205Chapter 21Philosophical Implications of
Quantum Mechanics
At the end of the last chapter we discussed several quantum mechanical
phenomena, which are impossible to conceptualize from a classical point
of view. The diffraction of electrons, the expansion of wave packets and
the tunneling of potential barriers all involve the breakdown of causality.
Causality is the concept, which forms the very foundation of classical
physics. Even relativity did not change the notion of causality. In fact,
causality plays an important role in the formulation of relativity. The
breakdown of the concept of causality, intrinsic to the formulation of
quantum mechanics by Heisenberg and Schrödinger, produced shock
waves among physicists and philosophers, which persist to this day.
Although the formulators of quantum mechanics were forced to give
up the notion of causality, they were still able to construct a theory of
which possessed predictive powers. They could no longer describe the
behaviour of an individual particle. They were able, however, to provide
a probabilistic description of individual particles, which enabled them to
predict the behaviour of statistically large ensembles of particles. Thus,
they were able to preserve the most basic aspect of a scientific theory,
namely its ability to make predictions, which can, in turn, be verified by
experiment. In fact, quantum theory was able to explain a great deal of
the behaviour of atoms and molecules. Perhaps the most important of
these results was the description of the spectral and chemical properties
of various atoms and molecules as well as the structure of matter such as
solids and liquids.
The success of quantum physics as a descriptive theory of large
numbers of atoms was universally accepted within the physics
community. A schism developed within the community, however,
regarding the interpretation and meaning of the theory. A number of