- #1
Lynch101
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- TL;DR Summary
- Trying to understand what the different interpretations of QM say and don't say and which interpretations fall into which category.
I was originally going to start a thread on individual interpretations of quantum mechanics to try to understand them better, but after reading this article by @PeterDonis it might make more sense to use that as a starting point and try to understand how the different interpretations fit into the framework outlined by Peter. In the article, Peter outlines two fundamentally different interpretations:
Type 1 - Instrumentalist?
The article also mentions
Particular Interpretations
Which particular interpretations fall into this category? Am I right in saying that QFT is such an instrumentalist interpretation? Is it possible for Copenhagen to be interpreted both instrumentally and non-instrumentally? I'm thinking where the superposition of the wave-function is taken to be a physical representation of the system. Is this interpretation what gives rise to the Schrodinger's cat problem?Type 2 - Deterministic?
Does the statement above, that we can never directly observe the state of the system, equally apply to interpretations of this type? As in, is there a fundamental limit to what we can know about the physical system that is simply unavoidable?
Particular Interpretations
Which particular interpretations fall into this category? Is de Broglie-Bohm Pilot Wave one such interpretation? Is this the same thing as Bohmian mechanics? Does the Many Worlds Interpretation fall into this category? Is it possible to interpret Copenhagen in this manner also?
I thought I had read somewhere that hidden variables theories, or the MWI, cannot reproduce all of the predictions of quantum mechanics. Is there any truth in that, or have I again misinterpreted something along the way?Other interpretations
I'm not too familiar with the other interpretations of QM. I've heard of QBism but I'm not too sure what it says. Which category would that fall into? Are there others?
Type 1 - Instrumentalist?
I think I am correct in stating that interpretations of this type are referred to as "Instrumentalist" interpretations because the mathematical machinery of QM is a tool or an instrument that allows us to make [probabilistic] predictions about macroscopic events. In such interpretations, the mathematical formalism is not taken to represent an underlying ontology or the physical state of the system. As such, interpretations of this type do not allow us to make deterministic predictions about the outcome of individual experiments, nor do they tell us what happens in individual experiments, or how the quantum state interacts with the macroscopic measuring device. For this reason, such interpretations are often criticised as being "incomplete". Is that much correct?(1) The state is a tool that we use to predict the probabilities of different results for measurements we might choose to make of the system. Changes in the state represent changes in the predicted probabilities; for example, when we make a measurement and obtain a particular result, we update the state to reflect that observed result, so that our predictions of probabilities of future measurements change.
The article also mentions
Does this have something to do with the Heisenberg uncertainty principle, where we can never precisely know both the momentum and position of a particle, because there is a trade-off between the information that can be known about either? I thought I had read something about no-go theorems which suggest that incompleteness is not particular to QM, that it is not possible to develop a more complete theory. Am I correct in any of that, or am I misinterpreted some information along the way?For #1, the obviously true part is that we can never directly observe the state
Particular Interpretations
Which particular interpretations fall into this category? Am I right in saying that QFT is such an instrumentalist interpretation? Is it possible for Copenhagen to be interpreted both instrumentally and non-instrumentally? I'm thinking where the superposition of the wave-function is taken to be a physical representation of the system. Is this interpretation what gives rise to the Schrodinger's cat problem?Type 2 - Deterministic?
Are interpretations of this type considered to be non-instrumentalist and deterministic? Under these interpretations, is the mathematical formalism taken to represent an underlying ontology i.e. it describes something physically real? Do interpretations of this type purport to tell us what is happening in individual experiments, although they are unable to offer deterministic predictions because there are hidden variables which are unaccounted for leaving us with only the ability to make probabilistic predictions?2) The state describes the physically real state of the system; the state allows us to predict the probabilities of different results for measurements because it describes something physically real, and measurements do physically real things to it. Changes in the state represent physically real changes in the system; for example, when we make a measurement, the state of the measured system becomes entangled with the state of the measuring device, which is a physically real change in both of them.
Does the statement above, that we can never directly observe the state of the system, equally apply to interpretations of this type? As in, is there a fundamental limit to what we can know about the physical system that is simply unavoidable?
Particular Interpretations
Which particular interpretations fall into this category? Is de Broglie-Bohm Pilot Wave one such interpretation? Is this the same thing as Bohmian mechanics? Does the Many Worlds Interpretation fall into this category? Is it possible to interpret Copenhagen in this manner also?
I thought I had read somewhere that hidden variables theories, or the MWI, cannot reproduce all of the predictions of quantum mechanics. Is there any truth in that, or have I again misinterpreted something along the way?Other interpretations
I'm not too familiar with the other interpretations of QM. I've heard of QBism but I'm not too sure what it says. Which category would that fall into? Are there others?
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