In both cases charge is conserved and we meet our conservation law about baryon number equaling lepton number. The Y's can decay into either a proton (one baryon) and an electron (one lepton), or an anti-neutron (one anti-baryon) and one anti-neutrino (one anti-lepton).
MATTER VS ANTIMATTER FULL
So let's say the Universe is full of - among other things - Y's and Y*'s. The one way they're allowed to be different is known as CP violation, which means that particles can decay through one decay route more frequently than their antiparticles do, and antiparticles can decay through an alternate route more frequently. We also have to conserve charge, and we need for the Y and the Y* to allow the same types of decays. We need to produce a lepton for every baryon we produce, and an anti-lepton for each anti-baryon we produce. This is both necessary and reasonable in fact, it seems unreasonable to imagine that we've discovered every single particle in the Universe, considering that there's such a significant energy range left to explore. Imagine that we have a new particle called Y, which is neutral and unstable, and its antiparticle, Y*. There are many different ways, including (here come some scientific names) GUT baryogenesis, leptogenesis, electroweak baryogenesis, and the Affleck-Dine mechanism.īut let's make up a way to do this that's even simpler than any of these, just to show you how this is possible. This works out to be amazingly convenient, because we do have a Universe with equal numbers of protons and electrons! But, I wanted to tell you how this happened. And finally, whatever it is that they decay into, there is a conservation law telling us that the net number of baryons (protons & neutrons) must equal the net number of leptons (electrons and neutrinos) that you create. Because of symmetries between matter and antimatter, they need to have the same total decay rate, which means they need the same lifetime and they need to be able to decay into the opposite, corresponding particles.
First off, if you have an unstable matter particle, its corresponding antimatter particle is also unstable. So what happened? Well, we know that there are a few constraints between matter and antimatter. (This is down by a factor of about 10 20 from the particles & antiparticles that existed at the end of inflation.) So something had to have happened that made the Universe choose matter over antimatter, and at the level of about one extra matter particle for every billion matter/antimatter particles out there, otherwise nearly everything would have annihilated away into photons (i.e., light) by now. But if this was all we had in the Universe - matter and antimatter in equal amounts - they would annihilate away (like matter and antimatter are wont to do), until there were so few particles left that they couldn't find each other in this huge and expanding Universe.īut this didn't happen if it did, only one in every hundred billion particles that exist now would still be here, and half of them would be antiparticles. They're also way more abundant at this time - by about a factor of a billion - than matter particles are today. This means electrons, muons, taus, all six quarks, neutrinos, and all of their antiparticles in equal abundance, in addition to whatever else may be out there. What you need to do, if you want to understand what the Universe looked like at this time, is imagine the tiniest point particles and all of their antiparticles, flying around in great abundance, as close to the speed of light as the conservation of energy allows them. It was so energetic that there were no atoms, nuclei, or even protons or neutrons. The radiation and these particles were incredibly energetic, even compared to anything we've ever created in a laboratory. This part, when inflation ended, could be called the "classical" big bang. Then inflation ended, and all the energy that was making it inflate got dumped into particles and radiation. The Universe inflated first, stretching it flat and making it uniform, both everywhere in space and in all directions equally. Here's the explanation, starting at the beginning. And many of you correctly responded that I had given too much detail and not enough explanation. Yesterday, I wrote to you about part 5 of The Greatest Story Ever Told, about how the Universe came to have more matter than antimatter in it.
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