So did you ask it how MWI deals with continuous splitting, as in
detecting the decay of radioactive atoms?
Brent
On 8/8/2025 6:19 AM, John Clark wrote:
*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*
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