A great debate has raged over what precisely this field can tell us. Ninety years later physicists still can’t decideby Jim Baggott / August 2, 2018 / Leave a comment
Everybody knows by now that quantum mechanics is an extraordinarily successful scientific theory, on which much of our modern, tech-obsessed lifestyles depend. It is also completely mad. Although the theory quite obviously works, we’re left to puzzle over what we think it’s telling us, with all its ghosts and phantoms; its cats that are at once both alive and dead; its collapsing wavefunctions; and its seemingly “spooky” goings-on. It leaves us with a rather desperate desire to lie down quietly in a darkened room.
This business has been going on for more than 90 years, and shows no signs of letting up. The debate about the interpretation of quantum mechanics began in 1927, as Albert Einstein and Niels Bohr faced off about the nature of quantum reality. And it continues today, as witnessed by a succession of recent popular books on the subject, including Philip Ball’s Beyond Weird, Adam Becker’s What is Real?, and Anil Ananthaswamy’s Through Two Doors at Once, soon to be arriving on bookshelves. We can also look forward to Lee Smolin’s Beyond the Quantum, to be published next year, and my own A Game of Theories in 2020 (though I’m pretty confident that this title will not survive to publication).
What is it about this question of interpretation that has proved so stubbornly intractable, yet provokes such seemingly endless fascination?
As the name implies, quantum mechanics is the extension of the science of mechanics to the quantum domain of molecules, atoms, and sub-atomic particles. Mechanics is simply concerned with stuff that moves, governed by a very handy set of physical laws and mathematical equations of motion. In the 200 years after Newton, physicists worked to establish these laws and equations, employing concepts that are entirely familiar, such as mass, velocity, momentum and acceleration. These concepts sit right “on the surface” of the equations, and scientists don’t typically trouble themselves much about what they mean. It’s obvious.
But as physicists sought to extend this mechanics to describe the inner workings of atoms, in which the things that move are electrons orbiting atomic nuclei, they found that the old laws and equations no longer applied. The quantum nature of matter and radiation means that a particle like an electron can behave as though it is distributed through space, like a wave. In 1926, Erwin Schrödinger developed a theory to describe such combined wave-particle behaviour, in which the electron’s…