Quoting [this page from CERN](https://home.cern/science/physics/matter-antimatter-asymmetry-problem):
>If matter and antimatter are created and destroyed together, it seems the universe should contain nothing but leftover energy.
>Nevertheless, a tiny portion of matter – about one particle per billion – managed to survive. This is what we see today.
But if the difference is a billion universe’s worth of matter-antimatter annihilations, shouldn’t there be a billion times more of this ‘leftover energy’ in the universe than we see today?