Summary
Highlights
Quantum mechanics describes a universe where particles exist in superpositions, defying classical determinism. The double-slit experiment illustrates this weirdness, where single electrons act as waves, passing through both slits until observed, then behaving like particles. This behavior leads to fundamental questions about the nature of reality and measurement in quantum theory.
The Copenhagen interpretation suggests that superposition states collapse upon observation. However, this raises issues like Schrödinger's Cat, where a cat in a box is simultaneously dead and alive until observed. This highlights the problems with defining 'observation' and the role of consciousness, as well as the arbitrary nature of wave function collapse in this interpretation.
Hugh Everett proposed the many-worlds interpretation, where the wave function never collapses. Instead, all possible outcomes of a quantum measurement occur in separate, non-interacting branches of reality. Decoherence explains why these branches don't interfere, leading to a classical appearance. This branching, initiated since the Big Bang, implies a stupendous number of universes.
Max Tegmark popularized the concept of quantum Russian roulette: a gun fires based on a quantum measurement. According to many-worlds, a version of you would always survive, experiencing continuous clicks, thus proving the theory. This implies personal immortality, as your consciousness would only follow branches where you remain alive, leading to a 'strangely private proof'.
Philosopher David Lewis expanded this to universal quantum immortality, suggesting that all causes of death have quantum probabilities of survival. This means a version of you would always escape fatal events but would likely lead to a deteriorating, eternally tormented existence known as 'Struldbrugg' years, as you would accumulate injuries and outlive loved ones.
The concept faces challenges regarding the imperceptibility of unconsciousness and sleep, and the mediocrity principle suggests it's unlikely we'd be in our youthful state if we live forever. However, these are not definitive dismissals. The core issue lies in David Lewis's 'corrected intensity rule,' which discards branches where one dies, a move that critics like David Deutsch and David Papineau dispute as an arbitrary addition to quantum theory.
Analogies like Star Trek transporters highlight the difficulties with identity in a branching universe. If a transporter malfunction creates two versions of you, which one is 'you'? Sean Carroll argues against Lewis's premise that not experiencing death makes it acceptable. The core debate shifts to the nature of consciousness and selfhood in a multiverse, with some suggesting many-worlds dismantles the very notion of 'self'.
Quantum immortality, similar to the black hole information paradox, suggests a collision between quantum mechanics and our understanding of self. The Cuban Missile Crisis serves as an example of how 'improbable' events could lead to our current existence in certain branches. While the concept is hard to rigorously dismiss, many argue against its plausibility, especially the idea of an ever-deteriorating immortal self. However, the many-worlds interpretation does imply that in other branches, positive outcomes and alternative lives for us and our loved ones do exist, offering a source of inspiration and comfort.