Determinism, Indeterminism, Libertarianism, Compatibilism – Who is right?
Since the 20th century, not only philosophers and psychologists have been concerned with the topic of free will. Chapters 3 to 5 of my new book on the subject address the positions of various physicists regarding free will. In the illustration, we see clockwise: Max Planck (left, 1858-1947, Nobel Prize 1919), Albert Einstein (1879-1955, Nobel Prize 1921), Frits Zernike (1888-1966, Nobel Prize 1953), Anton Zeilinger (Nobel Prize 2022), and Sabine Hossenfelder.
Planck’s essay from the 1930s on free will inspired the entire book (it is newly published in the appendix). For the founder of quantum physics, it depended on the perspective whether we have free will or not. The causal closure of the world was for him a prerequisite of science par excellence.
Max Planck brought his former friend Albert Einstein from Switzerland to Germany and Berlin. Along with Planck’s son Erwin, the three regularly played music together: Einstein played the violin, Erwin played the cello, and Max Planck played the piano; the latter had wavered between studying classical philology, music, and physics as a young man.
However, the friendship between Planck and Einstein broke due to the militarization of Germany and the Nazi dictatorship. The pacifist and Jew Einstein increasingly faced public attacks and eventually had to flee. In the field of physics, he opposed the idea of indeterminism throughout his life (e.g., in a letter to Max Born dated December 4, 1926): God does not play dice!
(In)Determinism
I hold the position (Chapter 4) that the question of determinism cannot be resolved at all: sensibly, one could only speak of the (in)determinism of the entire universe. However, this cannot be proven or disproven with the known scientific means. Whether there is real chance behind the uncertainty at the quantum level still depends on the interpretation.
In subsystems like the brain or a vending machine, one cannot reasonably assume determinism, as they are open systems that are constantly influenced from the outside. In computer science, an algorithm is deterministic if the same input (under the same internal state) always leads to the same result.
A simple example is the state table of a vending machine: Suppose a drink costs 2 euros. The machine accepts 1 and 2-euro coins. Then (simplifying) two 1-euro coins or one 2-euro coin will result in the dispensing of the drink. Is that really always the case? In the real world, one only has to unplug the machine, and it will no longer dispense anything.
What sounds like a trivial example simply illustrates the point that deterministic rules of real systems can always be broken – then these systems are no longer deterministic. What it then still benefits to talk about the theoretical determinism of ideal systems, each may judge for themselves. I want to treat free will as a practical problem.
Brain Equations
In any case, Sabine Hossenfelder’s (alleged) refutation of free will from a physical perspective also fails on this. She simply assumes that brains could be described by deterministic differential equations. Yet there are neither such equations – nor can there be, if my argument is correct. Rather, such an equation would have to be rewritten constantly. According to deterministic or indeterministic rules?
Moreover, Hossenfelder simply rejects compatibilist ideas of free will, as held today by the majority of philosophers, as “conceptual confusion.” Is that a good academic style? Many philosophers and psychologists have argued that freedom and determination are not contradictory but that free will actually presupposes a certain form of determination.
Physics and Philosophy
Frits Zernike is mentioned in the book because he participated in a lecture series on free will at the University of Groningen in the 1930s. In it, he abandons the notion of causal determinism, contrary to Max Planck. He was (as an experimental physicist) also not a fan of philosophizing. In his view, philosophers would take far too long to respond to empirical findings – which would then already be outdated.
In the book, I take the position that both quick and reflective consideration in science and philosophy have their justification. In science, often only the one who makes a discovery first receives the fame. However, the actual significance of such a discovery often only becomes apparent in a more profound and long-term consideration. Additionally, today in the philosophy of science and physics, there are many academics who have studied both fields.
Anton Zeilinger is mentioned briefly in the book, along with Swiss quantum physicist Nicolas Gisin, because he simply considers free will necessary for scientific work. This closes the loop back to Max Planck.
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Licenses of the images: Anton Zeilinger by Jaqueline Godany, CC BY 4.0, Sabine Hossenfelder by HossenfelderS, CC BY-SA 4.0