Pendant des décennies, des scientifiques sont restés perplexes sur la façon dont certaines limaces de mer acquierent la capacité à pratiquer la photosynthèse après l’ingestion d’algues. Une technique d’imagerie de pointe confirme maintenant que les limaces volent littéralement des gènes d’algues, ce qui est considéré comme le premier exemple de "
Des scientifiques ont calculé qu’il y a des centaines de milliards de planètes comme la Terre dans notre galaxie qui pourraient être favorable à la vie (telle que nous la connaissons).
La nouvelle recherche, dirigée par le Professeur Charley...
Une nouvelle série de cartes de notre Voie lactée présente la répartition du gaz, de la poussière, des particules et des champs magnétiques. Elles sont basées sur des observations de l’observatoire spatial Planck de l’Agence spatiale européenne....
Voilà une magnifique ode au Dieu Soleil, pourfendeur des ténèbres; une vidéo à vous décrocher la mâchoire et qui célèbre le cinquième anniversaire de la sonde
Un énorme panache de brume s’étendant sur plus de 950 km de la surface de Mars a déconcerté les astronomes, suscitant encore bon nombre de spéculations. Repérées pour la première fois en 2012, les émissions à haute altitude ont d’abord été suivies par des amateurs qui ont d’abord douté de leurs télescopes, étant si différents des nuages et des aurores polaire habituels. Maintenant, les chercheurs de l’Agence spatiale...
Des scientifiques se concentrant sur la matière et qui étudient les rongeurs, comme le ragondin (en image d’entête) et les castors, ont découvert pourquoi ces animaux à la dent dure n’ont jamais de caries : l’émail de leurs dents est riche en fer. Ils ont déterminé que le fer résiste plus efficacement à l’acide que le fluorure.
Ce n’est pas surprenant que l’Asie du Sud abrite d’innombrables anciennes statues de Bouddha, mais quand l’une d’entre elles contient un moine momifié, c’est une surprise.
En utilisant des données satellitaires, des scientifiques de la NASA ont créé le premier modèle 3D présentant la quantité de poussière voyageant du désert du Sahara à la forêt amazonienne. Aussi incroyable que cela puisse paraitre, cette poussière ensemence la forêt tropicale...
La peste noire était sans aucun doute l’une des pandémies les plus dévastatrices de l’histoire humaine. Elle a atteint un sommet en Europe entre les années 1346-1353 et elle est estimé avoir causé entre 75 000 000 à 200 000 000 décès, avec de nombreuses flambées successives au cours des quatre siècles suivants. A ce moment-là, la population mondiale était d’environ 450 millions d’âmes.
There are, as we have seen, certain structural properties that are necessary conditions on rational belief. What exactly these are depends on your views. However, there are further ways of assessing belief. Strongly believing true things and strongly believing the negations of false things seem like good-making-features of beliefs. For the case of precise credences, we can make this precise. There is a large literature on “scoring rules”: methods for measuring how good a probability is relative to the actual state of the world (Brier 1950; Savage...
Imprecise probabilities is a theory born of our limitations as reasoning agents, and of limitations in our evidence base. If only we had better evidence, a single probability function would do. But since our evidence is weak, we must use a set. In a way, the same is true of precise probabilism. If only we knew the truth, we could represent belief with a truth-valuation function, or just a set of sentences that are fully believed. But since there are truths we don’t know, we must use a probability to represent our intermediate confidence. And indeed,...
Imprecise probabilities aren’t a radically new theory. They are merely a slight modification of existing models of belief for situations of ambiguity. Often your credences will be precise enough, and your available actions will be such that you act more or less as if you were a strict Bayesian. One might analogize imprecise probabilities as the “Theory of Relativity” to the strict Bayesian “Newtonian Mechanics”: all but indistinguishable in all but the most extreme situations. This analogy goes deeper: in both cases, the theories are “empirically...
One important use that models of belief can be put to is as part of a theory of rational decision. IP is no different. Decision making with imprecise probabilities has some problems, however. The problem for IP decision making, in short, is that your credal committee can disagree on what the best course of action is, and when they do, it is unclear how you should act (recall the definitions in
This section collects some problems for IP noted in the literature.
3.1 Dilation
Consider two logically unrelated propositions [ltr][size=18]H[/ltr] and [ltr]X[/ltr]. Now consider the four “state descriptions” of this simple model as set out in
Suppose we wanted our epistemology to apply not just to individuals, but to “group agents” like committees, governments, companies, and so on. Such agents may be made up of members who disagree. Levi (1986, 1999) has argued that representation of such conflict is better handled with sets of probabilities than with precise probabilities. There is a rich literature on combining or aggregating the (probabilistic) opinions of members of groups (Genest and Zidek 1986) but the outcome of such aggregation does not adequately represent the disagreement among...
Haenni et al. (2011) motivate imprecise probabilities by showing how they can arise from precise probability judgements. That is, if you have a precise probability for [ltr][size=18]X[/ltr] and a precise probability for [ltr]Y[/ltr], then you can put bounds on [ltr]p(X∩Y)[/ltr] and [ltr]p(X∪Y)[/ltr], even if you don’t know how [ltr]
You are sometimes in a position where none of your evidence seems to speak for or against the truth of some proposition. Arguably, a reasonable attitude to take towards such a proposition is suspension of judgement.
اقتباس :
When there is little or no information on which to base our conclusions, we cannot expect reasoning (no matter how clever or thorough) to reveal a most probable hypothesis or...
Evidence influences belief. Joyce (2005) suggests that there is an important difference between the weight of evidence and the balance of evidence. He argues that this is a distinction that precise probabilists struggle to deal with and that the distinction is worth representing. This idea has been hinted at by a great many thinkers including J.M. Keynes, Rudolf Carnap, C.S. Pierce and Karl Popper (see references in Joyce 2005; Gärdenfors and Sahlin 1982). Here’s Keynes’ articulation of the intuition:
Various arguments for (precise) probabilism assume that some relation or other is complete. Whether this is a preference over acts, or some “qualitative probability ordering”, the relation is assumed to hold one way or the other between any two elements of the domain. This hardly seems like it should be a principle of rationality, especially in cases of severe uncertainty. That is—to take the preference example—it is reasonable to have no preference in either direction. This is an importantly different attitude to being indifferent between...
Let’s consider, in general terms, what sort of motivations one might have for adopting models that fall under the umbrella of IP. The focus will be on models of rational belief, since these are the models that philosophers typically focus on, although it is worth noting that statistical work using IP isn’t restricted to this interpretation. Note that no one author endorses all of these arguments, and indeed, some authors who are sympathetic to IP have explicitly stated that they don’t consider certain of these arguments to be good (for example...
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