The disagreement with regard to the validity of the principle of causality, existing to-day among scientists, has its roots in the diversity of definitions of the principle itself rather than in a problematic scientific situation. As far as the formulation of quantum theory is complete its bearing upon philosophical questions can be fixed with precision provided the questions are phrased intelligibly. But a question is intelligible from a scientific point of view only if it satisfies two conditions: (1) the meaning of its terms must be fixed; (2) it must be in accord with the conventions of the science to which the question is put.
The disagreement with regard to the validity of the principle of causality, existing to-day among scientists, has its roots in the diversity of definitions of the principle itself rather than in a problematic scientific situation. As far as the formulation of quantum theory is complete its bearing upon philosophical questions can be fixed with precision provided the questions are phrased intelligibly. But a question is intelligible from a scientific point of view only if it satisfies two conditions: (1) the meaning of its terms must be fixed; (2) it must be in accord with the conventions of the science to which the question is put.
In a recent number of Blackfriars (July, 1949) Dr A. W. Gledhill has discussed very competently some aspects of the statistical method as used in modern physics. He has tried to show there ‘that modern physical theory does not contradict the principle of causality’. Having made a study of this subject over quite a number of years, the writer, while agreeing with some of Dr Gledhill’s conclusions, feels nevertheless that there are a few points which have not been covered as adequately as the importance of the subject for modern philosophy seems to warrant. In order to understand the controversy about the validity or non-validity of the principle of causality, which has been initiated by Heisenberg’s uncertainty principle, it is necessary to realise, first of all, that when a physicist speaks about causality, he usually does not mean the same thing as a scholastic philosopher. In scholastic philosophy one distinguishes different kinds of causes, such as the material, the efficient, the final, as well as the formal and exemplary causes. The classical physicist, on the other hand, since the time of Galileo, admits only efficient causes. Let us therefore give a brief sketch of the development of this concept of scientific causality and show the reasons for this limitation. The purpose of a scientific theory is the prediction of events among the natural objects which form the field of enquiry of the particular science concerned. Evidently, the more certain the prediction, the better the theory on which it is based.
Causalism is the traditional attitude of disowning all noncausal categories of determination, holding dogmatically that every connection in the world is causal. The entirely negative attitude taken by indeterminism and by empiricism toward the principle of causation is inconsistent with the very goal of science, which is the search for the objective forms of determination and interconnection. This chapter deals with the question concerning the range of validity of the causal principle. The notion of causal range of the laws of nature will be clarified and illustrated, by analyzing in some detail a typical physical law with which every student of electricity is familiar. Science seems to show neither an enlargement nor a progressive shrinking of the domain of validity of the causal principle. Most scientists and philosophers of science believed that quantum mechanics had given causality the death blow, by showing that quantum phenomena are inherently random, hence only statistically predictable.
In the 19th century, determinism was often seen as a presupposition of scientific thinking, although its validity was not universally accepted among scientists and philosophers. There were different conceptions of causality, and the concept of cause was often linked to that of force or energy; but toward the end of the 19th century, the causal conception of forces was increasingly criticised and some argued that the concept of cause should be abandoned altogether. After the development of the modern theory of quantum mechanics in 1925, many physicists and philosophers claimed that this theory implied an overthrow of the classical conception of causality; however, only few authors abandoned causality altogether. The debate of the implications of quantum mechanics for causality soon became muddled because of the many different meanings attached to the term “causality”.
During the past two or three centuries western philosophy and science have confirmed each other in their ontological attitude towards external reality. The particular opinion that physical objects have an existence completely independent of observation was established as the necessary basis for all scientific investigation. The discovery in quantum physics that the phenomena ultimately constituting the stability of the material world cannot be separated from the instruments of observation was necessarily felt disastrous to the scientific world-picture, and many philosophers and scientists, including celebrated physicists, are still trying by all means to save ontology in quantum physics. The motive power behind this activity is the belief that the objectivity of science can be maintained only if the elementary particles of matter can be objectified in the usual way. The present chapter deals with the fundamental conditions in quantum physics which entail a complete breakdown of the conceptual frame of classical mechanics
The foundations and meaning of quantum theory became a central issue to Albert Einstein and Niels Bohr since the onset of their impassioned debate in the 1920s, enriched by the contributions of many other distinguished scientists and philosophers.The questions are not settled down at all, despite the great achievements of the theory, its impressive accordance with experiment and predictive power.The fundamental and technological applications range from cosmology to biology, with the development of invaluable instruments and the design of new materials.Is quantum mechanics a complete or an incomplete theory?Is there an objective reality independent of the observer or is the reality created by the measurements?Are hidden-variable theories justifiable?Is there a quantum theory founded in a local-causal and non-linear approach that formally contains the orthodox linear theory as a special case?Can such a formulation unify classical and quantum physics?Are Heisenberg's uncertainty relations valid in all cases?Here, the subject is addressed as an adaptation of our contribution to the Colloquium "Quantal aspects in Chemistry and Physics.
Quantum mechanics, even in its early and simple phases, has often been regarded as a non-causal discipline. The argument supporting this view cites the uncertainty principle as prohibiting the ascertainment of complete knowledge concerning physical states upon which causal prediction could be based. Recent developments in atomic physics have added new and puzzling features to the problem of causality insofar as they operate, not only with intrinsically unmeasurable states, but also with time reversals which have been interpreted to mean that the effect can be prior to the cause. Feynman's theory of quantum electrodynamics is particularly rich in unorthodox suggestions which tantalise philosophers. The purpose of the present paper is to exhibit them, appraise their methodological function and see in what manner they violate the rules of causal description. This purpose, it seems, is best achieved by a sequential discussion of three questions: What does causality mean in physics? What is the new method of quantum electrodynamics? Is this new method compatible with the causal doctrine in some satisfactory form?