DOES reality exist without us? Albert Einstein appeared to be in no doubt: surely the moon doesn’t vanish when we aren’t looking, he once asked incredulously. He had been provoked by the proposition, from quantum theory, that things only become real when we observe them. But it is not such a daft idea, and even Einstein kept an open mind. “It is basic for physics that one assumes a real world existing independently from any act of perception,” he wrote in a 1955 letter. “But this we do not know.”

In the decades since, physicists have found it maddeningly difficult to write the observer out of quantum theory. Now some are contemplating a mind-boggling alternative: that a coherent description of reality, with all its quantum quirks, can arise from nothing more than random subjective experiences. It looks like the “perspective of a madman”, says the author of this bold new theory, because it compels us to abandon any notion of fundamental physical laws. But if it stands up, it would not only resolve some deep puzzles about quantum mechanics, it would turn our deepest preconceptions about reality itself inside out.

When it comes to forecasting how the world will behave, quantum theory is unsurpassed: its every prediction, no matter how counter-intuitive, is borne out by experiment. Electrons, for instance, can sometimes display behaviour characteristic of waves, even though they seem in other circumstances to behave like particles.