Single Electron Theory
Antimatter is similar to the matter that appears to make up most of the universe we have observed except that it has an opposite charge. One example of this is the positron which is just like an electron except that it has a positive charge instead. Everything like the mass and the spin is identical.
Sometimes a matter and antimatter pair will pop into existence ravelling in opposite directions so as to preserve momentum. However, because they have opposite charges they attract each other and usually smack back into each other after a short amount of time where they annihilate and pop out of existence again. However sometimes they manage to escape each other if other matter intervenes with enough force to tear them apart. This happens on the event horizon of black holes in a process predicted and named after Stephen Hawking: Hawking radiation. Because black holes are strong enough to prevent light escaping them, you would think that they would be hard to spot. However, with the huge surface area that the event horizon around the hole presents that makes a lot of active sites for matter and antimatter pairs to be torn apart on, with one particle falling into the hole and the other escaping into space. It is this escaping particle that we can observe.
But you can frame the annihilation of an electron and positron in a different way. If you think of the electron travelling through space, but then bouncing on, well something, and starting to travel backwards through time. Something with a negative charge revelling forward in time is identical to something with a positive charge travelling backwards through time. So instead of a positron and an electron meeting and then disappearing, you can think of it as an electron turning into a positron.
At the other end of time, you can think of the positron turning around and becoming an electron again. One consequence of this is that you can think of the universe as only having a single electron which is bouncing backwards and forwards in time. Because all electrons are identical in spin, mass, charge etc. there is no examination that we can do to test this and so it is impossible to say that this isn’t true. It even goes some way to explain why all electrons are identical. Similar arguments can be made for all of the fundamental particles.