Ernst Mach

Austrian physicist and philosopher

• Born: February 18, 1838; Chrlice, Moravia, Austrian Empire (now part of Brno, Czech Republic)
• Died: February 19, 1916; Munich, German Empire

Ernst Mach lived and worked during the nineteenth century, when the study of science was closely related to the study of philosophy, especially in German-speaking countries. Mach was influential in both disciplines but is probably best remembered for his contributions to the development of Einstein’s theories of relativity. His ideas also contributed to the fields of physiology and psychology, and he is notorious for having stubbornly denied the existence of the atom.

Primary field: Physics

Specialty: Relativity

Early Life

Ernst Waldfried Joseph Wenzel Mach was born on February 18, 1838, in what is now part of the Czech Republic. Young Mach performed so poorly as a student that after only a year, he was not allowed to return to the school near Vienna where he was studying. Since his father Johann was a teacher, Mach was able to continue his education at home, and enrolled in the University of Vienna when he was seventeen years old.

In 1860 he was awarded a doctorate in physics and went on to work as a tutor in Vienna for several years, addressing students of medicine on topics in physics. This resulted in his book “Compendium of Physics for Medical Students” (1863). In 1864, Mach joined the University of Graz as a professor of mathematics and later taught physics there.

He lectured at Graz until 1867, when he took on a professorship in experimental physics at Charles University in Prague, where he would remain for nearly thirty years. During this time Mach carried out a considerable amount of original research in areas such as optics, waves, and the study of sensory perceptions.

In 1895 Mach found himself back at the University of Vienna, as professor of inductive philosophy (inductive logic is a type of reasoning in which specific observations lead to more general conclusions). However, in 1898 he experienced a severe stroke that paralyzed the right half of his body, and he was forced to resign from his professional position. He did continue to speak, publish, and pursue independent scientific study, however. In 1901 the Austrian government honored him with an appointment to parliament.

Throughout his life Mach was particularly interested in a field called epistemology, which refers to the study of human knowledge and the limits of understanding. One of his last two books dealt with this discipline; titled Knowledge and Error, it appeared in 1905. Mach also wrote an autobiography, published in 1910. He died six years later on February 19, 1916, at the age of seventy-eight.

Life’s Work

One of Mach’s most important epistemological ideas was that all of our insights about the world are based on imperfect and fallible sensory information. According to him, what we call scientific laws are not really absolute laws of nature, but reflections of how human beings perceive the universe. Mach wrote about these ideas in his book The Analysis of Sensations (1897).

As a result, Mach refused to accept any scientific hypothesis that could not be proven through testing. His strict insistence on being able to verify theory was somewhat revolutionary at the time, when many complex scientific ideas were put forward and accepted without experimental proof. (This is also the reason Mach doubted that atoms were real, since during his lifetime there were no electron microscopes that could be used to view individual atoms.)

Mach’s firm belief that scientific ideas needed to be provable led him to reject Isaac Newton’s abstract notions of “absolute,” or unchanging, space and time. Mach’s book The Science of Mechanics (1883), generally considered his masterpiece, strongly criticized these concepts. It also introduced a sophisticated idea that Albert Einstein later came to call “Mach’s principle.” Part of Mach’s disagreement with Newton had to do with the question of how an object’s acceleration (the change in its speed) is measured through space. When physicists measure an object’s change in speed, they always think about what that change is relative to. In other words, the object may be speeding up or slowing down, but speeding up or slowing down compared to what?

To solve this problem, Newton came up with the idea of absolute space: a theoretical constant that no one had ever seen, but that scientists could always use as a point of comparison. Mach, on the other hand, suggested that physicists should calculate an object’s acceleration not in relation to Newton’s abstract and invisible constant, but in relation to all of the other matter in the entire universe.

What Einstein dubbed “Mach’s principle” is the idea that when an object has inertia (when it resists a change in its speed), the source of that inertia is the object’s relationship to all the other matter in the universe. This proposal helped Einstein think about gravity and movement in new ways. Einstein always said that the concepts in The Science of Mechanics were enormously powerful influences on him as he was working on his general theory of relativity. Despite this fact, Mach’s principle was never included in Einstein’s calculations, and there is still some disagreement among physicists about whether Newton’s ideas or Mach’s more accurately describe the way the universe really works.One of Mach’s first projects after he received his doctorate was an attempt to prove the Doppler effect, a theory proposed in 1842. The theory states that light and sound waves increase in frequency as their source draws nearer to an observer, and decrease in frequency as their source moves away from an observer. In 1860 scientists were still trying to design experiments that would show that the Doppler effect was real. Mach devised a simple, portable set of equipment that could be used to clearly demonstrate the effect.

Impact

Besides the principle Einstein named after him, Mach’s name is preserved in at least two other scientific concepts. The first is the “Mach number,” which describes the relationship between the speed of an object and the speed of sound in whatever medium the object happens to be traveling through. A rocket or a jet plane moving at greater than “Mach 1” is traveling at supersonic speeds, or faster than the speed of sound.

Mach was the first scientist to realize that a projectile moving faster than the speed of sound actually creates shock waves around itself. He was then able to photograph the effects of the shock waves created by a bullet moving at supersonic speeds. In order to do this, Mach invented an entirely new photographic method, taking advantage of the fact that shock waves cause light to refract (bend). The resulting image he called a shadowgraph.

A second well-known scientific phenomenon named after Mach is an optical illusion he discovered. Mach showed that when a person is looking at two regions of space that are side by side, and when those regions are of significantly different levels of lightness or darkness, the eye tends to see bands of either brighter or darker space at the border between them. The bands do not really exist, but our brains perceive them nonetheless. They are known as “Mach bands.”

Mach’s research into sensory awareness also included investigations of hearing, movement, and the human perception of time.

Bibliography

Blackmore, John T. “Three Autobiographical Manuscripts by Ernst Mach.” Annals of Science 35.4 (July 1978): 401–19. Print. Offers a collection of original source material as an aid to understanding Mach’s role in the history of physics, psychology, and science in general.

Hoffmann, Christoph. “Representing Difference: Ernst Mach and Peter Salcher’s Ballistic-Photographic Experiments.” Endeavour 33.1 (Mar. 2009): 18–23. Print. Presents photographs depicting the bullet experiment conducted by Mach.

Karwatka, Dennis. “Ernst Mach and the Mach Number.” TechDirections 69.5 (Dec. 2009): 14. Print. Recounts Mach’s life and career, noting his contributions to the development of several branches of physics, including optics and mechanics.