Nobody Really Understands Quantum Mechanics

Question: How can philosophers help us to understand quantum mechanics?

Tim Maudlin: How should anybody think about quantum mechanics? Quantum mechanics is a perfect example.  So you have Richard Fineman famously saying he can safely say nobody understands quantum mechanics.  Right?  One of the greatest physicists of the 20th century who’s main work was in quantum mechanics claiming he didn’t understand it.  He says he himself does not really understand the picture of the world that quantum mechanics is presenting us with.  I would think a physicist, as I say, as a physicist should find that frustrating and upsetting and a failure of physics that this fundamental mathematical theory they’re using they find they don’t really even have in themselves the sense they understand what it’s telling you about the world.  

It’s just that if you’re a philosopher, you have the luxury of spending all of your time with that worry of beating your head against it.  As a matter of fact, it’s a hard question and it requires people thinking very carefully and very deeply and furthermore, coming up with detailed physical theories, detailed physical accounts to try to understand quantum mechanics.  And that foundational work tends not to have immediate payoff practically.  It doesn’t mean that the predictions of the theory when you make sense of quantum mechanics will change or will change much.  Sometimes they even change a little.  Sometimes people trying to understand quantum mechanics will propose a way of understanding it that actually means the very predictions it makes will be altered a tiny bit, often such a tiny bit that you can’t even check it in the lab.  

But there’s not that much practical payoff, and insofar as you are a physicist who care about practical payoff or you’re embedded in a larger enterprise that cares about practical payoff, then you’re going to regard these questions as not of immediate interest.  Right?  They’re not going to repay you thinking about them.  And the luxury that philosophers have is that as we’re paid to think about things that don’t pay to think about.  And so we can spend our time worried about these foundational issues and not feeling guilty about them.

What is the payoff that you get from this kind of inquiry?

Tim Maudlin: Well there are two things you would like to do.  Ultimately you would like to settle on a clear physical account of the world.  Like, what’s going on, like I say, go back to my electron.  What’s really going on with that electron?  The aim you have is to answer that question.  Now as it turns out, if you look at the precisely defined interpretations of quantum mechanics that exist today; and by precisely defined, I mean the ones where you have a clear mathematical account of what’s going on, in terms that are not vague and ambiguous.  For example, if someone in the standard theory you say, “Oh, a system will develop in a certain way until you measure something on it.  And when you measure something, then things go very differently.”  And as John Bell pointed out, that’s just unacceptable vagueness because, what does it mean to measure something?  You know, you’re saying in on circumstance it does one thing in another circumstance it does another very different thing, but the difference between those two circumstances it not well defined.  

So the first ting you want to do is have a clear theory.  A theory that tells you clearly what exists, tells you clearly what it does, and that you see, well given that, I can understand the world around me.  As it turns out, there are various ways to do this; quite different ways to do it.  Ways that give you very, very different pictures of what’s going on in the world in a microscopic scale.  

What you’d like to then do is choose among them.  Now, you may not be able to do it.  How do you choose among them?  Ultimately you’d like to do it empirically.  You’d like to say, well there’s some experiment I’d like to run to decide between these.  But in certain cases, it’s sort of provable that no experiment can decide between them.  Or you might hope that one of these pictures and not another, one of these models and not another can be extended to cover gravity or can be extended to cover some new phenomenon.  And then that would give you a reason to prefer one.  

It may turn out that at the end of the day, we will never know.  It may turn out that the world has not been made and our brains have not been made and our access to the world through our senses has not been made to allow us to discover all of the facts about it.  And then you’d be depressed a little bit.  Those are the breaks, right. 

Recorded September 17, 2010
Interviewed by David Hirschman

Physicists should find it frustrating and upsetting that they don't really get what this fundamental mathematical theory tells us about the world.

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