Do we have any theories on why the (presumed) balance in the universe around the BB tilted to one side over the other?
From www.superstringtheory.com :
Someone with a great deal more knowledge then me in physics can explain this better but Dr. Leon Lederman explained this in the God Particle
More or less (the best I remeber) he said when matter/antimatter is created from energy more matter is created. I don’t know if he said how or why …
this page
http://www.npl.washington.edu/AV/altvw67.html
says
In other words:
Figure it out, learn Swedish, win a prize!
(Motto of my brother’s optometry school class)
I like the string theory, because even though I might be a loser in this alternate reality, but in the next one I rule this entire planet.
It occurs to me that if there were more anti-matter than matter, we’d be calling anti-matter matter and matter anti-matter.
Which answers your question, after you assume one or the other predominates. It does not answer your question, given that the default assumption is that they should have been created in equal amounts.
The real answer, of course, is that we just don’t know. There are all sorts of wild and wonderful speculations, of course. Here’s a few possibilities:[ul][li]String theory will tell us the answer.[/li][li]CP violation, as it treats matter and antimatter differently, could be an explanation. (Heh. CP violation. Deja vu, eh? )[/li][li]It just happened that way, and we choose to call the one that predominates matter instead of antimatter.[/li][li]There isn’t a matter/antimatter imbalance. The idea here is that you’d have equal amounts of matter and antimatter, but in some local region of space there’d be an imbalance. If there was then a superluminal expansion after this imbalance started up, the matter and antimatter in that region would mostly annihilate, but there’d be an excess of matter in the observable universe. This would imply that somewhere out in the unobserved universe is an area with an excess of antimatter.[/li][/ul]
These statements, from the sites quotes by Alphagene and Boobka respectively, aren’t as contradictory as they might appear. For there’s rather more to the matter dominance in our universe than just CP violation. In a famous paper back in 1967, Andrei Sakharov pointed out that such a mismatch required three different conditions be met. We’ll take them in reverse order to the way they’re normally listed.
First, there has to have been a stage where the universe wasn’t in thermal equilibrium. This tells us something about the early history of the universe.
Secondly, you have to have both C and CP violation. This is not necessarily that big a deal in the Standard Model, though there are open research questions here, as I’ll comment on below.
Thirdly, baryon number conservation must be violated. This is the killer from the point of view of the Standard Model, since it always conserves baryon number. Many other models, be they string theories or simple GUTs, do violate it, so this is interesting as evidence of unknown physics. However, nobody’s ever observed such a process (the classic example would be proton decay), so the Standard Model still fits the expermental evidence.
So a matter excess can’t be explained by the Standard Model (SM), but CP violation might be. Regarding the latter, this is because if you write down the most general version of the SM, then you automatically get CP violation. As the NPL site mentions, there’s a free parameter involved that sets the amount of CP violation that your particular version of the general SM has. To find the value of that parameter, you have to measure it. However, the SM still has predictive power here, since there are patterns within CP violation that it predicts and patterns it predicts can’t happen. Lots of theorists have come up with alternative means of getting CP violation and these tend to predict different patterns. It’s thus been a very active field of experimental research over the last few decades in looking at what the actual patterns are, to try to rule out some of these rivals or, indeed, the SM. The data to date is consistent with the SM and its version of CP violation remains the concensus conclusion. Everybody also realises that this is a very good area where future experiments might disagree with it, so it continues to be an active research question.
Wow, interesting. And since it was mentioned twice, I wasn’t worried about the whole “but if it was the other way we’d just call antimatter ‘matter’” thing 
Am I right in thinking that the whole CP violation thing, though, would imply that there would be a preference for this matter (not antimatter ‘matter’)?
Could there be a relationship between dark matter and anti-matter? Since nobody seems to have a handle on the dark matter, maybe that’s where the anti-matter resides…
Dark matter is merely matter which does not shine on its own (stars) or reflect light from a nearby light source (planets).
Go in the basement and turn out the lights.
Nou you are dark matter.
bonzer’s mention of proton decay made me wonder what the current lower bound was. After Googleing, I came across this link which is directly relevant, and expands on bonzer’s post:
(italics mine) From the same link, that “current empirical lower limit” is about 10[sup]33[/sup].
That’s 10[sup]33[/sup] years, of course.
Unfortunately the only stuff I could find regarding leptogenesis was rather too technical. But that just might be the nature of the question.
As for dark matter: Some dark matter is perfectly well understood. At least some of it (about 30% of the glactic dark matter, last estimate I saw) is in the form of things like MACHOs, which are basically Jupiter-sized objects which happen to not be orbiting a star. However, it can’t all be baryonic matter (i.e., matter which gets most of its mass from protons and neutrons). Based on the relative abundances of various isotopes of hydrogen, helium, and lithium in the Universe, we can make a pretty solid model of how much baryonic matter there should be, total, in the Universe, and it’s not enough. Currently, the favored theory is that most of the dark “matter” is actually “dark energy”, or “quintessence”, which is also the stuff responsible for the acceleration of the cosmic expansion. That still doesn’t tell us much, though: There’s still far too much freedom in models of the quintessence, such that we essentially can’t predict any of its properties, other than what’s already been observed.
How does this relate to the matter surplus problem? Not very directly, so far as is known. They’re both physics puzzles, to be sure, and a good Grand Unified Theory would probably shed light on both of them, but other than that, I don’t think that any connnection has been proposed.
Along the lines of what bup says sounds right. This seems like one of those anthropic questions. Given the aversion matter and anti-matter have for each other, if they were present in exactly equal amounts, they would immediately annihilate each other, hence no matter or anti-matter and no observers to wonder why nothing exists. I’m an amateur at all of this, but it is my understanding that in the primordial universe, what we call matter had only a very slight edge over what we call anti-matter (This web page says only 1 extra electron per billion positrons: cite ).
Yeah, that’s about it exactly. Sakharov’s condition on baryon number violation is there because without that you get nowhere. If you start off with equal numbers of baryons and anti-baryons, there has to be some process converting one to the other if you’re ever going to get an imbalance. However, if CP were an exact symmetry, then the schematic baryon-number-violating process
baryon -> anti-baryon
would just have exactly the same rate as the opposite process
anti-baryon -> baryon
and they’d cancel out. That CP-violation leads to the second of these being faster (and hence more common) than the first is indeed what means that it’s baryons that can be more common. The final condition, about thermodynamics, is however still needed to ensure that the imbalance does come about, at least to some degree.