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Home SCIENCE What was it like when the last antimatter disappeared? | by Ethan Siegel | Starts With A Bang! | Dec, 2023

What was it like when the last antimatter disappeared? | by Ethan Siegel | Starts With A Bang! | Dec, 2023

by California Digital News

Bubble chamber tracks from Fermilab, revealing the charge, mass, energy and momentum of the particles and antiparticle created. This recreates similar conditions to what was present during the Big Bang, where matter and antimatter can both be readily created from pure energy. At the highest energies, all particles and antiparticles can be created, but at energies corresponding to “only” a temperature of ~10 billion K or so, electron-positron pairs can still be spontaneously created. (Credit: Fermi National Accelerator Laboratory/DOE/NSF)

In the early stages of the hot Big Bang, matter and antimatter were (almost) balanced. After a brief while, matter won out. Here’s how.

Things happen fast in the earliest stages of the Universe. In the first 25 microseconds after the start of the hot Big Bang, a number of incredible events have already occurred. The Universe created all the particles and antiparticles — known (as part of the Standard Model) and unknown (including whatever makes up dark matter) — it was ever capable of creating, reaching the highest temperatures it ever attained. Through a still-undetermined process, it created an excess of matter over antimatter: just at the 1-part-in-a-billion level. The electroweak symmetry broke, allowing the Higgs to give mass to the Universe. The heavy, unstable particles decayed away, and the quarks and gluons bound together to form protons and neutrons.

But that only gets us so far. At these early stages, there may be protons and neutrons in the Universe, as well as a high-energy bath of photons and neutrinos-and-antineutrinos, but we’re still a long way from the Universe as we recognize it today. In order to get there, a number of other things must occur. And the first of those, once we have protons and neutrons, is to get rid of the last of our antimatter, which is still incredibly abundant.

At the high temperatures achieved in the very young Universe, not only can particles and photons be spontaneously created, given enough energy, but also antiparticles and unstable particles as well, resulting in a primordial particle-and-antiparticle soup. Although the laws of physics are largely symmetric between matter and antimatter, it’s very clear that today’s Universe is filled with matter and nearly completely devoid of antimatter. Any asymmetry must have been generated in the very early Universe, shortly following the hot Big Bang. (Credit: zombiu26 / Adobe Stock)

You can always make antimatter in the Universe, so long as you have the energy for it. Einstein’s most famous equation, E = mc², works two ways, and it works equally well for both applications.

  1. It can create energy from pure matter (or antimatter), converting mass (m) into energy (E) by reducing the amount of mass present, such as by annihilating equal parts matter with antimatter.
  2. Or it can create new matter from pure energy, so long as it also makes an equivalent amount of the antimatter counterparts for each matter particle it creates.

These annihilation-and-creation processes, so long as there’s enough energy for creation to proceed smoothly, balance…

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