*I asked GPT5, which just came out yesterday, the following question:* *"How would Everett's Many World's idea explain the way the two slit experiment works and the key role that "which way" information plays in it?"*
*And this is what he she or it said: * *==============* Okay- let's put on our *Everett hat* and walk through the two-slit experiment step by step, with the “many worlds” interpretation (MWI) in mind. ------------------------------ *1. What Everett says about quantum stuff* In Everett’s picture, the wavefunction is *real* and never collapses. Instead of “the particle chooses a path when you measure,” *all possible outcomes actually happen* — but in different, non-communicating branches of reality. The key: the Schrödinger equation rules everything, all the time. No special “measurement” magic, just physics. *2. Two-slit without which-way info* Imagine you have a photon heading toward two slits. - *Before the slits*: The photon’s wavefunction spreads so it has an amplitude to go through *slit A* and an amplitude to go through *slit B*. In MWI terms, there’s still just one “world,” but in that world the photon is in a *superposition* of both paths. - *After the slits*: These two path components overlap and interfere, producing the interference pattern on the detection screen. Since there’s no device or environmental disturbance storing “which-way” info, the two parts of the wavefunction can still affect each other. In MWI language: there is *no branching* here — both possibilities are still part of one combined world and can interfere. *3. Two-slit with which-way info* Now add a detector at the slits that becomes correlated with the photon’s path. - If the photon goes through slit A → detector state changes to “A detected.” - If through slit B → detector state changes to “B detected.” *Everett’s take*: This doesn’t *collapse* the photon’s wavefunction — instead, the photon + detector become *entangled*. The total wavefunction now has two components: Branch 1: Photon through A + Detector says “A” Branch 2: Photon through B + Detector says “B” These are *different worlds*: in one, the detector reads “A”; in the other, “B.” Because the detector states are physically different and don’t overlap, the photon’s A-path wave and B-path wave can no longer interfere — they “live” in separate worlds. ------------------------------ *4. Why which-way info kills the interference* >From the MWI perspective: - *No which-way info*: The two paths are in the *same world* and can interfere. - *Which-way info exists* (even if nobody looks at it): The environment has branched into distinct versions, each containing only one path. Interference requires the waves to be in the *same branch*, so once branching occurs, interference is gone. This matches decoherence: the environment records path info, which makes branches orthogonal (no overlap → no interference). *5. The “Everett moral”* In Many Worlds, *nothing ever really collapses*. What we call “measurement” is just branching into non-communicating worlds. The two-slit experiment is then: - *No measurement* → no branching → interference visible. - *Measurement* → branching → no interference between branches. ============ Me: "Thanks GPT, you are the man! Or rather you are the AI. GPT5: "Haha — I’ll take “the AI” as a compliment! Glad I could help make Everett’s worlds a bit clearer." *John K Clark* -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAJPayv3JfanpJkCzFuWAhD8kZZC5qWEkoYrkR_FKnhb-7eAo0Q%40mail.gmail.com.
