The best books on Quantum Physics and Reality

You’ve written a few books about quantum physics now, some are for a popular audience, one is about the math you need to do quantum physics. Why are you so concerned about its relationship to reality? Are you worried that some physicists around the world have lost their grip on reality?

To a certain extent, it depends what you mean by the word ‘reality.’ There are some notable, public-facing physicists like Jim Al-Khalili who are really quite wary whenever people want to talk about the relationship between quantum mechanics and reality. The word reality is used very loosely, which is a great pity because whilst on the one hand it’s fascinating—don’t we all want to know more about the nature of reality?—it can become very quickly obfuscated. The kind of conversations you then start to have can become bogged down, because people are talking at cross purposes. They’re actually talking about different things.

We’re at a stage in the development of our understanding of the physical world where the theories that we’ve developed to explain what we see have lots of unanswered questions—and we don’t appear to have an easy or straightforward means to get answers to those questions. So there are questions about dark matter, dark energy and there is this whole mystery around how quantum mechanics should be interpreted as a theoretical structure. It’s quite clear that many of the discussions that are going on are actually quite philosophical in nature. If you strip away some of the scientific jargon, what you’re actually witnessing is a debate that has gone on about the nature of reality since the ancient Greeks.

These are the eternal philosophical problems that, if you’re a scientist, you don’t have any time for. That’s what philosophers do, they spend all their time waxing lyrically about ideas about reality, without really taking us any further forward or resolving any of the issues. Whereas science is supposed to be getting to some answers. It’s getting the evidence. It’s getting the facts, comparing those with theories, seeing what works, seeing what doesn’t work, throwing away what doesn’t work and making progress that way.

We’re now at the stage where we’re waiting 50, maybe 100, years before we’re able to answer a question that we want to put today, before we can get an answer with any kind of legitimacy. It’s a sign of where we are in the 21st century that we don’t have the patience anymore. So, we get lots of speculation: ‘Oh, yes, well, this could be true. That could be true.’  You are endlessly cycling the same kinds of conversations that philosophers have been having for centuries, but we’re calling it science. That’s where I start to get nervous.

“If you strip away some of the scientific jargon, what you’re actually witnessing is a debate that has gone on about the nature of reality since the ancient Greeks”

I won’t name names, but we get some leading theoretical physicists publishing books that strip away some of the jargon and the scientific language and effectively they’re writing about what I would consider metaphysical speculation. In my book, Quantum Reality, I’ve got a metaphor that I use for scientific theorising which says science is all about having the ideas, but then finding ways to confront those ideas with the facts, the empirical data, the evidence. You’ve got this ship of science that travels between these shores—between gathering the ideas and the facts and bringing them together into what we then accept to be a valid scientific theory, in that it says something meaningful about the way we understand the world. At the moment, we’ve got lots of ideas and we don’t have many facts to back those ideas up. So, we’re constantly spinning like a mouse on wheel, with endless debates and not much prospect of getting answers anytime soon.

When you say it takes 50-100 years, what do you mean?

To give an example, Peter Higgs published a paper proposing what is now understood to be the Higgs mechanism in 1964. Yet we had to wait nearly 50 years—49 years, in fact—to find the Higgs boson at the Large Hadron Collider at CERN. That’s becoming more and more typical. You’re having to wait 50 years to close off an idea that seems to make perfect sense. It becomes incorporated in a theoretical structure, it even becomes essential to a theoretical structure, which is why there was so much interest in finding this particle, to the point where we built a billion dollars’ worth of kit in order to get evidence for it. I’m not saying progress wasn’t made in the theory in the intervening time, while we waited, but it would have been a disaster for the standard model of particle physics if the Higgs boson hadn’t been found. It still causes some problems—why does it have the mass that it does? and so on—but nevertheless, we’ve had to learn to be patient.

But then isn’t it OK that people are speculating wildly, because maybe they’ll turn out to be right a century from now? Maybe we’ll get evidence that there are multiple universes?

