Pusey and all that jazz

In this post I’m going to present some philosophical dialogues to help explain what’s wrong with some current debates about quantum mechanics.

Philosophical Dialogue 1: The Right Argument

Scene: the living room of John’s house, where John is sitting at his computer. Jane enters.

Jane: This house does not exist.

John looks around, he seems appropriately puzzled.

John: Why do you say that?

Jane: I admit that the idea that this house exists can be used to do calculations of things like air currents, but it doesn’t actually exist, it’s just a rule for computing temperature and air currents.

John: That’s dumb. All you’re doing is taking the idea that the house does exist relabelling part of it as not existing. What you’re saying just makes the explanation of the air currents and temperature more complicated and less clear.

Jane: Oh, this metaphysical fantasy that the house actually exists is just complete hogwash, it’s not the sort of thing with which I, as a practical person, can possibly be expected to believe.

John: Your incredulity is not an argument. Kindly go away you silly person.

Philosophical Dialogue 2: The Wrong Argument

Scene: the living room of John’s house, where John is sitting at his computer. Jane enters.

Jane: This house does not exist.

John looks around, he seems appropriately puzzled.

John: Why do you say that?

Jane: I admit that the idea that this house exists can be used to do calculations of things like air currents, but it doesn’t actually exist, it’s just a rule for computing temperature and air currents.

John: But when I do experiments I find that the house does exist.

Jane: No you don’t. You just find that the air currents and temperature can be predicted with the house formulae, which are just tools for calculation.

John: Oh yeah. Well, I’ll prove it by coming up with a great experiment to test your idea. An experiment that will trash your idea forever.

Jane: So what?

Commentary

The statistical interpretation of quantum mechanics is the idea that quantum mechanics is just a set of formulae for calculating probability. The appropriate response to this is to say something similar to what John said in the first dialogue. A few years ago, Pusey et al proposed an experiment that they claimed would test the statistical interpretation of quantum mechanics. This is analogous to what John said in the second dialogue. Pusey et al are wrong, not because the statistical interpretation is right but because they give it too much credit. The statistical interpretation is complete garbage and cannot be tested by any conceivable experiment because it says nothing about anything. The statistical interpretation may or may not lead people into making some mistakes when doing calculations, but it is mistaken about physics and epistemology.

Physics is about what exists in reality. It is not about formulae for calculating stuff. The formulae are useful for testing ideas about what exists in reality and they may also have technological applications. But in both applications it is important to keep your eye on the underlying physical reality so you understand what you’re doing with the formulae. If you don’t keep your eyes on the prize you will end up making epistemological and technological mistakes.

To understand better what quantum mechanics says about reality read the structure of the multiverse, The Fabric of Reality and The Beginning of Infinity by David Deutsch.

About conjecturesandrefutations
My name is Alan Forrester. I am interested in science and philosophy: especially David Deutsch, Ayn Rand, Karl Popper and William Godwin.

3 Responses to Pusey and all that jazz

  1. Rami Rustom says:

    I think “too much credit” is wrong. Sounds like you’re talking about degrees, when it’s boolean — refuted or unrefuted.

  2. odo says:

    You claim that, “Pusey et al proposed an experiment that they claimed would test the statistical interpretation of quantum mechanics,” and also claim that, “statistical interpretation is complete garbage and cannot be tested by any conceivable experiment”. So, do they propose an experiment or not? They seem to propose an experiment, but you claim that is impossible?

    I think the problem is that you misrepresent the PBR paper, and the “statistical interpretation” of quantum mechanics for that matter. It seems pretty clear to me that PBR have found an argument against the idea that the house really exists but our theory of houses can only provide probabilities of finding the house on a particular street. i.e. PBR have shown that a certain class of realist theories is wrong – those that simultaneously hold scientific realism and psi-epistemicism.

    So, where does this leave us? It appears to leave us exactly where it all started. The only options now are anti-realist-psi-epistemicism or realist-psi-ontologism, which are just different names for Copenhagen and Many-Worlds.

    I actully think that you should be pleased with the PBR result.

    • PBR do propose an experiment, but the experiment doesn’t test the SI, which isn’t testable. They claim it tests various models that have been proposed under the name of the SI. Let’s say that they’re right about that. It doesn’t matter if they rule those models out because others will be proposed. The reason why they will be proposed is that they don’t solve any outstanding scientific or philosophical problem, so there is absolutely nothing to constrain the content of the models. Lo and behold:
      http://arxiv.org/abs/1312.1345
      As an experimental test of QM I don’t have a problem with PBR. Great, do it, knock yourself out. Even better would be if they would explain what’s going on in reality to produce those results.
      But if you say that you’re refuting an idea that can’t be experimentally tested, or where a purported refutation doesn’t matter, then you shouldn’t labour under the illusion that you’re going to change the way your opponents think.

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