Modern physics has provided a range of motivations for holding time to be fundamentally undirected. But how does a temporally adirectional metaphysics, or ‘C-theory’ of time, fit with the time of experience? In this chapter, I look at what kind of problem human time poses for C-theories. First, I ask whether there is a ‘hard problem’ of human time: whether it is in principle impossible to have the kinds of experience we do in a temporally adirectional world. Second I consider (...) the ‘easy problem’: how specific directed aspects of our temporal experience are to be explained by C-theorists. This leads to a greater issue: is there such a thing as an experience of time direction at all to even be explained? I show how the kinds of experience we have that we typically associate with the idea of time being directed can be accommodated within a directionless picture of time. (shrink)

In what sense is the direction of time a matter of convention? In 'The Direction of Time', Hans Reichenbach makes brief reference to parallels between his views about the status of time’s direction and his conventionalism about geometry. In this article, I: (1) provide a conventionalist account of time direction motivated by a number of Reichenbach’s claims in the book; (2) show how forwards and backwards time can give equivalent descriptions of the world despite the former being the ‘natural’ direction (...) of time; and (3) argue that this offers an important middle-ground position between existing realist and antirealist accounts of the direction of time. (shrink)

It is often said that the world is explained by laws of nature together with initial conditions. But does that mean initial conditions don’t require further explanation? And does the explanatory role played by initial conditions entail or require that time has a preferred direction? This chapter looks at the use of the ‘initialness defence’ in physics, the idea that initial conditions are intrinsically special in that they don’t require further explanation, unlike the state of the world at other times. (...) Such defences commonly assume a primitive directionality of time to distinguish between initial and final conditions. Using the case study of the time-asymmetry of thermodynamics and the so-called ‘past hypothesis’ — the hypothesis that the early universe was in a state of very low entropy —, I outline and support a deflationary account of the initialness defence that does not pre- suppose a basic directionality of time, and argue that there is a relevant explanatory asymmetry between initial conditions and the state of systems at other times only if certain causal conditions are satisfied. Hence, the initialness defence is available to those who reject a fundamental direction of time. (shrink)

“The universe is expanding, not contracting.” Many statements of this form appear unambiguously true; after all, the discovery of the universe’s expansion is one of the great triumphs of empirical science. However, the statement is time-directed: the universe expands towards what we call the future; it contracts towards the past. If we deny that time has a direction, should we also deny that the universe is really expanding? This article draws together and discusses what I call ‘C-theories’ of time — (...) in short, philosophical positions that hold time lacks a direction — from different areas of the literature. I set out the various motivations, aims, and problems for C-theories, and outline different versions of antirealism about the direction of time. (shrink)

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 the definition of the entropy of the universe 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 global arrow of time.” In this paper we will argue that: (i) if certain conditions are satisfied, it is possible to define a global arrow of time for the universe as a whole, and (ii) the standard models of contemporary cosmology satisfy these conditions. (shrink)

I distinguish three views, a defence of any one of which would go some way towards vindicating the view that there is something objective about the passage of time: the view that the present moment is objectively distinguished; the view that time has an objective direction – that it is an objective matter which of two non-simultaneous events is the earlier and which the later; the view that there is something objectively dynamic, flux-like, or "flow-like" about time. I argue that (...) each of these views is not so much false as doubtfully coherent. In each case, it turns out to be hard to make sense of what the view could be, at least if it is to be non-trivial, and of use to a friend of objective passage. I conclude with some remarks about avenues that seem worth exploring in the philosophy of time, when we are done with trying to make sense of passage. (shrink)

Roughly speaking, classical statistical physics is the branch of theoretical physics that aims to account for the thermal behaviour of macroscopic bodies in terms of a classical mechanical model of their microscopic constituents, with the help of probabilistic assumptions. In the last century and a half, a fair number of approaches have been developed to meet this aim. This study of their foundations assesses their coherence and analyzes the motivations for their basic assumptions, and the interpretations of their central concepts. (...) The most outstanding foundational problems are the explanation of time-asymmetry in thermal behaviour, the relative autonomy of thermal phenomena from their microscopic underpinning, and the meaning of probability. A more or less historic survey is given of the work of Maxwell, Boltzmann and Gibbs in statistical physics, and the problems and objections to which their work gave rise. Next, we review some modern approaches to (i) equilibrium statistical mechanics, such as ergodic theory and the theory of the thermodynamic limit; and to (ii) non-equilibrium statistical mechanics as provided by Lanford's work on the Boltzmann equation, the so-called Bogolyubov-Born-Green-Kirkwood-Yvon approach, and stochastic approaches such as `coarse-graining' and the `open systems' approach. In all cases, we focus on the subtle interplay between probabilistic assumptions, dynamical assumptions, initial conditions and other ingredients used in these approaches. (shrink)

In this survey, we discuss and analyze foundational issues of the problem of time and its asymmetry from a unified standpoint. Our aim is to discuss concisely the current theories and underlying notions, including interdisciplinary aspects, such as the role of time and temporality in quantum and statistical physics, biology, and cosmology. We compare some sophisticated ideas and approaches for the treatment of the problem of time and its asymmetry by thoroughly considering various aspects of the second law of thermodynamics, (...) nonequilibrium entropy, entropy production, and irreversibility. The concept of irreversibility is discussed carefully and reanalyzed in this connection to clarify the concept of entropy production, which is a marked characteristic of irreversibility. The role of boundary conditions in the distinction between past and future is discussed with attention in this context. The paper also includes a synthesis of past and present research and a survey of methodology. It also analyzes some open questions in the field from a critical perspective. (shrink)

The present article proposes to re-examine the parity-of-reasoning or double-standard fallacy argument, which favours a time-symmetric Gold universe model over a cosmological arrow of time. There are two reasons for this re-examination. One is empirical: the recent discovery of an expanding and accelerating universe questions the symmetry assumption of the Gold universe on empirical grounds. The other is theoretical: the argument from t-symmetry fails to take into account some important aspects of the topology of phase space and recently developed typicality (...) arguments. If the parity-of-reasoning argument, which depends on the t-symmetry of probability, is reconsidered in terms of the topology of phase space and typicality arguments, the double-standard fallacy argument loses much of its appeal. The Gold universe model itself suffers from unexplained dynamic asymmetries. The upshot of this article is that the Gold universe model is implausible or far less plausible than asymmetric models. (shrink)

This paper investigates what the source of time-asymmetry is in thermodynamics, and comments on the question whether a time-symmetric formulation of the Second Law is possible.

The purpose of this paper is twofold: a) to explore the compatibility of Minkowski’s space-time representation of the Special theory of relativity with a dynamic conception of space-time; b) to locate its roots in invariant features - like entropic relations - of the propagation of signals in space-time. From its very beginning Minkowski’s four-dimensional space-time was associated with a static view of reality, e.g. a block universe. Einstein added his influential voice to this conception when he wrote: ‘From a “happening” (...) in three-dimensional space, physics becomes (…) an “existence” in the four-dimensional “world”.’ (Einstein, Relativity 1920, 122) Yet it is by no means clear that Minkowski himself was a believer in the block universe. In his 1908 Cologne lecture on ‘Space and Time’ he speaks of a four-dimensional physics but concedes that a ‘necessary’ time order can be established at every world point. Although the conception of the block universe has gained much currency, an alternative view has been in circulation since the 1910s according to which the trajectories of particles constitute histories in space-time. (Robb 1914, Cunningham 1915, Carathéodorys 1924, Schlick 1917, Reichenbach 1924). (shrink)