Courtesy of Detlef Dürr, Ludwig Maximilian University of Munich
VIENNA—One night in 1952, Richard Feynman and David Bohm went bar-hopping in Belo Horizonte. Louisa Gilder reconstructs the night in her brilliant book on the history of quantum mechanics, The Age of Entanglement. Feynman was on a sabbatical in Rio and, ever exuberant, raved about local beers, drumming lessons, and Brazilian girls. Bohm, teaching at the University of São Paulo, never took to the place. He had just been hounded out of Princeton University and out of the U.S. by the McCarthy witch hunt. He felt exiled not just from his country but from the mainstream of physics. Bohm perked up only when Feynman expressed some fleeting interest in his new way of thinking about quantum mechanics.
Bohm had developed the first comprehensive alternative to the orthodox Copenhagen Interpretation of quantum mechanics. Building on earlier work by Einstein and Louis de Broglie, Bohm showed that quantum randomness need not be intrinsic to nature. It might simply reflect our bull-in-a-china-shop way of probing the quantum realm. In Bohm’s original formulation, particles always have well-defined positions and are shepherded by a “quantum potential” similar in general spirit to electric and gravitational forces. Because this potential operated instantaneously, linking together everything in the universe no matter how far apart it may be, Bohm later came to think that quantum physics was just the surface view of a radically holistic reality.
Physicists tend not to like Bohm’s theory, for reasons both sociological and scientific, but at the least it broke the spell of Copenhagen. Léon Rosenfeld, an especially pugnacious partisan of Copenhagen, slammed him and even worked behind the scenes to get journals to reject his papers, as if trying to complete what the McCarthyites had started. Yet Bohm’s work inspired Irish physicist John Bell to revolutionize thinking about quantum physics in the 1960s.
At a conference a few week ago, I had the pleasure of meeting Basil Hiley, Bohm’s longtime collaborator and co-author of his final book, The Undivided Universe. Hiley is a theoretical physicist at Birkbeck College of the University of London, where Bohm ended up after he couldn’t take Brazilian food anymore. What follows in an abridged transcript of our chat. Hiley, like his late mentor, has such an unconventional way of thinking about physics that I didn’t really follow much of what he said. In this transcript, I took the liberty of shifting around blocks of text and omitting passages on technical mathematics to try to make sense of it all. If it piques your interest, a good next step would be Hiley’s exhaustive Wikipedia page. If nothing else, Bohm’s theory is a good subject to talk about with a beer in hand.
When did you first meet David and how did you begin your collaboration?
I was just finishing my Ph.D., which I was doing on solid-state physics. Had a couple of papers published, hadn’t quite finished the thesis, but I was looking around, “What am I going to do at the end of summer?” I didn’t know David Bohm. I hadn’t read his work. He was giving two talks, and I went in at the back as I usually do. Suddenly I hear this man talking and I said, “Wow, this is what I wanted to study at university.”
I was always very interested in quantum mechanics and relativity, even at school. I picked up Mr. Tompkins in Wonderland. One of our math teachers had come in with The Mysterious Universe by Sir James Jeans, and I went straight up and bought it for six pence. That was tremendous for me to part with six pence. When I went to university, I was hoping that I would be able to discuss these ideas. But everybody would say, “You mustn’t waste time thinking about it.” I was very frustrated, actually. Even at the postgraduate level, I organized some informal seminars between the postgraduate students, and I was called in and asked what I was doing. It didn’t make sense to me at all.
I was in the library doing my Ph.D. and I was reading Louis de Broglie’s nonlinear wave theory. And my supervisor, and I’m not going to name his name, said, “You can’t read that rubbish.” Took it from my hands, closed the book, and put it on the shelf.
Of course, as soon as he left the room, I went back and picked it out. If you want get someone to read something, you should tell them not to read it!
And then David came in, with all these exciting ideas, suggesting that quantum mechanics was a beautiful wine, but we were putting it in old bottles. And the idea was to make new bottles, so that the beautiful wine would fit consistently. That’s not an easy thing to do—to think deeply about the nature of reality.
