Beyond Weird

by Philip Ball

We must never forget that ‘reality’ too3 is a human word just like ‘wave’ or ‘consciousness

It is a theory about information. This new perspective gives the theory a far more profound prospect than do pictures of ‘things behaving weirdly’.

Quantum physics implies that the world comes from a quite different place than the conventional notion of particles becoming atoms becoming stars and planets. All that happens, surely: but the fundamental fabric from which it sprang is governed by rules that defy traditional narratives.

Even the term ‘quantum’ is something of a red herring, since the fact that the theory renders a description of the world granular and particulate (that is, divided into discrete quanta) rather than continuous and fluid is more a symptom than a cause of its underlying nature. If we were naming it today, we’d call it something else.

grant the rules of quantum mechanics and you must get quantization, but the reverse is not true.

Quantum objects are what they are, and we have no reason to suppose that ‘what they are’ changes in any meaningful way depending on how we try to look at them. Rather, all we can say is that what we measure sometimes looks like what we would expect to see if we were measuring discrete little ball-like entities, while in other experiments it looks like the behaviour expected of waves

The wave in Schrödinger’s equation isn’t a wave of electron charge density. In fact it’s not a wave that corresponds to any concrete physical property. It is just a mathematical abstraction – for which reason it is not really a wave at all, but is called a wavefunction.

there simply is no ‘where the electron is’. OK then, let’s accept that the electron doesn’t have a location. It’s not after all a concrete little particle, but is truly smeared, a kind of washed-out blot of electrical charge in the weft and warp of space.

Bohr asserted that instead the entire experiment is the phenomenon that we must understand. Whether we have one slit open or both of them, or whether we have a particle detector lurking in one slit or not, are not experiments that explore different manifestations of the same underlying phenomena. They are different phenomena.

To the question ‘What was happening to the photon between its emission from the laser and its detection?’, we can’t simply reply ‘I don’t know, I wasn’t looking.’ We have to say ‘Because I wasn’t looking, that question has no meaning.’

Wavefunction collapse is then a generator of knowledge: it is not so much a process that gives us the answers, but is the process by which answers are created.

So if you read somewhere (as one sometimes does) that the quantum spin of an electron is weird because two complete revolutions are needed for a ‘full turn’, don’t take too much notice. We just don’t know how to picture quantum spin. It is some property that makes the particle respond, like a magnet, to an external magnetic field, and that’s all. There is no classical analogue.

The quantization is not so much a property of the system we are studying; it is a property of measurements we make on it.

Spacetime is really just a fabric we posit to describe how one thing affects another, and to express the limitations on such interactions. It’s an emergent property of causal relationships. And as we’ve now seen, quantum mechanics forces us to revise our preconceptions about causation.

Measurement now means ‘strong interaction with the environment’: strong enough, that is, to enable the quantum state to be deduced in principle from the imprint it has left, regardless of whether we actually make that deduction or not.

if we take the epistemic view that a quantum state reflects a state of knowledge about a system, then an ‘unknown quantum state’ is an oxymoron: if there’s no knowledge, there’s no state.

quantum mechanics is at root a theory not of tiny particles and waves but of information and its causative influence. It’s a theory of how much we can deduce about the world by looking at it, and how that depends on intimate, invisible connections between here and there.

there’s no guarantee that the world’s innermost workings will fit a language developed mostly to conduct trade, courtship and banter.

You probably know the guessing game of Twenty Questions, in which one player leaves the room and the others agree on a word, or a person, or an object. Then the questioner returns and asks questions to which the only permitted answers are ‘Yes’ and ‘No’. (You see: now you realize that this is a quantum game!) Imagine you’re the questioner. You start your questions, and receive the answers – but you find that after a few questions the answers take longer and longer to arrive. That’s odd. Still, you sense you’re closing in on the word, and finally you are sure you’ve got it: ‘A cloud!’ And everyone laughs and tells you you’re right. But then they explain what was going on. While you were out of the room, they didn’t decide on that word at all. They didn’t decide on any particular answer. The rule was simply that each person had to make sure that the answer they gave was consistent with the previous ones in fitting with something. And so the options became more and more constrained as the questions proceeded, and it took ever longer to figure out which word would still work. And everyone was forced, by the nature of the questions, to converge on the same word. If you had asked different questions, you’d have ended up with a different word: the answer was contextual. So there never was a preordained answer – you brought it into being, and in a way that is fully consistent with all the questions you asked. What’s more, the very notion of an answer only makes sense when you play...