Quantum mechanics is the branch of physics that describes the rules that govern the universe on the microscopic scale. It tries to explain how subatomic particles can behave as both particles and as waves. It also offers an explanation about why particles appear to exist in multiple positions at the same time. [ The 9 Biggest Unsolved Mysteries in Physics ]
This fuzzy clump of possible positions is described by a "wave function" — an equation that predicts the many possible spots a given particle can occupy. But the wave function collapses the second anyone measures the actual position of the particle. This is where the multiverse theory comes in.
Some physicists believe that once a particle's position is measured, the many other positions it could take according to its wave function split off and create separate, parallel worlds , each only slightly different from the original.
Hugh Everett was the first physicist to propose the possibility of a multiverse — an infinite number of parallel universes that exist alongside our own. He published his "Many Worlds" theory in the 1950s, but the idea was not well-received in the academic world.
Everett ended his career in physics shortly after getting his Ph.D., but many physicists now take the multiverse and parallel-worlds idea seriously. Poirier reworked the Many Worlds theory into the less abstract "Many Interacting Worlds" (MIW) theory, which could help explain the weird world of quantum mechanics.
Quantum mechanics has existed for more than a century, but its interpretation is just as controversial today as it was 100 years ago, Poirier wrote in his original paper.
Albert Einstein was not a fan of quantum mechanics. The idea that a particle could exist in a haze of probability instead of a definite location did not make sense to him, and he once famously said, "God does not play dice with the universe." However, this new MIW theory might have helped to put Einstein's mind at ease. In the MIW theory, quantum particles don't act like waves at all. Each parallel world has normal-behaving particles and physical objects. The wave-function equation doesn't have to exist at all.