From Adam Becker at Scientific American:
Quantum physics, Everett pointed out, didn’t really reduce to classical physics for large numbers of particles. According to quantum physics, even normal-sized objects like chairs could be located in two totally separate places at once—a Schrödinger’s-cat–like situation known as a “quantum superposition.” And, Everett continued, it wasn’t right to appeal to classical physics to save the day, because quantum physics was supposed to be a more fundamental theory, one that underpinned classical physics.
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Everett’s work fell into deep obscurity. It wasn’t revived until the 1970s, and even then, it was slow to catch on. Everett did make one last foray into the academic debate over his work; Wheeler and his colleague Bryce DeWitt invited Everett to speak about his work at the University of Texas in 1977. One of the young physicists in Austin at the time was David Deutsch, who later became a staunch advocate of the many-worlds interpretation. Everett “was full of nervous energy, high-strung, extremely smart,” Deutsch recalled. “He was extremely enthusiastic about many universes, and very robust as well as subtle in its defense.”
The work of DeWitt, Deutsch, and others led the many-worlds interpretation to become much more popular over the ensuing decades. But Everett didn’t live to see the many-worlds interpretation achieve its current status as the most prominent rival to the Copenhagen interpretation. He died of a massive heart attack in 1982, at the age of 51. In accordance with his wishes, his family had him cremated, and left his ashes out to be collected with the trash. More.
If people in science have decided to believe this stuff, no one can stop them, but there is also no reason to believe them. Over time, that will matter.
See also: In what sense is Stephen Hawking equivalent to Isaac Newton?
Cosmologist Sean Carroll: A multiverse is “beyond falsifiability” – and that’s okay with him
and
The multiverse is science’s assisted suicide