There are infinite timelines and infinite yous
Quantum physics is mind-bending, counter-intuitive, and close to impossible to understand. It’s so complicated that a theory saying our reality is just one of an infinite web of infinite timelines is one that’s actually simpler than what most quantum physicists believe. That neat-and-tidy explanation is known as the many-worlds interpretation, and it has caused plenty of controversy in physics circles.
In the 1950s, a student at Princeton University named Hugh Everett III was studying quantum mechanics. He learned about the Copenhagen interpretation, which says that at the very, very smallest level — what we mean when we say quantum — matter exists not just as a particle and not just as a wave, but in all possible states at once (all of those states together is called its wave function; the phenomenon of existing in all of those states at once is called superposition). It also says that when you observe a quantum object, you break that superposition and it essentially “chooses” one state to be in. He also learned about the Heisenberg Uncertainty Principle, which says that because we affect a quantum object’s behavior through observation, we can never be completely certain where it is or what it’s doing at any given time.
Everett understood these principles, but he took issue with one part: what if, instead of a quantum object “choosing” a state when you observe it — say, it becomes a particle instead of a wave — there was an actual split in the universe that created separate timelines? According to Everett’s theory, in this timeline, the object is a particle, but there’s another timeline where it’s a wave. Even more baffling, this implies that quantum phenomena aren’t the only things that split the universe into separate timelines. For everything that happens, every action you take or decide not to take, there are infinite other timelines — worlds, if we may — where something else took place. That’s the many-worlds interpretation of quantum physics. It may not seem like it, but it’s actually simpler than the Copenhagen interpretation — it doesn’t strike an arbitrary line between the quantum world and everything else, because everything behaves in the same way. It also removes randomness from the picture, which helps the math work out nicely.
Not all physicists subscribe to this theory — a recent poll found that the majority are Copenhagen all the way — but a growing minority do. Sean Carroll, for one. He explains that many objections to the theory arise because people come at it from a classical physics point of view. “In classical mechanics…it’s quite a bit of work to accommodate extra universes, and you better have a good reason to justify putting in that work,” he writes. “That is not what happens in quantum mechanics. The capacity for describing multiple universes is automatically there. We don’t have to add anything.”
If the many-worlds interpretation is true, what does this say about the nature of reality? It says there are infinite versions of you living in infinite alternate timelines. There’s a version of you that got out of bed on a different side this morning, one that ate a different breakfast, one that has differently colored hair, one that’s a different gender, one that’s a foot taller, one that’s a psychopath, one that — we can hardly stomach it! — didn’t decide to read this article. That might make you feel less than unique. On the contrary, the you that you are right now is the only you there will ever be. The moment you do anything, the universe splits and you’re a you that’s living in a different timeline than the you that didn’t take that action. Wild, isn’t it?