QR3.8.7 The Uncertainty Principle

Heisenberg’s uncertainty principle is that one can’t know a quantum entity’s exact position and momentum at once. This complementarity, that position and momentum are separately knowable but together unknowable, is part of quantum mechanics but why does the one deny another?

In quantum realism, measurement is an information transfer:

… a measuring instrument is nothing else but a special system whose state contains information about the “object of measurement” after interacting with it:(Audretsch, 2004) p212

Figure 3.25. Waves interacting

And it occurs when a quantum wave interaction causes a node of the quantum network to overload. Figure 3.25 shows a simple case of two waves interacting in two nodes. If they are in phase, one node overloads to give a position exactly but the wavelength is unknown. If they are out of phase, both nodes cancel to define the wavelength exactly but there is no position information. Waves interacting reveal position or wavelength but not both, with no repeats. If the result gives position there is no wavelength data and if it gives wavelength there is no position data. In both cases, the observed wave has given all the information it has to the interaction. One wave “observing” another can give position or wavelength information but not both.

The quantum uncertainty principle comes from the nature of wave interactions based on De Broglie’s equation of momentum and wavelength. The information change in any photon interaction can’t be less than a quantum process so position plus momentum can’t be less than Planck’s constant.