Terms in Classical Physics

A. Matzkin

Realism - the idea that the concepts in physical theories refer to `things' existing in the real world - is introduced as a tool to analyse the status of the wavefunction. Although the physical entities are recognized by the existence of invariant quantities, examples from classical and quantum physics suggest that not all the theoretical terms refer to the entities: some terms refer to properties of the entities, and some terms have only an epistemic function. In particular, it is argued that the wavefunction may be written in terms of classical non-referring and epistemic terms. The implications for realist interpretations of quantum mechanics and on the teaching of quantum physics are examined.

Henry Pierce Stapp

Brain data pertaining to control of emotions through conscious effort is explained by using a quantum mechanical model of the body/brain of the subject. Unlike the classical model, in which all the causal structure is expressed exclusively in terms of the physical variables, the quantum mechanical model involves causal connections between aspects of the subject described in physical termss with aspects described in psychological terms, and it can explain how the latter affects the former. The data is expressed partially in psychological terms of emotions and conscious effort and partially in terms of observations by the scientists of devices that measure physically described properties of the brain. The quantum model allows these differently described aspects to be causally connected, whereas the classical model must reduce everything to the physical description, in order to display the causal links. But the failure of classical mechanics is the failure of the idea that, in situations such as this, where the behaviour of the physical system (the brain) depends sensitively upon the motions of its atomic and ionic constuents, the purely physical descriptions are causally complete.

A. O. Bolivar

Paul K. Feyerabend

THE PROBLEM Within classical physics the relation between physical theory and ordinary experience was conceived in the following way: ordinary experience is something that can be described and understood in terms of physics. Such a description involves, apart from physical theory, certain approximations. But the conditons under which those approximations apply (they correspond to the initial conditions of, say, celestial mechanics), taken together with the theory, are supposed to be sufficient for giving a full account of ordinary experience. Consequently, classical theory of measurement (which, like any other theory of measurement, links together terms of ordinary experience and theoretical terms), is a piece of applied physics and all processes which happen during measurement can be analysed on the basis of the equations of motion only. When we enter quantum mechanics (QM), we are apparently presented with a completely different picture. For according to the current interpretation of elementary quantum mechanics, ordinary experience – and this now means classical physics – and physical theory (and this now means QM), belong to two completely different levels and it is impossible to give an account of the first in terms of the second. Any transition from the quantum level to the level of classical physics must be taken, not as a transition within QM from the general to the particular, but as an essentially new element which is incapable of further analysis.

Detlef Dürr, Stefan Teufel