Lorentz , Hendrik Antoon

(1853–1928) Dutch theoretical physicist

Lorentz, who was born at Arnhem in the Netherlands, studied at the University of Leiden and received his doctorate in 1875. In 1877, aged only 24, he became professor of theoretical physics at Leiden. This was the Netherlands' first chair in the newly independent field of theoretical physics, and one of the first in Europe, and Lorentz did a great deal in shaping and developing the field. On his retirement in 1912 he was appointed director of the Teyler Laboratory in Haarlem, a museum of science and art with a laboratory where he could continue his research. He still retained contact with the world of advanced physics, giving every week at Leiden his famous ‘Monday morning lectures’ on current scientific problems.

Lorentz had wide-ranging interests in physics and mathematics, his linguistic abilities allowing him to follow the scientific trends in Europe. His major work, however, was spent in the development of the electromagnetic theory of James Clerk Maxwell. He brought this to a point where a need for a radical change in the foundations of physics became noticeable and thus provided the inspiration for Einstein's theory of relativity.

Lorentz's early work on this highly complex and confused subject followed from the writings of Hermann von Helmholtz and began in his doctoral thesis. Lorentz refined Maxwell's theory so that for the first time various effects including the reflection and refraction (bending) of light could be fully explained. In a series of articles published between 1892 and 1904 Lorentz put forward his ‘electron theory’: he proposed that the atoms and molecules of matter contained small rigid bodies that carried either a positive or negative charge. By 1899 he was referring to these charged particles as ‘electrons’. It was through the effects of these electrons that many phenomena in science were explained. Lorentz believed that matter and the wave-bearing medium known as the ‘ether’ were distinct entities and that the interaction between them was mediated by electrons. He saw that the interaction of light waves and matter resulted from the presence of electrons in matter and that if set into vibration these charged particles would produce light waves, as predicted by Maxwell's equations.

In 1895 he described the force, now known as the Lorentz force, on charged particles of matter in an electromagnetic field. In 1900 he identified the negatively charged particles that had been found to constitute cathode rays as the negative electrons of his theory. He also used the theory to explain the effect discovered by PieterZeeman in 1896 whereby the spectral lines of sodium atoms were split by the action of a magnetic field. Lorentz and Zeeman shared the 1902 Nobel Prize for physics for their investigations of the influence of magnetic fields on radiation. However, other phenomena, such as the photoelectric effect, could not be explained and, in fact, were inconsistent with Lorentz's theory; it was these anomalies that inspired the development of the quantum theory.

The other work for which Lorentz is famous is his suggested method of resolving the problems raised by the experiments in the 1880s of Albert Michelson and Edward Morley on the motion of the Earth through the ether. Lorentz showed that if it were assumed that moving bodies contracted in the direction of motion, then the observed effects would follow. This solution was derived independently by George Fitzgerald and came to be known as the Lorentz–Fitzgerald contraction. Lorentz extended his idea, putting it on a firmer mathematical footing, and in 1904 published in final form what became known as the Lorentz transformations. These transformations of the space and time coordinates of an event in one frame of reference to those in another frame again figured largely in Einstein's theory of special relativity (1905), in which Einstein could be said to have reinterpreted Lorentz's ideas.

Lorentz devoted much time to education and the teaching of science and medicine. In later life he was very active in international science conferences, acting as president of the first Solvay Congress for physics in Brussels and continuing as president until his death. He also played a major role in restoring international scientific relations after World War I.