David Peat

Quantum Uncertainty 15words, Heisenberg pointed out, as soon as you try to measure positionyou change the electron’s speed, and as soon as you try to measurespeed you change the electron’s position. There is always an irreducibleelement of uncertainty involving speed and position. 1It is in this way, Heisenberg argued, that uncertainty arises. It is theresult of the disturbances we make when we attempt to interrogate thequantum world. Because the quantum is indivisible this uncertainty istotally unavoidable. The French physicist Bernard D’Espagnat coinedthe term “a veiled reality” for this property. Quantum reality by its verynature, he observed, is veiled and concealed from us. No matter howrefined our experiments may be, the ultimate nature of this reality cannever be fully revealed.The Disappearance of Quantum RealityThere the matter stood until Niels Bohr stepped in. While physicistssuch as Werner Heisenberg, Wolfgang Pauli, Erwin Schrödinger, andMax Born were working at the mathematical formulation of the newtheory, Niels Bohr was thinking about what the theory actually meant.For this reason he summoned Heisenberg to Copenhagen and confrontedhim about the deeper significance of his “microscope experiment.”Bohr argued that Heisenberg’s explanation began by assuming theelectron actually has a position and a speed and that the act of measuringone of these properties disturbs the other. In other words, Bohrclaimed that Heisenberg was assuming the existence of a fixed underlyingreality; that quantum objects possess properties—just like everydayobjects in our own world—and that each act of observation interfereswith one of these properties.He went on to argue that Heisenberg’s very starting point was1Because a quantum is indivisible and shared between observer and observed,physics cannot say if a particular photon was produced by the apparatus, or by theobserved electron, or both together. For this reason it is not possible to calculate theeffect of perturbations on speed and position and thereby compensate to reduce theuncertainty.