Feb 182018

Today is the birthday (1838) of Ernst Waldfried Josef Wenzel Mach, Austrian physicist and philosopher. The ratio of an object’s speed 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 Newton’s theories of space and time, he foreshadowed Einstein’s theory of relativity.

Mach was born in Chrlice (German: Chirlitz) in Moravia (then in the Austrian empire, now part of Brno in the Czech Republic). His father, who had attended Charles University in Prague, acted as tutor to the noble Brethon family in Zlín in eastern Moravia. Up to the age of 14, Mach received his education at home from his parents. He then entered a Gymnasium in Kroměříž (German: Kremsier), where he studied for 3 years. In 1855 he became a student at the University of Vienna. There he studied physics and medical physiology, receiving his doctorate in physics in 1860 under Andreas von Ettingshausen with a thesis titled “Über elektrische Ladungen und Induktion”, and his habilitation the following year. His early work focused on the Doppler effect in optics and acoustics. In 1864 he took a job as Professor of Mathematics at the University of Graz, having turned down the position of a chair in surgery at the University of Salzburg to do so, and in 1866 he was appointed as Professor of Physics. During that period, Mach continued his work in psycho-physics and in sensory perception. In 1867, he took the chair of Experimental Physics at the Charles University, Prague, where he stayed for 28 years before returning to Vienna.

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 were able to photograph the shadows of the invisible shock waves. During the early 1890s Ludwig was able to invent an interferometer which 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 which helps control human balance.

One of the best-known of Mach’s ideas is the so-called “Mach principle,” the name given by Einstein to an imprecise hypothesis often credited to the physicist and philosopher Ernst Mach. The idea is that local inertial frames are determined by the large-scale distribution of matter, as exemplified by this anecdote:

You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don’t move?

Mach’s principle says that this is not a coincidence—that there is a physical law that relates the motion of the distant stars to the local inertial frame. If you see all the stars whirling around you, Mach suggests that there is some physical law which would make it so you would feel a centrifugal force. There are a number of rival formulations of the principle. It is often stated in vague ways, like “mass out there influences inertia here”. A very general statement of Mach’s principle is “local physical laws are determined by the large-scale structure of the universe.” This concept was a guiding factor in Einstein’s development of the general theory of relativity. Einstein realized that the overall distribution of matter would determine the metric tensor, which tells you which frame is rotationally stationary

Mach also became well known for his philosophy developed in close interplay with his science. Mach defended a type of phenomenalism recognizing only sensations as real. This position seemed incompatible with the view of atoms and molecules as external, mind-independent things. He famously declared, after an 1897 lecture by Ludwig Boltzmann at the Imperial Academy of Science in Vienna: “I don’t believe that atoms exist!” From about 1908 to 1911 Mach’s reluctance to acknowledge the reality of atoms was criticized by Max Planck as being incompatible with physics. Einstein’s 1905 demonstration that the statistical fluctuations of atoms allowed measurement of their existence without direct individuated sensory evidence marked a turning point in the acceptance of atomic theory. Some of Mach’s criticisms of Newton’s position on space and time influenced Einstein, but later Einstein realized that Mach was basically opposed to Newton’s philosophy and concluded that his physical criticism was not sound.

In 1898 Mach suffered from cardiac arrest and in 1901 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, only one day after his 78th birthday.

Most of Mach’s initial studies in the field of experimental physics concentrated on the interference, diffraction, polarization and refraction of light in different media under external influences. From there followed important explorations in the field of 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 vp/vs is now called the Mach number. It is a critical parameter in the description of high-speed fluid movement in aerodynamics and hydrodynamics.

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 which became influential in the 19th and 20th centuries. He 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.

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 to Mach to be unwarranted, and perhaps not sufficiently “economical”. Mach had a direct influence on the Vienna Circle philosophers and the school of logical positivism in general.

According to Alexander Riegler, Ernst 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, von Glasersfeld, gave a nod to Mach as an ally.

In 1873, independently of each other Mach and the physiologist and physician Josef Breuer discovered how the sense of balance (i.e., the perception of the head’s imbalance) functions, tracing its management by information which the brain receives from the movement of a fluid in the semicircular canals of the inner ear. That the sense of balance depended on the three semicircular canals was discovered in 1870 by the physiologist Friedrich Goltz, but Goltz did not discover how the balance-sensing apparatus functioned. Mach devised a swivel chair to enable him to test his theories, and Floyd Ratliff has suggested that this experiment may have paved the way to Mach’s critique of a physical conception of absolute space and motion.

Mach’s home town of Brno is in Moravia which is now part of the Czech Republic, and much of the cuisine is common to the nation as a whole. But there are some distinctive dishes. Moravian chicken pie is one. It can be made as a simple two-crust pie, but is often made with a crumb topping as well, as in this recipe.

Moravian Chicken Pie


Pie Crust

2 cups all-purpose flour
1 tsp salt
3⁄4 cup shortening
6 -8 tbsp cold water


2 ½ cups chopped cooked chicken
salt and pepper
3 tbsp flour
1 cup chicken broth
1 -2 tbsp butter, cut in small pieces

Crumb Topping

¼ cup all-purpose flour
1 tbsp butter


For the pie crust: combine the flour and salt in a food processor. Add the shortening and pulse until the mixture is like coarse cornmeal. Gradually stir in cold water just until a dough forms. Divide the dough into two equal pieces. Cover and chill 30 minutes, or until ready to use.

Preheat the oven to 375˚F/190˚C degrees.

Roll out one piece of dough to cover the bottom and sides of a 9-inch pie plate and place in the plate. Roll out the second piece of dough for the top crust and set aside.

For the filling: combine all the ingredients in a bowl and season with salt and pepper to taste. Pour the ingredients into the pie crust and top with the second crust, moisten the edges, and crimp to seal.

For the crumb topping: pulse the butter and flour in a food processor until it is like coarse cornmeal. Sprinkle the topping over the top crust of pie. Cut a few slits in the top crust to allow steam to escape.

Bake the pie 45 minutes to 1 hour, until golden and bubbly.


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