When looking at the immensity of the known universe and imagining everything found in and out of it, to the proper mind one question becomes obvious:
Why is there something instead of nothing?
Yet, I am afraid that the answer to said question cannot be deduced by simple means given the laws of physics that govern our Universe. Especially when considering the Standard Model of particle physics, as it tells us that:
the Big Bang had to produce matter and antimatter in symmetric (or equal) quantities and these had to destroy each other whenever they touched.
That is to say the Universe had to annihilate itself from the beginning and, therefore, be non-existent.
But, as we know, this was not the case.
For reasons unknown, an asymmetry (or inequality) between matter and antimatter at the baryon scale  was presented during the first moments of the formation of the Universe. And it was this variation, known as baryogenesis, the one that gave rise to the great amount of residual ordinary matter that forms the cosmic variety seen today.
So impressive is the portion of matter in the Universe, in fact, that there is no evidence, even by gamma ray signatures, to confirm the presence of stars or galaxies made of antimatter.
However, in each of the interactions between particles that we have observed, a single particle of matter has never been created or destroyed without creating or destroying an equal number of antimatter particles.
So, if there is no known way to make more matter over antimatter due to the way in which particles interact in the Universe: why does the Universe exist?
In the late 1960s, physicist Andrei Sakharov identified three necessary conditions for baryogenesis, according to which the Universe must:
- be an out of balance system,
- exhibit a violation of C and CP symmetries, and
- have interactions that violate the baryon number.
Solving the first is easy, because an expanding Universe with unstable particles (and / or antiparticles) is, by definition, out of balance. Likewise, the second premise is solved in a simple way, since the “C” symmetry (which replaces the particles with antiparticles) and the “CP” symmetry (which replaces the particles with mirrored antiparticles) are violated during weak interactions.
Which leaves us with only one problem: how to violate the baryon number.
In the standard model of particle physics, despite the observed conservation, there is no explicit conservation law in relation to the number of baryons (protons and neutrons) or the number of leptons (electrons). Instead, it is only the difference between baryons and leptons, B-L, the one that gets preserved.
And this indicates that, under auspicious circumstances not only could additional protons be formed, but the necessary electrons to accompany them could also be generated.
Although what these circumstances are remains a mystery.
But this does not prevent us from elaborating speculative conjectures. So, theoretically, there are three main possibilities:
- New physics at the electroweak scale could greatly improve the amount of violation of C and CP in the Universe, which leads to an asymmetry between matter and antimatter. Particularly, sphaleron interactions, which violate B and L individually (but retain B-L), could generate the correct amounts of baryons and leptons with or without supersymmetry (depending on the mechanism).
- New physics based on high-energy neutrinos could create a fundamental asymmetry of leptons from the very beginning (phenomenon best known as leptogenesis ). Then the sphalerons, which retain B-L, would use this lepton asymmetry to generate a baryon asymmetry.
- And lastly baryogenesis at the GUT scale, since this could generate new particles and physical relationships through the unification of the electroweak force with the strong nuclear force.
But all these inferences keep the same general idea:
the possibility of starting with a completely symmetric Universe capable of:
- obeying all known laws of physics,
- spontaneously creating matter and antimatter in equal and opposite pairs, and
- culminating with an excess of matter at the end.
So, moral of the story:
Don’t try to understand the Universe. Not even with Physics. For it can pretty much do and undo as it pleases, without caring about the sense behind its actions.
Thanks for the read. ♥
 A tiny but important asymmetry of: 10,000,000,000 antimatter baryons for each 10,000,000,001 matter baryons.
 For further info, visit: The Standard Model of Particle Physics.