That’s a good argument, but at some point—and this is very much a personal opinion—you cross a threshold. You are now engaging in the kind of speculation that makes science indistinguishable from pseudoscience. And at that point I, for one, get very nervous, because if well-established professors of theoretical physics can pontificate publicly on things that, as far as we understand their status today, are no different from astrology, then why should anyone have any faith in what scientists say? Physics is supposed to be the hardest of the hard sciences. You wouldn’t look to physics to find lots of pseudoscientific psychobabble. The way it’s taught to kids in school and at university, it’s tough, it’s difficult and it’s very mathematically demanding. And yet here we are, with leading theorists saying all this stuff and saying, ‘This is the latest scientific thinking.’ That’s what worries me. I don’t mind them thinking it. I don’t mind them publishing papers on it. But they shouldn’t use a public platform to say, ‘Come and do physics because we can all then speculate about the multiverse and have a great time’—because that’s not what physics is.

When you say, at the end of the prologue of your book, Quantum Reality, ‘I still don’t understand quantum mechanics, but I think I now understand why’—could you explain what you mean by that?

Funnily enough, I’m working on another project with a well-known historian of science and as a result of our dialogue I had cause to reach to my shelves for a book by Steven Weinberg called Dreams of a Final Theory. That book was about the ultimate theory that brings general relativity—our description of space-time and the universe—together with quantum mechanics in some kind of great synthesis. This would be the theoretical structure that would end all theoretical structures and he made a point in his introduction to the book, that what a final theory would mean is that it would mean the end of a certain kind of science. We would cease looking for deeper principles and would basically have to accept that we have the principles and there’s nothing more to learn. There’s nothing deeper than this. That’s what he means by a final theory.

And I’ve interpreted that to mean that it’s the end of a certain type of science, but it’s not the end of a certain type of question. It’s just that the questions then become philosophical questions and not scientific ones. If there are no deeper principles, then you know everything there is to know from a scientific point of view, but that won’t stop someone saying, ‘okay, but what if? are we sure? how do we know that we’ve reached the end of that particular way of understanding the physical world?’ That resonates with me.

You can understand the great debate between Niels Bohr and Albert Einstein as a debate about whether we’ve got to a final theory or not. Is quantum mechanics the end? Are the only questions you ask about quantum mechanics now philosophical in nature, or are there deeper principles? Are we seeing the end of our understanding of the world at the quantum level in quantum mechanics or are there deeper principles, if only we have the wit to find a way to explore a little bit further? That’s why I say I think I understand why I don’t understand quantum mechanics, because the nature of the debate has shifted from being an entirely scientific debate about right and wrong in relation to facts, to being a philosophical debate about how we understand scientific theories to work and what they represent.

Over the years—the 40 years since I’ve been puzzling over quantum mechanics—you might be shocked and surprised to learn that I’ve almost gone backwards. Having been fairly sympathetic to Einstein’s arguments, which said, ‘No come on, we haven’t reached the end. The great scientific enterprise means we can never shut down and stop, we’ve got to keep looking for deeper principles’, I’m now very worried. I like to quote from Star Wars, the Han Solo character. The actors working on George Lucas’s movies always complained that the dialogue was so horrendously written that they could barely bring themselves to speak it, but Han Solo would frequently say, ‘I’ve got a very bad feeling about this.’ That’s where I am. There are some arguments coming from the other side, from Bohr’s side, that maybe we’ve been kidding ourselves all this time. The game that we’ve been playing with science ever since Galileo—creating a way of representing reality using mathematics to help us understand how this connects with that, what causes that and to predict what is going to happen next—is entirely, I won’t say artificial, but it’s a very human way of thinking about reality. We’ve fooled ourselves into thinking that what we do when we play that game represents reality much more deeply than it really does. It’s worked very well for us. Classical mechanics was a great structure. But maybe in quantum mechanics, there are no deeper principles.

This is the nature of the debate right now.

On that note, let’s start going through the books you’re recommending. The first one is The Construction of Social Reality (1995) by the American philosopher John Searle, who I think is at UC Berkeley. I was worried picking it up that it might be quite dense, but it’s very readable and engaging isn’t it? Tell me why you chose it.

This is about how we think about reality. Rather than dive straight in and say, ‘Okay. What does quantum physics say about our understanding of reality?’ I think it really helps to get the ideas organized in your head if you say, ‘what is reality? What do you mean when you talk about reality?’ I think a great place to start is actually one that doesn’t require a laboratory or a laser or a particle collider. You can just sit back in your chair, wherever you are—in your lounge, in your study, in the office, at home—and look around you and play with the idea of what is real. What John Searle does in The Construction of Social Reality is he really brings home—for me at least—the very fragile nature of what we tend to take for granted as reality as human beings living these very complicated lives that we lead.

