What if every electron in the universe is actually the exact same electron?
This idea, called the one-electron universe, came up during a telephone conversation between theoretical physicists John Wheeler and Richard Feynman back in 1940.
Electrons and positrons, Wheeler suggested, are actually a single entity moving forwards and backwards in time.
As the electron moves forwards, he mused, it is observed as an ordinary electron; as it moves backwards, it is observed as a positron (a positively-charged electron). To us, living one-way through time as we do, these electrons and positrons seem to individually fill the universe, each with their own world lines. But this is an illusion. In reality, we’re observing the same particle repeatedly at different points in a single world line that resembles a “tremendous knot.”
Or something like that.
Wheeler proposed this idea in order to explain one peculiar fact about our universe: every electron is exactly the same — the same charge, mass, and spin — as every other electron. Richard Feynman recounted his conversation with Wheeler in his Nobel lecture on December 11, 1965:
“…I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, ‘Feynman, I know why all electrons have the same charge and the same mass’
‘Because, they are all the same electron!’
And, then he explained on the telephone, ‘suppose that the world lines which we were ordinarily considering before in time and space – instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing. If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time – to the proper four velocities – and that’s equivalent to changing the sign of the charge, and, therefore, that part of a path would act like a positron.’
‘But, Professor’, I said, ‘there aren’t as many positrons as electrons.’
‘Well, maybe they are hidden in the protons or something’, he said.
I did not take the idea that all the electrons were the same one from him as seriously as I took the observation that positrons could simply be represented as electrons going from the future to the past in a back section of their world lines. That, I stole!”
As Feynman said, the idea that all electrons in the universe are the same electron wasn’t something he took seriously. Neither did John Archibald Wheeler, for that matter, and he’s the one who came up with it! But Wheeler was an unending well of incredible ideas.
For example, another of his students, Hugh Everett III, would go on to propose the Many-worlds interpretation of quantum mechanics. And we all know how that goes.
Just as an addendum: I wanted to share this “one electron” business because it reminds me of an interesting short story I once read right here on the Internet. It’s called “The Egg,” written by Andy Weir. I don’t want to give anything away, because it’s very, very short, but I think it’s worth it look. You can read it here.