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. (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)

The problem of reconciling a reversible micro-dynamics with the second law of thermodynamics has been a scientific and conceptual challenge for centuries and it continues to animate heated debate even today. In my opinion, one key point lays in the interrelation between the physical, the mathematical and the philosophical aspects of the problem. In many treatments those domains of knowledge dangerously mix, generating confusion and misunderstanding. In this short work I will show how disentangling these three domains for the problem (...) at hand will give a better understanding of the enigma of irreversibility and opens up possibility for future research. (shrink)

From time to time, in the scientific literature or in science popularization articles, appears the question: Why do we remember the past but we can’t remember the future? This question, of course, finds its legitimacy in the time symmetry of the equations of physics. However, it is not always answered clearly, and there are still debates about the best way to explain this paradox. In the present article, I analyze the remembering process in the perspective of the entropic arrow of (...) time to grasp the possibility of memories of the future, and to understand what that would actually mean. (shrink)

A comparison is made of the traditional Loschmidt and Zermelo objections to Boltzmann's H-theorem, and its simplified variant in the Ehrenfests' 1912 wind-tree model. The little-cited 1896 objection of Zermelo is also analysed. Significant differences between the objections are highlighted, and several old and modern misconceptions concerning both them and the H-theorem are clarified. We give particular emphasis to the radical nature of Poincare's and Zermelo's attack, and the importance of the shift in Boltzmann's thinking in response to the objections (...) as a whole. (shrink)