Question: What did Ernst Mach foreshadow in his study with assistant Anton Wassmuth? 
Context: Albert Einstein presented the theories of special relativity and general relativity in groundbreaking publications that either contained no formal references to previous literature, or referred only to a small number of his predecessors for fundamental results on which he based his theories, most notably to the work of Hendrik Lorentz for special relativity, and to the work of Carl F. Gauss, Bernhard Riemann, and Ernst Mach for general relativity.  Subsequently, claims have been put forward about both theories, asserting that they were formulated, either wholly or in part, by others before Einstein.  At issue is the extent to which Einstein and various other individuals should be credited for the formulation of these theories, based on priority considerations. Shock diamonds (also known as Mach diamonds, Mach disks, Mach rings, donut tails or thrust diamonds) are a formation of standing wave patterns that appear in the supersonic exhaust plume of an aerospace propulsion system, such as a supersonic jet engine, rocket, ramjet, or scramjet, when it is operated in an atmosphere.  The diamonds are formed from a complex flow field and are visible due to the abrupt changes in local density and pressure caused by standing shock waves. Mach diamonds (or disks) are named after Ernst Mach, the physicist who first described them. Ernst Waldfried Josef Wenzel Mach ( ; ] ; 18 February 1838 – 19 February 1916) was an Austrian physicist and philosopher, noted for his contributions to physics such as study of shock waves.  The ratio of one'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. Robert Bouvier (1886–1978) was a Swiss philosopher noted for popularising the work of Ernst Mach in French. He studied mathematics, philosophy and natural sciences at the University of Prague, where he subsequently became an assistant to Ernst Mach (1838-1916).  In 1871 he obtained his habilitation on electricity and magnetism from the University of Vienna.  In 1876 became an associate professor at the recently established University of Czernowitz, where in 1882 he was appointed a full professor of theoretical physics.  In 1890 he relocated to Innsbruck as a professor and director at the institute of mathematical physics.  Here he served as dean to the faculty in 1891.  From 1893 to 1914 he served as chair of theoretical physics at the University of Graz.  Following retirement, his position at Graz was filled by Michael Radaković (1866-1934). Mach bands is an optical illusion named after the physicist Ernst Mach.  It exaggerates the contrast between edges of the slightly differing shades of gray, as soon as they contact one another, by triggering edge-detection in the human visual system. In physics, the Mach–Zehnder interferometer is a device used to determine the relative phase shift variations between two collimated beams derived by splitting light from a single source.  The interferometer has been used, among other things, to measure phase shifts between the two beams caused by a sample or a change in length of one of the paths.  The apparatus is named after the physicists Ludwig Mach (the son of Ernst Mach) and Ludwig Zehnder: Zehnder's proposal in an 1891 article was refined by Mach in an 1892 article. In theoretical physics, particularly in discussions of , Mach's principle (or Mach's conjecture) is 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: Mach reflection is a supersonic fluid dynamics effect, named for Ernst Mach, and is a shock wave reflection pattern involving three shocks. The Fraunhofer Institute for High-Speed Dynamics (German: "Fraunhofer-Institut für Kurzzeitdynamik"), commonly known as the Ernst Mach Institute and also by the abbreviation Fraunhofer EMI, is a facility of the Fraunhofer Society in Germany.  The Institute is based in Freiburg im Breisgau.  Its activities are applied research and development in the fields of materials science and high-speed measurement techniques.  The Institute also has offices in Efringen-Kirchen and Kandern.
Answer: Einstein's theory of relativity