The Order of Time

by Carlo Rovelli

RELATIONS “Fluctuation” does not mean that what happens is never determined. It means that it is determined only at certain moments, and in an unpredictable way. Indeterminacy is resolved when a quantity interacts with something else.* In the interaction, an electron materializes at a certain point. For example, it collides with a screen, is captured by a particle detector, or collides with a photon—thus acquiring a concrete position. But there is a strange aspect to this materialization of the electron: the electron is concrete only in relation to the other physical objects it is interacting with.56 With regard to all the others, the effect of the interaction is only to spread the contagion of indeterminacy. Concreteness occurs only in relation to a physical system: this, I believe, is the most radical discovery made by quantum mechanics.* When an electron collides with an object—the screen of an old television set with a cathode ray tube, for example—the cloud of probability with which we conceived of it “collapses” and the electron materializes at a point on the screen, producing one of the luminous dots that goes into the making of a TV image. But it is only in relation to the screen that this happens. In relation to another object, the electron and screen are now together in a superposition of configurations, and it is only at the moment of further interaction with a third object that their shared cloud of probability “collapses” and materializes in a particular confi...