expanding in some kind of a space, the idea that they may in some way interfere with each other becomes almost unavoidable. you could come up with scenarios where we gained matter from a different universe that consequently has a surplus of anti-matter.
i don't have a really good argument, or anything. i guess it's sort of similar to an aspect of m-theory. it's more just probabilistic. if there's one universe, there pretty much has to be many universes. i can't fathom that our big bang could be a singular, unique event - it would have to have a naturalistic explanation, and that would have to be something that occurs repeatedly and regularly. and, then, if you accept that, arguing for a closed universe strikes me as kind of ridiculous. it becomes a question of determining how universes interact.
but, looking for any evidence of this strikes me as rather hopeless - and even pointless.
maybe an easy way to think of it is like this...
in order for the universe to expand, there has to be something outside of it to expand into. if there is some kind of block of energy or something in the way, it would not be able to expand. if there was some kind of friction slowing it down, we'd likely be able to infer it from calculations.
but what is nothing? let's not get lost in the standard kantian discussion. even if it's a vacuum, the effects of that vacuum still need to be understood on the expansion.
but, what is the likelihood of expanding into an absolute vacuum with absolutely no possibility of it interacting with anything? it seems remotely slim. i mean, we can't understand this. can't. but, it really seems obvious that there's something in the space that the universe is expanding into. and, it's going to have some effect on the way the universe expands.
so, how can we claim to have this understanding of the history of the universe, when we have no understanding of any forces acting outside of it, and it's obvious that there are forces acting outside of it?
universes might crash into each other. they might repel each other. they might stick together. there might be exotic objects flying through the cosmos that slice through universes. there might be forces that act on it's expansion.
i'm not denying that a big bang happened - there's the cosmic radiation and the experiments and the whatnot. it seems like a good basic start to understanding this.
but, i don't think we can get to a full understanding of things until we acknowledge that the universe is likely not a closed system, and that these various mysteries that seem to have no local explanation are probably actually the result of the universe interacting with the environment outside of it.