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Topic Series
Christopher Isham
- Robert Lawrence Kuhn
- Chris, I ask myself a strange question: what things are real? And it's important to me. I want to know what reality is composed of. So, let's start really simple. What is a thing? How do you define it? As a physicist, someone who's interested in philosophy, what is a thing?
- Christopher Isham
- Well, let's be clear what you mean by things, and also the word real, if we may. By things, do you mean physical things?
- Robert Lawrence Kuhn
- No. I mean, what things are real? But let's start with physical things.
- Christopher Isham
- No, no, no. Well, that's turning the question around. Alright, let me ask you, then, what do you mean by real?
- Robert Lawrence Kuhn
- Okay, well let's—let me go back to thing, then. There are categories of ideas in the world that are concrete things, like this table. So, we want to ask, is this table real, and/or is it just a composite of different particles and forces, and that it's not really real, it's just sort of a composite? That's a question that people ask. Another way to approach it is, what about abstract objects? Are abstract objects real? Numbers, logic, possibilities? Another question is, are there things beyond the physical? This is – the category of real is all that is. But I want to start simple. I want to start with physical things. As a physicist, someone who has thought about philosophical things as well, what is a thing? Help me. I don't have the answers.
- Christopher Isham
- Okay, let's conclude [unintelligible] for example, from the discussion, from a physicist's point of view.
- Robert Lawrence Kuhn
- Okay.
- Christopher Isham
- If you ask me, what is a physical thing –
- Robert Lawrence Kuhn
- Okay.
- Christopher Isham
- Well, it is a great question, actually. Because of my interest in philosophy, going back to Plato, and of course, Plato had very clear ideas about what was real, and that would include things like numbers, and so on, feeling they were equally real. For years, I wanted to write a paper with what is a thing; I thought it'd be great. And a couple of years ago, the opportunity arose, and I and my collaborators, in fact, wrote a terribly long paper called "What is a Thing." Now, one of my philosophical interests is Heidegger, is existentialism, and he wrote a book called What Is A Thing, and right at the very beginning, there's a wonderful paragraph – I can't remember exactly – it's this – it sounded to the effect that, what is a thing is the most important question anyone can ask in any generation. What is surprising is that the question has to be asked over and over again, i.e., it's never resolved. From a physicist's point of view, a thing, classically, is a bundle of properties or attributes. So, a particle, say, has a position and momentum, and that's what it is, in a way. The thing in itself is not discussed by physicists, not classically – only the properties. Heidegger, interestingly, says that in his book. He didn't know about physics, what he says. Now, in quantum physics, it's quite different, because you can't say that, you see, normally. In quantum physics, it is purely empirical. You talk about measurements, but you don't refer to a thing in itself, because you can't. Now, in my own recent work, I've tried to get around this sort of dichotomy. You see, one interesting thing is this; if you think about how physics is structured, you have, on one hand, space and time, on the other hand, things. And space and time is the arena in which we encounter things, you see?
- Robert Lawrence Kuhn
- It's a classical view.
- Christopher Isham
- Yeah, classical realism. But the first question you have to ask yourself, are space and time a thing? So, I'll ask you this question. Are space and time real?
- Robert Lawrence Kuhn
- Yeah, I'm the one person there. You've got to tell me. I'm coming to you. Well you know, our perception of it is real.
- Christopher Isham
- Yes, we all – now, I'm asking; we all have views about time, right?
- Robert Lawrence Kuhn
- Right.
- Christopher Isham
- To us it's real, yes. But if you're asking, is it real in itself or is it just an empirical experience we have? Maybe it is the latter. I don't know.
- Robert Lawrence Kuhn
- Yeah, and that's a question for physicists more than psychologists.
- Christopher Isham
- Yeah.
- Robert Lawrence Kuhn
- We have to get to the fundamental nature of stuff.
- Christopher Isham
- Yes, though of course, in saying that, you're automatically cutting away certain possible answers to the question, which may be more idealist.
- Robert Lawrence Kuhn
- Well, maybe, if – that's right. You're right. You're right. Maybe that's a mistake.
- Christopher Isham
- If you ask a physicist, what is a physical thing, well, they can't possibly answer the question, because things in general – you don't mean, what is an electron, what is a proton – things in general. It's not a subject a physicist could ever answer, beyond what I've said. Then, in classical physics, the way we talk about things is as a collection of properties –
- Robert Lawrence Kuhn
- Okay.
