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10.4 Measuring as Actualising

In the previous chapters, we saw how actualisation could be a spontaneous mode of action of propensities, whereby potentiality was transformed into an actuality at a specific place in space and time, and whereby future potentialities were restricted to take into account the consequences of that event having definitely happened. The point to realise now is that this process can be used to replace the special category of measurements that had been postulated in quantum theory ever since von Neumann [1929]. For measurements are also assumed to have definite outcomes without equivocation, to be historically irreversible,   and to be essentially `projections' or `selections' of the wave function at some time onto one of a selection of eigenstates of some `measurement observable'.   Von Neumann called this process the reduction of the wave packet, and had to postulate it separately from the time evolution governed by Schrödinger's equation.

In our philosophy of nature, however, it is to be expected that propensities, as well as having forms of distribution in space and time, also have a characteristic mode of operation wherein some one possibility becomes actualised to the exclusion of its competitors. Although quantum measurements can be performed for any of a wide range of quantum variables, and actualisations were assumed to be always point localisations in space-time, it can be argued, following Feynman and Hibbs [1965] and     N. Maxwell [1976], that arbitrary quantum mechanical measurement processes can always be reduced to be essentially a set of localisations in space and time. Whether this argument can be carried through will be reconsidered in chapter 12.    

Irreversible Processes

Some physicists have taken the view that there is an objective sense of `irreversibility', in large thermodynamic systems for example, of which the irreversibility of measurement events in the quantum domain is a special case.

  Prigogine [1980, 1984], holds, for example, that the second law of thermodynamics has to be introduced before one is able to define any level of `elementary particles'.   As Rae [1986] puts it, Prigogine `suggests that it is the irreversible changes that are the really fundamental entities in the universe, and that the idea of microscopic particles moving subject to reversible laws is an approximation that is valid only in the very special circumstances where a particle, or particles in cooperation, are effectively decoupled from their interaction with the rest of the universe. Notice that the fundamental concepts are the events or changes rather than the objects that are doing the changing'10.8. Coordinate with Rae's view is a `traditional, serial way of considering the nature of time', as against the `fashion since Einstein to look at time as just another dimension and to talk of space-time.   However, time and space are not equivalent concepts $\ldots$ Without the possibility of change the idea of existence is meaningless, so for me at least there is no being without becoming $\ldots$' [Perhaps] `time really does flow in one direction'10.9.

There are numerous points of similarities between these views and the ideas which I have been discussing in this book. My chapter 6 started with the notion of `purely actual entity', and it turned out that, as `past events', these are `the irreversible changes that are the really fundamental entities in the universe'. The idea of a microscopic particle, however, is not merely an approximation, but can be constructed after an analysis of the propensities for the irreversible changes.   These `irreversible changes' involve an essential `becoming' in the theory of time and space, and cannot be properly accounted for in the `block universe' theory of space-time.

Prigogine and Rae, in contrast to my view, do not see irreversible changes occurring in quantum physics specifically.   Prigogine thinks that they only occur in large complex systems in which there are sufficient instabilities that `chaotic behaviour' follows. (This is when any arbitrarily small change in a starting condition will result in completely different future behaviour.) However, he does not know the precise microscopic conditions for the occurrence of irreversible events. Although he declares that there is a transition between the reversible quantum world and the irreversible thermodynamic world, he does not say exactly at what point this transition occurs. These questions will be discussed further in chapter 12.

Prigogine [1980] consists largely in an exploration of `concepts' rather than the `details' of irreversible processes10.10, and he develops some mathematical formalisms (e.g. for entropy measures) which he expects to prove useful in their description.   His endeavours are therefore similar to mine in this book: we are both developing general frameworks in which it is possible to formulate specific theories of reversible and irreversible processes.    

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Next: 10.5 Nonlocalities Up: 10. Quantum Substances Previous: 10.3 Waves, Particles and
Prof Ian Thompson


Author: I.J. Thompson (except as stated)