## H. A. Lorentz as the Grandfather of Quantum Physics

##### Author: Xavier Bick

#####

The first Solvay Conference in the fall of 1911 set a precedent for how leading physicists
collaborate in order to solve difficult problems such as blackbody radiation and the
photoelectric effect. By the end of the fifth Solvay Conference in 1927, the foundation
had been laid for the theory of Quantum Mechanics. Besides featuring many prominent
scientists in the field of quantum physics such as Einstein and Bohr, the first five
Solvay Conferences had one very important characteristic that they all shared: they
were chaired by Hendrik Lorentz. Following the first Solvay Conference, physicist
Henri Poincar said this of Lorentz's importance to the beginning of quantum theory:

... at every moment [we] could be heard talking of the [quantum mechanics] which [we]
contrasted with the old mechanics. Now what was the old mechanics? Was it that of
Newton, the one which still reigned uncontested at the close of the nineteenth century?
No, it was the mechanics of Lorentz, the one dealing with the principle of relativity;
the one which, hardly five years ago, seemed to be the height of boldness.

Prior to the first Solvay Conference in 1911, H. A. Lorentz had published pioneering
work concerning electromagnetism, the luminiferous aether, relativity, and the Zeeman
effect. Lorentz paved the way for scientists such as Planck, Einstein, and the other
participants of the early Solvay Conferences to develop the modern theory of quantum
mechanics.

Hendrik Antoon Lorentz began teaching in 1878 at the University of Leiden in the Netherlands.
Over the last few decades of the 19th century, he solidified then-revolutionary theories
about the propagation of electromagnetic radiation which eventually led to an interested
in relativity and electrodynamics by the turn of the century.

In 1904, one year before Einstein published his theory of Special Relativity, Lorentz
published a paper collecting all his work over the past several years concerning the
motion of bodies through the aether with a focus specifically on bodies moving slower
than the speed of light. Here, Lorentz gave us his space-time transformations, along
with the ideas of length contraction and time dilation, which were derived over the
course of a few years in response to the failure of the Michelson-Morley experiment,
saying, "... the negative result of [the Michelson-Morley experiment] has led FITZ
GERALD and myself to the conclusion that the dimensions of solid bodies are slightly
altered by their motion through the aether." Although Lorentz used his transformations
to correctly explain experiments concerning light aberration, his paper was unsuccessful
in explaining the Michelson-Morley experiment because he attempted to use the first-order
ratio of velocity to the speed of light v/c rather than the second order ratio v^2/c^2
which he derived for other scenarios. A year later, Einstein used algebraically equivalent
versions of the transformations mentioned in Lorentz's paper to describe his theory
of special relativity.

While Lorentz's contributions to relativity were important, it was his work on the
Zeeman Effect that earned him the Nobel Prize in 1902 with Pieter Zeeman. The Zeeman
Effect was first observed in 1897, and Lorentz published a paper with its theoretical
interpretation in 1899 based on an application of the Hamiltonian operator. Because
the intrinsic spin of an electron wasn't discovered until 1925, the "Normal" Zeeman
Effect is the one which involves a zero net spin. Even though it is the more unusual
case, it is called the Normal Zeeman Effect because it was the only case that could
be explained by Lorentz's theory without taking spin into account.

Hendrik Lorentz may be considered the last great contributor to classical physics
with the ideas of Lorentz Force and the Lorentz Ether Theory. Although his early contributions
to quantum mechanics were slightly off the mark, his ideas and the scientific method
allowed and inspired other scientists fill in the gaps and emerge with the theory
of quantum mechanics that was eventually adopted into the Standard Model. If Newton
is the father of modern physics, then Lorentz is the grandfather of quantum physics.