▶︎ 0:00 What I hope I'm going to be able to do in these sessions is offer some kind of an invitation to the foundations of quantum mechanics. Offer an account of the sense in which I think there are big, interesting questions at stake here. And let me talk in a little bit more detail about what I want to do.
▶︎ 0:36 What I think is primarily, and in the first instance, interesting about the story of quantum mechanics, about the foundations of quantum mechanics, is that it was a sort of unique episode in the history of modern science. By modern science, I mean science since the scientific revolution. In that it was widely thought, it was widely announced that the discoveries about the bizarre behaviors of subatomic particles that led to the development of quantum theory represented a sort of really decisive collapse of the traditional aspirations of the scientific project. So, over and above being a set of discoveries,
▶︎ 1:39 As I say, about the behaviors of subatomic particles, about the kinds of mathematical apparatus that are required in order to describe those behaviors, what's interesting to me, primarily and in the first instance about this story, is that it was taken in by the people who discovered it. It was understood by the people who discovered it as a very powerful demonstration that the traditional aspirations of the scientific project, of the modern scientific project, the aspirations very crudely to give us a straightforward, flat-footed, literal, realistic, complete account of the physical world had collapsed, and were now exposed as naive, as impossible, as presumptuous.
▶︎ 2:43 What I'd like to give a sense of, in these sessions, is first of all what the phenomena were that people felt justified such a conclusion, justified such a claim, and how that claim has since been pushed back against. That is, in what sense it is that one can say, notwithstanding these developments, that the original aspirations of the scientific project are still very much alive and represent a going concern.
▶︎ 3:27 There is, it's a quite astonishing story. Astonishing in the following sense: it goes without saying that there's a long, long history of what you might call philosophical critiques and concerns about the completeness of the scientific project. There's a long history of what you might call philosophical worries about the traditional claims of the scientific project. There are worries to the effect that it can't refute skepticism. There are worries about the kind of image of ourselves that something like fundamental physics presents to us, worries about where our conception of ourselves as rational, where our conception of ourselves as free. All kinds of other stuff would fit into such a picture. There are worries about what kind of sense one can make of reference and intentionality in the context of the picture of the world that physics seems to be presenting us with. There are all kinds of worries.
▶︎ 4:51 What happened in the case of quantum mechanics is of an utterly different kind. What happened in the case of quantum mechanics is that something that amounts to a radical critique of the scientific project emerges within and in the course of the scientific project itself. Milo, I remember, once said to me, I thought nicely, "This is the occasion when the call is coming from inside the house." The idea here was not that there were external critiques that may or may not be devastating to various aspirations of the scientific project, but that the scientific project did something more along the lines of committing suicide in the course of quantum mechanics.
▶︎ 5:44 And astoundingly, not because of any kind of philosophical reflection, but because of where pointers on measuring devices ended up pointing at the conclusions of various straightforward physical experiments, it could be argued on the basis of how these experiments came out that any attempt to tell an objective, literal, third personal, realistic story about what was going on behind the curtain, about what's going on under the table, that produces an understandable account of why these experiments came out in the way they do, any attempt to do that was, it was argued by people like Bohr and his circle in Copenhagen, it was argued, inevitably going to collapse into paradox or self-contradiction or something like that.
▶︎ 6:46 And it's quite astounding to think that anybody could even have imagined that there were distinct results of how certain experiments came out that somehow showed that any attempt to tell a realistic story about what was going on behind these experiments couldn't possibly succeed.
▶︎ 7:06 The first thing I hope to do here is to tell a story that makes it understandable, even if I don't think it turns out to be right, that makes it understandable that people could have drawn such shocking and radical conclusions from the way some experiments on subatomic particles came out. Once again, what's striking about this episode in the history of science is that this is not a critique arising from general philosophical reflection. You got these working physicists minding their own business, minding what everybody agrees is their own business.