We tend to think of reality as being physical reality—it’s mountains, trees, lakes, streams, animals and other things in our immediate environment that we can perceive directly. Searle says, ‘those are brute, empirical facts about physical reality, but there’s way more to our reality than those brute facts.’

There are also what he calls ‘institutional facts’, stuff that we’ve created to help us live: money being a very, very good example. The five pounds in your wallet, I can guarantee you the paper (now plastic) it’s printed on, and the ink, are not worth five pounds. It only continues to have the value that we believe it to have for as long as we all believe it has a value of five pounds. The status of these things that we’ve created to assist us in living our lives are objects in our social reality. I just thought that was incredibly fun to think about.

“Physics is supposed to be the hardest of the hard sciences. You wouldn’t look to physics to find lots of pseudoscientific psychobabble”

I was married for the second time in 2012 and I wear a wedding ring. What John Searle would say about a wedding ring is that we use objects in our physical reality—like a piece of metal fashioned into a ring that I wear on my finger—but it’s so much more than a piece of metal. It brings with it a whole set of social obligations to my wife—to remain faithful, to honour and to love, all of those things—entirely created by us. It exists only in our heads, for as long as the institutions remain. And we can see that over the years, they have evolved. That can be a good thing, but it can also be incredibly easily distorted.

Once you’ve understood and appreciated that the nature of objects in our social reality are created by humans, you realize how fragile they are and how easily our perception of them can be shifted by what we read, by what we’re bombarded with, the images that we see. This, to a certain extent, explains our current situation with regard to what’s going on in the world. Others have used the way that we perceive things to distort those images and to change our perceptions and understanding of them.

One way of thinking about them is to imagine a world where we’ve just disappeared. (In fact, it’s been rather easier to imagine that during the pandemic than perhaps before). All you’re left with are the brute facts: the mountains and the rivers and streams. What’s gone is money. What’s gone is marriage, what’s gone is all of these social structures that we have created in order to live. We blindly assume when we get up in the morning and look at our bank accounts and we reassure ourselves we’ve got enough money to pay the bills for this month. This whole thing is being created by us. It’s been fashioned by our own innate human, mental capacity to create these things and one can have a bit of a debate about the reality of those things as a consequence.

Aren’t the brute facts a bit iffy too?

Once you’ve got your head around the idea that a lot of social reality only sits up here in your head, then you’ve got a whole other set of philosophical questions to ask about the brute facts, and how we acknowledge the existence of mountains and rivers and trees. It’s not so difficult, then, to swallow what philosophers have been telling us down the centuries—that our entire perception of physical reality is based on electrical signals interpreted by our brain. That’s why my second choice is the screenplay for The Matrix (2001).

It doesn’t need to be the screenplay, does it? You could just recommend watching the film.

Yes. I happen to have my copy of the screenplay right here. Whether it’s still available through bookstores I don’t know.

It’s rare for a Hollywood blockbuster movie like The Matrix to pose really rather fascinating philosophical questions and conundrums. This is a film that was written by the Wachowski sisters and pursued through a trilogy, although for me it was always the first film that was by far the best.

The Matrix was set up in such a way that they could open it to some wonderful special effects, but the idea is a very simple one, it’s what philosophers call a ‘brain in a vat’ scenario. How do you know that your brain isn’t actually in your body, but sitting in a vat wired up to a computer which is delivering signals to your brain, which you then interpret as sensory experiences? What you see, what you touch, feel and hear is all a set of signals that are giving you the illusion of living in a reality. That’s the premise of the movie, that Neo (Keanu Reeves) wasn’t actually living his life, he was sitting in a vat contributing to a human battery cell and the machines were in control.

Fans of the movie enjoyed it for all sorts of different reasons, but few, perhaps, would have picked up the connections to the postmodernist philosopher and commentator Jean Baudrillard. There’s actually a scene, early on in the film, where Neo gets a knock at the door. He part times as a producer of illicit software—for what purposes we’re not clear—and he reaches for a couple of disks in a book. The book is a called Simulacra and Simulation and it’s by Jean Baudrillard. The book is saying that there’s a sense in which the lives we’ve created have become unreal. He’s a French philosopher (so his criticisms are of course always of America) and he points, in one passage on post-war American consumerism, to those great gas-guzzling cars that were built, fashioned with fins and lights that looked like rocket ships. These cars were completely absurd from the point of view of physics, those fins would slow the vehicle down rather than speed it up, and he’s saying this is part of the creation of an illusion, an illusory reality whereby what you feel becomes more important than any kind of practical benefit. Our sense of what we would regard as reality becomes less and less important and it becomes about a different set of experiences.

