How certain can measurements ever be?

Look, to know the exact value of some physical quantity you have to measure it using some instruments — devices made of artificial and natural materials. In the process of measurement, the material of instruments interacts with with the object you study. Indeed, any thermometer slightly changes the internal energy of the substance whose temperature is being measured. Voltmeters and ammeters, whatever good, still change currents in a circuit. This is called the observer effect. In particle physics the influence of an act of measurement appears to be particularly pronounced. The measuring apparatus there inevitably includes crystal lattice while we know electrons diffract passing by the lattice, changing their trajectories stochastically. In other words, an attempt to localize an electron in between of two neighboring atoms results in the appearance of some speed transverse to that of incidence. The less is the electron position uncertainty — which is the step of the lattice — the greater is the uncertainty in the transverse speed. The speed uncertainty also depends on the particle mass: the lighter is the particle, the greater transverse speed it can possibly acquire. This principle was first realized by W. Heisenberg. Later they have understood the uncertainty principle can not be eliminated by any sophistication of the measurement technology and is instead a distinctive feature of quantum mechanics.

About certain opportunities 🙂

Uncertainty in speed is caused by a certain position

The diffraction above happens due to interaction of electrons with atoms. Without the interaction the transverse speed would not appear whereas we would not know the position of an electron however precisely.

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