Beyond Weird: Why Everything You Thought You Knew about Quantum Physics Is Different

by Philip Ball

Take radioactive decay. Some radioactive atoms will decay by emitting an electron from inside the nucleus: this electron is, for historical reasons, called a beta particle, but it’s just a common-or-garden electron. Atomic nuclei don’t exactly contain electrons – we saw that these orbit outside the nucleus. But they do contain particles called neutrons, which may spontaneously decay into an electron, which gets spat out, and a proton, which stays in the nucleus.*1 Beta decay of carbon-14, one of the natural forms of carbon atoms, is the process used for radiocarbon dating, and it transforms the carbon atom to a nitrogen atom. Beta decay is a quantum process, so the probability of the neutron decaying is described by a wavefunction. (It’s actually a kind of quantum tunnelling process: the electron tunnels out of the nucleus, where it would otherwise be bound by electrical attraction.) All the wavefunction can tell you is the probability that the decay will occur – not when that will happen. Take any specific atom of carbon-14, and its decay could happen tomorrow, or in 1,000 years. And there’s nothing, nothing, you can do to figure out which it will be, for all the carbon-14 atoms look alike. However, once you know the probability of beta decay, you can estimate when, from a sample of a billion or so atoms, exactly half of them will have decayed. This