The past few weeks I’ve been reading a textbook written by David Bohm called Quantum Theory, an advanced undergraduate textbook he developed for his students at Princeton in the 1950s. If you don’t know about David Bohm, he was a theoretical physicist who taught at Princeton and the University of London. As a colleague and good friend of Albert Einstein, they worked together in developing quantum physics.
What I particularly enjoy is its philosophical speculations and ideas, such as this passage on how quantum mechanics relates to thought. He believed that quantum effects within the brain were directly related to consciousness. It seems that Niels Bohr entertained similar ideas as the textbook mentions discussions they had together. Bohm argues that there are strong similarities between our thought processes and how matter behaves at small scales, tying together these ideas with the uncertainty principle.
There are wide ranges of experiences in which occur phenomena possessing striking resemblances to quantum phenomena. These analogies will now be discussed, since they clarify the results of the quantum theory. Some interesting speculations on the underlying reasons for the existence of such analogies will also be introduced.
The Uncertainty Principle and Certain Aspects Of Our Thought Processes
If a person tries to observe what he is thinking about at the very moment that he is reflecting on a particular subject, it is generally agreed that he introduces unpredictable and uncontrollable changes in the way his thoughts proceed thereafter. Why this happens is not definitely known at present, but some plausible explanations will be suggested later. If we compare (1) the instantaneous state of a thought with the position of a particle and (2) the general direction of change of that thought with the particle’s momentum, we have a strong analogy.
We must remember, however, that a person can always describe approximately what he is thinking about without introducing significant disturbances to his train of thought. But as he tries to make the description precise, he discovers that either the subject of his thoughts, or their trend, or sometimes both become very different from what they were before he tried to observe them. Thus, the actions involved in making any single aspect of the thought process definite appear to introduce unpredictable and uncontrollable changes in other equally significant aspects.
A further development of this analogy is that the significance of thought processes appears to have indivisibility of a sort. Thus, if a person attempts to apply his thinking more and more precisely defined elements, he eventually reaches a stage where further analysis cannot even be given a meaning. Part of the significance of each element of a thought process appears, therefore, to originate in its indivisible and incompletely controllable connections with other elements. Similarly, some of the characteristic properties of a quantum system (for instance, wave or particle nature) depend on indivisible and incompletely controllable quantum connections with surrounding objects. Thus, thought processes and quantum systems are analogous in that they cannot be analyzed too much in terms of distinct elements, because the “intrinsic” nature of each element is not a property existing separately from and independently of other elements but is, instead, a property that arises partially from its relation with other elements. In both cases, an analysis into distinct elements is correct only if it is so approximate that no significant alteration of the various indivisible connected parts would result from it.
There is also a similarity between the thought process and the classical limit of the quantum theory. The logical process corresponds to the most general type of thought process as the classical limit corresponds to the most general quantum process. In the logical process, we deal with classifications. These classifications are conceived as being completely separate but related by the rules of logic, which may be regarded as the analogue of the causal laws of classical physics. In any thought process, the component ideas are not separate but flow steadily and indivisibly. An attempt to analyze them into separate parts destroys or changes their meanings. Yet there are certain types of concepts, among which are those involving the classification of objects, in which we can, without producing any essential changes, neglect the indivisible and incompletely controllable connection with other ideas. Instead, the connection can be regarded as causal and following the rules of logic.
Logically definable concepts play the same fundamental role in abstract and precise thinking as do separable objects and phenomena in our customary description of the world. Without the development of logical thinking, we would have no clear way to express the results of our thinking, and no way to check its validity. Thus, just as life as we know it would be impossible if quantum theory did not have its present classical limit, thought as we know it would be impossible unless we could express its results in logical terms. For instance, many people have noted that a new idea often comes suddenly, after a long and unsuccessful search and without any apparent direct cause. We suggest that if the intermediate indivisible nonlogical steps occurring in an actual thought process are ignored, and if we restrict ourselves to a logical terminology, then the production of new ideas presents a strong analogy to a quantum jump. In a similar way, the actual concept of a quantum jump seems necessary in our procedure of describing a quantum system that is actually an indivisible whole in terms of words and concepts implying that it can be analyzed into distinct parts.
Possible Reason for Analogies between Thought and Quantum Processes
We may now ask whether the close analogy between quantum processes and our inner experiences and thought processes is more than a coincidence. Here we are on speculative ground; at present very little is known about the relation between our thought processes and emotions and the details of the brain’s structure and operation. Bohr suggests that thought involves such small amounts of energy that quantum-theoretical limitations play an essential role in determining its character. There is no question that observations show that the presence of an enormous amount of mechanism in the brain, and that much of this mechanism must probably be regarded as operating on a classically describable level. In fact, the nerve connections found thus far suggest combinations of telephone exchanges and calculating machines for complexity that has probably never been dreamed of before. In addition to such a classically describable mechanism that seems to act like a general system of communications, Bohr’s suggestion involves the idea that certain key points controlling this mechanism (which are, in turn, affected by the actions of this mechanism) are so sensitive and delicately balanced that they must be described in an essentially quantum-mechanical way. (We might, for example, imagine that such key points exist at certain types of nerve junctions.) It cannot be stated too strongly that we are now on exceedingly speculative grounds.
Bohr’s hypothesis is not, however, in disagreement with anything that is now known. And the remarkable point-by-point analogy between the thought processes and quantum processes would suggest that a hypothesis relating these two may well turn out to be fruitful. If such a hypothesis could ever be verified, it would explain in a natural way a great many features of our thinking.
Even if this hypothesis should be wrong, and even if we could describe the brain’s functions in terms of classical theory alone, the analogy between thought and quantum processes would still have important consequences: we would have what amounts to a classical system that provides a good analogy to quantum-theory. At the least, this would be very instructive. It might, for example, give us a means for describing effects like those of the quantum theory in terms of hidden variables. (It would not, however prove that such hidden variables exist.)
In the absence of any experimental data on this question, the analogy between thought and quantum processes can still be helpful in giving us a better “feeling” for quantum theory. For instance, suppose that we ask for a detailed description of how an electron is moving in a hydrogen atom when it is in a definite energy level. We can say that this is analogous to asking for a detailed description of what we are thinking about while we are reflecting on some definite subject. As soon as we begin to give this detailed description, we are no longer thinking about the subject in question, but are instead thinking about giving a detailed description. In a similar way, when the electron is moving with a definite trajectory, it simply can no longer be an electron that has a definite energy.
If it should be true that the thought processes depend critically on quantum-mechanical elements in the brain, then we could say that thought processes provide the same kind of direct experience of effects of quantum theory that muscular forces provide for classical theory. Thus, for example, the pre-Galilean concepts of force, obtained from immediate experience with muscular forces, were correct, in general. But these concepts were wrong, in detail, because they suggested that the velocity, rather than the acceleration, was proportional to the force. (This idea is substantially correct, when there is a great detail of friction, as is usually the case in common experience.) We suggest that, similarly, the behavior of our thought processes may perhaps reflect in an indirect way some of the quantum-mechanical aspects of the matter of which we are composed.