Yes, that is a superposition! I don’t think it can leave any “ghastly traces”—there are billions or more particles which moved differently (at least several angstroms away) depending on which exact number you see in my comment, and interference—even on amplitude level—fades. Presumably exponentially.
Ok. That’s an argument for decoherence..but not an argument for multi branch decoherence.
And minor remnants can be left, so long as they stay minor… they are not going to affect observation much. (Although the reasons for that could be cosmological..an expanding universe with slightly negative curvature is the ideal way to get rid of unwanted information).
What would happen to decoherent branches which had their distinguishing features “evolve out to nothing” (become very close to “our” branch)? They will come back and influence the amplitudes and probabilities we observe once again.
But not much? Theres an argument that decoherent splitting can’t be completely irrevocable, because it emerges from time reversible microphysics … but there’s also an argument that the “losing” branches spread out, and become so thinly distributed in the overall mish mash that they can no longer matter in practice..and for for macrophysical reasons.
Though it is very convenient when the wavefunction factors into several world parts—say, it would be very strange if my generating a random number would influence a LW non-reader—in that sense they can subjectively just not consider that I had done anything.
That’sexactly how decoherent branching works .. if it works. It’s not a causal process that leaves causal traces.
but there’s also an argument that the “losing” branches spread out
They don’t spread much faster compared to “winning” branches I guess? World has no particular dependence on what random number I generated above, so all the splits and merges have approximately same shape in either of the eight branch regions.
That’sexactly how decoherent branching works .. if it works. It’s not a causal process that leaves causal traces.
With a remark that “decoherent branching” and “coherent branching” are presumably just one process differing in how much the information is contained or spreads out, and noting that should LW erase the random number from my comment above plus every of us to totally forget it, the branches would approximately merge,
yes I agree. Contents of worlds in those branches do not causally interact with us, but amplitudes might at some point in future. AFAIK Eliezer referenced the latter while assigning label “real” to each and every world (each point of wavefunction).
They don’t spread much faster compared to “winning” branches I guess
They don’t spread faster, they spread wider. Their low amplitude information is smeared over an environmental already containing a lot of other low amplitude information, noise in effect. So the chances of recovering it are zero for all practical purposes.
With a remark that “decoherent branching” and “coherent branching” are presumably just one process differing in how much the information is contained or spreads out
Well, no. In a typical measurement, a single particle interacts with an apparatus containing trillions, and that brings about decoherence very quickly, so quickly it can appear like collapse. Decoherent branches, being macroscopic , stable and irreversible, for all practical purposes, are the opposite to coherent ones.
Ok. That’s an argument for decoherence..but not an argument for multi branch decoherence.
And minor remnants can be left, so long as they stay minor… they are not going to affect observation much. (Although the reasons for that could be cosmological..an expanding universe with slightly negative curvature is the ideal way to get rid of unwanted information).
But not much? Theres an argument that decoherent splitting can’t be completely irrevocable, because it emerges from time reversible microphysics … but there’s also an argument that the “losing” branches spread out, and become so thinly distributed in the overall mish mash that they can no longer matter in practice..and for for macrophysical reasons.
That’sexactly how decoherent branching works .. if it works. It’s not a causal process that leaves causal traces.
They don’t spread much faster compared to “winning” branches I guess? World has no particular dependence on what random number I generated above, so all the splits and merges have approximately same shape in either of the eight branch regions.
With a remark that “decoherent branching” and “coherent branching” are presumably just one process differing in how much the information is contained or spreads out,
and noting that should LW erase the random number from my comment above plus every of us to totally forget it, the branches would approximately merge,
yes I agree. Contents of worlds in those branches do not causally interact with us, but amplitudes might at some point in future. AFAIK Eliezer referenced the latter while assigning label “real” to each and every world (each point of wavefunction).
They don’t spread faster, they spread wider. Their low amplitude information is smeared over an environmental already containing a lot of other low amplitude information, noise in effect. So the chances of recovering it are zero for all practical purposes.
Well, no. In a typical measurement, a single particle interacts with an apparatus containing trillions, and that brings about decoherence very quickly, so quickly it can appear like collapse. Decoherent branches, being macroscopic , stable and irreversible, for all practical purposes, are the opposite to coherent ones.