The phenomenon of probability backflow, previously quantified for a free nonrelativistic particle, is considered for a free particle obeying Dirac's equation. It is shown that probability backflow can occur in the opposite direction to the momentum; that is to say, there exist positive-energy states in which the particle certainly has a positive momentum in a given direction, but for which the component of the probability flux vector in that direction is negative. It is shown that the maximum possible amount of (...) probability that can flow “backwards,” over a given time interval of duration T, depends on the dimensionless parameter ε = (4ℏ/mc2T)1/2, where m is the mass of the particle and c is the speed of light. At ε = 0, the nonrelativistic value of approximately 0.039 for this maximum is recovered. Numerical studies suggest that the maximum decreases monotonically as ε increases from 0, and show that it depends on the size of m, ℏ, and T, unlike the nonrelativistic case. (shrink)

It has been shown earlier that while strict localization of the free Dirac particle is not describable within the usual mathematical formalism, it is possible to describe sequences of positive-energy states whose spread Δ x =〈(x−x 0)2〉 about any given point x 0 approaches zero, where x is Dirac's position operator. The concept of a generalized function is extended here to allow for the succinct description of localized states in terms of “Asymptotic Localizing Functions.” Localization of both the nonrelativistic particle (...) and the Dirac particle can be adequately represented in this new formalism. (shrink)

Does action always arise out of desire? G. F. Schueler examines this hotly debated topic in philosophy of action and moral philosophy, arguing that once two senses of "desire" are distinguished - roughly, genuine desires and pro attitudes - apparently plausible explanations of action in terms of the agent's desires can be seen to be mistaken. Desire probes a fundamental issue in philosophy of mind, the nature of desires and how, if at all, they motivate and justify our actions. At (...) least since Hume argued that reason "is and of right ought to be the slave of the passions," many philosophers have held that desires play an essential role both in practical reason and in the explanation of intentional action. G. F. Schueler looks at contemporary accounts of both roles in various belief-desire models of reasons and explanation and argues that the usual belief-desire accounts need to be replaced. Schueler contends that the plausibility of the standard belief-desire accounts rests largely on a failure to distinguish "desires proper," like a craving for sushi, from so-called "pro attitudes," which may take the form of beliefs and other cognitive states as well as desires proper. Schueler's "deliberative model" of practical reasoning suggests a different view of the place of desire in practical reason and the explanation of action. He holds that we can arrive at an intention to act by weighing the relevant considerations and that these may not include desires proper at all. (shrink)

Physico-chemical sciences are dominated by the deterministic interpretation. Scientific medicine has generally been assigned to the area of functional biology and thence to the physico-chemical sciences. In as much as diseases are alterations of physiological processes, they share the ontological status of the latter. However, many diseases cannot be accommodated within a deterministic interpretation. First, many diseases are initiated by errors in transmission of information and followed by natural selection. These diseases, such as tumoural transformations and autoimmune processes, behave as (...) evolutionary processes. Second, physiological processes do not cause irreversible changes while diseases may do so when not followed by restitutio ad integrum. The tendency of living organisms to maintain stationary states of great stability and minimum energy dissipation is largely due to intermolecular forces-stabilized structures, the information for which is selected during phylogenesis and decodified during ontogenesis. Diseases cause alterations of the biological structures, thereby shifting living organisms toward stationary states of lower stability and increased dissipation. The shift, reversible or irreversible, to less stable and efficient stationary states is a common thermodynamic feature of diseases. In spite of the uniqueness of their genotype, living organisms, during ontogenetic development, form spatio-temporal unrestricted classes of infinite membership. Neither stationarity nor environment-induced perturbations and consequent adaptations are sources of historicity because of the genomic programme constraint. Historicity is conferred, however, to each organism by the permanent record of such unique events as: a) the variation-selection processes occurring in the brain-mind and immunological systems; and b) irreversible alterations induced by diseases. The disease-induced changes have ontological and epistemological consequences. Since biological structures and functions are transformed into individual, historical entities, the laws of scientific medicine must be applied in clinical practice to higher levels of organization, namely to the ensembles or groups of individuals affected by the diseases. (shrink)

People act for reasons. That is how we understand ourselves. But what is it to act for a reason? This is what Fred Schueler investigates. He rejects the dominant view that the beliefs and desires that constitute our reasons for acting simply cause us to act as we do, and argues instead for a view centred on practical deliberation--our ability to evaluate the reasons we accept. Schueler's account of 'reasons explanations' emphasizes the relation between reasons and purposes, and the fact (...) that the reasons for an action are not always good reasons. (shrink)