Quantum Theory: Photons that didn't

Daniel J. Rogers

Brian L. Silver

Abstract The quantum theory is not explicable in common sense terms. Its axioms, and some of its predictions, go against all our built-in preconceptions as to the nature of reality. In the 1930s Niels Bohr, one of the theory’s fathers, was reported to have said that if you weren’t confused by quantum mechanics you didn’t really understand it.

Klaus Mølmer

‘Coherent states may be of use, so they say, but they wouldn't be missed if they didn't exist. This is my modification of the ‘grook’ by the Danish mathematician, designer and poet Piet Hein, which reads as follows. ‘The Universe may be as large as they say but it wouldn't be missed if it didn't exist.

Walter J. Deal

Alejandro González-Tudela, J. I. Cirac

N. David Mermin

Attitudes toward quantum mechanics differ interestingly from one generation of physicists to the next. The first generation are the Founding Fathers, who struggled through the welter of confusing and self contradictory constructions to emerge with the modern theory of the atomic world and supply it with the “Copenhagen interpretation.” On the whole they seem to have taken the view that while the theory is extraordinarily strange (Bohr is said to have remarked that if it didn't make you dizzy then you didn't really understand it), the strangeness arises out of some deeply ingrained but invalid modes of thought. Once these are recognized and abandoned the theory makes sense in a perfectly straightforward way. The word “irrational”, which appears frequently in Bohr's early writings about the quantum theory, is almost entirely absent from his later essays. The second generation, those who were students with the Founding Fathers in the early post-revolutionary period, seem firmly – at times even ferociously – committed to the position that there is really nothing peculiar about the quantum world at all. Far from making bon mots about dizziness, or the opposite of deep truths being deep truths, they appear to go out of their way to make quantum mechanics sound as boringly ordinary as possible. The third generation – mine – were born a decade or so after the revolution and learned about the quantum as kids from popular books like George Gamow's. We seem to be much more relaxed about it than the other two. Few of us brood about what it all means, any more than we worry about how really to define mass or time when we use classical mechanics.