Beyond Weird

by Philip Ball

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...