The Philosophy of Quantum Mechanics

"So, again, with Searle’s construction of social reality we’ve thought about things that we have created and that cease to exist if there are no minds to appreciate them. Then we started to look at physical reality itself—the rivers, the trees, the streams, the electrons and photons, and we then start to question our perception of everything that leads us to The Matrix and what philosophers like Kant have said about how to reconcile this conflict between ideas and experience. Then you start to come to physics. Everything we’ve talked about so far was philosophy, let’s chuck that out because science gets the ultimate answer to everything. We can rely on science. We can trust science. Science must know how this all works. What do the scientists say? Then you go to Max Jammer’s The Philosophy of Quantum Mechanics and you start to appreciate that there’s more to quantum mechanics than scientific analysis and rationality. If you want to understand what quantum mechanics is saying, you can’t do that without an appreciation of all the philosophy that talks about the relationship between ideas and experience, that talks about how we should interpret a mathematical representation of reality which we know to work extraordinarily well and yet predicts things that seem bizarre puzzles, conundrums that won’t easily go away—depending on how you want to interpret the symbols that sit in those mathematical equations. “Einstein read Kant’s Critique of Pure Reason at the age of 13” I picked Max Jammer’s book because it’s still one of my favourites. When I was an academic scientist, I wrote a paper with a colleague and it won a prize and I spent the prize money on The Philosophy of Quantum Mechanics , and I’ve never regretted it. It was an expensive book in those days. Whenever I’m working on a project—and it doesn’t necessarily even have to be about quantum mechanics, it can be about reality or it can be about philosophy—more often than not I’ll reach for it. It’s an excellent book. It’s tough going if you don’t have a background in physics and, to a certain extent, philosophy. When I first looked at it, I didn’t understand hardly a word of it. Over the past 40 years I’m now capable of understanding many of them, though not necessarily all. I relied on Jammer for both the philosophy and the history. His is a careful analysis, for example, of the Bohr-Einstein debate. For readers of this piece who are not so familiar with it, almost from its inception as a theoretical structure, what quantum mechanics meant was debated. The physicists who worked on it and developed it weren’t blind to the fact that it seemed to suggest some things that didn’t sit comfortably with classical principles like causality and determinism—if we do this, then that will happen. That’s a principle of physics that’s prevailed for hundreds of years. We’ve no good reason to want to abandon it and yet quantum mechanics suggests we possibly should and must. These were very uncomfortable things. So, it’s not surprising that those involved in its early stages of development—Niels Bohr, Albert Einstein, Erwin Schrödinger, Werner Heisenberg and to a lesser extent Wolfgang Pauli and others—endlessly debated what this meant. That debate crystallized into a debate between Bohr and Einstein, which has become one of the most famous debates in the history of science. You can look at it in a number of different ways. Bohr, if you like, was the empiricist. I say that with some caveats, but he was saying, ‘Look, we can’t go beyond experience. We have the experience of quantum physics, and we know that when we use this procedure and this set of mathematical equations you predict the right answers. We can predict this will happen with a certain probability and lo and behold it does happen with a certain probability.’ “You are endlessly cycling the same kinds of conversations that philosophers have been having for centuries, but we’re calling it science” Einstein was more wedded to the ideas. Not that he wanted to indulge in metaphysics. Remember that in his general theory of relativity, he had managed to eliminate Newton’s metaphysical action at a distance, replacing this with the notion of curved space-time. In other words, Einstein preferred to avoid speculation that was too distant from the facts. Bohr was saying, ‘We’re done. Quantum mechanics has no deeper principles. That’s it.’ And Einstein was saying, ‘No, that’s not science, we must push.’ There are some really puzzling things going on here—phrases that you might have heard like the collapse of the wavefunction and spooky action at a distance. Schrödinger came up with this notion of a cat in a box that was somehow both alive and dead at the same time. The nature of the debate going back and forth between these protagonists is absolutely fascinating and I’ve learned more from Jammer than possibly any other book. There have since been some very detailed analyses of the Bohr-Einstein debate published in book form, which I’ve looked at at great length, but Jammer, for me, is still the source of first resort. To my mind, he gets it nearly right. He paints this debate the way it should be painted. Now, there’s a kind of pop history version of the Bohr-Einstein debate that you’ll find in many books which paints Bohr as some kind of egotistical, dogmatic individual browbeating a senile Einstein into submission. There are all sorts of different reasons why that kind of pop history take has come about, usually it’s from theoretical physicists who should really know better, wanting to push it as a reason for giving their own views as to what’s right and wrong in this particular area. But the simple truth of the matter is that both these guys were right. What is needed for science to make any sense at all is for there to be almost always a conflict between what we take as experience, as evidence, as data, as facts and our ideas about how nature should be or how reality should appear. There has to be this constant tension between them. It’s when you don’t have that tension, when you’ve only got the ideas, that you’re off into a metaphysical wilderness. That’s where, for me, it’s not science anymore. It’s not about being right or wrong, it’s about the tension in the debate. That’s the most important thing. Historically, Bohr was seen to have won the debate. After World War II , American science came to dominate all of Western science, because Europe was still recovering. This post-war American scientific hegemony had all sorts of ways of manifesting itself, but there was a view among physicists at the time that this didn’t matter. If a young student had a question, ‘What does this mean?’ they’d be told, ‘Don’t waste your time’ or ‘Go and read a textbook.’ The textbooks themselves were almost lamentable in the way they covered this particular question and debate, with a couple of exceptions. Yes, this is the origin of the ‘shut up and calculate’ view. That phrase comes from a physicist called David Mermin. In an article in Physics Today some years ago, he wrote about how he came up with the phrase, and it was exactly because he had asked his professors at Harvard ‘What does this mean?’ and they said, ‘Don’t waste your time, shut up and calculate.’ He said he regarded them as ‘agents of Copenhagen’ i.e. they were agents of the Copenhagen interpretation, which is traced back to Niels Bohr. The logic is that Bohr won the debate with Einstein, what Bohr said goes, and we don’t need to ask any questions anymore because there are no deeper principles. I actually went back to Mermin just last December on email and I asked, ‘What did you mean by that?’ And he told me that he saw them as agents of Copenhagen not in the sense that they understood what Niels Bohr had said, but because, effectively, they were saying, ‘this isn’t physics anymore. This is philosophy. Don’t waste your time with it.’ It was an indifference to the question. Many people who came later—like David Bohm and John Bell—rejected that. They puzzled over what quantum mechanics means and reacted against the indifference of the physics community. But that indifference persists today. I’ve experienced it myself. ‘Oh no Jim, nobody cares about that. Just get on and do the sums and do the calculations and make the predictions.’ That, for me, is what is not science. Lining up on either side of the argument, creating that tension between experience and ideas and knocking it back and forth and challenging each other, that’s science; being indifferent to these questions means you’ve basically given up. It brings us back to that comment by Steven Weinberg in the opening pages of Dreams of a Final Theory; when will we ever be able to accept that there are no deeper principles? It’s not human nature ever to say, ‘Okay, we’ve come to the end, draw a line under it, time to stop.’ Jammer is great on the philosophy and the history of the period that gave rise to these questions."

