Whitehead and the Copenhagen Interpretation

Introduction | Quantum Mechanics | Whitehead and Bell's Inequality | Whitehead and the Copenhagen Interpretation
Conclusion | Footnotes | Bibliography

Because most physicists accept the Copenhagen interpretation of quantum mechanics, it is important for Whitehead to be able to account for its major features, since supposedly this interpretation is our best understanding of 'the way things are'. The issues dealt with here are realism, indeterminacy, complementarity and the measurement problem, but it will be apparent that only one small conceptual change need be made in order for Whitehead to deal successfully with all of these phenomenon. We begin with the problem of the rejection of realism.


When Whitehead talks about the concrescence of an actual occasion, he makes it very clear that the satisfaction is real in the fullest sense of the term. How is it, then, that Whitehead can retain his form of metaphysical realism, which is an essential feature of his whole scheme, if rejecting the objective reality of quantum objects makes the most sense given experiments like Aspect's?

A proposal by Shimony provides one way out. Rather than postulate that actual occasions are the final real constituents of the universe, Shimony toys with the idea that there is a more general form of ultimate reality underlying the existence of actual occasions. He proposes that this more general reality might be a type of "'field' of diffused primitive feeling, of which the actual occasions are 'quanta' "existing whenever there are individual loci of feeling." (1993:305) In this conception, actual occasions are not the ultimate real things of the universe, but rather special cases of the more basic reality of the field of feeling.

To Whitehead this sort of solution would be unacceptable. It is imperative that a real universe has as its final constituents real entities.14 But quantum mechanics treats quantum objects not as independently real entities, but rather as probability fields which establish the possibility of obtaining any particular result in the measurement of a quantum system. The actual properties of the quantum system have only secondary reality, and are not the most fundamental constituents of the universe.

However, by modifying the conception of the actual occasion only very slightly, it seems that Whitehead may be able to stay afloat. In the actual occasion are multiple sub-processes (the prehensions) which lead the actual occasion to its satisfaction. None of these sub-processes can be said to be real in an objective sense, as they are only derivatively real in relation to the satisfaction of the actual occasion. The probability field of quantum mechanics is none other than a description of a complex interaction between certain of these indefinite sub-processes. In fact it can be said that the probability field is just the combination of the phases of concrescence abstracted from the satisfaction. Of course these phases of concrescence cannot be fully abstracted from the satisfaction itself,15 and it is exactly for this reason that such an abstraction is inherently indeterminate--it is itself merely probabilities for a certain satisfaction.

Whitehead is able to maintain that actual occasions are, in the final analysis, the ultimately real constituents of reality. The satisfaction of an actual occasion is the culmination of the indefinite sub-processes (the phases of concrescence) into one definite, and hence objective unified feeling. Abstraction of sub-processes from the satisfaction is always just that--abstraction. This is why the phases of concrescence are said to have only derivative reality. Let me explain how this thesis is in accord with modern quantum theory.


It is a consequence of the fact that quantum mechanics deals fundamentally with probabilities that it is impossible to ever know in advance the exact outcome of an experiment. This has been confirmed extensively in various experimental situations and forces us to conclude that it is a fundamental fact that the universe is not deterministic in the Newtonian sense. Whitehead would joyfully accept this premise, as it conforms perfectly with his idea of the intrinsic freedom of actual occasions.

When we perform a measurement of the polarization of a photon, we cannot say whether a particular photon will be either passed or blocked by the polarization filter. The best that we can do is calculate the probability that in any given instance a photon will pass or not. In such cases (which apply to all measurements of quantum properties) our certainty of what will happen is never complete, although in general we can say what will happen. When the polarization measurement has been made, however, we can definitely say that the particular photon really is polarized in such a way. If the photon passes through a +45 degree polarization filter, then at any time in the future (assuming that the photon is not disturbed) we can perform another polarization test, and we will always find that it is polarized at +45 degrees.

For Whitehead, this indeterminacy is due to the fact that each actual occasion has at least some level of individual freedom, and in fact can never be predicted in a complete sense. As discussed above, quantum objects have very little freedom, and are very much bound up in their tradition. Consequently, our measurements of a property of a quantum system always seem to fall within certain limits (defined by quantum mechanics which is itself defined by the actual occasions themselves); there are only certain values that are possible for any given experiment measuring a quantum property. Within a tradition there are only certain 'occupations'16 that are acceptable (the details are provided by the laws of the tradition), and any actual occasion that is a part of the tradition must choose one of the available occupations if it is to remain a part of the society of which the tradition is an integral component. The actual occasion can in principle choose any path, but this would mean that it could not be a part of the society whose laws require certain types of behaviour.17 The fact that we cannot tell what any one property of a quantum object will be with complete certainty is a testimonial to the freedom inherent in the natural world.