He got appointed to the chair of theoretical physics at Birkbeck College, and they wanted an assistant lecturer. The trouble was the assistant lecturer was supposed to run demonstrations in the laboratory, and I was a theoretician. So I had to convince them I was an expert at experimental physics. I thought I did a good job, and I was under this illusion for 10 years when I was at a party and we were chatting about these things. I said I really convinced all them. Someone said: “Don’t you believe it. It was nothing to do with that. David Bohm wanted a theoretician, so we appointed you.”
You know, most experimentalists wouldn’t let a theorist near their equipment.
I know. But I didn’t mind doing it because I think it’s very important if you’re doing theoretical physics to get a feel of what it’s like in a laboratory, making things work. I’ve heard some theoreticians talking and it’s quite clear they don’t even know what a laboratory is. They’ve never been in a laboratory and they’ve never tried to get even simple bits of apparatus working. They just have ideas of what the measurement is—and it’s nothing like that. It’s much too idealized.
Now, the interesting thing: the first 10 years I worked with David Bohm, we never mentioned his ’52 paper, we never mentioned hidden variables, we never mentioned particle trajectories.
What were you doing in that 10-year period?
When I joined him, we had Roger Penrose in the maths department, and we had David Bohm and we had myself. We were looking at algebras; we were looking at general relativity; we were looking at pre-space. Pre-space is like pre-geometry, but David and I didn’t want to give the impression that we were thinking the same way as John Wheeler was.
Penrose had his twistors, and then he had his spin networks. Both of them were how to construct spacetime out of physical objects. He had some beautiful ideas with the twistors. He wanted a space where there were no points, so you start with the light rays, and then where the light rays intersect, you construct your points.
My contribution to twistors was how to spell it. He came into my room one day and he started talking about his idea. “I don’t know whether to spell it E-R or O-R.” And I said: “Roger. O-R.”
“Twister” is a party game, and “twistor” is a high-end concept.
[Laughs.] Anyway, that started me on the different algebras. I had come from solid-state physics, and I’d done a lot of work on lattices. Could it be that spacetime is structured like a lattice, but very small? Take the edge dislocations wandering through the crystal, and you find you get Riemannian geometry. So I did a lot of that, wondering about whether space was discrete.
So, for the first 10 years—for the entire ’60s—you didn’t even touch a pilot wave.
We might have touched it, but I dismissed it. I hadn’t read the paper! That’s a fact. Students said, “Why haven’t you read it?” And I said, “Oh, it’s wrong.” Because I’d picked up the general philosophy that hidden variables were rubbish. Not only that, I had a very strange feeling that somehow if I’d read the paper, I would get infected in some way. Now, looking back on it, it was extraordinary. But as a young guy just setting out, that’s the sort of message you picked up.
What revived your and David’s interest?
Because these two students said, “Look, what’s wrong with the paper?” I started to bullshit, like we all do, and then they said: “Oh, stop bullshitting. You haven’t read it, have you?” So I took it away and read it. And I was amazed. Because what he was doing was just standard mathematics. It had this thing called the quantum potential and trajectories. I said to a student, “Let’s calculate the trajectories.” And that’s where Chris Philippidis and Chris Dewdney started his work producing quantum potentials for the two slits (see diagram at top) and for the particle in a well. And then it just grew. When we showed it to people, they said, “Oh yeah, but you can’t do so-and-so.” So we used to go away and do so-and-so. Bring it back, they say, “But you can’t do….” All I did for years was get these guys to do calculations to show that we could do all these things with it.
Therefore, my problem was: what’s wrong with it? It works. Whether particles actually follow trajectories or not, I don’t know. But there are the formulae, you just apply them, and there it is.
Did that start to get David interested?
