Have you ever laid wide-awake in the late hours of the night wondering what your life would look like if you took that other job, moved countries, or ended up with someone else? While there’s no definite answer — and probably never will be — the idea that there’s multiple versions of you, living in various universes, isn’t as make-believe as you might think. 

According to Sean Carroll, a theoretical physicist at the California Institute of Technology and author of Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime, the increasingly popular theory of Many Worlds Interpretation suggests every fundamental event has multiple possible outcomes and splits the world into alternate realities. 

The birth of the multiverse

This mind-bending idea originally came from Hugh Everett, a graduate student who wrote just one paper in the 1950s. Everett’s theory describes the universe as a “changing set of numbers, known as the wave function, that evolves according to a single equation.” According to Many Worlds, the universe continually splits into new branches, to produce multiple versions of ourselves. Carroll argues that, so far, this interpretation is the simplest possible explanation of quantum mechanics. 

“The ideas we have had for at least 25 years, before Everett came along, was this puzzle in quantum mechanics that there’s one set of rules of how wave functions behave when you’re not looking at them and there’s another set of rules for how they behave when they get measured,” Carroll told TNW. 

According to Live Science, quantum mechanics is the body of scientific laws that describe the bizarre behavior of photons, electrons, and any other particles that make up the universe. At the scale of atoms and electrons, many of the equations of classical mechanics, which describe how things move at everyday sizes and speeds, cease to be useful.

“A lot of people, including Everett, thought this didn’t sound right, he said you are quantum mechanical also because you’re made of atoms and particles, and there’s only one wave function so you’re really part of this function.”