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thème: le Déterminisme

Citation:

“Everything is determined, the beginning as well as the end, by forces over which we have no control. It is determined for the insect as well as the star. Human beings, vegetables, or cosmic dust, we all dance to a mysterious tune, intoned in the distance by an invisible player.”

Albert Einstein

Freedom and Determinism

"Faux de Verzy"

Carried out in the 80's by

Yves Flatard

From the book "Freedom and Determinism"

Topics in Contemporary Philosophy, Bradford Books Series

Cambridge, Massachusetts Institute of Technology, ©2004

Freedom and Determinism: A Framework

Authors : Joseph Keim Campbell, Michael O'Rourke, and David Shier

Numerical version from MIT Press

Thoughts about freedom and determinism have engaged philosophers since the days of ancient Greece. On the one hand, we generally regard ourselves as free and autonomous beings who are responsible for the actions that we perform. But this idea of ourselves appears to conflict with a variety of attitudes that we also have about the inevitable workings of the world around us. For instance, some people believe that strict, universal laws of nature govern the world. Others think that there is an omnipotent God who is the ultimate cause of all things. These more global views suggest that each particular event —including each human action— is causally necessitated, and so they suggest a conflict with the claim that we are free. Hence, the problem of freedom and determinism is, at base, a problem about reconciling attitudes we have toward ourselves with our more general thoughts about the world around us. It is a problem about locating our actions within those streams of events that make up the broader universe.
Freedom is usually discussed within the context of theoretical concerns about the nature of moral responsibility. For it is a basic assumption that some kind of freedom —call it "moral freedom"— is a necessary precondition for our being accountable for our actions. Moreover, even those who endorse moral nihilism, the claim that no one is ever morally responsible for anything, usually do so because they also believe that we lack moral freedom. Consequently, the assumption of freedom plays a role in our beliefs about the appropriateness of moral praise and blame. We find it absurd to blame a rock that happens to crash through our living room window but acceptable to blame the child who threw the rock. And we would consider such blame more legitimate were the rock knowingly and intentionally thrown by an adult with normal cognitive capacities. In trying to uncover the basis for these differences in attitude, we encounter other, more fundamental distinctions in moral psychology between action and passion, belief and desire, reason and emotion, and control and compulsion. Not surprisingly persons in the fields of ethics, philosophy of psychology, and philosophy of law all share an interest in understanding the nature of moral freedom. This remains true for moral nihilists since some understanding of the nature of moral freedom is implicit in its denial.
There are a variety of kinds of determinism that have been offered as potential threats to our freedom. For instance, there is logical determinism, the view that all propositions —including those reporting our future actions— are either true or false. There is also theological determinism, according to which an omniscient God knows about the future in complete detail. T. S. Eliot (1943) notes a problem between freedom and temporal determinism, which claims that time is another dimension like any of the other three spatial dimensions, so that the difference between what is in your past and what is in your future is a lot like the difference between what is to your left and what is to your right. Lastly, there is causal determinism, which claims that the past facts, together with the laws of nature, entail all future facts. Each of these determinisms is a global thesis, making a claim about all propositions. It is then suggested that this global property carries with it the kind of necessity that is itself a threat to our freedom.
Of course, the term 'freedom' is also ambiguous. There is political freedom and freedom of religion. These and other freedoms are characterized in a negative way, as the absence of certain constraints on one's activities or beliefs. Since there are many kinds of constraints, there are many negative freedoms. But the kind of freedom that metaphysicians are interested in —call it 'metaphysical freedom'— can also be described in a positive way, as an active power to do things that are up to us. In this sense, metaphysical freedom seems more fundamental than the other, merely negative freedoms. Metaphysical freedom may be even more fundamental than moral freedom, for as the problems noted in the previous paragraph indicate, threats to our freedom can be presented without mentioning attributions of moral praise or blame. On the other hand, each of the determinisms noted above is also a potential threat to our moral freedom. By and large, folks in the twentieth century are concerned with moral freedom —the freedom-relevant condition necessary for moral responsibility— and causal determinism.
For this reason, debates about freedom and determinism center on a set of distinct, though related, questions.
1. What is the thesis of causal determinism?
2. What is the nature of moral freedom?
3. Is moral freedom compatible with causal determinism?
4. Is causal determinism true?
5. Are any persons morally free?
The first three questions are conceptual and, thus, the primary focus of philosophers is directed towards answering those questions. A provisional answer to (1) was given above, but more precisely, determinism is the conjunction of the following two theses:
• For every instant of time, there is a proposition that expresses the state of the world at that instant;
• If p and q are any propositions that express the state of the world at some instants, then the conjunction of p with the laws of nature entails q. (van Inwagen 1983, 65)
Note that there are no temporal restrictions on p and q. Still if p is a proposition that expresses the state of the world at some time in the past, then when conjoined with the laws of nature it entails each and every future fact.
Until recently, all parties in the freedom and determinism debate accepted a short answer to (2), regarding the nature of moral freedom. First, it was held that the kind of freedom required for moral responsibility was free will. Second, it was accepted that free will requires that persons have alternatives to at least some of their actions, where a person S has an alternative to an action if S can do otherwise, or if S is able to do otherwise, or if it is within S's power to do otherwise. Call the identification of moral freedom with free will, the 'traditional view' of moral freedom.

