It's the 'one-electron universe' theory [0]. In short: there is one electron that keeps going back and forth in time to play the role of every electron we see. A particle 'going backwards in time' is mathematically identical to its anti-particle, which we know exists, so the whole idea isn't too far fetched.

I don't think it is falsifiable, so not really scientific, but a fun theory to believe in.

[0]: https://en.wikipedia.org/wiki/One-electron_universe