Lorentz, Hendrik Antoon (1853-1928) was a Dutch physicist who became famous for his electron theory of matter. He shared the 1902 Nobel Prize in physics with Dutch physicist Pieter Zeeman for explaining the effects of magnetism on light.

Lorentz was the son of Gerrit Frederik Lorentz, a nursery owner, and Geertruida (van Ginkel) Lorentz. His mother died when Lorentz was 4 years old, and within a few years, his father married Luberta Hupkes. Attending a grade school that held classes in the morning, afternoon, and evening helped Lorentz enter high school in 1866 as a gifted pupil at an advanced level. He entered the University of Leyden in 1870 and obtained his bachelor of science degree in mathematics and physics in less than two years. He returned to Arnhem in 1872 to become a night school teacher. During this time, he continued preparing his doctoral thesis on the reflection and refraction of light.

In 1875, at the remarkable age of 22, Lorentz obtained his Ph.D. degree. A few years later, he became the first chair of theoretical physics at the University of Leyden. This position was the first of its kind in the Netherlands and one of the first in Europe, as the field of theoretical physics newly emerged as a separate discipline. Lorentz remained at Leyden as a professor through the years, declining many invitations to universities abroad. His Monday morning lectures, which he gave for the rest of his life even after he retired, became famous.

Very early in his work, Lorentz sought to develop Scottish physicist James Clerk Maxwell's theory of electricity and of light. Maxwell had shown that light consists of waves in combined electric and magnetic fields, called electromagnetic waves. In Lorentz's thesis, which quickly became recognized as an important work, he addressed the reflection and refraction of light using Maxwell's new theory.

In the 1870's, Lorentz published a paper on the relation between the velocity of light and the density and composition of the medium through which it passed. The resulting formula, proposed almost simultaneously by the Danish physicist Ludwig Lorenz, was known as the Lorenz-Lorentz formula. Lorentz based his paper on the assumption that matter contains oscillating electrically charged particles that interact with light waves. This supported the idea that matter is composed of atoms and molecules, a view not completely accepted at that time.

In 1881, Lorentz married Alette Catharina Kaiser, daughter of J. W. Kaiser, a professor at the Academy of Fine Arts and director of what became the famed Rijksmuseum, the National Gallery of Amsterdam. The couple had two daughters and two sons. Their eldest daughter, Dr. Geertruida de Haas-Lorentz, became a physicist.

Lorentz's work gave rise to the concept of the electron. In 1892, Lorentz began to formulate a theory of what he and others later called electrons. He proposed that matter contained tiny particles that carried either a positive or negative charge. Although he thought there were positive and negative electrons, scientists later established that all electrons are negatively charged. Lorentz deduced that oscillations of these charged particles produced electromagnetic waves, including light and also including radio waves, which were predicted by Maxwell and later discovered by Heinrich Rudolf Hertz in 1888. Lorentz's work led others to apply the molecular theory to the understanding of electricity, and to explain the behavior of light waves passing through moving, transparent bodies.

During the 1890's, Lorentz published many important papers in physics. He made fundamental contributions to the study of the phenomena of moving bodies, beginning with the assumption that matter and a substance called ether interact by means of electrically charged particles.

Scientists of Lorentz's day believed that all of space was filled by the ether. Some physicists had tried unsuccessfully to measure the speed of the earth relative to the ether. According to classical physics, the ether was motionless. In the 1880's, two American physicists, Albert Abraham Michelson and Edward W. Morley, had conducted experiments to prove the ether theory. They had used an interferometer, a newly designed instrument that made far more precise measurements than earlier devices. Their experiments failed, and the failure helped destroy the ether theory. Lorentz's solution, which eventually led to the development of the Lorentz transformations, showed how motion deforms bodies.

Lorentz explained the failure of Michelson and Morley's experiments by assuming that the ether was partially dragged along as the earth moved through it. Lorentz's electron theory suggested that moving bodies are shortened in their direction of motion through the ether. This shortening occurs because motion affects forces between the charged particles that make up matter. Such a change in length actually occurs. It is too small to notice, however, except in precise experiments carried on at very high speeds.

The Lorentz transformations, which Lorentz introduced in 1904, were based on the fact that electromagnetic forces between charges are subject to slight alterations due to their motion. This causes moving bodies to contract slightly in size. The contraction explained the apparent absence of the relative motion of the earth with respect to the ether. Scientist Albert Einstein (1879-1955) resolved the problem in 1905, when he analyzed the measuring process itself and, as a result, proposed the special theory of relativity.

Lorentz came to be regarded as the world's leading theoretical physicist. While taking major steps toward resolving questions left by his predecessors, he also paved the way for the new ideas based on quantum mechanics, the field of physics that describes the structure of the atom and the motion of atomic particles. Quantum mechanics also explains how atoms absorb and give off energy as light, and it clarifies the nature of light.

In 1902, the Nobel Prize committee awarded the physics prize jointly to Lorentz and Pieter Zeeman, one of his students. Zeeman had verified experimentally Lorentz's theoretical work on atomic structure.

Lorentz earned a great number of other honors from all over the world. He was elected a fellow of the Royal Society in 1905. The Society awarded him their Rumford Medal in 1908 and their Copley Medal in 1918. Lorentz had a mastery of languages, and presided over international gatherings with exceptional skill. He led the first Solvay Congress in Physics in Brussels, Belgium, in the autumn of 1911.

In 1919, the Dutch government appointed Lorentz chairman of a committee to study the movements of seawater that could be expected during and after the reclamation of the Zuider Zee, a large inlet of the North Sea. Lorentz spent eight years making theoretical calculations. In 1932, builders cut off the inlet from the sea with a dike 20 miles (32 kilometers) long, changing the inlet into a freshwater lake. Much of the lake was then drained, adding 637 square miles (1,650 square kilometers) of land to the Netherlands. This was one of the greatest hydraulic engineering works of all times. Lorentz's calculations proved correct in practice and gained a permanent place in the science of hydraulics, the branch of physics that studies the behavior of liquids at rest and in motion.

Following World War I (1914-1918), Lorentz became active in the cause of restoring scientific cooperation among nations that had been at war with each other. In 1923, he was elected to the membership of the Committee on Intellectual Cooperation of the League of Nations. The committee consisted of only seven of the world's most eminent scholars, and Lorentz became its president in 1925. Highly respected in his own country, Lorentz convinced the government to form the Netherlands Organization for Applied Scientific Research.

Lorentz died in Haarlem on Feb. 4, 1928. On the day of his funeral, the nation acknowledged his death with a three-minute moment of silence during which all telegraph and telephone services in Holland were suspended. Many colleagues and distinguished physicists from foreign countries attended his funeral.