Philip Ball is one of the UK’s leading science writers and his new book, Beyond Weird, takes a fresh look at the subject, opening the quantum world up to the lay reader – as far as such a thing is possible.
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Quantum theory is much referenced but rarely – and possibly never – understood. Philip Ball is one of the UK’s leading science writers and his new book, Beyond Weird, takes a fresh look at the subject, opening the quantum world up to the lay reader – as far as such a thing is possible.
Nick Spencer talked to Philip about the book, quantum theory, and – lest you are already wondering why Theos is engaging with such a topic – about how both quantum theory and theology come up against, and try to deal with, the same problems concerning the limits of language.
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Quantum theory is a slightly unusual topic for Theos, to put it mildly, but there is specific reason why we are talking about it today. I guess the best place to start is with your book, Beyond Weird.
The aim of this book is not to explain quantum theory in the normal sense of what we might mean. It has a message more than an explanatory function. The message is, for too long when quantum theory has been talked about in the popular sphere and within science itself, there is a set of metaphors and even clichés that we use to tell people about it.
So we say that in quantum theory, particles are sometimes waves, and they can sometimes be in two places at once, and they can communicate with each other instantaneously over huge distances in some spooky way – things like this. It has become clear to me in writing about this subject that these are obsolete ways of talking about quantum theory and we can do better now.
In fact, we need to do better now because they are not just inadequate. They are misleading and sometimes plain wrong. So I want to try and change the story we tell about quantum theory and what it means and the story it tells us about the everyday world.
The story is less about what we know and more about how we know, isn’t it?
I want to suggest that rather than it being a story about particles being waves and the mysterious thing called the ‘wave function’, which Erwin Schrödinger came up with in the 1920s, I think it increasingly is a theory about what can and can’t be known about the world. Even those words I use are inadequate as I say them. It’s really a theory about what can be said to be knowable about the world and what is not.
Niels Bohr, the Danish physicist who was at the centre of the development of quantum physics in the 20s to the 40s, and someone who worked under him – John Wheeler, an American physicist – had a nicer way of putting this. They spoke very carefully about what we are permitted to say by quantum theory, and that to me seems to be the crucial thing: it permits us to say certain things about nature and doesn’t give us licence to say other things.
So, for example, it permits us to say what we will see when we look at a system that is governed by quantum mechanics. Now, every system is governed by quantum mechanics, but we usually only see quantum effects in often quite esoteric laboratory set–ups. In those circumstances, quantum mechanics will tell us what we are likely to see if we make a measurement. And when I say ‘likely’, I mean what it tells us is a set of probabilities for particular outcomes.
Say we are making a measurement on an electron. There is a property it has that we call ‘spin’, and all you need to know about that is it has two possible values, which can be called either ‘up’ or ‘down’. Quantum mechanics says, if we measure the spin we will see one or the other of these values but that is all we can say about the spin. And it will also tell what the probabilities are that we will see one or the other of these values, and they depend on how the experiment is set up. In that circumstance, we can never use quantum mechanics to tell us exactly what we will measure, but only what the probabilities are of the different possible outcomes.
One of the fascinating things about quantum mechanics, and why many people are so intrigued by it, is because it seems to re–introduce the observer/participant as a relevant entity within an experiment. For 300 years, science had been systematically trying to exclude that subjective perspective, and all of a sudden quantum mechanics invites it back in and says this is relevant and meaningful.
That was the unsettling thing for the pioneers of the theory and it is the thing that is still unresolved now. One way of looking at it is that quantum mechanics points in the opposite direction to most scientific theories. Most theories propose to tell us something about the underlying phenomena that are causing what we see – they point down into the world if you like, perhaps down into the microscopic properties of matter or something about objective reality.
Quantum mechanics, if we are very strict about how talk about it (as Niels Bohr was), is instead pointing towards us, towards our experience. It says, ‘this is what you will see’. And it’s rather specific about that. It is not saying this is what one will measure in general. It is saying ‘you under these circumstances in this experiment will see this.’ If you measure the same system in a different experimental set up, you may see something different, and the theory can tell you what that will be as well.
