Mitja Perus: QM (quantum mechanics) has predictive power and is
not in contradictions with experiments, but there are a lot of problems
with fundamentals of QM. How do you see this situation?
BASIL J. HILEY: QM enables you to calculate the correct probabilities for given experimental situations, but I think we need more from science than just predictions. It is in this area that there are problems with QM. I am not the only one who believes this. Murray Gell-Mann said that we all know how to calculate, how to use QM, but none of us really understands what is behind the formalism, what it is saying about nature. That has to be answered in some way.
M.P.: There is a revival of Professor Bohm's and your ideas in last years, isn't it? Examples are Holland's book "The Quantum Theory of Motion - An Account of the de Broglie-Bohm Causal Interpretation of QM" and many others, your book "Undivided Universe", many articles, for example in New Scientist (February 27, 1993), Scientific American (May 1994), etc. Where are reasons for this?
HILEY: First of all, I think, the existence of collective works showing how much has been done on this alternative interpretation, which is called the de Broglie-Bohm interpretation, or as I would call it, the ontological interpretation. There is a great unease about quantum physics in general. Some of the experiments are reaching the level where you can observe the behaviour of individual quanta or individual particles etc. Point number two, there has been a through-examination of the Bell inequality and the various experiments that have arisen out of that. These show that QM has some non-local feature. This has created a lot of interest. There is also a crisis in attempts to quantize gravity. There are fundamental problems and we are more or less forced to say that we have not really understood QM properly. Maybe QM is limited and that is why we cannot unite gravity with QM. In general relativity the question of time, for example, is difficult to understand. So we must reexamine the foundations. I think, the books by Peter Holland, and by David Bohm and myself have suggested an alternative that might show a new way forward.
M.P.: Electron undergoes continuous transformation between its wave-like and particle-like aspects. How would you explain this double nature, perhaps using your notions of implicate and explicate order?
HILEY: I find the notion of continuous transformations between
wave-like and particle-like aspects very confusing. No one actually
observes the wave-like properties. What one observes is a statistical
distribution of individual events. When one analyses it, it LOOKS
as if one can account for the result by some wave-like feature.
But we have never actually seen the wave-nature of the quantum.
The results of experiments are discrete events, which can be explained
if we assume the wave-like quality. The continuous transition between
wave and particle becomes blurred, it is not smooth.
The de Broglie-Bohm interpretation is the only interpretation of QM that provides an ontology. If one looks at the position of Niels Bohr, and particularly the people who analysed Bohr, you get a feeling that Bohr has given us the most consistent interpretation of QM, but it is an epistemological interpretation. This arises, it is argued, because of the problem of separating the observed from the observing apparatus. John Wheeler has written to me saying that there is no ontological interpretation of QM, but we have shown that one is possible. Here it seems that you have to move away from mechanism into some kind of organism or organicism. In that context you can still maintain a particle with the wave influencing the particle. The wave now seems to have a new quality; it is like an informational field. But when you go to relativity, even this view becomes difficult to maintain. We are not sure whether there is a permanent structure of electrons and whether they are always following continuous traectories. So maybe something deeper is involved. The wave function approach was maintained because it managed to provide a KIND of ontology, but the individuality could not be fitted into the Cartesian category. There is a contradiction. David Bohm and myself were addressing the question of alternative categories for QM. In that context Bohm had the idea of implicate and explicate order. The particle now was a series of unfoldements from a more deeper structure which we call holomovement.
M.P.: Due to your interpretation a particle has simultaneously well defined position and momentum which are uncertain to us. In what sense might this claim be a negation of the Heisenberg uncertainty principle?
HILEY: Some people certainly take this claim as a negation of the uncertainty principle. And they are very puzzled. In non-relativistic QM we assume that there is a particle, that it has a definite position and momentum, but these are unknown to us. In order to determine its position and momentum, we have to bring pieces of apparatus to bear on the particle. We have a beam of particles coming in, and we have to find the position of one of them. One way to do this is to put a slit in front of the beam. There is an uncontrolable change of momentum between the slit and the particle that comes through the slit, so consequently the momentum before the measurement is now not the same as the momentum after the measurement. We actually have to participate in the process of measurement and we have to transform the process we are examining. We and our instruments play an active role in the quantum processes. It is in this way that the uncertainty principle comes back again into the ontological interpretation. So it is not a negation of uncertainty principle; it is an explanation of how the uncertainty principle arises.
M.P.: So we have to distinguish the epistemological aspect of uncertainty principle and the ontological aspect of it?
HILEY: Yes. In fact, I prefer to look it at two levels: We have got a level of the actual entity. John Bell called this the "beable" level, the level at which we say that things are actually what they ARE. Then we have another level, called the observable level - the epistemological level. Thus there is an ontology underlying this level. It is not to say that the ordinary interpretation is wrong. The ordinary interpretation is confined at the level of observables, and then adding that there is nothing beneath it. Whereas we are saying that we can explain appearances from a deeper underlying ontology. (One could say reality, but one has to be very careful in using that word!)
M.P.: What are so called "hidden variables" and what role do they have? Would you give some examples? During our discussion in London you said that you dislike the word "hidden variables". Why? What second word would you suggest?
HILEY: Yes, I feel very uneasy by the word "hidden variables" for two reasons. Firstly, the word was coined, I think, by von Neumann in his book "Mathematical Foundations of QM". He constructed a proof saying that if there were additional parametres (if there was an underlying ontology) then QM could not be re-derived with their help. Thus you would not get agreement with experiments if you introduce these parametres. They became known as "hidden variables" and this term is automatically associated von Neumann's theorem. Now we know that von Neumann's theorem is wrong, not because anything in proof is wrong, but because of the assumptions he made. He was only talking about a very limited type of additional parameters.
