### Symmetry is beautiful, but asymmetry is why the Universe and life exist

Marcelo Gleiser / Big Think:

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We left-handed people are a minority among humans, roughly a 1:10 ratio. But make no mistake: the Universe loves left-handedness, from subatomic particles to life itself. In fact, without this fundamental asymmetry in Nature, the Universe would be a very different place bland, mostly filled with radiation, and without stars, planets, or life. Still, there is a prevalent aesthetic in the physical sciences that pushes for mathematical perfection expressed as symmetry as the blueprint for Nature. And, as is often the case, we get lost in a falsely fabricated duality of having to choose camps: are you for “all is symmetry” or are you an imperfection iconoclast? (The interested reader can check my book about this, where I cover a lot of what follows.)

Antimatter: why physicists love symmetry

We all love Keats’ famous line, “Beauty is truth, truth beauty.” But if you insist in equating Keats’ beauty with mathematical symmetry as a path toward finding the “truth” about natural laws something that is quite common in theoretical physics the danger is that you relate symmetry with “truth” in such a way that the mathematics we use to represent the Universe through physics should reflect mathematical symmetry: the Universe is beautifully symmetric, and the equations we use to describe it must reveal this beautiful symmetry. Only then we can approach the truth.

Quoting the great physicist Paul Dirac, “It is more important to have beauty in one’s equation than to have them fit experiment.” If any other less known physicist said that, they would probably be ridiculed by colleagues, considered a crypto-religious Platonist, or a quack. But that was Dirac, and his beautiful equation, built upon symmetry concepts, did predict the existence of anti-matter, the fact that every particle of matter (like electrons and quarks) has a companion anti-particle. That’s a truly amazing accomplishment the mathematics of symmetry, applied to an equation, guided humans to discover a whole parallel realm of matter. No wonder Dirac was so devoted to the god of symmetry. It guided his thought toward an amazing discovery.

Note that antimatter doesn’t mean anything as eccentric as it seems. Anti-particles do not go up in a gravitational field. They have a few of their physical properties reversed, most notably electric charge. So, the anti-particle of the negatively charged electron, called the positron, has a positive electric charge.

We owe our existence to asymmetry

But here is the problem that Dirac didn’t know about. The laws that dictate the behavior of the fundamental particles of Nature predict that matter and anti-matter should be equally abundant, that is, that they should appear in a 1:1 ratio. For each electron, one positron. However, if this perfect symmetry prevailed, fractions of a second after the Big Bang, matter and antimatter should have annihilated into radiation (mostly photons). But that’s not what happened. About one in a billion (roughly) particles of matter survived as an excess. And that’s good, because everything that we see in the Universe — the galaxies and their stars, the planets and their moons, life on Earth, every kind of matter clump, living and nonliving came from this tiny excess, this fundamental asymmetry between matter and antimatter.

Contrary to the expected symmetry and beauty of the cosmos, our work in the past decades has shown that the laws of Nature do not apply equally to matter and antimatter. What mechanism could have created this tiny excess, this imperfection that is ultimately responsible for our existence, is one of the greatest open questions in particle physics and cosmology.