“It would have been a disaster for the standard model of particle physics if the Higgs boson hadn’t been found”

There’s that thread running through The Matrix as well. There’s a wonderful scene where they’re all gathered around in the hovercraft that they’re living in after Neo has been pulled out from his battery cell, where they’re discussing chicken. And they’re wondering, if you’re sitting in your pod being fed these signals, how did the machines know what chicken tastes like? Well, maybe it’s because everything tastes like chicken. All of these little philosophical conundrums: if you’re being fed an illusion of reality directly to your brain, how does whoever’s doing the feeding know what your experience is meant to be like, because these are very uniquely your experiences. How do they know how you know what chicken tastes like?

So, for me, The Matrix as a film and as a screenplay opens up a whole bunch of questions that, again, have been the traditional fare of philosophers down the centuries—but in a way that’s accessible. For me, that’s important. I’m a science popularizer, so making these complex ideas accessible to people who haven’t got a degree in philosophy is, I think, a great thing.

Just even pondering the question can lead an individual who’s fascinated by this kind of stuff in all sorts of different directions. The Matrix was screened back in 1999, more than 20 years ago, and I hope it has encouraged at least some people to say, ‘I’d like to find out a bit more about that’ and gone into deeper texts, or taken a course. I can only imagine that it’s been good from that point of view.

Are we ready to tie this into the science and quantum physics?

For me, it’s a stepwise process. The Construction of Social Reality gets us to question the significance of what philosophers would call the ontological status of objects in our reality. Once you start questioning, that’s the sign of an awakening of an interest and a spark of curiosity that is easy then to feed. That’s social reality. Then you start to look at physical reality and the way that we process information delivered by our senses as human beings. We start to question the reality even of mountains and rivers and trees and streams and other things that we can see in our immediate environment. That leads you to questions like brain in a vat and other things that are fascinating but don’t necessarily have any easy answers that you can give. It’s just a set of philosophical questions you can explore. Before we bridge from The Matrix to science, I personally would want to take another step, to a period in philosophy which is known as the classical modern period.

So classical modern philosophers include René Descartes, David Hume, Baruch Spinoza, Immanuel Kant and George Berkeley and John Locke. It’s that period from the 15th century through to the early 18th century. A lot of very powerful philosophies were generated in that period and one of my favourites comes from Immanuel Kant.

You’re confronted with this issue of, how do you know what’s real? How do you know you can trust your senses? That was Descartes’s launching off point, and he came up with his solution, which is “I think therefore I am.”

But throughout the history of philosophy, there’s been this polarization between those philosophers who want to give priority to ideas, to the way we think, and those philosophers who came somewhat later in history, who wanted to put experience up on a pedestal, like the philosopher David Hume. There’s clearly a conflict here. We have ideas and we have experience.

Kant was one of the first, in my view, to successfully bring these together. And you can begin to see the origins of my personal metaphor for scientific reasoning. You can’t just imagine that because you can have an idea of something it must exist in reality. That was Plato’s world of ideas, that at some level of reality everything we can think about—Gandalf or unicorns or Westeros—must exist somewhere; versus the only thing that exists is experience, everything else that we conjure from our understanding of experience is fabricated by us. Hume was big on saying that there’s no such thing as causality. We just happen to have an association between this happening and then that happening and when we see this happening and then that happening, and then this happening and then that happening over and over again, we tend to identify that as a causal mechanism; this causes that. He says that that’s metaphysics. All we experience is this and then that. So you’ve got this extreme view—this later became known as empiricism or positivism—that experience triumphs everything and you can only draw knowledge from what you experience.

Kant brought these together. He said that in order for us to understand things like causal mechanisms—this and then that—his logical structure was to say that we have, in our own minds, intuitions of space and time. Space and time don’t exist in reality, it’s what we bring to our set of perceptions, our understanding of the nature of the world. Space and time are something innate in us and in the way the mind works and we draw on those experiences. So, you can’t divorce the two. It’s not all about experience on the one hand, and it’s not all about ideas on the other. Kant says we’ve got to bring these two together and he had a philosophy which allowed that to happen.

