The Beginning of Quantum Theory

We shall keep this short. Classical physics, by which we mean Newton’s laws and the Maxwell–Lorentz theory (see Chap. 2), fails to explain many atomistic phenomena, apart from the coarse-grained phenomena we discussed in previous chapters. This means that attempts to explain atomistic detail look artificial, and are no longer believable. In other words, straightforward application of classical physics yields descriptions that contradict experience in certain situations. In that sense, for example, Newtonian mechanics is superior to the theory of epicycles, which was invented to save Ptolemy’s geocentric astronomy, because the Newtonian explanation of the motion of heavenly bodies is straightforward and reduces to a single equation: Newton’s equation. The failures of classical physics in the atomistic regime are mirrored in the names of certain effects, such as the anomalous Zeeman effect. This refers to the complicated splitting of spectral lines in magnetic fields that was found experimentally, while Lorentz’s classical analysis led to the “normal” Zeeman effect.