= 27d567bc2d48d9f40e9ccc20ea370b15)
siodine comments on Philosophy Needs to Trust Your Rationality Even Though It Shouldn't - Less Wrong
You are viewing a comment permalink. View the original post to see all comments and the full post content.
= 783df68a0f980790206b9ea87794c5b6)
Loading…= b715d02e85f7b3b4ae65ca3d3e450868)
Subscribe to RSS Feed
Powered by Reddit
= f037147d6e6c911a85753b9abdedda8d)
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (169)
You seem to be trying to explain something rather clear with something less clear. The sentence in question is simply affirming that the wave function captures everything that is true of the system; thus (if you accept this view) there are no hidden variables determining the seemingly probabilistic outcomes of trying to measure non-observables. There's nothing mysterious about asserting that there's a hidden cause in this case, any more than science in general is going Mystical when it hypothesizes unobserved causes for patterns in our data.
To say that the outcome is not "definite" is to say that it is false that a particular measurement outcome (like 'spin up'), and not an alternative outcome (like 'spin down'), obtains. "Definite" sounds vague here because the very idea of "many worlds" is extremely vague and hard to pin down. One way to think of it is that the statistical properties of quantum mechanics are an epiphenomenon of a vastly larger, unobserved reality (the wave function itself) that continues merrily on its way after the observation.
Where's the 'verbal play'?
Say there are no hidden variables and the evolution is probabilistic. Does then the wave function capture everything that is true of the system? It seems to me that it doesn't: it is true that the system will be measured spin up in the next measurement, but the wave function is as well compatible with spin down. But you seem to assert that if I don't believe in hidden variables then the wave function does capture everything that is true of the system. Thus I don't find it rather clear. Neither does "epiphenomenon of a vastly larger reality" seem clarifying to me even a little bit.
At a given time, yes. But over time, the way a wave function changes may (a) be determined entirely by the Schrödinger equation, or (b) be determined by a mixture of the Schrödinger equation and intermittent 'collapses.' Given (a), the apparently probabilistic distribution of observations is somehow mistaken, and we get a many-worlds-type interpretation. Given (b), the probabilities are preserved but the universe suddenly operates by two completely different causal orders, and we get an 'objective collapse' interpretation. These are the two options if the wave function captures all the variables.
I am now interested in clarification of "everything that is true of the system". I have an electron whose spin I am going to measure five minutes from now. Does the proposition "the spin will be measured up" belong to "everything that is true about the electron"? Presume that the spin will indeed be measured up (or I will perceive the world in which it was up or whatever formulation will suit you the best). To me it appears as a true proposition, but there may be philosophical arguments to the contrary (problem of future contingents comes to mind).
Physics-inclined people tend to be 4-dimensionalists, so I don't think they'll object to describing wave functions in terms that account for them at all times. Even indeterminists (i.e., collapse theorists) can accept that we can talk about what will be true of electrons in the future, though we can't even in principle know some of those facts in advance.
de Broglie sez: "Yes, that belongs to everything that is true (about the electron's wave function). But at least one truth about the electron (its position at any given time) is not accounted for in the wave function. (This explains why the Schrödinger equation, although a complete description of how wave functions change, is not a complete description of how physical systems change.)"
von Neumann sez: "Yes. And the wave function encompasses all these truths. But there is no linear dynamical equation relating all the time-slices of the wave function. There are more free-floating brute facts within wave functions than we might have expected."
Everett sez: "Yes... well, sort of. The formalism for 'the spin will be measured up' is a component of a truth. But it would be more accurate and objective to say something like 'the spin will be measured up and down' (assuming it was in a prior superposition). Thus the wave function encompasses all the truths, and evolves linearly over time in accord with the Schrödinger equation. Win-win!"