"By this time, I’m snowballing a little bit. I’m still trying to earn a crust as a university lecturer and researcher. I co-wrote a research paper that won a prize—nothing grand by today’s standards—but enough for me to afford what was an expensive book then. It’s by Max Jammer and it’s called The Philosophy of Quantum Mechanics. This really appealed to me. This is a proper textbook. It’s detailed, it’s not for the layman. There’s bits of it that I still don’t understand. Again, this is somewhat outdated and the world has moved on. I was challenged so much by grappling with these ideas, that I felt that I really did need to get a better grip on them and understand them better. Not because that would aid my abilities as a researcher doing what I was doing, or, in fact, aid my abilities as a teacher because I was teaching a completely different subject. This was certainly off-piste, as far as anything to do with my research or teaching career was concerned. But I was just deeply disturbed. I needed to know, I needed to understand a bit better. And Max Jammer’s book allowed me to do that, enough to give me confidence that I could actually make sense of this, to the point where I could begin to write about it myself. I actually wrote a short article that was published in, I think, the Journal of Chemical Education , and, eventually, I wrote a book called The Meaning of Quantum Theory which was published by Oxford University Press back in 1992. But, in order to do all of that, I had to make the decision to quit. I left academia at the end of 1988. I finally got to write about this but, in order to do that, I had to stop working in a university. Yes, which I’ve always been interested in. There had been the odd flirtation where I’d buy an introduction to philosophy, but there’s a lot of stuff in there about metaphysics and moral philosophy. That is interesting—don’t get me wrong—but what I was really interested in was the place where philosophy meets physics. And this is one of those places. You can’t have a conversation, really, about quantum theory without introducing some arguments and points that are really philosophical in nature. It also helped me understand a little bit about what science is trying to do. What has happened in contemporary physics is the rise of string theory, these guys who argue in favour of the multiverse theory. I felt anger at the capabilities of scientists, seeking their own self-promotion, who really ought to know better, advertising what string theory can achieve. That actually encouraged me to write a book called Farewell to Reality , which was published in 2013. This argued that all of this is rather metaphysical in nature; there is no experimental evidence for any of it. There is not a leg for string theory to stand on. Now, is it a valid theoretical structure that’s worth pursuing? Probably, yes. But people really shouldn’t be saying that string theory is the answer, because we don’t know that. It’s interesting because there was a time when some well-known, Nobel Prize winning physicists were quite derogatory about philosophy. Some argued that philosophers put a nice historic gloss on science but can add nothing to how we think about problems that we face today. “There is not a leg for string theory to stand on” I just find that incredible and absurd because, by its very nature, if your interest is in the fundamental nature of things, then you are in the realm of philosophy. It’s a game that scientists play rather well, particularly the theoreticians. In a sense, what you do is that you’ve got a problem, there’s something you can’t explain, there’s no data out there that says why it’s wrong or where it’s wrong. So, you speculate. Maybe nature looks like this—and you develop a structure. And the idea is that you torture that structure such that it eventually spits out a prediction of some kind. You twist it, you torture it. And then you say, ‘Well, if this is true then we should see this.’ So, what you do is you play a game. You wander into metaphysics because there is absolutely no evidence, by definition, for your speculation. That’s why it’s a speculation. I would prefer to call it a hypothesis, not a theory—but that’s semantics. The challenge you have, because science is about data and it’s about empirical facts, is to find a way of connecting your speculation—your piece of metaphysics—back with the real world, with the empirical world that we live in. And the string theorists spectacularly fail to do that and have spectacularly failed for forty years. Arguably, string theory isn’t actually even a theory. It’s a hypothesis that has no foundation in empirical data. There is no evidence for it. It’s a nice way of looking at how elementary particles might be structured but it’s telling us nothing that we don’t already know. “If you interest is in the fundamental nature of things, then you are in the realm of philosophy” For a time, it seemed that publishers didn’t want to do anything other than publish reams of bestselling books about the elegant universe and the fabric of reality and the hidden universe—whatever it is. All I would say is, ‘For heaven’s sake, don’t get me started on the multiverse because that would really have me going off on one.’ I actually watched a BBC Horizon documentary, I think in January 2011, called “What is Reality?” It started off really quite nicely. There was a lovely introduction to particle physics, the discovery of something called the ‘top quark’ at Fermilab. Then there was a little sequence on the more weird results of quantum theory. And then, we were off into the realms of fantasy with string theory, the multiverse, the mathematical universe hypothesis—all of this stuff. And I got really quite nervous. Horizon has got an incredible reputation in the UK and I just sat there worrying, after half an hour, that people were actually taking this seriously. Were they really thinking that this is what scientists agree reality looks like? That encouraged me to write a book about it."