One of the weirdest theoretical implications of quantum mechanics is that different observers can give different—though equally valid—accounts of the same sequence of events. As highlighted by physicist Carlo Rovelli in his relational quantum mechanics (RQM), this means that there should be no absolute, observer-independent physical quantities. All physical quantities—the whole physical universe—must be relative to the observer. The notion that we all share the same physical environment must, therefore, be an illusion.

Such a counterintuitive prediction—which seems to flirt dangerously with solipsism—has been clamoring for experimental verification for decades. But only recently has technology advanced far enough to allow for it. So now, at last, Massimiliano Proietti and collaborators at Heriot-Watt University, in the U.K., seem to have confirmed RQM; as predicted by quantum mechanics, there may well be no objective physical world.

Yet, our perceptions of the world beyond ourselves are quite consistent across observers: if you were to sit next to me right now, we would describe my study in very similar, mutually consistent ways. Clearly, observers must share an environment of some sort, even if such an environment is not physical—i.e., not describable by physical quantities.

To read more, click here.