[…]

Many standard ways of treating the problem of freedom and determinism presume answers to questions (1) and (4) above. As it turns out, it is not easy to say what it would be for the world to be deterministic, and even less easy to see whether, on any plausible account of what determinism amounts to, the world is in fact deterministic. In "Determinism: What We Have Learned and What We Still Don't Know," John Earman briefly reviews relevant parts of current physics with respect to their compatibility with determinism. He begins by distinguishing between determinism and prediction. While the latter may entail the former, the converse is false. Hence, one cannot infer from an inability to predict future states of a system that the time evolution of the system is indeterministic. Earman's review covers determinism and predictability not only of quantum systems, but also classical and relativistic systems. One of the interesting results he reaches is that, contrary to naive intuition, classical Newtonian physics is more hostile to determinism than either quantum mechanics or special relativity. Another is that the prospects for a deterministic theory unifying general relativity and quantum theory are rather grim. After noting various points of tension between determinism and each of these parts of current theory, Earman identifies ways in which extensions of the theories might save determinism, but argues that, as things now stand, questions about the truth or falsity of determinism remain open.

De la probabilité

Extrait de l'œuvre de Pierre-Simon Laplace (1749-1827)

"Essai philosophique sur les probabilités"

publiée en 1814 par Mme Ve Courcier

Version numérique réalisée par le réseau de bibliothèques NEBIS

De la probabilité

Tous les événements, ceux mêmes qui par leur petitesse, semblent ne pas tenir aux grandes lois de la nature, en sont une suite aussi nécessaire que les révolutions du Soleil. Dans l’ignorance des liens qui les unissent au système entier de l’univers, on les a fait dépendre des causes finales, ou du hasard, suivant qu’ils arrivaient et se succédaient avec régularité, ou sans ordre apparent ; mais ces causes imaginaires ont été successivement reculées avec les bornes de nos connaissances, et disparaissent entièrement devant la saine philosophie, qui ne voit en elles que l’expression de l’ignorance où nous sommes des véritables causes.

Les événements actuels ont, avec les précédents, une liaison fondée sur le principe évident, qu’une chose ne peut pas commencer d’être, sans une cause qui la produise. Cet axiome, connu sous le nom de principe de la raison suffisante, s’étend aux actions mêmes que l’on juge indifférentes. La volonté la plus libre ne peut sans un motif déterminant, leur donner naissance ; car si toutes les circonstances de deux positions étant exactement semblables, elle agissait dans l’une et s’abstenait d’agir dans l’autre, son choix serait un effet sans cause : elle serait alors, dit Leibnitz, le hasard aveugle des épicuriens. L’opinion contraire est une illusion de l’esprit qui, perdant de vue les raisons fugitives du choix de la volonté dans les choses indifférentes, se persuade qu’elle s’est déterminée d’elle-même et sans motifs.

Nous devons donc envisager l’état présent de l’univers, comme l’effet de son état antérieur, et comme la cause de celui qui va suivre. Une intelligence qui, pour un instant donné, connaîtrait toutes les forces dont la nature est animée, et la situation respective des êtres qui la composent, si d’ailleurs elle était assez vaste pour soumettre ces données à l’analyse, embrasserait dans la même formule les mouvements des plus grands corps de l’univers et ceux du plus léger atome : rien ne serait incertain pour elle, et l’avenir comme le passé, serait présent à ses yeux. L’esprit humain offre, dans la perfection qu’il a su donner à l’Astronomie, une faible esquisse de cette intelligence. Ses découvertes en Mécanique et en Géométrie, jointes à celle de la pesanteur universelle, l’ont mis à portée de comprendre dans les mêmes expressions analytiques, les états passés et futurs du système du monde. En appliquant la même méthode à quelques autres objets de ses connaissances, il est parvenu à ramener à des lois générales les phénomènes observés, et à prévoir ceux que des circonstances données doivent faire éclore. Tous ces efforts dans la recherche de la vérité, tendent à le rapprocher sans cesse de l’intelligence que nous venons de concevoir, mais dont il restera toujours infiniment éloigné. Cette tendance, propre à l’espèce humaine, est ce qui la rend supérieure aux animaux ; et ses progrès en ce genre, distinguent les nations et les siècles, et font leur véritable gloire.

