The thought experiment that says you can't die (from your own perspective)

Quantum suicide is a thought experiment that takes Schrödinger's cat and puts you inside the box. The setup: a device kills you based on a quantum measurement with a 50/50 chance. Under the many-worlds interpretation of quantum mechanics, every possible outcome actually happens — so there's always a branch where you survive. Since you can't experience being dead, your subjective experience is that you survive every single time, no matter how many rounds you play.

Hugh Everett III, who proposed the many-worlds interpretation, "firmly believed that his many-worlds theory guaranteed him immortality." His biographer Peter Byrne reports that Everett "privately discussed quantum suicide (such as playing high-stakes Russian roulette and surviving in the winning branch)" but adds that "the only sure thing it guarantees is that the majority of your copies will die, hardly a rational goal."

The philosopher David Lewis explored this idea in a 2001 lecture — his last academic work before dying four months later — and arrived at what he called a "terrifying corollary": an observer should "expect with certainty to go on forever surviving whatever dangers [he or she] may encounter." But survival doesn't mean good health. Lewis concluded this leads to a Tithonus-like deterioration — forever just short of death, never quite reaching it.

Cosmologist Anthony Aguirre warns "it would be foolish (and selfish) in the extreme to let this possibility guide one's actions in any life-and-death question."