Lorentz H

FNAME: Lorentz, Hendrik Antoon

ACHIEVEMENT(S): FitzGerald-Lorentz contraction (relativity)

NICKNAME/ALIAS: None

DATE/PLACE OF BIRTH: 18 July 1853, at Arnhem, Netherlands

DATE/PLACE/AGE AT DEATH: 4 February 1928, in Haarlem, Netherlands.  Aged 74

DISCIPLINE: Physicist

FIELD: Theoretical physics

LANGUAGE: Dutch

PARENTS: Gerrit Frederik Lorentz and Geertruida van Ginkel (d. 1857)

SIBLINGS: ?

SPOUSE: Aletta Catherina Kaiser, married 1881

CHILDREN: Three surviving children (one died in infancy) - Geertruida

Luberta (b. 1885), Johanna Wilhelmina (b. 1889) and Rudolf (b. 1895)

EDUCATION: Arnhem High School, 1865-70; University of Leyden, 1870-75

MAJOR WORK:  'The Theory of Electrons', 1909

LIFE AND TIMES: In 1877  the University of Leyden offered Lorentz its new chair of theoretical physics, the first in the Netherlands and one of the first in the world.  Arriving in Leyden in 1878, Lorentz published a paper containing a formula relating the density of a substance to its index of refraction (the ratio of the velocity of light in a vacuum to its velocity in the body, which determines how much the substance bends light).

In the early 1890s, Lorentz examined defects in <work related to> Maxwell's* electromagnetic theory, in particular its inability to predict the formula experimentally observed by <work related to> Fresnel* for the convection of light in moving media. In a series of publications beginning in 1892, Lorentz solved this and other problems through the development of his famous electron theory, in which the generation of light by atoms of matter was attributed to oscillations of charged particles (electrons) within them.

One of Lorentz's most important theoretical contributions, the term 'electron theory' is, however, misleading, as electrons had not yet been discovered: instead, Lorentz was

hypothesizing the existence of tiny, charged particles to explain a number of physical phenomena, and these particles had properties very similar to those of the electron that was discovered by <anticipated> J.J. Thomson* in 1897. (Lorentz suggested, for example, that electromagnetic radiation is produced by the vibration of the tiny charged particles, and this has turned out to be true of electrons).

In subsequent papers on the electron theory, Lorentz attempted to unify and simplify Maxwell's electromagnetic theory and predicted that spectral lines would be split if the source of light from which they came was placed within a strong magnetic field.  [Spectral lines are an optical phenomenon occurring when the light from a gas flame is split by a spectroscope into its component frequencies, or colours - the different colours appearing as a line spectrum (a series of bright lines on a black background whose

positions indicate their frequencies) characteristic of a particular gas.]

Assuming that the frequencies of oscillations of electrons determined the frequencies in the emitted light, Lorentz hypothesized that the presence of a magnetic field would alter the motion of the charged particles which produced the spectral lines, causing them to

shift positions, splitting the single spectral lines into multiples.

In 1896, Lorentz's theory was confirmed by a series of experiments conducted by

a younger colleague at Leyden, Pieter Zeeman, who placed a sodium flame between the poles of an electromagnet and found that sodium's two most prominent spectral lines broadened into groups of separate components. For their discovery and explanation of the splitting of spectral lines (which became known as the Zeeman effect), Lorentz and Zeeman were jointly awarded the 1902 Nobel Prize in physics.

By the end of the 19th century, Lorentz was recognized as the world's leading theoretical physicist, and Leyden became a highly important centre of teaching and research, attracting physicists from across Europe (including <influenced> Einstein*, who visited Lorentz frequently and later claimed that Lorentz had been the greatest influence on his life).

During the 1890s, Lorentz began increasingly to analyse and investigate electrodynamic theory, at the foundations of which was the theoretical existence of a substance called ‘ether’  -  a mysterious,  invisible,  intangible substance then thought to fill all space, the existence of which was necessary as the medium through which a number of physical phenomena, such as electromagnetic (e.g. light) waves, moved.

However, in 1887, Albert Michelson & Morley had performed a classic experiment (an attempt to measure the velocity of the Earth through the hypothetical ether by comparing the velocities of light from different directions) which failed to find any evidence for the existence of the ether, and Lorentz became concerned that his electron theory was not able to explain this negative result.

To resolve the problem, in 1895 Lorentz decided to assume that objects travelling through the ether (in which he continued to believe) underwent a contraction in length in the direction in which they were moving, and then derived a mathematical formula that predicted an amount of shortening that would exactly account for the failure of Michelson & Morley to find any evidence of the motion of light through the ether.

Lorentz published his formula in 1904, at almost the same time as the Irish physicist <formula simultaneous with> FitzGerald* suggested the same thing.

The Lorentz-FitzGerald transformations are mathematical formulas which describe the increase of mass, the shortening of length, and the time dilation of a body moving at relativistic speeds (those close to the velocity of light) that form the basis of Einstein's special theory of relativity (1905).

However, although Lorentz's work brought him to the brink of the theory of relativity, he never ventured beyond, and in particular could not accept the full implications of the revolutionary view of space and time put forward by Einstein.

ASSESSMENT: Lorentz foreshadowed some of the fundamental concepts that were later to become part of the theory of relativity."

EXTRA CONNECTIONS:  Was followed as President of the Solvay Institute by <succeeded by> Langevin*.

His work related to that of <work related to> Roentgen*

ONELINER;  Hendrick Lorentz, physicist and major influence on Einstein

BIBLIOGRAPHY:

DSB, EB

Newton, David E., "Hendrik Antoon Lorentz", in Notable Twentieth- Century Scientists, ed. Emily J. McMurray, New York & London:  Gale Research, 1995