Second, if we look at the ontological interpretation, we find that there are no additional parameters, we only have momentum and position. Therefore, when we use the word "hidden parameters", one might think that there is some additional structure which one has to use. But there is not. The reason why David Bohm in his paper called them "hidden" was because they are hidden in the sense the position and momentum are not simultaneously known to us: you cannot observe them directly together. To observe them you have to change the situation, to participate.
I prefer the more neutral word "beables" coined by John Bell. Here we have a new situation. It comes from an ontology which works. It does not add any new parameters. So if we just call momentum, position, angular momentum etc. "beables", then we do not need any exotic new type of strange parameters. The classical variables are used, but in a different way.
M.P.: Would you then explain what beables are?
HILEY: Beables are just those properties that the particle actually posesses independently of our measurements.
M.P.: So, including position and momentum, but without involvement of observer. That would be the intrinsic momentum?
HILEY: Yes, something intrinsic to the particle that can have these properties - that is "being". That is, where the word comes from - from "to be". It is what is. What we see are the appearances, and we have to explain these appearances in terms of what IS. Therefore the intrinsic properties that we attribute to the particles are called beables.
M.P.: Beables are some characteristics on this ontological level, not epistemological.
HILEY: Yes, precisely. They are variables that we need to make the ontology into a coherent whole.
M.P.: Are they attributed to particles or to fields? nbsp;
M.P.: You say that "hidden variables" or, better to say, beables are non-local? What does this mean?
HILEY: Let us consider a simple case when we have two particles. Then you have as "beables" position and momentum of both particles. They are parameters associated with the local particle. But it is not possible to explain results of experiments without introducing a connection or some sort of interaction between two particles. If QM is STRICTLY true, then that connection is INSTANTANEOUS. In the ontological interpretation at this level there is some instantaneous action-at-a-distance. That is the non-local feature. So, it is not that the parameters are non-local. It is the coupling between them that is instantaneous and therefore non-local. So, we have non-local "hidden variable" THEORIES.
M.P.: What puzzles me here is the following: You say that "hidden variables" are non-locally instantaneously CONNECTED. It sounds that they themselves can even be local.
HILEY: Yes, this is a very interesting question. You make the assumption in the Bohm ontological interpretation that particles are centres of activity in the holomovement and these centres of activity are in different spatial positions.
In the ontological interpretation you have a particle and a wave. The wave is not something that is independent of the particle. They are two facets of the same process. Therefore you are right in asking, can we actually separate the two? The reason why we go to implicate order is because strictly at the deeper ontological level they should not be separated, but at one level it is possible to see these two entities as separate. So it is as if they are together, yet somehow spatially apart. It is very difficult to find words to describe it at this level unless you go into deeper questions of the implicate order. Maybe the categories that we are still using are inadequate...
M.P.: You also said that you dislike the notion "subquantum medium". I understand that such division into lower and higher levels is artificial, but we need some concepts for the sake of analysis. How would you solve that problem?
HILEY: "Subquantum medium" was in fact the way in which de Broglie and Jean-Pierre Vigier talk (he feels this medium is actually the reality). Here I recall the early discussions of the role of an ether for electro-magnetic phenomena. The conclusion was that we do not need an ether - the vacuum would do. What Einstein actually said was that we did not want to explain the electro-magnetic ether in terms of mechanical properties of a substance. I see that people now, forgetting Einstein's remarks, want to provide a MECHANISTIC subquantum medium; they want to keep Cartesian categories and that is wrong direction.
In quantum field theory there is the concept of vacuum. Normally people would say: Vacuum means that it is nothing there. But then you find that there are terms like "inequivalent vacuum states", vacuum fluctuates etc. What does it mean to have inequivalent nothingness? It is either nothingness or it is something. So, the idea is that the vacuum in fact is not empty. It maybe "full". We see these notions as vacuum polarisation in which virtual positron-electron pairs are created from the vacuum.
It looks as if the vacuum state is not empty, but that it is a medium of some kind. Einstein said: "I did not ban the 'quantum ether', but I do not want it to have mechanical properties." Now, if you remove the mechanical notion, then I see no harm in reintroducing the notion of the subquantum medium. But it has got to be a medium which is much subtler than a mechanical medium. Indeed, I believe, there is some deeper underlying process that we have not begun to understand yet.
M.P.: This underlying process you call holomovement?
HILEY: Yes, that can be thought of as a subquantum medium, if you like. Only I do not like the word medium, because of its mechanical connotations. There is something, but it is going on so fast that we cannot discriminate, we cannot pick out any detailed features of it yet. The invariances are dissolving far too quickly for our instruments to catch them. This fast activity we call holomovement.
M.P.: In your interpretation you take processes (not some elementary particles) as basic. But some people would say that processes are composite non-elementary phenomena arising from a disequilibrium between more elementary features, wouldn't they?
HILEY: Yes, but that is then going back to the reductionist philosophy. I feel that the non-locality in QM is telling us that we have to abandon reductionism. The idea of a holistic approach does not come only from the ontological interpretation of David Bohm. If you read Niels Bohr very carefully, you find terms like "wholeness of experimental conditions", "wholeness of phenomena", implying that you cannot analyze things. Bohr was right on this point. This holistic feature is revealed in the ontological interpretation as non-locality.