My first encounter with quantum mechanics occurred in my very first term as an undergraduate, studying for a bachelor’s degree in chemistry in a rather damp and gloomy Manchester, England, in the autumn of 1975.
Looking back, it’s no real surprise that all the students in my class (me included) were utterly baffled by what we were taught. Until that moment, we had all been blissfully unaware that there was anything more to be learned about the physical world beyond the smooth continuity and merciless certainties of Newton’s clockwork mechanics.
Our understanding of atoms was limited to the ‘planetary model’ associated with the names of physicists Niels Bohr and Ernest Rutherford. If we had thought about it at all (and I can tell you that we really hadn’t), then we would have supposed that the classical theories we use to describe planets orbiting the Sun could simply be extended to describe little balls of electrically charged matter orbiting the central nucleus of an atom. Yes, the forces are different, but surely the results would be much the same.
But now we were told that the physics of atoms and molecules is governed by a very different set of laws, with which even chemists must come to terms. Nothing had prepared us for this. In our first lecture we chomped our way through Max Planck’s discovery of the quantum, Einstein’s ‘light-quantum’ hypothesis, Bohr’s quantum theory of the atom, Louis de Broglie’s wave-particle duality,* Erwin Schrödinger’s wave mechanics, and Werner Heisenberg’s uncertainty principle.
I thought my head was going to explode.
Mechanics is that part of physics concerned with the how and why of stuff that moves, governed by one or more mathematical equations of motion. In hindsight, our problems were compounded by the fact that the evolution of our understanding of classical mechanics had stopped with the school textbook version of Newton. We were not being trained to be physicists, and so missing from our education was the elaborate reformulations of classical mechanics, first by Joseph-Louis Lagrange in the eighteenth century, and then by William Rowan Hamilton in the nineteenth. These reformulations weren’t simply about recasting Newton’s laws in terms of different quantities (such as energy, instead of Newton’s mechanical force). Hamilton in particular greatly elaborated and expanded the classical structure and the result, called Hamiltonian mechanics, extended the number of situations to which the theory could be applied.
We were therefore confronted not only with this extraordinary thing called the quantum wavefunction, but also with the challenge of writing down something called the ‘Hamiltonian’ for a specific physical system or situation, such as the orbit of an electron in an atom or the vibrations of a chemical bond holding two atoms together, without really understanding where either of these things had come from.*
But, make no mistake, I was completely hooked. I filled my notebooks with equations that looked…. well, they looked beautiful. I still didn’t really understand what any of it meant, but I learned how to use quantum mechanics as best I could and set aside any concerns. I went on to complete a doctorate at Oxford University and a couple of years of postdoctoral research at Oxford and at Stanford University in California, before returning to England to take up a lectureship in chemistry at the University of Reading. Although I was never blessed with any great ability in mathematics, I learned a great deal more about quantum mechanics from Ian Mills, professor of chemical spectroscopy in my department, and I take some pride in a couple of research papers I published on the quantum theory of high-energy molecular vibrations.
Then, in 1987, whilst working for a couple of months as a guest researcher at the University of Wisconsin-Madison, I happened upon an article that sent me into a tailspin. This was written by N. David Mermin.1 It told of something called the Einstein–Podolsky–Rosen ‘thought experiment’, which dates back to 1935, and some laboratory experiments to probe the nature of quantum reality that had been conducted by Alain Aspect and his colleagues in 1982.
I felt embarrassed. I had come to this really rather late. Why didn’t somebody tell me about all this before?
I had allowed my (modest) ability in the use of quantum mechanics to fool me into thinking that I had actually understood it. Mermin’s article demonstrated that I really didn’t, and marked the beginning of a 30-year personal journey. I’m now the proud owner of several shelves overflowing with books on quantum mechanics, science history, and philosophy, and a laptop filled with downloaded articles. I’ve written a few books of my own, the first published in 1992.
I can happily attest to the fact that, like charismatic physicist Richard Feynman, I still don’t understand quantum mechanics.2 But I think I now understand why.