- #36
Sherlock
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You can have the words, objective reality, refer to anything you want. We define these terms differently, that's all --- and there's no point in arguing about which definition is better. The history of the development of modern science has already decided that for us.vanesch said:... let's accept your point of view, namely that "objective reality" is a matter of convention. Well, I'm proposing the convention that "objective reality" is nothing else but the mathematical structure of the best physical theory that is around at a certain moment.
You say that we MUST assume that the mathematical structure of quantum theory is in 1-1 correspondence with an underlying reality --- that, in other words, the theory is defining an underlying reality. I say, no, that idea is not a necessary part of the interpretation and development of the theory.
The development of quantum theory is almost a purely mathematical enterprise with the aim of accounting for, and hopefully predicting new, experimental phenomena. The theory's relationship to an underlying reality depends on one's speculative vision of an underlying reality. You say that the mathematical structure of the theory implies that there are an infinite number of simultaneously existing subjective worlds. I don't know what that might mean. I say that at least one mathematical formulation of the theory indicates that nature is fundamentally interacting waves. But of course neither one of us has any way of knowing the truth of either of these interpretations. The upside is that the science of physics doesn't depend on these sorts of speculations.
The validity of the MWI, just as with my current metaphysical view, can neither be verified nor falsified. The difference is that the current predictive state and the development of quantum theory doesn't depend on the existence or development of the MWI at all, whereas wave mechanics is an important part of the most widely used formulation of the theory --- and the Born rule is part of the wave mechanical picture.
There is some logic behind it.vanesch said:The problem with your view is the circularity of it: this is the main critique of positivism. WITHOUT a metaphysical frame, there is NO LINK between any formalism and any empirical observation. You *always* sneak in some metaphysical hypothesis when doing so. At a certain point, you ALWAYS identify certain aspects of the formalism with a reality. But you do so intuitively, in order to make things come out right, without any logics behind it.
Yes, defining agile terms is a matter of convention. Witness the fact that you have lots of ordinary language terms associated with various aspects of quantum theory and quantum experimental phenomena which, in that context, don't mean what they mean in ordinary discourse.vanesch said:... you first say that "reality" is a matter of convention.
Yes, I agree that it's all a matter of semantics. We decide whether something is real or not by, in effect, voting on it --- and MWI isn't getting too many votes.vanesch said:And then you wonder how you can KNOW whether or not the other branches in MWI are real. If it is a matter of convention, we can decide about it by, say, voting! You cannot IGNORE a convention you decided upon!
But if you decide, by convention, to call only your collective experiences as real, then I can decide to call the theoretical elements of quantum theory and the parallel worlds "hyporeal".
And if we now REDEFINE the words "real" into "subjectively experienced" and "hyporeal" into "objectively real", we arrive at MWI.
I have no idea. It sounds like a very hard question.vanesch said:If we keep the words as we have them, then, the wavefunction has a hyporeal meaning, and locality is a hyporeal concept about hyporeal worlds. Ok. So in this hyporeal meaning, dynamics is given by unitary time evolution. And now that I have hyporeal operators, corresponding to hyporeal interactions, how can I link them to "real" apparatus ?
At what point does a hyporeal structure of particles that looks like a hyporeal voltmeter, become a real voltmeter ?
Presumably, one would already have included the voltmeter in one's instrumental/material preparation, so one wouldn't have to worry about when it became real.
But I suppose that would depend on one's definition of real.
I thought that there is, presumed by MWIers, an inconsistency between the Born rule and the unitary evolution that is the problem that MWI is trying to fix? So, you now refer to this axiom (which was formerly about the objective world) as an axiom about subjective perceptions? That doesn't seem like much of a fix. But then, it does introduce a sort of creation mechanism where you get as many perceptual worlds from an experimental trial (or is it an entire run) as there are possible results ... and they're all undetectable except the one that we say we're percieving, and the unitary evolution marches on, apparently unimpeded. So, there's that.vanesch said:One shouldn't try to derive the Born rule, it is the rule that gives the relationship between the MWI ontology (the hyporeal world) and the subjective experience (the conventional "real" world). As such, it is an axiom of the theory, related to perception.
Or is the supposed inconsistency between the unitary evolution (the wavelike behavior in the underlying quantum world), and the appearance of measurement results on data tapes or monitors, etc., in the perceptual world? But that's just an apparent inconsistency. (Refer to the vibrating drumhead with powder on it example from my previous message.)
Or is it just that quantum theory doesn't detail precisely how and when measurement results occur. So, with MWI, you can do that?
This will be news to most professional users of quantum theory I think.vanesch said:Quantum theory (without MWI) does not make predictions, without you sneaking in some extra hypothesis.
I think that most working physicists don't actually bother to interpret the theory. Of those that do, a minority are fascinated by MWI.vanesch said:You cannot say that the wavefunction is NOT in correspondence with physical reality and then 2 minutes later, find it obvious how we can extract measurement results from it, because in order to do so, you have to find a link between the physical operation of your measurement apparatus, and your non-physical quantum state. That's where most people say the most schizophrenic things.
If you're referring to the collapse of the wave function as part of the schizo (in your opinion) standard interpretation, then it's good to remember that the wave function is not taken to be in 1-1 correspondence with an underlying quantum reality in that interpretation.
