Michael J. Ramsey-Musolf is a professor of physics at the University of Wisconsin-Madison. His research concerns the interface of theoretical nuclear physics, particle physics, astrophysics, and cosmology.
We think that the universe started with a big fireball, aka the Big Bang. After that, there was a period of rapid expansion, or inflation, as the universe cooled. At the end of this inflation, it’s likely that there was just as much matter as antimatter in the universe. This, however, presents a unique problem: If there were an equal number of quarks and antiquarks, we wouldn’t exist because they would cancel each other out. Since we do exist, we know there must be more quarks than antiquarks. If you assume that, at the completion of this inflation, the universe began with a balanced amount of matter and antimatter, that still doesn’t explain why we can touch and see certain things. This form of matter consists of particles called baryons, which are made of quarks. It was after the universe’s initial period of inflation that we believe baryons came to be. Another name for this process is baryogenesis. A simpler way to put this is the act of getting something from nothing.
One amazing facet of baryogenesis is something called the baryon asymmetry, which provides a basis for measuring the probability of baryons, aka any matter, existing in the first place. Since we know that for every 1010 antimatter particles, or antibaryons, the universe must have 1010 + 1 baryons, we are also certain that the baryon-favoring asymmetry is one part in 1010 , which means the probability of any matter existing at all is minuscule.
Baryogenesis theories attempt to address a fundamental question of particle physics and cosmology, basically, “What is the origin and composition of all the matter and energy in the universe?” There’s the biggest fraction, which is dark energy, and dark matter, the next biggest fraction. After that, there’s the smallest fraction, but the one most relevant to everyday life: the baryon fraction. None of those components can be explained by our standard cosmology and model of particle physics.The real question is to understand how all these things came to be at a fundamental level. Understanding baryogenesis is one piece of that pie.
Soviet nuclear physicist Andrei Sakharov realized that the early universe would need three basic ingredients in order for baryogenesis to be successful, which are now known the Sakharov conditions: One is that the baryon number must be violated. The second condition is that both C-symmetry (the symmetry of physical laws under a charge-conjugation transformation) and CP-symmetry (which takes place when a system doesn’t change under both charge-conjugation and parity) were violated at some point in the early days of the universe. The third is that, at some point, the universe shifted out of thermal equilibrium. Imagine a day where the weather’s so muggy that water starts to condense into little droplets—what’s known in physics as a phase transition, which is also an out-of-equlibrium phenomenon. To determine whether Sakharov conditions were in effect during the nascent universe, we must use insturments like the Large Hadron Collider, which may provide us with clues about phase transitions that happened immediately (as in 10-11 seconds) after the Big Bang, and insights into dark matter and dark energy. Equally important are very low-energy, highly precise “tabletop” experiments that look for properties of atoms and neutrons that—if found—would be the “smoking gun” of CP violation.
The more we learn about baryogenesis, the closer we will be to understanding why we exist, as well as how and when existence happened. It’s a question so fundamental that even partially answering it will change the meaning of life in ways we can’t imagine.
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