That got David interested in it again. We dropped the more speculative stuff, the more esoteric stuff about pre-space. It’s always in the background. But then we worked more closely on this. David was very excited by it. When we showed him the trajectories, he was: “Oh wow. We can get out that out of that?”
From my position, and also David’s position, this was just a sort of an average behavior of this deeper underlying process. And that’s what we were aiming to try to understand. We didn’t get very far, I’m afraid. You know, it’s a difficult thing. We’ve tried lots of different ideas, and none of it really seems to work. There’s something missing still.
Tell me some of those ideas that you played with.
We were interested in undivided whole. How do you describe wholeness without breaking it up into pieces? Bohr said you can’t analyze any further: don’t make the division between the subject and the observing apparatus, because everything is a whole, and as soon as you break it into pieces, you’ve lost it; you’ve changed the phenomenon. I took a lot of insight from Bohr. If you read our book, we never say Bohr was wrong, whereas most other people say Copenhagen is nonsense. What we disagreed with Bohr about is that he couldn’t analyze it further. What we’ve been trying to do is analyze it further.
Our idea was to say, yes, you can do it. You can talk about the individual, but it’s the quantum potential which puts in what you’ve left out. So it brings the information of the environmental conditions, the boundary conditions, and feeds it to this local entity—so this local entity knows that it’s part of the whole.
How this does it, I don’t know. But what David and I suggested was that the quantum potential is actually an information potential, and we introduced the idea of active information. I was very worried about using the word “information” because everybody would immediately go to Shannon information. Shannon information is not information; it’s just information capacity. There’s no meaning there, and the whole point was to get meaning into this and that this was information for the particle.
Then, of course, they thought we’d gone mystically East. But I mean the quantum potential is not a classical force. It’s not a classical potential. It’s something extraordinary, very strange. It doesn’t get propagated, as far as we can find out. But that was the way I reconciled wholeness with divisibility. If we divide, we must have something to put it all back together again.
It seems ironic that Bohr and some of his people reacted strongly against Bohm’s theory.
Yeah, but don’t forget, if you just do the simple Bohm theory, you don’t see any of this. I’m now telling you we see the Bohm theory in the light of this deeper process. I used to give the lectures on the Bohm theory, because you cannot ignore it. It’s there whether you like it or not. But then people believed that’s what I really thought nature was. But to me, that’s a Mickey Mouse model. It’s not the driving force of what David and I were doing. This would just be a certain level of abstraction.
So I am not a Bohmian in the Bohmian mechanics sense. Chris Fuchs came down to me once after a lecture and says, “How nice it is to meet a Bohmian.” And I said: “I beg your pardon? Where?” I’m not a Bohmian. What we are discussing is not mechanics. Bohm says in his quantum-theory book, the original one, quantum mechanics is a misnomer. It should be called quantum non-mechanics.
Because you shouldn’t think of it in terms of a mechanistic motion of particles?
Yes, it’s nothing like that. It’s not mechanism. It organicism. It’s organic. Nature is more organic than we think it is. And then you can understand why life arose, because if nature is organic, it has the possibility of life in it.
Let’s start this way. You’re looking for a fundamental particle. So you divide the material into atoms and think: this is where the real essence lies. Rutherford divided the atom and found the nucleus. OK. The nucleus is where matter resides. And then you look inside the nucleus and you find neutrons. OK, now we’re there. But then there’s quarks and we’ve never got a hold of a quark. We take a proton, an anti-proton, and it goes, poof, into radiation. So where is the solidity of matter? Where does it lie? Because wherever we look at it…
…it falls through our fingers.
OK. So you say, all right, suppose we start with something like process—no particles, just activity, just energy. Then the first battle was: what the hell do you mean?
I started reading. I read Grassmann, for example, and Grassmann was saying that mathematics was not about things in space and time, but it was about thought—it was about the order of thought. And he obtained his Grassmann algebra from that kind of consideration. And I read Clifford‘s original books, original papers, and it was all about process. Two times three is equal to six—it’s not two objects times three. It’s the doubling of three objects. It’s a process.