▶︎ 8:00 They're just trying, they're not trying to figure out how agents work, they're not trying to figure out how rationality works, they're not trying to figure out how freedom works, they're not trying to understand being qua being or anything like that. They're just trying to tell an intelligible story about what happens to rocks when you pass them through various kinds of measuring devices. And all of a sudden, things get weird and you're confronted with claims from smart people to the effect that this particular attempt to understand these particular kinds of very, very small rocks shows that the entire project was misguided, that the very aspiration to tell this traditional kind of scientific story about what these rocks are doing in between the time that they go into this machine and the time that they come out of this machine is not something that can be done without, as I said, collapsing into paradox or contradiction or some other kind of madness.
▶︎ 9:09 The first thing I want to try to do is make it plausible that smart, reflective people could have arrived at such conclusions, as a result of how these experiments came out. So the first part of these sessions will be devoted to trying to tell that story.
▶︎ 9:37 Then I'm going to move on a little bit, to very early attempts on the parts of people like von Neumann and Schrödinger and Wigner and so on and so forth to push back against this a little bit, to try to see what it would be like, to try to experiment with what it would be like, to attempt to construct the kind of realistic account that Bohr and his circle had declared, had argued, or so they thought, to be impossible, and to show how those initial attempts at pushing back against this, those initial attempts to be realistic run into a very daunting problem, which is referred to in discussions of foundations of quantum mechanics as the measurement problem. The second thing I want to try to do is to set that up.
▶︎ 10:45 The third thing I'd like to do is to report to you something that we've learned quite definitively about what any attempts to tell this story realistically are going to look like, and what I'm referring to here are the famous discoveries of John Bell coming out of some arguments by Einstein, Podolsky, and Rosen regarding the question of locality.
▶︎ 11:15 Very briefly, we have always approached the world, and I mean always, by always I mean prior to modern science, prior to science per se, this is a conviction with which I take it dogs approach the world and mice approach the world and so on, there is a conviction in the way we approach the world to the effect that conditions at some particular point in space and time can only be directly physically affected by conditions that are immediately adjacent to them in space and time. And in situations where something that happens here affects something that happens over there are always accompanied by a sort of process of propagation of the effect between adjacent spatio-temporal points stretching from the initial cause to the final effect.
▶︎ 12:15 Something we do know about quantum mechanics now is that any attempt to push back against the radical instrumentalism that I was talking about before, any attempt to push back against the radical anti-realism that I was talking about before, is going to result in a story which, in a really shocking way, violates this intuition, which we have long approached the world.
▶︎ 12:46 So, I want to tell a story about that too, and all of the stories I've referred to so far, I hope I'm going to be able to tell in a way that's both accessible and logically and conceptually rigorous. I think it is possible to tell those stories in a clear way and in a way that doesn't sacrifice logical or scientific rigor.
▶︎ 13:15 After that, I want to go on and talk in a little more detail about attempts to come to grips with this measurement problem that these attempts at being realistic, that these attempts at pushing back against the claims of Bohr and his circle run into, that's a fully logically rigorous discussion of those attempts to push back. And there are three interesting kinds of attempts to solve this measurement problem that I want to talk about.
▶︎ 13:58 A thorough discussion of those and a rigorous discussion of those would require a good deal more mathematical apparatus than I want to drag into these proceedings, so that's going to be a good deal sketchier than the presentation of the topics I've talked about so far. But this stuff is, it's just a matter of time, this stuff is very accessible at the end of the day. There are a bunch of good books that one can read that I think are very accessible books that will complement the latter parts of these lectures with much, much more detail about how those proposals work than you're going to hear here.
▶︎ 14:50 A couple of books that are worth mentioning, first of all, is a book that I myself wrote, years ago, called Quantum Mechanics and Experience, published by Harvard. There's a wonderful book by Tim Maudlin, called Philosophy of Physics: Quantum Mechanics, published by Princeton. There's a nice book by Jeff Barrett called The Conceptual Foundations of Quantum Mechanics, published by Oxford. There's a nice book by Travis Norsen called Foundations of Quantum Mechanics: An Exploration of the Physical Meaning of Quantum Theory, published by Springer.
▶︎ 15:30 There are lots of good, very accessible books about this. These are all books that are going to demand that you absorb some mathematical material, but they are also books, all of them, that introduce all the mathematical material you'll need in a self-contained way.
▶︎ 15:54 That's a crude outline of what I hope to do in these sessions.