Weirdly, then, it points up towards us – towards observation. And not only that: the most disconcerting thing is that what it seems to be saying is that until you look, you are not permitted to say what is going on. This is really at the crux of measurement. It’s already weird enough that it’s just telling us what we’ll see and not what’s causing it – but it appears to imply something more: that the very act of our looking is doing something to the “reality” we’re studying.
Which has caused some people to infer that we are in some way creating that reality.
Yes, and all the arguments are about what that can mean, because the temptation is to think that somehow we have a physical influence through our act of looking or our act of recognising… that this thing that is registered in our mind is somehow causing the world to change down there. That’s one way of looking at it that some scientists have suggested, and that seems, of course, deeply odd and is at total odds with how science is meant to work.
But I think it’s no longer clear that this is the way we have to think about it. Rather, what quantum mechanics seems to be saying is that what you will see depends on the questions you ask, and that’s subtly different. It’s saying there are various possibilities that this quantum system could produce. If you ask certain questions, it will produce these answers with these probabilities, but if you ask other questions it will produce these other answers.
That’s a little bit different, and I think it’s different in an important way. This is why I think of it as theory about know–ability: because what it really seems to be saying to us is not that we have a causative effect on what the world is like, but that what we are going to see depends on what questions we ask.
It’s very clear that we are operating in a field where what we consider to be ‘normal’ and ‘real’ is challenged, and we are required to think differently about it. And this is where I want to get on to the topic of language.
You use a lovely quote from Bohr in the book ‘we are suspended in language’, which is a rather poetic way of putting it. We can’t operate in any other field and yet self–evidently language is inadequate to describe what we are encountering.
In one sense, this is perennial problem as science is always encountering the new and therefore you are faced with generating a vocabulary to reflect that newness. That is a problem here but the additional problem is that the quantum world is not like the realm of classical physics, within which human language emerged. And so the task before people who are engaging with this subject is how do to use ‘classical’ language to describe a world that is profoundly unfamiliar? Language is a key theme in the book and its one that the quantum physicists you write about were alert to.
They were to different degrees, I think. Bohr himself was extremely careful with language and you can see the consequences of that in what he writes because it’s extremely hard to understand. It is very laborious because he was trying so hard to articulate what he meant. He recognised that part of this problem is a linguistic one and that is occasionally acknowledged by others as well.
I was thinking about the fact that the word ‘unspeakable’ is used by Augustine in City of God to talk about God, and he frets there, of course, that even if you call God unspeakable you are speaking about him. This just sounds so familiar to Bohr’s struggles. In fact, there was a particularly influential volume of writing about what quantum mechanics means from the physicist John Bell called Speakable and Unspeakable in Quantum Mechanics.
There is plenty in science that is very hard to explain, but that’s not the issue here. It’s that our language doesn’t permit us to talk about it. Wave–particle duality is an example of that, which people use to explain why sometimes quantum objects behave like waves and sometimes particles. The expression leads to a vision of something switching between two modes of existence, but that’s not the right way to think about it, and I think people working in the field would acknowledge that.
Quantum entities are what they are, and we have no reason to think that they sometimes change their character depending on the experiment we perform. It’s just that the behaviour that we see is, on the one hand, the classic behaviour we have associated with particles and, on the other hand, with waves. We have to be very careful with language.
That admission is not a bad place to start because if you are already alert that what you are trying to say is a priori unspeakable and then you go on speaking about it, you’re approaching it with due humility and caution.
I am struck by your analogy that quantum objects ‘are what they are’. The way that the writers of the Old Testament talk about God can be almost put into two registers. There is the kind of metaphysical approach; so when Moses asks God “Who shall I say sent me?” God’s response is “I am who I am”. That’s an indication of transcendence, in the sense that the reality of God is what it is, so don’t try and contain it or put labels on it.
At the same time, there is recourse to the most ordinary and worldly metaphors and similes, which populate the Old Testament – farmer, father, nursemaid, rock, eagle. So you get this tension between recognising what we are trying to talk about here is beyond our capacity for language and at the same time, appropriating mundane terms, which you know are inadequate, to try to put your finger on what you are actually talking about.
