There is something very strange about the universe we live in and the evidence is quite literally all around us. Go ahead, look around. What do you see? Stuff. Everywhere, stuff. Now that might not seem all that profound at first until you think about the conditions in the very early universe. In the smallest fraction of a second after the Big Bang, the entire Universe was compacted into a tiny volume. All the energy in the Universe was contained it this minuscule space. The temperature was so extreme that matter couldn’t yet even exist! The immense energy density would cause material to spontaneously pop in and out of existence. As the Universe expanded, energy was spread over a greater volume and the temperature dropped. Matter & antimatter began to condense out but would pair up and annihilate almost immediately.
Now we were taught that matter & antimatter are exactly symmetric differing only in the sign of some of their parameters, such as charge and spin. It would seem, therefore, that they should have been produced in equal quantities. But obviously this was not the case. After all the matter & antimatter paired up and converted back to energy, there was a small residual amount of matter left over – all the stuff you see around you! All matter we see today is a result of this minor excess in production of matter over antimatter. Apparently, our Universe has a slight proclivity for stuff versus anti-stuff. The fact that more matter was originally produced is what is known as a symmetry violation. (Specifically CP-violation. “C” for charge conjugate and “P” for parity meaning the particles are mirror images of each other.)
Why there is a preference for stuff over anti-stuff isn’t really understood. As a physicist, it would be more satisfying to have a nice simple symmetric universe but without this complication, the Universe would be a very bland place without any matter to look at, or for that matter, no “you” to look at it. It seems quite profound how perfectly CP-violation is tuned to allow a universe so well suited for things like us to exist. Many might see this as an example of intelligent design by some omnipotent deity. It is all too easy to come to such a conclusion. But, must such remarkable-seeming coincidences require invoking the supernatural? Some might argue “what else could it be?” Not at all if you assume ours is not the only Universe, only one amongst an unimaginably huge and diverse multiverse. It doesn’t matter how unlikely the combination of parameters are, if you try enough examples, you’ll eventually hit upon the ideal magical seeming mix. And of course, we find ourselves in one of the extraordinarily rare universes that is ideally fine-tuned to allow us to exist. If it weren’t, there wouldn’t be any stuff and wouldn’t be any you to look at it.
Claude Plymate, Engineering Physicist