Of course, I'm not a professional, but I did say that I think that the mathematical structure of the Schroedinger formulation seems like it might be very insightful wrt what is happening in an underlying quantum world. And, I think that proponents of the standard probabilistic interpretation would tend to think that way. That is, while the wave function might be an insight into an eventual conceptual (as well as mathematical) understanding, it is nevertheless most likely the case that the wave function isn't a 1-1 mapping of the underlying quantum world. Collapse, used in that interpretational context, doesn't mean what collapse does in ordinary discourse. It just means that when a sufficient number of detections are recorded, or by time-limiting, a run is over and the wave function that predicted the result(s) from a range of possibilities no longer applies to that particular run. Although, if it is in good approximation to the results, then you can have some confidence that not only does the theory work but that you used it correctly --- and so retain that formulation for that particular preparation.
You know the difference between a detector clicking or a light bulb lighting and a mathematical model. If you want to know when the click or the lighting-up did occur, then correlate a clock-time with the event. If you want to flesh-out quantum theory so that it tells you exactly when a certain possible result at a certain location WILL occur, then do that. And good luck. If MWI has any practical utility at all, it's that it AMPLIFIES the measurement problem.vanesch said:Look at a photomultiplier, with a single atom as a photocathode. The EM quantum field is in an excited state, described by a wavefunction in Fock space (but that's not real of course). We know how to calculate the interaction of an atom in the ground state with the EM field state, through unitary evolution. So now the atom's wavefunction becomes partly in a state that corresponds to an ionized atom, and partly in its ground state, entangled with the EM wavefunction (which did the opposite thing). But all this is not real of course. In the state with the ionized atom, the electron will accelerate towards the dynodes (in the other state, not, of course) through a unitary evolution. On the dynodes, it will interact (unitarily) with the metal and entangle with other electronstates, until we get an appreciable amount of electrons coming down on the anode. In the other state, no such thing will happen. But remember, that all this is just hyporeal mathematical manoeuvring on a wavefunction which has no physical meaning. So now we end with a wavefunction which is a superposition of the state where no charge arrives on the anode, and where a lot of charge arrives on the anode. We could continue that way, and we'd find that the amplifier and the light bulb attached to it, in their wavefunction are written as a superposition of a lightbulb that doesn't light up, and one that does light up. But all this is hyporeal of course (and the two branches are hyporeal). At what point did they become "real" ? At what point can I say that THIS corresponds to a genuine real effect, predicted by quantum theory ?
Your linkage is as problematic as the linkage you're trying to fix.vanesch said:BTW, have you noticed that we could reason in each branch, as if it were a world of its own, and that, in doing so, we took the implicit assumption that there was "something real" to them ? While nevertheless each individual operation was described by a UNITARY operator ? If I don't do that, how am I going to link the above wavefunction to my lightbulb lighting up or not ? How am I going to describe the unitary operator that describes the physics of the electrons within the apparatus ?
Bell's Theorem has nothing to do with the possibly insightful idea that the Schroedinger formulation of quantum theory hints that reality's deep nature might be understood in terms of wave mechanics.vanesch said:There's a theorem against that statement, which is Bell's theorem. No local realist field theory can have the same empirical predictions as quantum theory.
Especially since we have no underlying reality criteria for evaluating the rightness of the theory wrt an underlying reality --- only instrumental results. Yet, you've stated that we MUST assume that quantum theory is RIGHT wrt the behavior of the underlying reality --- and that assumption is what the convoluted ontology of MWI is based on.vanesch said:Now, as I said, experimentally there are strong indications, but no proof, that quantum theory is right.
Did you ever consider the possibility that maybe YOUR argument is circular?
There's a difference between noting the possible heuristic value of quantum theory, and saying that a deterministic wave theory employing precisely defined values and making precise predictions is possible. If anything, the wave heuristic gotten from quantum theory indicates that there are limits to what can be experimentally determined. So, even without Bell, it would seem to be a mistake to pursue a 1-1 mapping of some conception of the underworld.vanesch said:There is still room to wiggle in such a theory. Only, I don't know of any. And it will make in any case different predictions than quantum theory.
Quantum theory itself tells us that there can't be a 1-1 mapping between physical reality and precisely defined mathematical abstractions. It imposes limits. So, if you take the theory as right in this respect, then it can't ever be right in the respect that you assume it to be.vanesch said:So, in order to "interpret" quantum theory this way, you must make the assumption that quantum theory will make empirically WRONG predictions in certain respects, and you'll need to invent a realistic wave theory that DOES give you all the right other predictions. Some people (local realists) do try to do so. But you see that you are also TRYING to find a physical theory that is in 1-1 correspondence with a physical reality behind the scenes. You have 3 possibilities (if you accept a physical reality that can be mathematically described, and on which your mind has no physical influence on cosmic scales):
Well, we're presumably part of nature (whatever nature might BE), and we're somewhat inconsistent, so insofar as we're the creators of theories ABOUT nature, then the Bohr approach seems like the best one to me. But that's not to say that the behavior of nature is inconsistent. After all, we don't know what nature IS, do we?vanesch said:... other possibilities are to DENY a possibility of mathematical description of nature (like Bohr proposes) - hence accepting an inconsistent behaviour of nature ...
If you want to reify physical theories, then physicists are in the process of inventing nature via theory. And MWI seems like a silly invention to me.