Hendrik Lorentz

• 1. Introduction

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  Hendrik Antoon Lorentz died on the 4th of February 1928, and three days later something remarkable happened at his funeral in Haarlem. At the stroke of noon, the entire State telegraph and telephone network of the Netherlands fell silent for three minutes. Not by accident. By deliberate choice, as a tribute to one man. Albert Einstein and Marie Curie were among the mourners who gathered at the Grote Markt. Ernest Rutherford, as President of the Royal Society, delivered a graveside oration. The Dutch called Lorentz the greatest man the Netherlands had produced in their time, and the wider world of physics seems to have agreed. So who was this man born in Arnhem in 1853, and why did his work leave such a deep imprint on how science understands light, matter, time, and space?

• 2. The Making of a Physicist

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  Arnhem, in the province of Gelderland, was where Lorentz spent his childhood, born on the 18th of July 1853. His mother, Geertruida van Ginkel, died in 1861 when he was just eight years old. His father Gerrit remarried a woman named Luberta Hupkes, and though Lorentz was raised Protestant, he grew into a freethinker who attended Catholic mass at his local French church.

  At the Hogere Burgerschool in Arnhem, which he attended from 1866 to 1869, he excelled not only in science and mathematics but also in English, French, and German. By 1870 he had passed the classical language exams required for university entry, and he arrived at Leiden University that same year.

  At Leiden, astronomy professor Frederik Kaiser made a lasting impression on him. Kaiser's teaching led Lorentz toward physics rather than astronomy. He earned a Bachelor's degree in Mathematics and Physics the following year, then returned to Arnhem in 1872 to work as a night school teacher while continuing his doctoral studies. In 1875, under the supervision of Pieter Rijke, he defended a thesis on the reflection and refraction of light, in which he refined the electromagnetic theory of James Clerk Maxwell. That refinement would set the direction of his entire career.

• 3. The Chair at Leiden

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  In 1878, Leiden University established a new Chair of Theoretical Physics. The position had originally been offered to Johannes van der Waals, but van der Waals had just accepted a professorship at the University of Amsterdam. Lorentz, at twenty-four years old, was appointed instead.

  On the 25th of January 1878, he delivered his inaugural lecture under the title De moleculaire theoriën in de natuurkunde, which translates as "The molecular theories in physics." For his first twenty years in the post, his research centred on the electromagnetic theory of electricity, magnetism, and light. He eventually broadened his focus to include hydrodynamics and general relativity, without ever abandoning his home territory of theoretical physics.

  By 1910, the weight of teaching and administrative duties had become a serious problem. He wanted to free up time for research. He approached Albert Einstein about taking over the professorship, but Einstein had just accepted a position at ETH Zurich and, as the source records, the prospect of filling Lorentz's shoes made him shiver. Lorentz ultimately chose Paul Ehrenfest as his successor. In 1912, Lorentz resigned his full chair and became Curator of the Physical Cabinet at Teylers Museum in Haarlem, a post that gave him the research time he needed. He kept a teaching connection to Leiden as Extraordinary Professor, delivering what became known as his famous "Monday morning lectures" on new developments in theoretical physics.

• 4. Time, Space, and the Aether

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  In 1892 and 1895, Lorentz was working on a specific problem: how to describe electromagnetic phenomena, including the propagation of light, in reference frames that move relative to what physicists then called the luminiferous aether. He introduced a new time variable he called local time, which depended on universal time and the observer's location.

  With local time in hand, he could account for the aberration of light and explain the results of the Fizeau experiment. He also proposed, in 1892, that moving bodies physically contract in the direction of motion, a prediction aimed at explaining the Michelson-Morley experiment. In 1899, and again in 1904, he added time dilation to his framework and published the complete set of equations that Henri Poincare would name the Lorentz transformations in 1905.

  It emerged later that Joseph Larmor had used identical transformations to describe orbiting electrons in 1897, apparently without either man knowing of the other's work. Larmor's and Lorentz's equations look different on the page, but they are algebraically equivalent to what Poincare and Einstein published in 1905.

  Henri Poincare, in 1900 and 1904, called local time Lorentz's "most ingenious idea," illustrating it by showing that clocks in moving frames can be synchronized by exchanging light signals assumed to travel at the same speed in both directions. Poincare also, in his own 1905 work, corrected certain imperfections in Lorentz's equations and achieved the exact invariance that had eluded Lorentz. Lorentz himself acknowledged this openly, noting that Poincare had formulated the "postulate of relativity" and was the first to use that term.

• 5. Lorentz, Einstein, and a Graceful Yield

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  When Einstein published his 1905 paper Zur Elektrodynamik bewegter Körper, which introduced what we now call special relativity, he drew heavily on the concepts and mathematical tools Lorentz had developed. Some physicists initially did not understand the distinction between the two men's approaches and referred to the result as the Lorentz-Einstein theory.

