Does Antimatter Explain Why There's Something Rather Than Nothing?

**SPEAKER_1** (0:00)
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**Matt O'Dowd** (0:56)
The most precious substance in our universe is not gold, nor oil. It's not even printer ink. It's antimatter. But it's worth every penny of its very high cost, because it may hold the answer to the question of why anything exists in our universe at all.
Each particle in our universe has its exact counterpart. An antiparticle. Identical in every way, but with the opposite charge and spin. An electron has a positron, a proton has an antiproton, and so on.
And when a particle encounters its antiparticle partner, when matter encounters antimatter, the two can pair annihilate, canceling each other out completely, and leaving only two photons to carry away their energy. And it works in reverse too. Particle and antiparticle pairs can be created from pure radiation. In fact, that's how we think the first particles were created in the very early universe. But if matter and antimatter are always created in pairs, then in the beginning of time there should have been exactly the same amount of both. So where is all of the antimatter?
The better question is, why is there any matter at all? Shouldn't everything just have annihilated again, leaving only a vacuum bathed in light? The most likely answer seems to be that the universe started out with a little more matter compared to antimatter. If there were slightly more particles than antiparticles, then almost everything would have annihilated, leaving the universe full of photons, and only very few particles that couldn't find an annihilation partner.
These days there are around a billion times more photons than there are particles of matter, so we estimate that for every billion particles of matter that annihilated, only one survived. And there's the mystery. Why were particles created with that one in a billion overabundance compared to antiparticles? It seems there must be something inherently different in the way the universe interacts with particles versus antiparticles. The universe must not treat the two symmetrically. Indeed, many physicists think that the answer lies in the fundamental symmetries of the universe, or, rather, in the breaking of these symmetries. We've discussed this before. There are three symmetries of the universe that physicists once believed were fundamental. You should be able to perform any of these transformations, or all of them, and the laws of physics should be unchanged. We have charge conjugation, where positive and negative charges are swapped. We have parity inversion, where the universe is reflected through a mirror. And time reversal, where all particles have their direction of motion and spins exactly reversed. If you apply all three of these transformations to a particle, if you apply a CPT transformation, then With the under $3 menu of McDonald's, a McChicken is only $2.

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**Matt O'Dowd** (4:26)
It becomes its own antiparticle. Because we expect the universe to be CPT symmetric, we expect it to treat antimatter in exactly the same way as regular matter. But one by one, these presumed symmetries failed. The first to fall was parity, with Chiangchung Wu's famous Cobalt 60 experiment proving that a mirror image of our universe would be distinguishable from our own. Then charge and parity combined, or CP, also fell, with the observation of the peculiarity in the decay of K-mesons.