In general, I find physics to be the closest science to philosophy; I think we sell ourselves short to say that the one cannot inform the other.

The discussion so far has lacked a recognition of the importance of the philosophical struggle that has taken place in science in relation to the one in the greater society. In “The Ten Assumptions of Science” and “The Scientific Worldview” I framed that struggle, not as a battle between materialism and idealism, but as the opposition between determinism and indeterminism. I did this to establish a modern determinism (univironmental determinism) as the philosophical goal for scientists as well as for those interested in the scientific worldview. We can discard indeterminism altogether, but we can never discard idealism. We just need to put it in its proper place.

One decoherence argument looks at e.g. randomly-varying, relative phase shifts between different instances of a run of shots of single photons into a Mach-Zehnder interferometer. Their case goes, the varying phases cause the output to be random from either A or B channel instead of any guaranteed output (into e.g. A channel), that is otherwise dictated by interference – in the normal case where phase is strictly controlled. They tend to argue, such behavior has become “classical.” Somehow we are thus supposedly moved away from even worrying about what happened to the original superpositions that evolution of the WE says typically come out of both channels at the same time – until they get “zapped” by interaction with a detector.

Well, that argument is fallacious for many reasons. First and foremost is the very idea of using what may or may not happen in preceding or subsequent events of an experiment, to argue the status of any given event. I mean, if the phase between the split WFs happened to be 70°, then the output amplitude in channel A = 0.819…, and the output amplitude in channel B = 0.573576… . In another case, with a different relative phase, the amplitudes would be different, umm – so what? There is still a superposition of waves, and the total WF exists in both channels until “detection” works its magic. That’s what the basic equation for evolution of the WFs say. They don’t have a post-modernist escape clause that if things change around the next time and the next time you run the experiment, then any one case gets to participate in some weird “socialized wave function” (?!)

And, what about the case where we don’t have messed up phases but a consistent e.g. 70° phase delta across instances – then what? So there really isn’t or shouldn’t be a collapse then, but waves remaining in both output channels? That isn’t what happens, you know. Chad said, the other WF doesn’t have to go away (like to “another world”), they just don’t interfere anymore. But that isn’t really the issue: the issue is that the calculation says there’s amplitude in both channels – and then how the photon ends up condensed at one spot.

The use of the density matrix doesn’t really solve or illuminate any of this either. One trouble with the DM is, it’s a sort of two-stage mechanism (in effect.) First, you start with the “classical” probabilities of various WFs being present. OK, that makes sense for actual description because we don’t always know what WFs are “really there.” But then there’s mishandling of two types. First, the actual detection probabilities are usually compiled out of the WF interactions (squared combined amplitudes.) But that takes a “collapse” mechanism for granted and can’t be used later in an argument attempting to “explain” it. If we just have Schrödinger evolution, the DM would just tabulate the likelihood of having various combinations of amplitudes, and that’s all! Without the supervention of a special collapse process, the DM has to be just a tabulation of the chances of having various amplitudes, not of the “probabilities” that only collapse can create IMHO. There wouldn’t be any “hits” to even be trying to “explain.”

Briefly, roughly: the decoherence argument is largely an attempt to force an implicit ensemble interpretation on everyone, despite the clear conflict of the EI v. any acceptance of a “real” wave function each instance, that evolves according to e.g. a Schrödinger equation. Yeah, how can they “collapse”; well who knows, and cheating isn’t the right way to deal with it.

Better an honest mystery than a dishonest “solution.”