Physics and Philosophy

Summary

Physics and Philosophy: The Revolution in Modern Science is Werner Heisenberg's account of what quantum theory means for our understanding of nature, knowledge and language, set within the history of Western thought from the Greek atomists to the twentieth century. It grew from the Gifford Lectures he gave at the University of St Andrews in the winter of 1955-56 and was published in New York in 1958 by Harper and Brothers in the World Perspectives series, with an introduction by the Yale philosopher F. S. C. Northrop; a German edition, Physik und Philosophie, followed in 1959. The book is under copyright, so this library describes it in its own words and gives no quotations. Heisenberg begins by contrasting the old tradition of natural philosophy with the new situation forced on physics by experiment. He then tells the history of quantum theory from Planck's quantum of action in 1900 through Einstein's light quanta, Bohr's atom and the matrix and wave mechanics of 1925-26. The central chapter sets out the Copenhagen interpretation: the results of experiments must be described in the concepts of classical physics; these concepts limit one another, as the uncertainty relations show for position and velocity; the wave function expresses not a definite process but a tendency or possibility, close to Aristotle's potentia; and the act of observation, the interaction of the system with the measuring device, changes this possibility into a fact. He then traces the roots of atomic science to Leucippus and Democritus, contrasts their indivisible atoms with Plato's mathematical forms in the Timaeus, and argues that modern elementary particles resemble Plato's symmetries more than Democritus's hard bodies, and that energy is like the fire of Heraclitus, the substance from which all particles are made. A chapter on philosophy since Descartes argues that quantum theory unsettles the sharp division between thinking subject and extended world, and qualifies Kant's a priori categories of space, time and causality. Further chapters relate quantum theory to chemistry, biology and relativity, review and answer critics of the Copenhagen view, among them Einstein, de Broglie, Bohm and Soviet philosophers, and treat the structure of matter and the limits of language. Heisenberg concludes that plain language, though imprecise, remains indispensable, that science cannot reach absolute truth by pure reason, and that modern physics may help different cultures and traditions understand one another.

Top Lessons

• Observation as participation

  In the Copenhagen interpretation the experimenter does not simply look at an atom; the measurement is an interaction that turns a range of possibilities into one actual result. Heisenberg concludes that physics describes nature as it responds to our questions. The lesson is that knowing is an activity with its own conditions, not a passive copying.

• The ancients and the moderns

  Heisenberg reads the Greek philosophers as partners in present inquiry. Democritus gave physics the atom, but Plato's idea that the smallest units are mathematical forms seemed to him closer to the truth of modern particles. The history of ideas becomes a resource for current science.

• The limits of language

  The concepts of classical physics and ordinary speech were formed for everyday experience, and they fit the atomic world only partly. Yet Heisenberg insists that experiments must be described in those concepts, and that plain language remains the test of understanding. Science must speak clearly while knowing its words are approximate.

• A disputed interpretation

  Heisenberg devotes a chapter to the critics of the Copenhagen view, from Einstein's hope for a complete objective description to Bohm's hidden variables, and answers them. The debate over how to interpret quantum mechanics remains open among physicists and philosophers. Reading him well means hearing both sides.

Verified Quotes

Medical Lens

The book does not concern medicine. Its chapter relating quantum theory to other sciences asks whether physics and chemistry can fully account for living organisms, and Heisenberg suggests that biology may require concepts of its own, as quantum theory required concepts beyond classical mechanics. His discussion of the observer and of the Cartesian split between mind and matter touches the mind-body problem in a general philosophical way; any application to psychiatry is an interpretation beyond the text.

• Chapter on the relation of quantum theory to other parts of natural science

  Heisenberg discusses whether physics and chemistry suffice to explain living organisms.

• Chapter on philosophical ideas since Descartes

  The Cartesian split between thinking and extended substance reconsidered after quantum observation.