The most interesting and important conceptual tenet of the Copenhagen interpretation is that of complementarity. The most easily grasped manifestation of complementarity is in the Heisenberg Uncertainty Principle, which states that the position and momentum of a particle cannot be measured simultaneously--the two properties, position and momentum, are complementary.18

In the Copenhagen interpretation, this uncertainty arises not from the inadequacy of our ability to measure the properties, but from the nature of reality itself. It is actually that both a definite position and a definite momentum do not exist simultaneously in a particular measurement situation. It is important to note that this does not mean that position and momentum do not exist generally at the same instant, but that the more exactly we define the position of a quantum object, the more uncertain its momentum becomes. If we only define the position of a particle with a moderate degree of uncertainty, then we can also define the momentum of the particle with a moderate degree of certainty.

The Copenhagen interpretation states that if we define the position of a quantum object exactly, then it would be meaningless to even talk at all about the momentum of the object (even if it was just to say that the momentum doesn't exist!). Thus it is correct to say that in such a situation the position exists definitely (exactly), but it is not correct to say in the same instance that because of this the momentum does not exist--rather we cannot say in this case anything meaningful about the existence or nonexistence of the momentum of the quantum object. This point is very important and is often missed except in the most complete accounts of the Copenhagen interpretation: the fact that the statement "a definite position and a definite momentum cannot exist simultaneously in the same quantum object" is true does not necessarily result in the statement that "if the position of a quantum object is defined exactly then the momentum does not simultaneously exist", but rather results in a statement like "if the position of a quantum object is defined exactly then we cannot say anything about its momentum, including statements referring to the existence or nonexistence of this property". The key is that we are speaking of uncertainty-if we defined the position of a particle exactly, and then said that therefore the particle had no momentum, then essentially we are saying that its momentum is zero, which is another way of saying that we know exactly what the particle's momentum is, namely, zero! On the contrary, because of the Heisenberg Uncertainty Principle, in this case we must say not that the momentum is exactly zero, but that it is 100% uncertain--the only statement we can correctly make concerning the particle's momentum is an epistemological one: that we cannot make any correct statements concerning the ontology of the particle's momentum.19 The natural response from the philosophy of organism to the idea of complementarity20 is to say that such properties cannot exist simultaneously in the satisfaction of an actual occasion, but that they do exist as potentials in the actual occasion's abstracted phases of concrescence. These phases, as we have seen, are only derivatively real and correspond to the quantum idea of probability fields. Just as there appears to be an upper limit to the possibility of knowledge of the entire state of a quantum object, so there is an upper limit to the possibility of knowledge of the phases of concrescence in an actual occasion. In the phases of concrescence, a potential exists for the realization in the satisfaction of both properties in a complementary duality--the actual occasion could have an exact position by sacrificing the possibility for an exact momentum (or vice versa), or it could have a general position as well as a general momentum.

To say that complementary properties exist in the phases of concrescence is to say that complementary properties exist (in the sense of having derivative but not independent reality) as prehensions in the actual occasion. The properties are only real when they become incorporated into the final complex feeling which is the satisfaction. The derivative reality of the prehensions in an actual occasion is exactly analogous to the superposition of states in a quantum system: the wave-function of a quantum system is said to collapse when its superposition ends and one possibility becomes real, just as an actual occasion is said to be real in its culmination in a satisfaction. In other words, the satisfaction of an actual occasion is the collapse of the quantum mechanical wave function. This statement has very important implications, and provides a way of dealing with one of the major areas of debate in quantum mechanics today--the measurement problem.

The Measurement Problem

In the Copenhagen interpretation, it is meaningless to speak of the existence of a property (such as polarization) of a quantum object unless it is measured. Fine and good--but what exactly constitutes a measurement? The example of Schrödinger's Cat has served to explain the measurement problem for decades, and remains the easiest way to conceptualize the phenomenon. In Schrödinger's own words:

A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small that perhaps in the course of one hour one of the atoms decays, but also with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this system to itself for an hour, one would say that the cat lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it.

It seems clear that the cat is, at any given time, either quite alive or quite dead. Quantum mechanics, however, states that this is not the case, and that actually the total system within the box is in a superposition of two states, one with a live cat and one with a dead cat. But of course that seems absurd because how can the cat be both dead and alive at the same time? According to quantum mechanics, this superposition of two states collapses into one definite state (where the cat is either alive or dead), when a measurement takes place, but it does not say what constitutes a measurement.