- Christopher Isham
- And we regard those properties as being real. So, actually, we do regard this table as being here, or this certain cup, and so on. That's how you would think about things in classical physics. So, that's an answer to what is a thing, actually, classically, is a bundle of properties. But there's no talk about the thing in itself. But the assumption, in classical physics, is that there is some underlying thing in itself, but we don't talk about it as scientists. We can't possibly do that, see? When you come to quantum physics, it's very different, because there you have to ask the question more in a more deep way in a more [unintelligible] way, and then, the debate between realism and antirealism can become quite strident.
- Robert Lawrence Kuhn
- So, after you get a thing being a bundle of properties, what is the next step? How do you make progress? What follows from that?
- Christopher Isham
- Well, of course, the next step, if you're a physicist, is you measure the properties, you see? This is where empiricism comes in.
- Robert Lawrence Kuhn
- Oh, okay.
- Christopher Isham
- So, as far as classical physics is concerned, you can be a realist or antirealist. It doesn't matter, because if you're an antirealist, you're measuring the properties.
- Robert Lawrence Kuhn
- An antirealist being someone who just is – looks at the empirical data –
- Christopher Isham
- Yes, that's right.
- Robert Lawrence Kuhn
- – and doesn't infer that there's some deep law, or deep essence that we can immediately know.
- Christopher Isham
- Yeah, that doesn't – that's right. Doesn't infer there's, like, being in itself, as it were. That's right. But, it – but, yeah, so, they're classical physicists. You can take that view, if you want. However, in fact, the things you're measuring within classical physics, it does no harm to imagine this being real, because if you do that, there'll be no contradictions of anything that you experience. So, in other words, it's one of these situations where you can choose what philosophical position you like; it doesn't really matter. Now, in quantum physics, it's very different. Can I talk about quantum physics here?
- Robert Lawrence Kuhn
- Sure.
- Christopher Isham
- So, quantum physics is very different, because there, you cannot be a realist in the ordinary sense, because of this famous theorem called the Kochen-Specker theorem, which basically says, you can't do it. The world doesn't exist in the sense of being real, in the way I think you're using the word. And the normal physicist's response to that, at least traditionally, has been the empirical one. So, we talk about measurements only, and what's the average value of results, and so on. And now, if you ask, what are we measuring, then – it's an interesting question – is we're measuring quantities which no longer adhere to a thing in itself. You can't actually assay that anymore, you see? So, it's interesting.
- Robert Lawrence Kuhn
- But if you have enough of it together on a macroscopic level, it always results in—
- Christopher Isham
- Oh, indeed. And one of the big issues in quantum theory, for many years, is exactly how do you describe the transition between the atomic world and the microscopic world? Because what you say is absolutely correct. And that's never really been solved, I don't think, not at least satisfactorily. Many people have attempted, and some people would tell you they have solved it, no doubt, but I think I would say, it's still a very interesting question.
- Robert Lawrence Kuhn
- Well, what are the issues on that? Because that seems very fundamental. You can't – you don't know the reality at the micro level, and the micro level all – the macro level just sums up all the micro level, and so suddenly, you get real things when you didn't have it in your constituent parts.
- Christopher Isham
- Yeah. Interesting, isn't it? Yeah. I mean, there are many different answers to this, because many people get involved in these debates. It's a very – it is a very profound question, because there's no doubt about it that you cannot talk about ordinary realism at a subatomic level. So, what we have to somehow show is that, on the average, somehow, this table emerges from the property of all these electrons. I mean, the normal way this is treated these days is to argue there's some sort of, what we call, coarse graining principle at work. So, somehow, for some reason or another, we average out the real properties of the table and see only the average ones, and that's what we see. So, you'd have to say – if you're being honest – actually really, this table doesn't exist – at least not in a strict sense. However, there's something called decoherence that physicists also talk about, and that argues that, actually, all sorts of things will make the table appear as if it was real.
- Robert Lawrence Kuhn
- You comfortable with that? Are you?
- Christopher Isham
- Um, yeah. I've no objection to that, because it's [stumbles] this empirical answer, this instrumentalist answer, is simply saying that, on the average, we see something. Actually, always in physics, you have to somehow declare your boundaries. You can't study everything at once as a scientist. So, you have to decide if you're a classical physicist or a quantum physicist, quantum cosmology, or particle physics. In each one, you have your own philosophical domain, and you use that, but there's no overarching of philosophical structures, see.
- Robert Lawrence Kuhn
- But there has to be.
- Christopher Isham
- Ah. Maybe. Well, that's what our mind would tell us. One of the great things that I talked a bit about, quantum physics, of course, is it's showing us that instinctive reactions, like yours, are not necessarily correct.