- Person
- Albert A. Michelson
- Lived
- 1852–1931
- Field
- Optics
- From
- Prussian-born American
The story
In 1880 Albert Michelson, a young U.S. Navy officer who had already measured the speed of light with record accuracy, took leave to study in Europe, helped by a stipend donated by Alexander Graham Bell. In Berlin he worked in the laboratory of Hermann von Helmholtz. Physicists of the day believed that light travelled through an invisible medium called the luminiferous aether, and Michelson set out to detect the Earth's motion through it.
To do so he designed a new instrument. Light passes through a half-silvered mirror that splits it into two beams travelling at right angles. Mirrors at the ends of the two arms send the beams back, and when they recombine they produce a pattern of light and dark fringes. If one path takes even slightly longer than the other, the fringes shift.
The device was so sensitive that the smallest vibrations disturbed it, and Berlin proved too unsettled. In April 1881 Michelson carried out his measurements instead in a cellar of the Astrophysical Observatory at Potsdam, on the quieter edge of the city. He did not see the shift he had expected. Back in the United States he refined the design with Edward Morley, and their much more precise experiment of 1887 again found no sign of the aether, a result that later became a cornerstone of relativity.
The instrument proved far more important than the question it was built to answer. Michelson used it to measure the standard metre in wavelengths of light and to study the fine structure of spectral lines, work honoured with the 1907 Nobel Prize in Physics. Interferometers working on his principle are now used to measure distances, angles and vibrations, to test optical components and, in optical coherence tomography, to image the inner layers of living tissue.
The most dramatic descendant is LIGO. Its detectors are Michelson interferometers that use laser light and arms 4 kilometres long set at right angles. A passing gravitational wave stretches one arm while shortening the other. On 14 September 2015 LIGO sensed waves from two black holes that had collided 1.3 billion light-years away, the first direct detection of gravitational waves, a century after Einstein predicted them in 1916. The distortion it recorded was thousands of times smaller than the nucleus of an atom.
Why it matters
Michelson's instrument made it possible to measure astonishingly small changes in distance, and in LIGO it opened an entirely new way of observing the universe through gravitational waves.
About Albert A. Michelson
Physicist who measured the speed of light with unmatched precision, performed the Michelson–Morley experiment and in 1907 became the first American to win a Nobel Prize in science.
More about Albert A. Michelson
- Michelson measured the metre in wavelengths of lightIn 1892–93 in Paris, Albert Michelson measured the international prototype metre in wavelengths of cadmium's red light, showing a unit of length could be defined by nature.
- Michelson built Chicago's renowned physics departmentIn 1892 Albert Michelson became the first head of physics at the newly founded University of Chicago, leading it until 1929 and making it one of America's leading centres of physics.
- Michelson measured the size of a star for the first timeIn 1920 Albert Michelson and Francis Pease measured the diameter of the red giant Betelgeuse, the first time the size of any star other than the Sun had been measured.
- Michelson's famous null result paved the way for relativityIn 1887 Albert Michelson and Edward Morley found no trace of the supposed "aether", a result that became one of the classic foundations of Einstein's theory of relativity.
- Michelson timed light across 22 miles of CaliforniaUsing a 22-mile light path between Mount Wilson and Mount San Antonio, Albert Michelson measured the speed of light in 1926 as 299,796 kilometres per second, plus or minus 4.
- A young naval officer measured light's speed in 1879In June and July 1879, Albert Michelson, a 26-year-old instructor at the U.S. Naval Academy, measured the speed of light as 299,910 kilometres per second, far more accurately than anyone before.
Sources
- Albert A. Michelson Wikipedia
- What are Gravitational Waves? LIGO Caltech
- Michelson interferometer Wikipedia
Another act of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.