What is it?
Yes, that is what we said: a Cosmic Bias. Most scientists don't accept that our concept of matter needs a major revision. Rather, they believe that there is some natural bias towards matter over anti-matter. Or maybe, matter and anti-matter aren't exact opposites.
In 1968, physicist Andrei Sakharov, better known as the father of the Soviet bomb, proposed a theory (we emphasize that this is a theory) to explain the creation of more matter than anti-matter in the universe. He suggested that three conditions must be satisfied (in order to produce excess ordinary matter).
FIRST: Sakharov said that there must be a way of creating both matter and anti-matter particles of the kind which are essential to us--that is, the particles that make up what we are made of. At low energies, the number of baryons (particles interacting via strong nuclear force, i.e. proton, neutrons, quarks, etc.) participating in a collision between different particles is conserved. Like the total electric charge, their number of baryons before and after the collision must be equal. According to Sakharov though, at very high energies and temperatures, the interactions between elementary particles should not conserve the number of baryons. In other words, baryons and anti-baryons can be created from "other" particles. These high energies are predictably achieved in the scorching furnace of the early universe.
SECOND: But this does not limit one set of baryons over the other. At high temperatures, we could still create equal amounts of each. Thus, I bet your wondering how this creates a bias. Ah, well that is where the second condition comes in. Once the high energies of the primordial universe allow for the creation of baryons and anti-baryons, there must be some natural selection for the formation of just ordinary baryons. In 1964, J.H. Christenson and his associates found experimental evidence that shows that interactions between certain baryons do indeed exhibit this bias. In other words, the ordinary matter is simply favored in nature. Why exactly is this so? We don't know…put simply, at high temperatures nature is a racial pig.
THIRD: One of the properties of hot systems is that they have no "memory" of the past. Picture yourself with a cup of steaming hot chocolate. Now, there is a cold/lukewarm spoon resting on the table. You want to mix in the cream, so you pick up the spoon and put it in your hot chocolate. At first, only the end of the spoon in the hot chocolate warms, but after awhile, both ends warm up--so much that you can't tell which end was in the hot chocolate. The system of the spoon and hot chocolate has lost its "memory." Another term for this is thermal equilibrium. Now increase the scale of this event. If the early universe was in thermal equilibrium, any excess baryons would be deleted (or erased from the memory) because in equilibrium, the net baryon is zero. Thus, in order to sustain the baryon bias as the universe expands and cools, there must be a condition that prevents universal Alzheimer's and "memory” loss.
We need what are called "out of equilibrium" conditions in order to "freeze" the net baryon quantity assembled by the first two conditions. The standard model of particle physics successfully describes how particles interact at energies over a thousand times larger than nuclear energies. According to this model, at very high temperatures, all particles but one, the Higgs particle, have no mass; while at lower temperatures they acquire mass through interactions with the Higgs particle. The matter, therefore, has "phases"; above and below the temperature at which ordinary particles (electrons, quarks, etc.) gain mass.
So, as the temperature of the early universe dropped, it went through a "phase" transition, and baryonic particles gained mass. Since only in high temperature phase are baryons created in excess over anti-baryons (remember the first two conditions?), these excess baryonic particles will combine to form the net baryonic number in the low temperature phase. As the collecting baryonic particles grow, the whole universe is converted into the massive "phase". Ready for something that really fries your noodle? The creation of all these excess baryons took place when the universe was about one thousandth of a billionth of a second old. YOWSERS!
There is also evidence that suggests a difference between an ordinary particle and its anti-particle. This difference could lead to a concrete explanation of nature's bias. So far, physicists have found but a few subtle differences between matter and anti-matter.
Around 1965, physicists were studying a subatomic particle known as the K meson. The study was conducted at an accelerator at the Brookhaven National Laboratory in New York. The physicists observed a small discrepancy--just a few samples per thousand--in the ways that K mesons and their anti-particles decay. Physicists cite this discrepancy as evidence for a more general phenomenon known as "CP violation," or charge-parity violation (a.k.a. the charge to spin ratios of the K mesons were not equal and opposite). Thus there is a small, yet fundamental difference between anti-matter and matter. However, over three decades of searching has produced no other particles that show similar phenomenon.
How is "CP violation" important? Well, Andrei Sakharov suggested that it could be a possible, though tiny, mechanism by which matter could arise over anti-matter (in his second condition). The K meson CP violation also fits nicely into the Standard Model of Particles. However, it is too tiny to account for all the excess matter. Something, therefore, is wrong in our theories. But what? Your guess is as good as ours.