We’re not used to thinking about process. We communicate with an object-based language. David invented a thing called “rheomode“—language in which we speak to each other in a flowing mode. There are some ancient languages which do this—Hopi Indian and some others. In his book Wholeness and the Implicate Order, you’ll find a chapter on language, in which he discusses this rheomode. It didn’t work, because we were still thinking of objects.
How does this enter into quantum mechanics?
In noncommutativity. Every day in our life, we always have to be careful of the order. You’ve got a cup in the cupboard. You’ve got to open the cupboard door before you can the cup out. All our experience is doing things in the right order, so our activity is noncommutative. It comes into quantum mechanics because Heisenberg sought to explain atomic energy levels and what he found was he had to make his objects into things that didn’t commute with each other. The order was vital. There was a difference between first measuring the momentum and then measuring the position, from measuring the position and then measuring the momentum. That became the basis of his Uncertainty Principle.
It seemed to me that he was actually discussing a process. He was talking about how something goes from one to the other, and he called that a momentum transition, and a position from one position to another. In other words, it wasn’t x and p, p and x. It was rather x0 to x1, p1 to p2, and so on. The basic thing he discovered was a “groupoid,” and a groupoid is what is used in category theory nowadays. It’s to discuss process.
How does all this work with relativity theory?
You’re creating your space and time, People say, “Well, what do you mean we’re creating space and time?” Well, the world out there, there’s not a geometry which you somehow just discover by looking at it. You actually use physical processes to describe that geometry. How do we get the geometry of space? With a radar set and a clock. We send the light signal out, send it back again, and we construct the Lorentz transformation by what matter is doing.
Most people say you can’t do relativity in the Bohm theory. That’s wrong. Four years ago, I was able to get the Dirac equation in the Bohm theory. It’s all in the Clifford algebra.
But isn’t it peculiar that nature would be such that we could abstract a space from it? It seems like a high degree of order that’s implied.
Yeah, you’ve got to make the assumption that nature is ordered.
I’ve always been perplexed by the terms “implicate order,” “explicate order.” Could you go over those for me?
Why would we expect the fundamentals of nature to be the same as we experience in the macroscopic world? This idea is to say, no, the real world is not. If you look behind it, it’s a mirage in a way. The algebra is the implicate order. It’s the structure that’s there. Properties are given by the whole, but we’re taking them out and we are making an explicate order.
So the explicate order is what we perceive?
Yes, what we perceive. And it’s not everything. What the old classical physics said was that we just want to stand god-like outside and just look at everything without us being in there. We can’t. We’re in there, whether we like it or not. We’re inside looking out, not outside looking in. What the implicate is, you can’t explicate, but you must have different views because you’re inside it. You can’t stand outside it. You only get a partial view.
When I lecture on this, I always use the old lady/young lady—the gestalt. The lines are there, but what they mean depends how you explicate one order over the other. Because a lot of things are based on things that you can’t explicate at the same time. Nature is such that you cannot actually explicate the position space and the momentum space.
So instead having just a trajectory, you have an unfolding and enfolding process. The past actively works in the present. It reverberates in the present to produce the future. What looks like a particle tracking across, isn’t a particle tracking across. It’s just an explication.
I shouldn’t think of this particle as a persistent entity drifting through a void?
No, you’ve got to think of your entity not as billiard ball. Its properties are not independent of the underlying process. Change the underlying process, and the properties of this thing change. Don’t treat it as being separate. Because its properties depend upon the environment. You’re making objects out of things which continuously transform, but always into themselves. It takes a bit of getting used to!
In a sense, do we create that particle?
That’s a very interesting question. Do we create what we see? Maybe we do. I know people say, “Oh, it’s all subjective.” But there are only certain things you can do with it. You can’t magic things up. You can reorder things. You can rearrange things when you are making your reality. We’re rearranging the processes. We are part of the process.
Diagram courtesy of Detlef Dürr, Ludwig Maximilian University of Munich