Experiments like the double slit experiment have spawned multiple interpretations of quantum physics, including the Copenhagen interpretation and Pilot Wave Theory. But the Many Worlds Hypothesis might be the most mind-blowing of all.
The most popular interpretation of quantum mechanics over the past hundred years was developed by Niels Bohr and Werner Heisenberg in Copenhagen, around 1925. This was fittingly named the Copenhagen Interpretation.
Louis de Broglie [de Broy] came up with the Pilot Wave Interpretation of Quantum Mechanics at about the same time, which I’ve also covered.
Both of these interpretations share the belief that the measured path of a particle is the only real path. The other paths are mere possibilities.
About 30 years later, a slightly drunk Princeton student disagreed. While sipping sherry, or so the story goes, Hugh Everett III started asking, what if all the paths do exist, but are just taken in different realities?
Everett’s ideas were… not well received to say the least. At the time, Niels Bohr was then alive and active in scientific circles. He had a reputation for shutting down any physicist who dared challenge the Copenhagen Interpretation.
And that was where the idea stayed, relegated to the dustbin of history, for the next 2 decades, before it got rediscovered by Bryce DeWitt.
He was the acting editor at Reviews of Modern Physics in 1973 when he ran across the paper and was stunned that nothing ever came of this idea.
Since the 1970s, the Many Worlds Interpretation has gone from being fringe science to an idea mainstream physicists can get behind.
Stephen Hawking was a fan, as was Richard Feynman...though to hear physicists tell it, Feynman was a fan of literally EVERYTHING.
One prominent proponent of Many Worlds working today is David Deutsch, who is a quantum computer pioneer whose cool factor went through the roof when he was mentioned in Avengers: Endgame.