He also agreed with Hume in the sense of saying, ‘Let’s be absolutely clear. We can have no knowledge of things in themselves’. In other words, if you imagine the Moon: is the Moon there when nobody looks? That’s not an easy question to answer, because of course the minute you don’t look at it, you can’t tell whether it’s still there or not. But the point Kant was making is that it’s true. The answer to that question is, ‘No, we can’t know that the Moon is still there when nobody looks, but, on the other hand, in order for things to exist at all there has to be something that appears. In other words, if we are going to go on appearances, then underneath those appearances there must be something that is. And although it’s an assumption—that the Moon is still there when nobody looks—it’s a perfectly valid assumption. I don’t think anybody’s going to lose any sleep over it. You’re not going to want to get out of bed on a Monday morning because you’re not sure whether the Moon is there when nobody’s looking. Kant agreed that our experience is limited, by definition. We can’t know the reality of something that we don’t perceive—and I don’t mean perceive directly with our own senses. I mean, we don’t even perceive it with the aid of instruments like a telescope or a big particle collider and however we analyze the data that come out of the particle collider. I mean everything, by whatever device we use to look at something, we have to accept that we are seeing it as it appears, not in itself. And that leads you logically to start to think about what physics has to say about this.

The book you’re recommending on all this is Sophie’s World (1995) by the Norwegian author Jostein Gaarder. 

I used Sophie’s World as an example because it’s such a wonderfully gentle introduction to that classical modern period. Jostein Gaarder starts with the Greek philosophers, but for me the book is most powerful when Sophie is learning about the classical modern philosophers. And if you ever try to read Kant, if you ever try to read The Critique of Pure Reason, you’ll understand why it’s good to learn about Kant’s philosophy another way. Einstein read it at the age of 13. Well, I’m no Einstein. I’ve tried to read The Critique of Pure Reason and it’s hard going and not everybody agrees how to interpret it.

Sophie’s World is a wonderful introduction to ideas amongst these philosophers about the nature of reality, about what we can hope to know about the nature of epistemology, the nature of ontology, things in themselves, metaphysics. It’s a really, really nice way to get to grips with what some of these great philosophers were saying about the world.

Then you can start to talk about how that leads into physics and, in particular, quantum mechanics.

I remember reading Descartes as part of my history degree. He was regarded as a natural philosopher, what we would now call a scientist. For the purposes of this discussion, it’s worth bearing in mind that, in the 17th century, philosophy and science were one and the same.

It’s also true of Newton. I’ve got a very good friend who’s a philosopher, based in New York, who says the reason that Descartes is considered a philosopher and Newton is considered a scientist is because Descartes got the physics wrong. I find it fascinating. When you look very hard at Descartes’s cosmology, his understanding and his description of the universe, there were certain principles that we would regard today as being scientific. For example, you can’t have forces that act at a distance in Descartes’s cosmology. If something’s going to be moved, then something needs to move it. There needs to be a contact or a collision or whatever it might be. Leibniz, Newton’s archrival–who is also regarded as a philosopher, not as a scientist—also pushed back on notions that were effectively built in and intrinsic to Newton’s classical mechanics.

Newton had figured out that he could devise three laws of motion and a law of universal gravitation by assuming some things that other philosophers regarded as absurd and metaphysical. So absolute space and time—the idea that the universe is effectively infinite—is intrinsic to Newton’s three laws of motion. And of course Newton’s law of universal gravitation is action at a distance. Somehow there’s a force exerted between them that holds the Moon in orbit around the Earth. How was that supposed to work? Newton had no idea.

What he did have, though, was a set of mathematical structures that were undoubtedly better than anything that had gone before.

Descartes was, in many ways, more a scientist, wanting to adhere to scientific principles, than Newton was. Newton was prepared to accept some metaphysics, things you can’t explain or prove through evidence, because he got a set of principles that were really quite powerful and worked really well. There was more metaphysics in Newton than there ever was in Descartes. And we regard Newton as a scientist and Descartes and Leibniz as philosophers. It’s this really strange contradiction.