  Lorentz himself addressed this comparison directly in his 1906 lectures at Columbia University, published in 1910 under the title The Theory of Electrons. He quoted from the lectures to explain what made Einstein's approach different. Where Lorentz had labored to derive the equivalence of reference frames from the equations of the electromagnetic field, Einstein simply postulated it as a general principle. Lorentz acknowledged that this allowed Einstein to show that the negative result of experiments like Michelson's was not a lucky cancellation of opposing effects but the expression of a fundamental law. He also admitted that Einstein had achieved something he himself had not: a formulation in which the equations take exactly the same form in moving frames as in stationary ones.

  Yet Lorentz never fully abandoned the idea of an aether. In 1910 he wrote that if the relativity principle had general validity in nature, one would be unable to detect which reference frame was preferred, and the results would be the same as those reached by denying the aether entirely. He acknowledged, in so many words, that the choice between the two pictures could be left to the individual. Einstein later wrote that the special theory of relativity was "a more detailed expose of those concepts which are found in Lorentz's research of 1895."

• 6. The Zeeman Prize and the Electron

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  Lorentz theorized that atoms contain charged particles and that the oscillations of those particles produce light. This was the foundation for what became the Lorentz oscillator model, a classical description of anomalous dispersion in dielectric materials when the driving frequency of an electric field approached the resonant frequency of the material, causing abnormal refractive indices.

  His colleague and former student Pieter Zeeman discovered in 1896 that strong magnetic fields split spectral lines, a finding that had no explanation at the time. Lorentz provided the theoretical account of why this happens, rooting it in the behavior of the charged oscillating particles he had already theorized. Their joint work earned both men the Nobel Prize in Physics in 1902, awarded by the Royal Swedish Academy of Sciences "in recognition of the extraordinary service they rendered by their researches into the influence of magnetism upon radiation phenomena."

  Poincare, writing in 1902, described the breadth of what Lorentz had connected through the electron theory: the results of Fizeau on the optics of moving bodies, the laws of normal and abnormal dispersion and absorption, and the newly discovered Zeeman phenomenon, which even aided the classification of Faraday's magnetic rotation that had defeated all of Maxwell's efforts.

• 7. Dam Water and Civil Science

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  The Dutch government needed to build the Afsluitdijk, a massive flood control dam that would close off the Zuiderzee, and they had a problem: nobody could reliably predict what the dam would do to water levels in the Waddenzee. Hydraulic engineering at the time was largely empirical, and the disturbance to tidal flow was so unprecedented that the existing rules simply could not be trusted.

  Lorentz was asked to chair a committee to calculate these effects. He was originally intended to play a coordinating role, but it quickly became clear he was the only person with genuine mathematical traction on the problem. From 1918 until 1926, he invested a large part of his time on it. He proposed starting from the basic hydrodynamic equations of motion and solving the problem numerically, an approach that was feasible because the water flow in the Waddenzee is quasi-one-dimensional.

  The Afsluitdijk was completed in 1932, four years after Lorentz died, and the predictions his committee had made turned out to be remarkably accurate. One of the two sets of locks in the dam was named after him. It was a fitting tribute to a man whom the Nobel Foundation's biography described as having "completed what was left unfinished by his predecessors and prepared the ground for the fruitful reception of the new ideas based on the quantum theory."

• 8. Legacy and the Second Golden Age

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  From 1925 until his death in 1928, Lorentz served as Chairman of the International Committee on Intellectual Cooperation, the body that later became UNESCO. He had earlier chaired the first Solvay Conference in Brussels in the autumn of 1911, where twenty physicists from different countries debated the emerging quantum theory. Poincare noted afterward that the "old mechanics" those physicists contrasted with quantum theory was not even Newton's mechanics: it was Lorentz's, the mechanics of relativity that had seemed the height of boldness only five years earlier.

  His daughter Geertruida became a physicist and a doctoral student under her father. She married Wander de Haas, who directed the Kamerlingh Onnes Laboratory at Leiden University.

  The Royal Society awarded Lorentz the Rumford Medal in 1908 and the Copley Medal in 1918. The Franklin Institute gave him the Franklin Medal in 1917. He received the Pour le Merite from Kaiser Wilhelm II in 1908. M. J. Klein, writing in 1967, noted that for many years physicists had always been eager to hear what Lorentz would say about a new theory, and that even at seventy-two he did not disappoint them.

  Einstein's most personal tribute came in 1953: "For me personally he meant more than all the others I have met on my life's journey." Lorentz is counted among the prime representatives of the Second Dutch Golden Age, a period of several decades around 1900 when the natural sciences flourished in the Netherlands. The set of locks on the Afsluitdijk that bears his name stands in the Waddenzee to this day.