Online research in philosophy

This essay is a philosophical evaluation of some of the findings of Wald and Penrose in which they claim to have supported an arrow (or the irreversibility) of time in quantum gravity. First, the notion of lawlike irreversibility (or anisotropy) of time is spelled out, then the general situation in quantum mechanics is briefly discussed. Finally, the findings in quantum gravity are evaluated against such a background. My conclusion is that the arrow of time found in quantum gravity is at best de facto (nonlawlike).

The reason for the arrow of time in electromagnetic radiation is explicated.

David Lewis (1979) has argued that according to his possible worlds analysis of counterfactuals, “backtracking” counterfactuals of the form “If event A were to happen at tA, then event B would happen at tB” where tB precedes tA, are usually false if B does not actually happen at tB. On the other..

Scientific cosmology is an empirical discipline whose objects of study are the large-scale properties of the universe. In this context, it is usual to call the direction of the expansion of the universe the "cosmological arrow of time". However, there is no reason for privileging the ‘radius’ of the universe for defining the arrow of time over other geometrical properties of the space-time. Traditional discussions about the arrow of time in general involve the concept of entropy. In the cosmological context, the direction past-to-future is usually related to the direction of the gradient of the entropy function of the universe. But entropy is a thermodynamic magnitude that is typically associated with subsystems of the universe: the entropy of the universe as a whole is a very controversial matter. Moreover, thermodynamics is a phenomenological theory. Geometrical properties of space-time provide a more fundamental and less controversial way of defining an arrow of time for the universe as a whole. We will call the arrow defined only on the basis of the geometrical properties of space-time, independently of any entropic considerations, the "cosmological arrow of time". In this paper we will argue that: (i) it is possible to define a cosmological arrow of time for the universe as a whole, if certain conditions are satisfied, and (ii) the standard models of contemporary cosmology satisfy these conditions.

Recently Stephen Barker has raised stimulating objections to the thesis that, roughly speaking, if two events stand in a relation of counterfactual dependence, they stand in a causal relation. As Ned Hall says, however, this thesis constitutes the strongest part of the counterfactual analysis of causation. Therefore, if successful, Barker’s objections will undermine the cornerstone of the counterfactual analysis of causation, and hence give us compelling reasons to reject the counterfactual analysis of causation. I will argue, however, that they do not withstand scrutiny.

Linda Zagzebski has recently argued that there is a conflict between a common view of the asymmetry of time and various other metaphysical hypotheses. She identifies conflicts in the case of the modal arrow of time and in the case of the causal arrow of time. In the case of the modal arrow I argue that on one view there is no conflict and that on another the principle should be abandoned that there are entailments between propositions about the past and the future. In the case of the causal arrow I argue that the conflict can be avoided by the adoption of a suitable closure principle.

Linda Zagzebski has recently argued that there is a conflict between a common view of the asymmetry of time and various other metaphysical hypotheses. She identifies conflicts in the case of the modal arrow of time and in the case of the causal arrow of time. In the case of the modal arrow I argue that on one view there is no conflict and that on another the principle should be abandoned that there are entailments between propositions about the past and the future. In the case of the causal arrow I argue that the conflict can be avoided by the adoption of a suitable closure principle.

The thesis that a temporal asymmetry of counterfactual dependence characterizes our world plays a central role in Lewis’s philosophy, as. among other things, it underpins one of Lewis most renowned theses—that causation can be analyzed in terms of counterfactual dependence. To maintain that a temporal asymmetry of counterfactual dependence characterizes our world, Lewis committed himself to two other theses. The first is that the closest possible worlds at which the antecedent of a counterfactual conditional is true is one in which a small miracle occurs—i.e. one whose laws differ from the actual laws in a small spatiotemporal region. The second is that our world is characterized by a temporal asymmetry of miracles. In this paper, I will argue, first, that the latter thesis is either false or incompatible with the picture of the relations among temporal asymmetries endorsed by Lewis and, second, that former thesis conflicts with some of the intuitions which seem to guide us when engaging in counterfactual reasoning. If there is any fact of the matter as to which possible worlds in which the antecedent of a counterfactual conditional is true are closest to the actual world, these are not worlds at which a small miracle occurs.

A conclusion drawn after a conference devoted (in 1995) to the “arrow of time” was the following: “Indeed, it seems not a very great exaggeration to say that the main problem with “the problem of the direction of time” is to figure out exactly what the problem is supposed to be !” What does that mean? That more than 130 years after the work of Ludwig Boltzmann on the interpretation of irreversibility of physical phenomena, and that one century after Einstein’s formulation of Special Relativity, we are still not sure what we mean when we talk of “time” or “arrow of time”. We shall try to show that one source of this difficulty is our tendency to confuse, at least verbally, time and becoming, i.e. the course of time and the arrow of time, two concepts that the formalisms of modern physics are careful to distinguish.

In “Counterfactual Dependence and Time’s Arrow,” David Lewis defends an analysis of counterfactuals intended to yield the asymmetry of counterfactual dependence: that later affairs depend counterfactually on earlier ones, and not the other way around. I argue that careful attention to the dynamical properties of thermodynamically irreversible processes shows that in many ordinary cases, Lewis’s analysis fails to yield this asymmetry. Furthermore, the analysis fails in an instructive way: one that teaches us something about the connection between the asymmetry of overdetermination and the asymmetry of entropy.