Let’s move on to book number 4 and bring in the quantum mechanics. This is Max Jammer’s The Philosophy of Quantum Mechanics (1974).

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.

Can you given me an example of an insight you got from Jammer’s book when you were writing Quantum Reality?

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.

Was this the advice not to ponder the meaning of quantum physics, to just ‘shut up and calculate’?

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.

Let’s talk about your final book, Reality and the Physicist by the French physicist and philosopher, Bernard d’Espagnat.

So Jammer’s book was published in 1974. There were just the beginnings of an awakening of interest in experimental tests of the kind that John Bell had come up with. Even as a young student, Bell had railed against ‘shut up and calculate’, the indifference of the physics community, and as a result of not wanting to let go, he came up with Bell’s theorem and Bell’s inequality. In other words, there’s a way of explaining some of the more bizarre aspects of what quantum theory predicts if one assumes that there’s a hidden mechanism, that there are deeper principles that you can get to if you just drill down a little further. Now, there was no evidence for these hidden variables. But Bell asked, ‘if we were to assume that they exist, what could we expect to see?’ Bell’s theorem is effectively saying that for a certain type of hidden variable it will predict experimental results that don’t agree with what you’d get if you used quantum mechanics to predict the same things. That’s Bell’s inequality.

I don’t know if you’re familiar with David Kaiser’s book How the Hippies Saved Physics. They were a group in the late 60s who had some fun times mixing things like Bell’s theorem and Bell’s inequality with Eastern mysticism and taking narcotic substances while sitting naked in a hot tub (this is out in California, where it was okay to do that in those days). They had some wacky ideas, but they kept these ideas alive. They weren’t the only ones. David Kaiser distorts a little bit the importance of this group, who were known as the Fundamental Fysics Group. Among them was John Clauser, who was one of the first, along with Stuart Friedman, a student, to perform an experimental test of Bell’s inequality. In other words, is there this hidden layer underneath quantum mechanics that would predict that things would come out differently? And the results were pretty conclusive. The answer is no. Quantum mechanics predicts the correct results.

But there were all sorts of questions and doubts. I don’t want denigrate Clauser’s work, which was very good and highly motivational. Experimentalists continued to nag and worry about this problem with quantum mechanics. They wanted to repeat it, if not go a little bit further and make some more sophisticated experiments. It took another 10 years. In 1982, a French physicist called Alain Aspect and his colleagues at the University of Paris were the first to report definitive experimental results. These were really the earth-shattering results that most people point to when they talk about Bell’s theorem and Bell’s inequality. Now, there have been lots and lots of experiments since that have all simply deepened the realization that as far as this certain type of hidden variable is concerned, it’s not there. Quantum mechanics is correct, despite the fact that it predicts or seems to predict all these spooky things.

“We’re now at the stage where we’re waiting 50, maybe 100, years before we’re able to answer a question that we want to put today”

My fifth book is again a stepping-stone. Bernard d’Espagnat actually spent some time sitting in those hot tubs in California with the Fundamental Fysics Group. For me, Reality and the Physicist is a very, very good introduction to the conundrum, the realization that there isn’t an easy way out of this. If quantum mechanics is all there is, then we can still salvage some understanding of how we think reality works by producing more esoteric mechanisms that lie beneath quantum mechanics. These include something called the de Broglie-Bohm pilot wave theory where you have a wave and particle construction. The only trouble with that is that it means if I do something over here, it has to instantaneously affect something over there, even though over there could be halfway across the universe. The notion of spooky action at a distance is intrinsic to this kind of pilot wave theory.

Or you can say it’s all about consciousness. This idea of the collapse of the wave function doesn’t really happen, cats are both alive and dead at the same time—until we lift the lid of the box and look and it registers in our conscious mind. These are ways and mechanisms of salvaging a sense of realism in the quantum formalism.

Or you can go with what Bohr said, right from the beginning, all those years ago, that the formalism itself is a ‘a purely symbolic procedure.’ All we’ve got is experience. We know when we do this, that happens, we code for that in the mathematics and we have a finely-tuned mathematical structure that allows us to plug in what we’re going to do and predictions for the probabilities of what’s going to happen. That’s it. There’s nothing more to it than that.

