Ernst Mach
Ernst Mach | |
|---|---|
| Born | February 18, 1838 Chirlitz, Moravia, Austrian Empire |
| Died | February 19, 1916 (aged 78) Haar, near Munich, Germany |
| Nationality | Austrian |
| Known for | Mach's principle, critique of absolute space and time, Mach number, shock-wave photography, phenomenalist philosophy of science |
| Scientific career | |
| Fields | Physics, physiology of perception, philosophy of science |
| Institutions | University of Graz, Charles University (Prague), University of Vienna |
Ernst Mach (18 February 1838 – 19 February 1916) was an Austrian physicist and philosopher of science whose criticism of Newton's absolute space and absolute time is one of the deepest and longest-running threads in the literature collected on this wiki.
Mach held chairs at Graz, Prague and finally Vienna, where his professorship was in the history and theory of the inductive sciences. As an experimentalist he is remembered for the photographic study of supersonic projectiles — he and Peter Salcher published images of the shock cone in 1887, and the ratio of a body's speed to the speed of sound in the medium was later named the Mach number in his honour. He also did extensive work on the physiology of sensation, including the visual contrast effect known as Mach bands.
His lasting influence, however, is philosophical. In Die Mechanik in ihrer Entwicklung, historisch-kritisch dargestellt (1883, translated as The Science of Mechanics) Mach argued that physics should confine itself to relations among observable quantities, and that Newton's absolute space and absolute time were metaphysical additions doing no empirical work. His most famous target was Newton's rotating-bucket argument. Newton took the rise of water up the sides of a spinning bucket as evidence of rotation with respect to absolute space; Mach replied that the only rotation we ever actually observe is rotation relative to the fixed stars, and that the experiment had never been performed — and could not be performed — with the rest of the universe removed. Inertia, on this reading, is not a property a body has in isolation but an expression of its relation to all the other matter in the universe.
Einstein took this idea seriously, adopted it as a guiding heuristic while constructing general relativity, and in 1918 gave it the name Mach's principle. Whether general relativity actually satisfies the principle has been disputed ever since, and Mach himself appears not to have accepted relativity: a preface published under his name in Die Prinzipien der physikalischen Optik (1921) repudiates it, though the authorship and dating of that passage have been questioned. Mach was also a sceptic about atoms, which he regarded for most of his career as an unverified hypothesis rather than a physical reality.
Mach's principle on this wiki
Mach's principle is a live research programme here rather than a historical curiosity, and it has its own category: Category:Mach's Principle.
The most fully developed version is André Assis's Relational Mechanics, which attempts to implement Mach's principle quantitatively by replacing Newtonian gravitation with a Weber-type force law — see Relational Mechanics and Implementation of Mach's Principle with Weber's Gravitational Force and Webers Electrodynamics. In The Relationship Between Mach's Principle and the Principle of Physical Proportions (2002) Assis connects the principle to the requirement that the laws of physics depend only on dimensionless ratios, and in Arguments in Favour of Action at a Distance he defends the instantaneous relational picture that such a mechanics requires. The work of Wilhelm Eduard Weber is central to this line.
Other researchers catalogued here approach it from different directions:
- Peter Graneau, Mach's Principle & Nonlocal Mass Interactions (2009), and Neal Graneau, on nonlocal inertial interaction.
- Mendel Sachs, editor of Mach's Principle and the Origin of Inertia (2003), the proceedings of the Kharagpur workshop on the subject.
- Amitabha Ghosh and Anthony D Osborne on velocity-dependent inertial induction — see Origin of Inertia: Extended Machs Principle and Cosmological Consequences and Velocity-Dependent Inertial Induction: A Case for Experimental Observation.
- James F Woodward, Mach's Principle, Mass Fluctuations, And Rapid Spacetime Transport, which treats transient mass fluctuations as a testable Machian effect.
- Evert Jan Post and Michael Berg, Mach's Principle in a Mixed Newton-Einstein Context (1999).
- Lars Wåhlin, Mach's Principle vs. Einstein's Relativity (1993), which argues the two are not the same thing.
- Stewart Ian Wells, Gyroscopic Paradox of Motion: Validation of Mach's Principle? (2011).
- David F Roscoe, A Perspective on Mach's Principle and the Consequent Discovery of Major New Phenomenology in Spiral Discs.
- Julian B Barbour, Mach's Principle: From Newton's Bucket to Quantum Gravity, and Ram Gopal Vishwakarma, Alexander Unzicker, Hoff Lu, Lawrence M Stephenson, Peter Rowlands, Vivian Pope, Robert D Sadykov, Thomas E Phipps and Greg Volk, all of whom have work indexed under the category.
The disagreements among them are real. Some, following Assis, treat Mach's principle as a positive dynamical law to be written down; others, such as Georg Galeczki in Mach's Principle and the True Continuum, treat it primarily as a constraint on what a theory of space is allowed to assume. What they share is Mach's refusal to grant explanatory power to an unobservable absolute frame.
It should be said plainly that the status of Mach's principle in mainstream physics is itself unsettled. There is no agreed formulation of it, general relativity satisfies some versions and not others, and frame-dragging effects such as those measured by Gravity Probe B are usually described as partially Machian at best. This is a genuine open question, not a manufactured one.