Ernst Mach

Ernst Waldfried Josef Wenzel Mach was an Austrian physicist and philosopher who contributed to the understanding of the physics of shock waves. The ratio of the speed of a flow or object to that of sound is named the Mach number in his honor. As a philosopher of science, he was a major influence on logical positivism and American pragmatism. Through his criticism of Isaac Newton's theories of space and time, he foreshadowed Albert Einstein's theory of relativity.

Biography

Early life

Mach was born in Chrlice, Moravia, Austrian Empire. His father Jan Nepomuk Mach, who had graduated from Charles-Ferdinand University in Prague, acted as tutor to the noble Brethon family in Zlín in eastern Moravia. His grandfather Wenzl Lanhaus, an administrator of the Chirlitz estate, was also master builder of the streets there. His activities in that field later influenced Ernst Mach's theoretical work. Some sources give Mach's birthplace as Tuřany, the site of the Chirlitz registry office. It was there that Mach was baptized by Peregrin Weiss. Mach later became a socialist and an atheist, but his theory and life were sometimes compared to Buddhism. Heinrich Gomperz called Mach the "Buddha of Science" because of his phenomenalist approach to the "Ego" in his Analysis of Sensations.
Up to the age of 14, Mach was educated at home by his parents. He then entered a gymnasium in Kroměříž, where he studied for three years. In 1855, he became a student at the University of Vienna, where he studied physics and for one semester medical physiology, receiving a doctorate in physics in 1860 under Andreas von Ettingshausen, with his thesis Über elektrische Ladungen und Induktion and his habilitation the following year. His early work focused on the Doppler effect in optics and acoustics.

Professional research

In 1864, Mach became professor of mathematics at the University of Graz after having declined a chair in surgery at the University of Salzburg. In 1866, he was appointed professor of physics. During this period, Mach continued his work in psycho-physics and in sensory perception. In 1867, he took the chair of experimental physics at Charles-Ferdinand University, where he stayed for 28 years before returning to Vienna. In 1871, he was elected a member of the Royal Bohemian Society of Sciences.
Mach's main contribution to physics involved his description and photographs of spark shock-waves and then ballistic shock-waves. He described how when a bullet or shell moved faster than the speed of sound, it created a compression of air in front of it. Using schlieren photography, he and his son Ludwig photographed the shadows of the invisible shock waves. During the early 1890s, Ludwig invented a modification of the Jamin interferometer that allowed for much clearer photographs. But Mach also made many contributions to psychology and physiology, including his anticipation of gestalt phenomena, his discovery of the oblique effect and of Mach bands, an inhibition-influenced type of visual illusion, and especially his discovery of a non-acoustic function of the inner ear that helps control human balance.
One of the best-known of Mach's ideas is the so-called Mach principle, the physical origin of inertia. This was never written down by Mach but was given a graphic verbal form, attributed by Philipp Frank to Mach: "When the subway jerks, it's the fixed stars that throw you down."
File:Photography of bow shock waves around a brass bullet, 1888.jpg|thumb|upright=1.2|Ernst Mach's historic 1887 photograph of a bow shockwave around a supersonic bullet fired from a Werndl carbine.
In 1900, Mach became godfather of physicist Wolfgang Ernst Pauli, who was also named after him.
Mach was also well-known for his philosophy, developed in close interplay with his science. He defended a type of phenomenalism, recognizing only sensations as real. That position seemed incompatible with the view of atoms and molecules as external, mind-independent things. After an 1897 lecture by Ludwig Boltzmann at the Imperial Academy of Science in Vienna, Mach said, "I don't believe that atoms exist!"
In 1898, Mach survived a paralytic stroke, and in 1901, he retired from the University of Vienna and was appointed to the upper chamber of the Austrian Parliament. On leaving Vienna in 1913, he moved to his son's home in Vaterstetten, near Munich, where he continued writing and corresponding until his death in 1916, one day after his 78th birthday.