That’s not shut up and calculate. If you follow that logic, you’re coming to that conclusion on the basis of reasoned philosophical, logical arguments. That’s not saying it doesn’t matter. Bohr is not indifference; indifference is not science. Indifference is not really trying to push science that little bit further. For me, the Bohr-Einstein debate is the ultimate summation of what science should be, a constant to-ing and fro-ing on what we think this means.

Reality and the Physicist, my fifth book, is effectively, then, a springboard to the way I structured my own book, Quantum Reality. I spend quite some time—two chapters—trying to make sense of reality and what we mean when we talk about it. We’re often so loose in the way we talk about it, I think it’s important to get some definition in there. And there’s a very distinct difference between the way philosophers think about reality and the way scientists think about reality.

I wanted to bring those two together and I came up with a metaphor. You’ve got this island of ideas—the shores of metaphysical reality—and you’ve got the rather brutal, harsh shores of empirical reality where all the data sits, where all the facts are. And the ship of science ploughs back and forth on the sea of representation (yes, I’ve read too many fantasy novels). The idea is that you build a scientific theory as a result of accumulating new ideas and the facts and welding them together. There’s tension and a mix of the two.

They do become horribly entangled. You often can’t distinguish between the ideas and the facts anymore, and the ideas become part of our language for describing these things. You try and get someone at the Large Hadron Collider to explain what they do, and I can guarantee you they’re going to tell you about the standard model of particle physics. They’re going to tell you about quarks and gluons and so it goes on. It’s not clean. It’s messy, it’s profoundly noisy. It doesn’t always work. Sometimes it works brilliantly well, but then we have a scramble to understand what the hell it all means.

In the sea of representation, I put two dangers based on Homer’s epics. That’s Scylla and Charybdis. Scylla is the harsh rock shoal of instrumentalism or stark empiricism. This is the ‘shut up and calculate’, the indifference almost, where in effect you’re very close to the shores of empirical reality because it’s all about the experience, it’s all about the data. Don’t worry about what it means, just plug in the numbers and do the calculation. On the opposite side, you’ve got Charybdis, which is a whirlpool of metaphysical nonsense about the nature of reality. It’s ideas bereft of any data to back them up. That’s where I put the so-called many-worlds interpretation of quantum mechanics, the idea of Schrodinger’s cat which is in some kind of fantastic ghostly state of being both alive and dead, when you lift the lid of the box the universe splits and in one universe the cat is dead and in one universe the cat is alive. It’s a nice idea and a great basis for a whole raft of movies that have been made, but in my view it’s pure metaphysical speculation. There’s absolutely no evidence for the universe splitting like this and there can’t be.

I hope readers of my book will at least find it useful as a way of categorizing and thinking about all these different interpretations. But I’ve got a very bad feeling about quantum mechanics, in the sense that we could literally be at the stage where this is the final structure and there are no deeper principles, but it’s not in our nature ever to agree on that. And that’s again why the Bohr-Einstein debate is so important. There are arguments this way and there are arguments that way.

When you say you’ve got a bad feeling, does it mean that it’ll be forever unresolved and we’ll be unable to find out what it all means?

I think so. With the exception of the many-worlds interpretation, which I don’t like, I’m reasonably agnostic. I believe that what’s important is the debate. What’s not good is indifference. You can’t be indifferent to this and if you’re indifferent to it and your area is quantum physics, for me, you’re not really being true to yourself. There’s almost a moral imperative to be curious about this question. Otherwise you’re betraying science, to a certain extent.

And you feel there should be more philosophy in the science?

The more I’ve looked at it and the more I’ve studied it, the answer to that question is unequivocally yes. If you look back at the debates that went back and forth between the founders of quantum mechanics—people like Einstein and Bohr and Heisenberg and Schrödinger—these people were from a moment in time where it was expected that to be a scientist you would be a rounded scientist. You would know some philosophy. As I mentioned, Einstein read Kant’s Critique of Pure Reason at the age of 13. There were no ‘two cultures.’ You knew some philosophy, you could play a musical instrument. That says something about the class of people involved as well, and their access to quality education.

Today that is almost gone. Those who position themselves to pontificate about the grand questions in science don’t have that background in philosophy and they don’t have an understanding of history that would allow them to make more informed comments or draw more informed conclusions.

