For a century, physicists have known that the classical assumptions about the universe are incorrect — electrons do not orbit the nucleus of an atom, but exist in waves around it. So an electron can be in more than one place at once, until we observe it. Schrodinger’s cat is alive or dead: we can only know which by looking, which itself determines the answer. Why this is true is unclear.

This realisation is “almost psychedelic”, argues Carlo Rovelli, the Italian physicist who specialises in making complex ideas seem simple. Quantum physics has been used to develop semiconductors and lasers. But the first thing to understand is that you cannot truly understand it, because no one does.