Yes, you see the problems in doing that with theology and we face the same thing with quantum mechanics, in the sense that our habits of thinking, for very good reasons, are so ingrained that we keep tripping ourselves up on them.
The classic experiment in quantum mechanics is the double slit experiment, where – in one form – you fire a particle (I’ll use that word for now) like an electron at two slits in a screen and the question is which one will it go through. If you look at the results from the other side, it looks as though the particle has shown its wave–like behaviour and what you see is what you would expect from waves going through two slits. Yet there is just one particle. Surely, it’s gone through one slit or another? The only way we have habitually been able to talk about that is to say it went through both slits at once – both paths at once.
This why people say quantum mechanics is weird. I understand why it seems necessary to talk in those terms, but what Bohr would say is, ‘Stop, you are talking about the underlying phenomena here that are allegedly causing what you see. You’re talking about paths that this electron took, but we are not permitted to say anything about paths because quantum mechanics tells us nothing about them. What it tells us is that we see this pattern that is characteristic of wavy behaviour on the screen. All the rest is conjecture.’
That conjecture is one we construct in terms of classical ideas – things taking paths, balls going through the air – and we forget we are not permitted to say this in quantum mechanics. That’s what Bohr reminds us of.
And that’s really the problem – we feel the need to have some kind of way of talking about what is causing what we see. That’s just our instinct. But quantum mechanics does not support those stories.
You mention in the book that there are some physicists who effectively say ‘don’t bother, let the maths do the explaining and that will be sufficient’. But you think that is not sufficient, because we are linguistic animals and we need to understand through language, so we have to try to go beyond the maths and put pictures and words to this but caveat them or footnote them.
Yes, it’s true that some people see that as the logical end of Bohr’s position: If it’s just a case of looking at what we measure then let’s just stop there because the maths tells us how to do that, and the maths is always shown to be right. So we can predict for a tiny transistor governed by quantum mechanical principles in a computer how it will behave. What more do we need?
That is a perfectly valid position to have and it’s one that, consciously or otherwise, many physicists and engineers use daily to good ends. But it goes against our intuitions. We crave a story to tell about what is causing what we see and I don’t think we can get away from that. I think it’s entirely valid to say to Bohr, ‘Your prescription is not good enough, we need to be able to speak about what’s going on underneath this’.
What I try to do towards the end of the book is to suggest some of the stories that look like they’re emerging to supplant the classical ones that really don’t seem to give us the right picture. They come down to being stories about what can and can’t be done with information. They might, for example, be stories about how much information an object can hold.
Taking a step back and thinking about what this says about human cognitive capacity… We have evolved brains and that means our brains and the language that comes from them is very good at doing certain things that are, roughly speaking, human–sized. The metaphors and similes that we draw from that level function reasonably well for things that are bigger and smaller than us. So there is an area within in which we currently operate that we can be confident that we capable of knowing, understanding and talking about with a greater or lesser degree of accuracy.
But one of the things I take you’re writing about is that there are other things and other aspects of reality that we can get some grasp on, but it’s always going to be in some sense tenuous, simply because we have this cognitive range and beyond that we begin to flounder around a bit. Is that a fair assessment?
Yes, I think it is and that is why perhaps what we are seeing is a slight retreat from this process that’s been going on since the Copernican revolution of making us insignificant in the universe. We are no longer the centre of the solar system. We are one galaxy amongst others and possibly even one universe amongst others, so how insignificant could we be?
But the fact is that we are at the centre of everything we do and see and experience. What quantum mechanics may be telling us is ultimately we have to recognise that, and we have to build it into our theories. It’s very striking to me that some people who are really thinking hard about the foundations of quantum mechanics are starting to take an interest in phenomenology, a philosophical tradition that puts experience first. It doesn’t build from axioms, it starts with experience. It may be that that is a fruitful way to think about quantum mechanics.
Beyond Weird: Why Everything you thought you knew about quantum mechanics is different is published by Bodley Head.
