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Paradoxes of Time Travel is a comprehensive study of the philosophical issues raised by the possibility of time travel. The book begins, in Chapter 1, by explaining the concept of time travel and clarifying the central question to be addressed: Is time travel compatible with the laws of metaphysics and, in particular, the laws concerning time, freedom, causation, and identity? Chapter 2 then explores the various temporal paradoxes, including the double-occupancy problem, the no-destination argument, and the famous twin paradox of special relativity. Chapters 3 and 4 focus on the paradoxes of freedom, including various versions of the grandfather paradox. Chapter 5 covers causal paradoxes, including the bootstrapping paradox, the problems of backward causation, and the various puzzles raised by causal loops. Chapter 6 then concludes by looking at various paradoxes of identity. This includes a discussion of different theories of change and persistence, and an exploration of the various puzzles raised by self-visitation.

Previous theories of the relationship between dispositions and conditionals are unable to account for the fact that dispositions come in degrees. We propose a fix for this problem which has the added benefit of avoiding the familiar problems of finks and masks.It has proven difficult to articulate exactly how dispositions are related to subjunctive conditionals. The natural starting-point is a simple conditional analysis, according to which an object o is disposed to give response r to stimulus s if and only if, were o to undergo stimulus s, it would give response r. A glass is disposed to break when dropped, for example, if and only if it would break if dropped. For the moment, at least, we follow David Lewis in assuming that implicit dispositional ascriptions -'This glass is fragile' -can ultimately be understood in terms of explicit correlates -'This glass is disposed to break when dropped'. 1 This simple analysis is subject to familiar counter-examples involving finks and masks. A disposition is finkish if and only if it would disappear in the presence of the relevant stimulus. Example: a fragile glass is protected by a sorcerer who is prepared, should the glass fall, to cast a spell which will momentarily strengthen the physical structure of the glass, so that it will not break. The glass is disposed to break when dropped, but it will not break if dropped. 2 A disposition is masked, in contrast, when it would not disappear in the presence of the relevant stimulus, but where the characteristic manifestation would still be absent. Example: a fragile glass is protected by a sorcerer who is prepared, should the glass fall, to cast a spell which momentarily alters the physical structure of the floor so that the glass will not break. 3

Michelangelo's David is constituted by a particular chunk of marble. The flag that hangs at the nearby courthouse is constituted by a piece of fabric. I am constituted by my body. This much is familiar. But what is the relation of constitution at work in these various cases?In this paper I propose to address this question as it arises for one particular metaphysical view, what is sometimes called the constitution view. The defender of the constitution view makes three important claims. First, objects of the common sense ontology exist. So, for example, there are lumps of clay, human bodies, statues and persons. 1 Second, these objects have the sorts of de re modal properties and persistence conditions that common sense attributes to them. 2 Lumps of clay, for example, can survive being squashed, while statues cannot. Third, the defender of the constitution view claims that constitution is not identity. The idea that constitution is not identity follows quite naturally from the previous two assumptions. For consider a particular statue that is constituted by an ordinary lump of clay. Given the first assumption above, the constitution theorist recognizes the existence of the statue and the lump and, given the second, the constitution theorist claims that these objects differ in their de re modal properties. The constitution theorist concludes that, despite the fact that the statue and the lump stand in a very intimate relationship, they are nonetheless distinct. 3

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Invasive alien species impacts might be mediated by environmental factors such as climatic warming. For invasive predators, multiple predator interactions could also exacerbate or dampen ecological impacts. These effects may be especially pronounced in highly diverse coastal ecosystems that are prone to profound and rapid regime shifts. We examine emergent effects of warming on the strength of intraspecific multiple predator effects from a highly successful invasive gammarid Gammarus tigrinus, using a functional response approach towards larval chironomids (feeding rates under different prey densities). Single predator maximum feeding rates were three-times higher at 24 °C compared to 18 °C overall, with potentially prey destabilising type II functional responses exhibited. However, pairs of gammarids exhibited intraspecific multiple predator effects that were in turn mediated by temperature regime, whereby synergisms were found at the lower temperature (i.e. positive non-trophic interactions) and antagonisms detected at the higher temperature (i.e. negative non-trophic interactions) under high prey densities. Accordingly, warming scenarios may worsen the impact of this invasive alien species, yet implications of temperature change are dependent on predator–predator interactions. Emergent effects between abiotic and biotic factors should be considered in ecological impact predictions across habitat types for invasive alien species.

David Lewis has long defended an analysis of counterfactuals in terms of comparative similarity of possible worlds. The purpose of this paper is to reevaluate Lewis's response to one of the oldest and most familiar objections to this proposal, the future similarity objection. w 1 is a duplicate of w a until shortly before t, at which time the laws of w a are violated in a small way: a few extra neurons fire in Nixon's brain and, as a result, he presses the button. The signal races from the button, the rocket is launched and nuclear Synthese (2006) 150: 57-67 Ó Springer 2006