You probably remember electrons from science class. They're stable subatomic particles that have a negative electrical charge. They're found in atoms and are the primary carrier of electricity in solid materials. But, what you probably haven't heard of, is the idea that each and every electron in existence... is actually the exact same electron.
This theory states that every electron in the universe is actually one particle that continually travels backward and forward through time. There is a lot of complicated math involved, but it does solve some of quantum physics biggest unanswerable questions.
The theory was first thought up by John Archibald Wheeler, a theoretical physicist who worked on the hydrogen bomb at Los Alamos and later taught at Princeton. He is largely known for reviving interest in general relativity in the 1940s and 1950s.
Like many quantum theories, the idea that every electron is the same electron, known as the One Electron Theory, is more of a thought experiment than a theory.
So let's break it down.
Electrons all look the same
One of the biggest reasons that this thought experiment was proposed by Wheeler is that each and every electron looks exactly the same. They all have the same mass and the same electric charge.
This ultimately means that it's impossible to tell electrons apart at all. So, it's not surprising that Wheeler thought up the idea that if all electrons look the same and act the same, then maybe they are the same electron.
Proposing that the entire universe contains just one electron may not seem all that absurd, when we consider that the only change would be to the idea of what an electron is. In practicality, everything would still function the same.
According to the One Electron theory, in the same way as an electron can be bounced around in space when hit with light, the electron might also be able to bounce backward in time. The consequence of this is that electrons moving backwards in time are positrons, the antimatter component of electrons. So, not only are all electrons the same electron, but all positrons are also the same electron moving backward.
As a professor, Wheeler taught the now-famous physicist Richard Feynman, when he was a doctoral student. Feynman famously brought up Wheeler's theory when he accepted his Nobel Prize in 1965. Here's what Feynman said:
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." "Why?" "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."
To many physicists, what Wheeler was proposing really didn't seem that absurd. Physicists were already working with the idea of electrons and positrons, Wheeler just proposed a way to connect every single one in existence simultaneously as a way of explaining why no one could tell the difference between them.
What would this theory actually look like?
It is estimated that there are roughly 10 to the power of 80 atoms in the universe. If we ignore the fact that many atoms have more than one electron, we can simplify the number of electrons in the universe as around 10 to the power of 80.
Although electrons are treated as stable for theoretical purposes, the experimental lower bound for the electron's mean lifetime is often given as 6.6×1028 years. Using this, we can get an idea of how this theory actually plays out.
The theory and these numbers imply that the one electron in existence has traveled through the universe 1080 times, each time taking 460 septillion years. We can double these numbers for each time that the electron had to go back through time, which equates to the one electron in the One Electron Theory being 10105 years old.
The data flaw in the theory
All of this is rather interesting to consider, but there's an issue at the root of this thought experiment.
If a single electron travels forward through time as an electron and backward through as a positron, that would mean that at any given point, there should be the same number of positrons as there are electrons.
We know this is not true, and since that is the case, we can deduce with strong confidence that the One Electron Theory cannot hold.
It is likely that Wheeler knew this was the case all along. In his memoir, he writes:
"I knew, of course, that, at least in our corner of the universe, there are lots more electrons than positrons, but I still found it an exciting idea to think of trajectories in spacetime that could go unrestricted in any direction — forward in time, backward in time, up, down, left, or right."
Wheeler was nearly certain that his thought experiment wasn't a reflection of actual quantum reality, but he did note that the idea that there aren't the same number of positrons as electrons is only true for our observable universe. It's possible that it isn't the case for the sum total of the universe.
At the end of the day, the One Electron Theory is a rather interesting thought experiment to ponder, even if physics isn't your jam. To think that it's theoretically possible, although highly unlikely, that a particle that exists everywhere throughout the universe is actually the same particle, traveling through time – well, that's pretty cool.