Introduced by Victor Suchar on 4 April 1997

This was Victor Suchar's fourth presentation in a series on the evolution of concepts in Physics,
which started with "Physics and Philosophy in the 19th Century" in November 1995.
The subject in this session was the development of quantum physics from Plank's formulation of
the quantum hypothesis in 1900 to Dirac's axiomatic approach in "The Principles of Quantum Mechanics" of
1930 and v. Neumann's reformulation within the geometrical framework of Hilbert spaces.
Quantum mechanics raises three fundamental questions which should be examined, in my opinion,
in the context of this evolution:
1) Status of classical mechanics - is classical mechanics presupposed or subsumed in quantum
mechanics, and can it be derived from it?
2) Technology - is the uncertainty in measurement a consequence of the limitations of measuring
apparatus or of natural law?
3) Epistemology - is there a completely formulated theory of knowledge associated with quantum
mechanics as Kant's is with Newtonian Physics?
The theoretical framework of quantum mechanics stands on three principles:
correspondence - relating to the first question; uncertainty - relating to the second, and
complementarity - relating to all three.
On the first question, a study of the evolution of concepts in quantum mechanics leads me to
David Bohm's conclusion:
"Quantum theory presupposes a classical level and the correctness of classical concepts in
describing this level.

Classical definitness and quantum potentialities complement each other in providing a complete description
of the system as a whole"
On the second question, the development of nano-technology may provide new methods of
measurement using instruments at a micro-scale which may confirm that in quantum mechanics, probabilities
are primary, not merely a reflection of our ignorance.
On the third, we should distinguish the powerful and highly successful scheme constituting
quantum mechanics, from the Copenhagen Epistemology -the traditional interpretation, and from the current
attempts to build a quantum logic in the form of propositional calculus which is, in my opinion, still in a
fragile state.
1. The theory is concerned with individual objects.
2. Probabilities are primary.
3. The frontier separating the observed object and the means of observation is left to the choice of the
4. The observational means must be described in terms of classical physics.
5. The act of observation is irreversible and it creates a document.
6. The quantum jump taking place when a measurement is made is a transition from potentiality to actuality.
7. Complementary properties cannot be observed simultaneously.
8. Only the results of a measurement can be taken to be true.
9. Pure quantum states are objective but not real.
There are now four fundamental theories in physics:
1) quantum mechanics, 2) particle theory, 3) gravitation and 4) thermodynamics and statistical mechanics.
The four, although interrelated, stand on their own set of principles.
There was active discussion of these concepts and, in particular, of two issues: first, the confusion
created by terminology, for example the "collapse of the wave equation" - the transition from potentiality to
actuality when a measurement is made and second, the feasibility of a unified theory, "a theory of
everything", an issue which we agreed to take up in a future session.
Victor Suchar