Politics

Born to a liberal family, Mach lamented that a "very reactionary-clerical" period followed the 1848 revolutions, prompting him to plan to emigrate to America, although he never did.
In 1901, Mach accepted an appointment to the Austrian House of Lords but declined a nobility because he thought it inappropriate for a scientist to accept such a thing. He was on good personal terms with the Social Democrat politician Viktor Adler and left money in his will to the Social Democrat newspaper Arbeiter-Zeitung.
Mach was critical of the European powers' colonial conquests, saying that they "will constitute...the most distasteful chapter of history for coming generations".

Physics

Most of Mach's initial studies in experimental physics concentrated on the interference, diffraction, polarization and refraction of light in different media under external influences. From there followed explorations in supersonic fluid mechanics. Mach and physicist-photographer Peter Salcher presented their paper on this subject in 1887; it correctly describes the sound effects observed during the supersonic motion of a projectile. They deduced and experimentally confirmed the existence of a shock wave of conical shape, with the projectile at the apex. The ratio of the speed of a fluid to the local speed of sound v_p/v_s is called the Mach number after him. It is a critical parameter in the description of high-speed fluid movement in aerodynamics and hydrodynamics. Mach also contributed to cosmology the hypothesis known as Mach's principle.

Philosophy of science

Empirio-criticism

From 1895 to 1901, Mach held a newly created chair for "the history and philosophy of the inductive sciences" at the University of Vienna. In his historico-philosophical studies, Mach developed a phenomenalistic philosophy of science that became influential in the 19th and 20th centuries, empirio-criticism, a rigorously positivist and radically empiricist philosophy established by the German philosopher Richard Avenarius and further developed by Mach, Joseph Petzoldt, and others, according to which all we can know is our sensations.
Mach originally saw scientific laws as summaries of experimental events, constructed for the purpose of making complex data comprehensible, but later emphasized mathematical functions as a more useful way to describe sensory appearances. Thus, scientific laws, while somewhat idealized, have more to do with describing sensations than with reality as it exists beyond sensations:
Mach's positivism influenced many Russian Marxists, such as Alexander Bogdanov. In 1908, Lenin wrote a philosophical work, Materialism and Empirio-criticism, in which he criticized Machism and the views of "Russian Machists". His main criticisms were that Mach's philosophy led to solipsism and to the absurd conclusion that nature did not exist before humans:
Lenin also accused Mach of plagiarizing George Berkeley's views on this basis:
In accordance with empirio-critical philosophy, Mach opposed Ludwig Boltzmann and others who proposed an atomic theory of physics. Since one cannot observe things as small as atoms directly, and since no atomic model at the time was consistent, the atomic hypothesis seemed unwarranted to Mach, and perhaps not sufficiently "economical". Mach had a direct influence on the Vienna Circle philosophers and logical positivism in general.
File:Ernst Mach - Rathauspark, Vienna.jpg|thumb|upright|right|Bust of Mach in the Rathauspark in Vienna, Austria
Several principles are attributed to Mach that distill his ideal of physical theorization, called "Machian physics":

It should be based entirely on directly observable phenomena
It should completely eschew absolute space and time in favour of relative motion
Any phenomena that seem attributable to absolute space and time should instead be seen as emerging from the distribution of matter in the universe.

The last is singled out, particularly by Einstein, as "the" Mach's principle. Einstein cited it as one of the three principles underlying general relativity. In 1930, he wrote, "it is justified to consider Mach as the precursor of the general theory of relativity" and "the whole direction of thought of this theory conforms with Mach's". Einstein further reported that he had read David Hume and Mach's work "with eagerness and admiration shortly before finding relativity theory" and that "very possibly, I wouldn't have come to the solution without those philosophical studies". Before his death, Mach apparently rejected Einstein's theory. Einstein knew his theories did not fulfill all Mach's principles, and no subsequent theory has either.

Phenomenological constructivism

According to Alexander Riegler, Mach's work was a precursor to the influential perspective known as constructivism. Constructivism holds that all knowledge is constructed rather than received by the learner. He took an exceptionally non-dualist, phenomenological position. The founder of radical constructivism, Ernst von Glasersfeld, gave a nod to Mach as an ally.
On the other hand, there is also a reasonable case for viewing Mach simply as an empiricist and a precursor of the logical empiricists and the Vienna Circle. On this view, the purpose of science is to detail functional relationships between observations: "The goal which it has set itself is the simplest and most economical abstract expression of facts."