David Peat

14 From Certainty to Uncertaintyknow the universe we act to disturb it. Science prides itself on objectivity,but now Nature is telling us that we will never see a pure, pristine,and objective quantum world. In every act of observation the observingsubject enters into the cosmos and disturbs it in an irreducible way.Science is like photographing a series of close-ups with your backto the sun. No matter which way you move, your shadow always fallsacross the scene you photograph. No matter what you do, you cannever efface yourself from the photographed scene.The physicist John Wheeler used the metaphor of a plate glasswindow. For centuries science viewed the universe objectively, as if wewere separated from it by a pane of plate glass. Quantum theorysmashed that glass forever. We have reached in to touch the cosmos.Instead of being the objective observers of the universe we have becomeparticipators.Heisenberg’s MicroscopeOur story of quantum strangeness has not yet ended. There is one furtherstep to take—a step that Einstein could never accept and whichhas implications for the very nature of reality. It is a step that arose in adispute between Bohr and Heisenberg over the interpretation of theuncertainty principle.In the early days of quantum theory Werner Heisenberg tried toexplain the origins of uncertainty much as I have done in the precedingtext, by analogy with the way radar is used to ascertain the positionand speed of a rocket. In the large-scale world of rockets and meteors acontinuous stream of radar signals is used, but Heisenberg was thinkingof an idealized sort of microscope that could be used to study anelectron. This microscope would use the minimum amount of disturbance—asingle photon, or quantum of light, at a time.First, a single photon determines the speed of the electron and theresult is written down. Next, a single photon determines the positionof the electron and that result is written down. But by measuring thisposition, the electron received an impact by a photon, which changedits speed. Alternatively, in measuring the speed, the impacting photondeflects the electron from its path, thus affecting its position. In other