The Everettian Relative State Interpretation, better known as the Many-Worlds Interpretation, suggests that all possible alternative histories and futures are real. Instead of a single unfolding reality, this theory posits a vast, and possibly infinite, number of universes where every quantum event branches into multiple outcomes, each existing in its own "world." This interpretation was first proposed by Hugh Everett III in 1957 as a solution to the quantum measurement problem.
The core idea behind the Everettian interpretation is that the universe is constantly splitting into multiple copies. Whenever a quantum event occurs with different possible outcomes, reality branches into separate paths. For example, when a photon hits a beam splitter, it doesn't just go one way or the other; instead, the universe divides so that in one reality the photon went through the splitter, and in another, it did not. Each outcome is realized in its own branch.
In this interpretation, the observer becomes part of the quantum system, and their experience is one of the many results in different branches. The universe is thus described by a grand wave function encompassing all possibilities. There is no wave function "collapse" to account for; everything that can happen does happen in some branch.
The weirdest and most captivating aspect of the Everettian interpretation is the notion of parallel universes. This interpretation eliminates randomness and the need for a special "observer" role in quantum mechanics.
Instead of wave functions collapsing into one outcome, all potential outcomes are equally real and exist simultaneously. It challenges our conventional understanding of history and existence, suggesting that every possible timeline is just as real as the one we perceive. For instance, in one universe, you made a different career choice and are living an entirely different life right now.
This multiverse view reshapes many philosophical questions, from the nature of individuality to the concept of fate, and has even led to discussions about "quantum immortality," a thought experiment that explores consciousness surviving beyond fatal events by simply continuing in non-fatal branches of the wave function.
The Many-Worlds Interpretation has gained significant traction in the physics community, with many advocates among quantum physicists and cosmologists. Notable proponents include physicists like David Deutsch and Sean Carroll, who find its deterministic approach compelling. Nonetheless, it remains only one of many interpretations and has both fervent supporters and critics.
The concept of parallel universes and branching realities has permeated popular culture, inspiring countless science fiction works. Movies like "Sliding Doors," TV shows like "Doctor Who," and the "Marvel Cinematic Universe" explore similar themes. In literature, Philip K. Dick often referenced multiple realities, questioning the nature of truth and perception.
On a scale from "rather tame" to "utterly mind-bending," the Everettian Relative State Interpretation leans heavily towards "mind-bending." It's an enthralling theory that challenges our perceptions of reality and encourages open-minded exploration of possibilities.