Ernst Mach (February 18, 1838 – February 19, 1916) was an Austrian physicist, philosopher and experimental psychologist. In physics, he was the first to systematically study super-sonic motion. He also made important contributions to the understanding of the Doppler effect. In psychology, he studied the relationship of our sensations to external stimuli. Mach was inspired by Gustav Fechner’s psychophysics. Psychologists today regard him as a founder of Gestalt theory as well as the discoverer of neural inhibition. Philosophers consider him as the founder of the philosophy of science.
For a serious academic review of Ernst Mach’s contributions I would recommend the SEP article but I was inspired to write this post by Amanda Gefter’s excellent Nautilus article titled “When Einstein Tilted at Windmills” in which she focuses on the relationship between Michele Besso and Albert Einstein and explains how Mach’s ideas influenced them both.
In Mach’s monism (a version of neutral monism), whether something is “mind” or “matter” is determined by its relations with other elements and not by anything inherent to itself. According to Amanda Gefter, Mach said: “There is but one kind of elements, out of which this supposed inside and outside are formed—elements which are themselves inside or outside, according to the aspect in which, for the time being, they are viewed.”
Mach considered each measurement as a relation and suggested that science should be rewritten in terms of what can be measured. That way all scientific theories would be built upon a relativistic (relational) foundation. Since measurement is observer dependent, a scientific paradigm based on measurable quantities only would be entirely observer dependent hence relational.
Mach’s dream was partially realized by the development of the Quantum Mechanics which focuses on epistemology (what we can know/measure about “reality”). Quantum Mechanics – especially its Copenhagen interpretation – is agnostic about “reality.” The observer dependence does not make Quantum Mechanics entirely relational but it was an important step towards the Machian ideal.
Einstein’s theory of relativity is another realization of Mach’s dream. In Einstein’s theory, space and time intervals are relative to the observer hence relational (relativistic).
In this context, Amanda Gefter’s additional comments are very informative
“it’s the profound context-dependency in quantum mechanics that makes it Machian. Quantum mechanics simply doesn’t allow you to decouple subject and object in the way that classic realism and dualism posit. Different interpretations of QM emphasize this in different ways – Everett talks about relative states, Rovelli talks about relationalism, Bohr talks about complementarity, etc – but what it comes down to is the fact that you can no longer specify the way something simply “is,” in and of itself, relative to nothing. You can only talk about its state relative to an observer or observing apparatus. That’s why when you don’t specify an observer (when the quantum object is “unobserved”) it is said to be in a superposition of all possible states at once – because its attributes are only defined relative to a given context. In this sense quantum mechanics makes everything profoundly relative in the way that Mach was hoping for but that Einstein never fully delivered. And I suspect that if Mach hadn’t rejected Einstein so harshly, he might have been more open to quantum mechanics.” – Amanda Gefter
“Einstein and Mach met in person only once, when Einstein went to visit Mach in his apartment outside Vienna in the fall of 1913, and they debated this very issue. Einstein was still extremely devoted to Mach’s views at that time, but there was a kind of disconnect because he was also very convinced by his work on Brownian motion that there was experimental proof for the existence of atoms. During the visit, he asked Mach whether he would accept their existence if by doing so one could account for directly observable effects (like Brownian motion) that would otherwise go unexplained. Mach responded that he would consider them “economical” – but not real. I think it was in this moment that Mach saw for the first time that Einstein was not a true disciple. If the world is purely relational – which Mach believed it had to be to unify mind and matter into a single reality – then atoms can’t exist as nonrelational entities. The very notion of substance as embodied in the atom, Mach said, “plays the same treacherous role in scientific physics as the thing-in-itself does in philosophy.” In other words, Mach rejected the idea that the world was made of atoms because he rejected the idea that the world was made of anything! If the world had some irreducible, basement-level, nonrelational structure, then neutral monism fails. So in debating the reality of atoms, Mach saw that Einstein had these realist tendencies and that even though he embarked on relativity in order to make everything relational, Mach suspected that deep down Einstein didn’t believe that reality had to be relational. Mach was right – Einstein eventually came to see spacetime itself as that irreducible, basement-level, nonrelational structure, and he couldn’t accept quantum mechanics because he continued to view atoms in this realist way.” – Amanda Gefter
Regarding the scientific paradigm based on measurable quantities only: what is unobservable today may become observable in the future. If you develop theories based on currently measurable quantities the explanatory power and the predictive power of the theory will be very limited. This is why, historically, the alternative scientific paradigm, the one based on “hypothesis –> theory –> testing the predictions of the theory” has been more successful. Some elements of a theory can be unobservable/unmeasurable today but if the logical consequences of that theory are measurable then we have to take that theory seriously.
Machian monism is considered a part of Neutral Monism which arguably includes names such as Baruch Spinoza , David Hume, Ernst Mach, William James, and Bertrand Russell as its originators.
SEP article titled Neutral Monism explains that:
“Neutral monism is a monistic metaphysics. It holds that ultimate reality is all of one kind. To this extent neutral monism is in agreement with the more familiar versions of monism: idealism and materialism. What distinguishes neutral monism from its monistic rivals is the claim that the intrinsic nature of ultimate reality is neither mental nor physical. This negative claim also captures the idea of neutrality: being intrinsically neither mental nor physical in nature ultimate reality is said to be neutral between the two.” – SEP
“Basic neutral entities form the bottom level of the hierarchy; the non-basic, non-neutral entities at the higher levels reduce to, or are in some sense derivative from, those lower level neutral entities. So we are dealing with an ontology that recognizes a plurality of levels or layers in reality.” – SEP
In modern times the basic neutral entities – neutral meaning neither physical nor mental – are sometimes referred to as “information” and sometimes as “mathematical elements.” I should add that perhaps microvita could be considered as basic neutral entities as well.
Why Einstein again?
The reason I am reading about Einstein again is because I am watching the TV series titled Genius produced by the National Geographic. Amanda Gefter’s Nautilus article has very interesting insights about Einstein-Besso friendship. There is another article about the role of Marcel Grossmann and Michele Besso on the development of the special and general theory of relativity. I highly recommend that article as well.
Marcel Grossmann (left), Albert Einstein (center), Michele Besso (right) in college years