David: Running through our conversation has been this sense, listening to you, that ideas, in your example ideas, that you find beautiful, are very powerful: they can guide what you think and what you do next. Do you think that ideas really do have that power? That they are as much a force in the world as the basic forces you are thinking about?

Because non-scientists tend to think physicists are always going to say that everything that happens is just these particles bumping into each other. And here you’ve been talking about it as if thoughts themselves shove the particles around: it was the thought which led you to the next idea. Do you see what I mean?

FW: Yes, I think I do.

David: It’s saying the radical reductionism that says everything that happens is determined by the bumping of the elementary particles, taking Laplace to the extreme…

FW: There’s a concept that Niels Bohr elaborated that I’ve fallen I love with that I think is very profound: it’s called complementarity. It’s something that’s just a true fact about quantum mechanics but is much more general. It’s the idea that you can have different descriptions of the same thing that are both valid, and both important for answering different kinds of questions, but they are mutually incompatible. It’s closely connected to wave particle duality. There are different ways, mathematically, of processing the wave function. I think that’s a much more general principle. Well I know it’s a much more general principle, and I think that it even applies to things like the problem of free will versus determinism.

There’s one description based on physics that tells you that, for practical purposes, in principle, the brain, for instance, is a pretty nearly deterministic, noisy, but deterministic system. Whereas if we want to deal with our own experience, if we want to interact with other people, if we want to have sensible systems of law, we need to use this concept of free will. And they are both valid descriptions, but they are meant to address different aspects.

David: But you think they are both genuine? Because listening to you, it was on the tip of my tongue to say there’s the rejoinder which says, ‘Yes, but that stuff about free will: that’s just a place-holder until we’ve really worked out the physics, and really, ultimately, there’s no such thing.’

I’ve talked to scientists who have said there is no such thing as free will; there is no such thing as the self; there’s no such thing as consciousness. I’ve had all those things said to me in the last five or six years, and the answer is always the same: ‘I know you think you’re conscious, but actually it’s just the chemicals in the air and they’re buzzing around and that’s why you’re laughing, it’s not because anything is funny.’

FW: This reminds me very much of Dr Johnson after hearing Bishop Berkley’s sermon about the unreality of matter, and famously Boswell said that this seems crazy but it’s impossible to refute. And Johnson kicked a stone and said, ‘I refute it thus.’ So when people say there’s no such thing as consciousness, come on!

David: I’m with you on that, but there is that sense that…

FW: Okay, we can illuminate it. It’s like saying there is no such thing as life because we can understand it on a molecular level. Life! There are useful concepts that are necessary in describing large domains of experience that aren’t going to go away. They may have alternative complementary descriptions.

David: But you think they’re real?

FW: Yes, I think they’re as real as anything can be. They are useful. They describe actual things in the world.

David: And ideas would be one of them? That realm of ideas?

Ard: And I think what you’re saying is that they may be contradictory if you try to have them at the same time?

FW: Yes, if you try to apply them at the same time, they can lead to contradictions.

Ard: But, nevertheless, they are both true if you are asking the right kind of question?

FW: They are both useful and necessary, I think, in addressing different kinds of questions.

Ard: In your book you say, for example, objects and persons are complementary.

FW: This is very much relevant to the discussion of free will. When we are trying to predict what they’re going to do, how we should interact with them, we are thinking of them in one way. If we are thinking about them as what their height is; what their mass is; what they are as physical objects; am I going to run into this object? If I’m diagnosing a disease, I want to analyse the chemistry. That’s a different way of thinking.

Ard: And those two ways are complementary to each other?

FW: They’re complementary. They’re both valid, but there’s a lot of tension if you try to apply them at the same time.

Ard: That’s really interesting. That’s a profound point that they’re both valid ways, so the world of the person is the world of intentionality, and the world of ideas as well. And then there is the world of the human being as a wet computer, a bag of chemicals, and they’re both useful. They may even illuminate one another, but if you try and apply them at the same time, or if you say that one is superior to the other, you’re missing something.

FW: Yes, that’s a good way to put it: you’re missing out. It’s not that you’re wrong in some sense, well I think actually that you are wrong, but at the very least it becomes very awkward to express concepts of intentionality, of emotion, of ideas in physical terms.

David: So are you sympathetic then to people like George Ellis who think emergence is something that’s a useful idea?

FW: The general concept, I think, is very much in line with these ideas about complementarity: that different levels of description can be useful, and if you’re describing the same thing in different ways, it’s also important, if you can do it, to make those consistent and get a rich interconnection between the two. So yes, I have a lot of sympathy for that. But where I don’t go is, I think our description of the world based on what Newton called analysis and synthesis – and I would like to call it that, but many people call it reductionism – the idea that the way you build up the description of the physical world is by understanding very small parts thoroughly and getting a complete description of those and then building out from there. That’s been extremely fruitful, extremely successful, and I don’t see any sign that it’s open to influence from higher levels. So specifically, for instance, at an accelerator, I don’t believe that no matter how hard you think about it, you’re not going to change how the protons collide.

David: It does sound a little bit like you’re trying to have your cake and eat it too. Obviously the accelerator, you chose the example because it works for what you were just saying, but then let’s take the mind again: does that mean the next word I’m going to say is forced upon me by the particular configuration of all of those particles? Or was it that I was having a thought and the logic of the thought dictated what I would say next?

FW: If you are discussing thoughts and how they evolve, then the appropriate language is cognitive language. That’s the way that people have found useful and have developed to express and analyse the development of thoughts. If you want to know about brain events, especially at a microscopic level, then you want to use quite a different description. Those can both be valid descriptions.

David: They have to be, in a sense.

FW: I think they are, but for different questions. If you want to use thought patterns to predict how chemical reactions and atoms are going to behave, I don’t think you can get very far. There are many, many different chemical reaction patterns and things that could correspond to the same thought, and conversely only slightly different chemical patterns could lead to grossly different thoughts. So it’s not a stable, simple mapping. It’s very complicated at best, and practically useless. So that’s why you have complementary descriptions of these different phenomena that are used in very different terms and superficially incompatible – and maybe not only superficially but just plain incompatible – but, in any case, appropriate for answering different kinds of questions.