# I "Knowledge" in Psi-Epistemic Interpretation Fundamental or Emergent?

#### lucas_

Is "Knowledge" in quantum Psi-Epistemic interpretation fundamental or emergent? And what does it mean? What do you think?

"One way to deal with the measurement problem is to argue that the wave-function does not describe a real object, but only encodes knowledge, and that probabilities should not be interpreted as frequencies of occurrence, but instead as statements of our confidence. This is what’s known as a “Psi-epistemic” interpretation of quantum mechanics, as opposed to the “Psi-ontic” ones in which the wave-function is a real thing.

The trouble with Psi-epistemic interpretations is that the moment you refer to something like “knowledge” you have to tell me what you mean by “knowledge”, who or what has this “knowledge,” and how they obtain “knowledge.” Personally, I would also really like to know what this knowledge is supposedly about, but if you insist I’ll keep my mouth shut. Even so, for all we presently know, “knowledge” is not fundamental, but emergent. Referring to knowledge in the postulates of your theory, therefore, is incompatible with reductionism. This means if you like Psi-epistemic interpretations, you will have to tell me just why and when reductionism breaks down or, alternatively, tell me how to derive Psi from a more fundamental law."

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#### Demystifier

2018 Award
Psi-epistemic interpretations are usually developed with a motivation to make quantum mechanics complete, i.e. to remove any need for "additional variables" or "realism". In such interpretations knowledge cannot be emergent, because if it was emergent one would need to answer the question "Emergent from what?", which would bring some kind of "additional variables" back.

In the past some physicists (notably Einstein) have been attempting to develop psi-epistemic interpretations in which quantum mechanics is not complete, but now such interpretations are ruled out by the PBR theorem.

#### DarMM

Gold Member
Psi-Epistemic views divide into those where the wave-function represents ignorance of underlying variables $\lambda$ and those where it merely carries information about future macroscopic impressions that result from experiments on the microscopic world. In the second case whatever the world fundamentally consists of cannot be described with mathematical variables.

The names for these aren't really standardised yet. Being called either:
1. Psi-Epistemic Type I, Psi-Epistemic Type II
2. Psi-Statistical, Psi-Doxastic
3. Psi-Epistemic, Psi-Doxastic
depending on the author.

The PBR theorem shows that without giving up conventional notions of causality (i.e. some sort of 3+1D dynamical account of events) the first type are not going to work.

#### vanhees71

Gold Member
Psi-epistemic interpretations are usually developed with a motivation to make quantum mechanics complete, i.e. to remove any need for "additional variables" or "realism". In such interpretations knowledge cannot be emergent, because if it was emergent one would need to answer the question "Emergent from what?", which would bring some kind of "additional variables" back.

In the past some physicists (notably Einstein) have been attempting to develop psi-epistemic interpretations in which quantum mechanics is not complete, but now such interpretations are ruled out by the PBR theorem.
Can I translate this to the statement: "Knowledge is just an illusion"? Well, that may well be true :-(((.

""Knowledge" in Psi-Epistemic Interpretation Fundamental or Emergent?"

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