Bohr dealt with this by stating that a measurement was an 'irreversible act of amplification'--that somewhere between the quantum world of atoms and the classical world of Geiger counters and cats, quantum physics 'turns into' classical physics, in which the cat is definitely either alive or dead. It seems clear that such an irreversible act of amplification must occur somewhere in between the quantum and classical worlds, and it also seems clear that this measurement takes place because of the coupling of a quantum system with a macroscopic measuring apparatus (in this case the Geiger counter).

The problem arises because the measuring apparatus, although macroscopic, is itself made up of atoms and so is subject to the rules of quantum mechanics. If quantum mechanics is to remain a consistent theory, then quantum effects must be present in the measuring apparatus, no matter how large it may be. Consequently, we can consider the measuring apparatus plus the measured object as a single large quantum system. Yet this presents a problem: if the system can be considered isolated from yet larger systems, the same rules of quantum mechanics still apply such that the entire system including the measuring apparatus exists in a superposition of states which requires a further measurement to occur in order to collapse into one reality.

Whitehead can avoid this type of von Neumann regress by defining the collapse of the wave function to be the concrescence of each actual occasion. Thus the 'irreversible act of amplification' is just the bringing into final reality the complex unification of feelings of the actual occasion in its satisfaction. According to Whitehead, "the subject completes itself during the process of concrescence by a self-criticism of its own incomplete phases."21 (Process and Reality:244) The process of self-criticism is the way in which an actual occasion determines its own final qualities--the measurement situation is provided by the satisfaction itself and is the satisfaction itself.

For this reason, the strange properties of quantum systems (the actual occasions) like complementarity, can be seen as applicable only to quantum systems. Medium and large-scale objects may be treated normally (classically) for all practical purposes. Thus locality and reality can be said to exist for objects of sufficient size, even if on the quantum level they cannot, because societies have their own laws which are not necessarily applicable to all other types of systems. For example, the laws of very complex societies (those described by the science of biology) follow laws that simpler societies (those described by the laws of physics) do not, although the laws of biology presuppose the laws of physics.

The laws that apply to quantum systems cease to have effects on medium and large objects because the level of complexity is sufficiently increased by the sheer number of actual entities involved in the society to allow for a new set of (classical-looking) rules to take over. Quantum mechanics can in principle talk of macroscopic systems as if they were merely large quantum systems. Whitehead, however, would call this an instance of the 'fallacy of misplaced concreteness', because quantum laws (which apply to quantum systems, which in this case means just actual occasions themselves) are applied to classical systems, for which different rules apply. Even though the classical rules rest upon the foundation of quantum systems which follow quantum rules, classical systems cannot be explained merely in terms of quantum rules, just as postulates of biology cannot be exactly reconstructed using only the laws of physics, even if biological rules necessarily require physical laws in order to exist.

The Rejection of Parameter Independence

Whitehead rejects the assumption of reality along with the Copenhagen interpretation, but at the same time he avoids the strange metaphysical consequences that the Copenhagen interpretation must deal with by keeping entities that are definitely real. Whitehead would also reject parameter independence as we have seen, but this rejection seems to have serious implications that conflict with much of modern physical theory.

The crucial point is that for Whitehead, time and space (or space-time, if you are so inclined) are not initial properties of a world in which actual occasions happen to find themselves, but are actually properties of the interactions between the actual occasions. Time and space are relative in the strict sense of the term--there is no such thing as an absolute frame of reference. We have seen that the laws of physics for Whitehead arise from the actual occasions themselves--so it is with space and time as well.

Thus, in a certain sense, there is a sort of initial nonlocality and atemporal form to the indefinite phases of concrescence of an actual occasion. Locality and temporality exist in the strong sense of the word only in the final satisfaction of the actual occasion and not before. By concrescing, an actual occasion becomes real and attains its place and its time. The occasion's place and time are relative to the other actual entities which it prehends. It is simultaneous with all those other actual entities with which no prehensions (positive or negative) are shared--all those actual occasions which are not prehended by the one actual occasion, and which do not contribute to the satisfaction of the one actual occasion are considered simultaneous.

The fact of selective simultaneity is what allows for differentiation in an actual occasion; the character of an actual occasion arises in large part from the selective process culminating in the delegation of the entire 'field' of satisfied actual occasions (the initial datum) into either the past, the future, or the simultaneous 'present'. The term 'present' is misleading; two actual occasions are simultaneous when they have no causal interaction of any sort (although in principle they always could have such interaction)--simultaneity does not necessarily mean contemporaneity.

Because the prehensions of an actual occasion are