Rappelons-nous qu’autrefois, et à une époque qui n’est pas encore bien reculée, une pluie ou une sécheresse extrême, une comète traînant après elle une queue fort étendue, les éclipses, les aurores boréales et généralement tous les phénomènes extraordinaires étaient regardés comme autant de signes de la colère céleste. On invoquait le ciel pour détourner leur funeste influence. On ne le priait point de suspendre le cours des planètes et du Soleil : l’observation eût bientôt fait sentir l’inutilité de ces prières. Mais comme ces phénomènes arrivant et disparaissant à de longs intervalles, semblaient contrarier l’ordre de la nature, on supposait que le ciel irrité par les crimes de la terre, les faisait naître pour annoncer ses vengeances. Ainsi la longue queue de la comète de 1456 répandit la terreur dans l’Europe, déjà consternée par les succès rapides des Turcs qui venaient de renverser le Bas-Empire. Cet astre, après quatre de ses révolutions, a excité parmi nous un intérêt bien différent. La connaissance des lois du système du monde, acquise dans cet intervalle, avait dissipé les craintes enfantées par l’ignorance des vrais rapports de l’homme avec l’univers ; et Halley ayant reconnu l’identité de cette comète, avec celles des années 1531, 1607 et 1682, annonça son retour prochain pour la fin de 1758 ou le commencement de 1759. Le monde savant attendit avec impatience, ce retour qui devait confirmer l’une des plus grandes découvertes que l’on eût faites dans les sciences, et accomplir la prédiction de Sénèque, lorsqu’il a dit, en parlant de la révolution de ces astres qui descendent d’une énorme distance : « Le jour viendra que par une étude suivie, de plusieurs siècles, les choses actuellement cachées paraîtront avec évidence ; et la postérité s’étonnera que des vérités si claires nous aient échappé. » Clairaut entreprit alors de soumettre à l’analyse les perturbations que la comète avait éprouvées par l’action des deux plus grosses planètes, Jupiter et Saturne ; après d’immenses calculs, il fixa son prochain passage au périhélie, vers le commencement d’avril 1759, ce que l’observation ne tarda pas à vérifier. La régularité que l’Astronomie nous montre dans le mouvement des comètes, a lieu sans aucun doute, dans tous les phénomènes. La courbe décrite par une simple molécule d’air ou de vapeurs, est réglée d’une manière aussi certaine, que les orbites planétaires : il n’y a de différences entre elles, que celle qu’y met notre ignorance.

Free Will or Determinism

Russell Stannard, Professor Emeritus of Physics at The Open University, asks if we’re really free to choose.
(source: OpenLearn)


Russell:
All day long we have to make choices. OK I happened to choose this one. I could just as easily have chosen a brown one or a red one. Or could I? Was I really free to choose? We do all our thinking with our brain. But the brain is a physical object. The behaviour of physical objects is governed by the laws of nature. Even with apparatus this complex, we can still predict how it's going to behave... Well, not me personally, I don’t understand these things but computer experts understand what’s going on there. For them it’s all predictable. In which case, what if someone were to examine the workings of my brain in the same way as a computer engineer can examine the workings of the computer? He examines my brain just before I make my decision over which sweet to take, he applies the laws of nature, and predicts with certainty what the state of my brain will be after making this decision – this so-called 'decision'. Surely, that way he will know what my choice is going to be, that I'm about to pick up the blue one, even before I know that that’s what I'm going to do. It's all pre-determined. I have no choice - no real choice. I am just going through the motions.

This is the so-called free will/determinism problem. How to reconcile the grinding predictability of the physical brain and the rest of the physical world, with the mental sense that the future is open - the sense that it's up to us to decide what it will be. We have freedom to make genuine choices. It's a problem that scientists and philosophers have wrestled with for... well for centuries. Recently some have sought to solve the problem by calling upon quantum theory. Quantum theory is necessary for the description of the behaviour of very small objects – atoms and sub-atomic particles. What it shows is that on the very small scale, the future is not predictable, not with absolute certainty. The electrons that make up an atom - we never know where we're going to find them when we next look. And no, it's not a case of: 'Look more carefully' or 'Invest in more expensive measuring equipment'. No this is a built-in uncertainty - an uncertainty that’s absolutely fundamental to nature itself. At the subatomic level, all we can ever hope to do is predict the odds of various possible outcomes. Which of course doesn't seem to square with normal everyday life - where things are predictable - up to a point.

There! I knew that was going to happen. It was fixed that way, predicatable. But here we're not looking at individual atoms. This array is made up of a vast, vast number of atoms. So what we are looking at here is the average behaviour of many, many atoms - and that average behaviour is predictable. But not the behaviour of the individual atom or subatomic particle. That is governed by chance - pure random chance. So this raises an intriguing possibility: If the action of the brain corresponding to the making of a choice, if that action is something happening on the very small scale up here - perhaps involving the movement of an individual atom, then the behaviour is not predetermined. It's subject to chance, random chance. And some have latched onto this to claim that that is how we come to make a free will decision.

But is this the answer? Suppose I can't make up my mind which one to choose, the blue or the red. What could I do? Okay, blue tails, red heads. But is that me making a decision - a conscious decision? No. That's me leaving it to chance, opting out of making a conscious decision. No. Quantum uncertainty, with its dependence on chance, seems to go the way of all previous attempts to solve the free will/determinism problem. It's a problem like that of consciousness itself, a problem we seem to be stuck with. I can't see how it will ever be solved. Not to everyone's satisfaction.


After piece

Tony:

Russell, with that coin business, you said it was pure chance. But it was your choice to leave it to chance. So you were exercising genuine free will then.
Russell:
No... No If what's going on up here is just chance, then my 'decision' to leave it to chance as you put it was itself just chance. Right?
Tony:
Yeah. Okay. Time to move on everybody.