The two scientific disciplines that seem most likely to be able to bring elements to the question of free will are physics (which studies the laws of nature) and neurosciences (which studies the functioning of the nervous system and therefore of the brain, organ decision-making). Physics makes it possible to better understand the notion of determinism while neurosciences really touch on free will.
From the philosophy of science
Today, modern physics eliminates the knowledge of causes without making quantum indeterminacy evidence of essential chance. Knowledge of causes, even limited to efficient causes, disappears from explanations in favor of predictive mathematical laws because they are probabilistic and calculable.
“belief in cause and effect is superstition”
— Tractatus logico-philosophicus, 5.1361, Ludwig Wittgenstein
Although, so far, this statement can only be generalized to the hard sciences where the fortuitous designates what intervenes not only without a final or efficient cause but above all without a calculable probabilistic law. Quantum indeterminism represents the consideration of the limits of knowledge: that of an impassable limit in practice as in theory with regard to reality itself. Unlike Kant’s reality per se, this indeterminacy does not clear the non-phenomenal space of a freedom: probabilistic laws apply at the level of observable phenomena. As far as the unobservable is concerned, Schrödinger’s equation accounts for it.
Belief in free will is generally thought to be the sole basis of an ethic of responsibility. Psychoanalysis considers that most of our actions depend more on our unconscious than on our conscious will. This knowledge leads to the paradox that sexual criminals are both criminals likely to be accountable to justice because of their responsibility and sick people, and controlled by their unconscious and their hormones who must be treated. Jurisprudence brings this paradox into its arsenal with the therapeutic injunction where medical monitoring becomes a penalty.
In this limitation, we encounter Nietzsche’s intuition when describing the eternal return, he intuits a creative will determined by the past which it attempts to justify:
“I taught them all my thoughts and all my aspirations: to unite and join all that in man is but fragment and riddle and gloomy chance, as a poet, as a guesser of riddles and redeemer of chance. I taught them to be a creator of the future and to save, by creating, all that was. Rescue the past in man and transform all that was until the will says, “But this is how I would have it be. But that’s how I would like it.””
— Thus Spake Zarathustra, III, 3 – Nietzsche
The impossibility of free will according to Donald Hebb
In his landmark work, The Organization of Behaviour: a Neuropsychological Theory, Hebb argues strongly against free will. In particular, he explains that there is no force that would influence neurons and make them do what they would not do otherwise. He also expresses a need for coherence in the different fields of science by saying that it is impossible to be deterministic in physics and to be mystical in biology.
Free will and the Everett hypothesis
In the event that Everett’s hypothesis is justified — hypothesis according to which parallel universes exist, which has not been established — all possible futures (or more exactly a number of possible futures having Planck’s constant as a denominator) in every moment of the universe in every place would indeed occur: there is no quantum chance; if a particle seems to have to choose at random between two directions, in reality there would be a universe in which the particle takes a left and another in which it takes a right.
Without being able to comment on the validity of Everett’s hypothesis, one can examine as a thought experiment in what terms it would influence the question of free will if it were correct: insofar as all the possible futures (possible according to the laws of quantum physics, which therefore does not mean all imaginable futures) occur and where each observer located in one of these improperly named parallel universes has the impression of being the only one , the paradoxes linked to free will are removed by denying the uniqueness of the observer in the future (but not in his present past, hence the asymmetry of these two time domains). Such a denial is not unique to this thesis and is found in some contemporary philosophers.
The Free Will Theorem
In 2006, the two mathematicians John Conway and Simon Kochen proved a theorem called “free will theorem”. They define the free will of an entity A as the capacity that A would have to make decisions not defined by a function (in the mathematical sense of the term) of the information accessible to A, that is to say observations available in the “past cone” of A.
The theorem then says that if an experimenter has this free will (in the sense thus exposed), then the elementary particles which compose it also have it.
Philosophers generally consider that experimenters have enough “free will” to choose how they organize their experiments in a way that is not determined by past history. The theorem deduces that if this is true the response of the particles is also not determined by past history.
Conway and Kochen begin by demonstrating that if we accept an axiom called Spin – admitted in quantum physics because it conforms to the results of the experiment – then a certain quantity measured by these physicists cannot pre-exist before the experiment, that is to say that it cannot be inscribed in the structure of the particle studied. This would therefore invalidate a “realistic” conception of the universe.
One could certainly assume this quantity instantly “calculated” from the information available in the universe accessible to these particles just before the measurement; however the theorem says that this is not the case if the experimenters have a free will and that one accepts two other axioms called Fin and Twin, them also simple and accepted by the physicists.
The theorem eliminates in this case the notions of “hidden variables” (for example that of David Bohm) assuming that the particles have properties that are not directly observable (for example position in one or more supernumerary dimensions) only manifesting themselves during the “reduction of the wave packet” that follows a measurement.
This free will theorem would establish the hidden variables as inconsistent with special relativity without resorting to quantum mechanics, since it is a simple mathematical reasoning using no physical properties of particles.
Descartes and after him Laplace imagined it possible to describe the universe as the evolution of a system from an initial state and according to deterministic laws, that is to say invariable in space and time. The reasoning followed in the demonstration of Conway and Kochen shows however, without assumption of free will but just the three axioms Fin, Twin, Spin, that no theory using independent laws of space and time cannot predict even the outcome of certain spin measurements on particles.
This does not invalidate determinism, however: if the universe is entirely deterministic, then there is no human free will and the theorem does not apply. But if there is indeterminism (a free will) in humans, there must also be one for elementary particles.
Especially since the existence of indeterminism at the level of elementary particles does not imply indeterminacy in humans.
Free will and precognition
In one of his conferences devoted to the theme of time travel, astronomer Sean Carroll explains that the concept of free will is only an approximation and that it is in theory completely compatible with determinism. Thus, he compares the notion of determinism to a rascal who claims to know the future but always refuses to reveal it in advance. Many people are disturbed by the idea of determinism: this idea that if we know the exact state of the universe at a given moment, we can predict the future. Determinism isn’t some wise old man saying, “This is what’s going to happen in the future and there’s absolutely nothing you can do about it”; the idea of determinism is more like a urchin saying, “I know what you’re going to do in a moment.” So you ask him, “Let’s admit it. So what am I going to do? and he replies, “I can’t tell you that.” Then you do something and the kid goes, “I knew you would do that.”
According to Caroll, determinism is therefore not incompatible with free will since as long as we do not know what we will do in the future, the range of possibilities remains at least theoretically realizable, so that a non- determinist seems to us quite equivalent.
(Includes texts from Wikipedia translated and adapted by Nicolae Sfetcu)