The basis of my book is to say, ‘Hang on, in order to understand the nature of why this is so bloody difficult, you’ve got to understand the heavy dose of metaphysics and philosophy that exists in all of this.’ What I’m hoping that readers will come away with from my book is the understanding that you can’t just separate these two. There’s not science on the one hand and philosophy on the other. To understand how science works, you need some grounding in philosophy to understand how a scientific theory comes together, what differentiates science from stuff that isn’t science—the demarcation criterion that philosophers have been nagging about for at least 100 years and still haven’t got anywhere and some have largely given up on.

In your books, and on Twitter as well, I’ve seen you being quite critical of ideas put out by some academic physicists. Do you ever get a chance to debate with them?

It’s funny, I got hooked on these questions about quantum mechanics from about 1987 onwards. Within 18 months of getting hooked, I quit academia. My first book on quantum mechanics was published in 1992, it was called The Meaning of Quantum Theory: A Guide for Students of Chemistry and Physics. There’s a bit of maths in it, but not much.

That commitment has never left me. I wrote a book called Farewell to Reality, published in 2013, which was quite a strong criticism of some aspects of modern theoretical physics, particularly string theory and the multiverse. I tried to put forward reasoned arguments—some of them based on philosophy and understanding what a scientific theory is and the importance of a connection with empirical data, all that stuff. As a result of that book, I got invited back to attend scientific conferences again. It was quite extraordinary, after all those years, to be invited back.

It’s been lovely to re-establish contact, but it’s a different community. I was a chemist—admittedly a chemical physicist, there are subtleties in all of these disciplines—but now the contacts I have are with physicists and some philosophers. It’s been a great journey. I have debated with some of them.

And your view is that it’s an important time for scientists to get this right, because science is under a lot of pressure, with lots of people distrusting it?

If you look at the website of the Discovery Institute, which is the intelligent design organization based in Seattle, it’s not too difficult to track down regular blogposts about what physicists are saying about the multiverse, as a way of saying, ‘here’s an example of scientists going way beyond any evidence, and speculating about stuff and calling it science. So why isn’t intelligent design science?’

It’s a general and slow erosion. As I said, physics is supposed to be the hardest of the hard sciences, but people position themselves, with a public platform, as leading theoretical physicists, and say this stuff. The risk is then that it becomes more and more necessary to build a scientific career publishing papers that are about this stuff, and less and less about doing the hard graft and finding ways to get supporting evidence for your ideas.

What kind of stuff?

String theory is a good example. The momentum now is moving away from it, people are turning their backs on it, but for a time, there were more string theorists than there were physicists in 1900. And all for a structure that was basically a house of cards based on metaphysics. Nature might be like this, and it might also be like that, and then it might also be like this. You’ve got this whole structure that has absolutely no supporting evidence, and people publishing paper after paper after paper and calling it science. Science goes through these spasms, it goes through these difficult periods, but again, you’ve then got leading theoretical physicists—for a time Brian Greene was publishing bestselling books about string theory and what string theory tells us about the latest scientific thinking—when there’s absolutely no foundation for it. I’m not saying it’s the same as astrology, but I’m saying that what we look for when we do science, is we look for evidence, it’s that bringing together of evidence and ideas that makes science tick. And if it’s okay to do science without evidence—hence the notion of post-empirical science, an oxymoron—the risk is that it undermines all the arguments you have against stuff that is potentially really damaging, like the anti-vaxxer movement, like intelligent design, all of these things that can really undermine the way people are thinking about things and affect their lives in very serious ways, because the trust has gone: ‘I don’t trust big pharma, I don’t trust scientists, therefore I’m going to make up my own mind and I’m not going to vaccinate my kids.’ That’s the way the logic goes. And then you’re in big trouble. Then you’ve gone backwards.

Speaking about the practical effects of what we’ve been talking about, does quantum mechanics power my phone or anything like that I should be aware of?

Anything that involves a computer processor of some description, so definitely your smartphone, will rely on quantum mechanics for its operation. One of my favourite examples is GPS. Do you use GPS on your phone?

All the time.

Do you know that GPS wouldn’t work without the special and general theories of relativity? Again, there have been arguments back and forth, but I can point you to papers that explain that without corrections—based on Einstein’s special and general theories of relativity—in the way data is reaching you from the system of six or seven satellites that you’re connected to at any one moment in time, you’d start to accumulate errors of the order of 11 km per day. So, after a couple of weeks, you could be anywhere on earth.