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)

But a body of rigorous mathematical theory has also gradually developed, and this is the first book to present that theory.

Payment for research participation has raised ethical concerns, especially with respect to its potential for coercion. We argue that characterising payment for research participation as coercive is misguided, because offers of benefit cannot constitute coercion. In this article we analyse the concept of coercion, refute mistaken conceptions of coercion and explain why the offer of payment for research participation is never coercive but in some cases may produce undue inducement.

Adolescence methamphetamine use is an issue of considerable concern due to its correlation with later delinquency, divorce, unemployment and health problems. Understanding how adolescents initiate methamphetamine abuse is important in developing effective prevention programs. We formulate a mathematical model for the spread of methamphetamine abuse using nonlinear ordinary differential equations. It is assumed that susceptibles are recruited into methamphetamine use through imitation. An epidemic threshold value, Ra\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathcal {R}}_a$$\end{document}, termed the abuse reproduction (...) number, is proposed and defined herein in the drug-using context. The model is shown to exhibit the phenomenon of backward bifurcation. This means that methamphetamine problems may persist in the population even if Ra\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathcal {R}}_a$$\end{document} is less than one. Sensitivity analysis of Ra\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathcal {R}}_a$$\end{document} was performed to determine the relative importance of different parameters in methamphetamine abuse initiation. The model is then fitted to data on methamphetamine users less than 20 years old reporting methamphetamine as their primary substance of abuse in the treatment centres of Cape Town and parameter values that give the best fit are chosen. Results show that the proportion of methamphetamine users less than 20 years old reporting methamphetamine as their primary substance of abuse will continue to decrease in Cape Town of South Africa. The results suggest that intervention programs targeted at reducing adolescence methamphetamine abuse, are positively impacting methamphetamine abuse. (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)

John McMillan's article raises numerous important points about the ethics of surgical castration of sex offenders.1 In this commentary, we focus solely on and argue against the claim that the offer of release from detention conditional upon surgical castration is a coercive offer that compromises the validity of the offender's consent. We take no view on the question as to whether castration for sex offenders is ethically permissible. But, we reject the claim that it is ethically permissible only if competing (...) ethical considerations outweigh worries about coercion. For in the situation described, the proposal is not coercive at all.McMillan states that if offenders agree to castration because they fear long-term detention, then ‘it seems, intuitively, as if agreeing to be castrated under these conditions makes the decision coerced in some way.’1 He adds that if castration is ‘the only way that they will be released back into the community, the status of this decision as a genuine expression of their autonomy is questionable.’1 In defence of his claim, he uses two analogies that he borrows from Joel Feinberg. First, if a governor offers to commute a death sentence if the prisoner agrees to participate in a medical experiment, then ‘it's clear that the governor is coercing the prisoner.’1 Second, if a millionaire offers to give a woman $1 000 000 …. (shrink)

We review current theoretical cosmology, including fundamental and mathematical cosmology and physical cosmology (as well as cosmology in the quantum realm), with an emphasis on open questions.

In the first part of this paper a logic is defined for propositions whose probability of being true may not be known. A speaker's beliefs about which propositions are true are still interesting in this case. The meaning of propositions is determined by the consequences of asserting them: in this logic there are debates which incur certain costs for the protagonists.The second part of the paper describes the mathematics of the resulting logic which displays several novel features.

Listening to someone from some distance in a crowded room you may experience the following phenomenon: when looking at them speak, you may both hear and see where the source of the sounds is; but when your eyes are turned elsewhere, you may no longer be able to detect exactly where the voice must be coming from. With your eyes again fixed on the speaker, and the movement of her lips a clear sense of the source of the sound will (...) return. This ‘ventriloquist’ effect reflects the ways in which visual cognition can dominate auditory perception. And this phenomenological observation is one what you can verify or disconfirm in your own case just by the slightest reflection on what it is like for you to listen to someone with or without visual contact with them. (shrink)

This paper argues that both teleological and causal concepts are required for explanations of intentional actions. It argues against ‘causalism’, the idea that action explanations are essentially causal. This requires analyzing Mele’s Q-Signals-from-Mars argument that having a purpose and behaving so as to achieve it aren’t sufficient to explain an intentional action. Though Mele’s example shows that external causal interference can defeat the claim that an intentional action has been performed, this is consistent with teleological concepts being required (even if (...) not sufficient) for action explanation. Mele’s example would work even if causalism were true. But causalism is false. Causalism depends on the idea that ‘agents always do what they want’ can be understood as saying agents have mental states, desires, that cause their behavior. But intentional actions involve what agents want only in the sense that actions have purposes, which are not mental states and cannot be the causes of actions. To perform an intentional action is to pursue some purpose in some way. This paper argues that neither the reference to the purpose that explains why the action was performed, nor the causal account of how this purpose was pursued, can be eliminated. (shrink)