When the maths works, but no one knows exactly why
ESCAPE FROM SHADOW PHYSICS Quantum theory, quantum reality and the next scientific revolution
ADAM FORREST KAY 496pp. Weidenfeld and Nicolson. £25.
A HUNDRED YEARS after quantum mechanics was invented, we still don’t know what it means. This is an unprecedented dilemma for science. In any other theory the meaning is inherent in the formulation. Newtonian mechanics tells us how objects move; Darwinian evolutionary theory tells us how types of organism change one to another over time. No one needs to ask: “What do you mean by object, by organism?” Quantum mechanics is different. It allows us to make predictions about the behaviour of particles, atoms and materials that experiments show to be astonishingly accurate. Yet there is still no consensus about what the theory implies for the nature of the world it describes.
How can a theory make predictions without specifying what manner of thing those predictions are about? The answer is that quantum mechanics points in a different direction to other scientific theories: not at the world it describes, but back at our perception of it. Whereas Newtonian mechanics predicts the path that an object will take when forces act on it, quantum mechanics – which replaces Newton’s laws for objects as small as atoms or electrons – tells us only what we can expect to see if we try to observe the object. Absent that observation, it is silent.
This is absurd, of course, and Albert Einstein said as much, complaining to a colleague that it is ridiculous to suppose that the moon is not there if we don’t look at it. But what quantum mechanics really says about such things is subtle. It is, for example, beyond question that what we see in the quantum world depends on what information we try to obtain about it. If electrons are fired at two narrow slits, what we see them do on the far side differs if we try to detect which slit each electron goes through or if we choose not to know. Worse, if we cunningly collect our “which way did they go?” information only after the electrons have passed through the slits, still we seem to affect what happens at the slits themselves. It is as if the act of collecting information about the world changes its nature: science’s wish to stand outside the world and observe objectively seems no longer to be possible. No wonder Einstein was upset.
He wasn’t alone. Many physicists today seem uneasy about what quantum mechanics implies, and Adam Forrest Kay is one of them. With PhDs in both mathematics and literature, he makes a vigorous and engaging case in his new book, Escape fr
