Asymmetry, abstraction and autonomy: justifying coarse-graining in statistical mechanics

Whilst the fundamental laws of physics are time-reversal invariant, most macroscopic processes are irreversible. Given that the fundamental laws are taken to underpin all other processes, how can the fundamental time-symmetry be reconciled with the asymmetry manifest elsewhere? In statistical mechanics, progress can be made with this question; what I dub the Zwanzig-Zeh-Wallace framework can be used to construct the irreversible equations of statistical mechanics from the underlying microdynamics. Yet this framework uses coarse-graining, a procedure that has faced much criticism. I focus on two objections in the literature: claims that coarse-graining makes time-asymmetry (i) `illusory' and (ii) `anthropocentric'. I argue that these objections arise from an unsatisfactory justi�fication of coarse-graining prevalent in the literature, rather than from coarse-graining itself. This justification relies on the idea of measurement imprecision. By considering the role that abstraction and autonomy play, I provide an alternative justi�fication and o�er replies to the illusory and anthropocentric objections. Finally I consider the broader consequences of this alternative justi�fication: the connection to debates about inter-theoretic reduction and further, the implication that the time-asymmetry in statistical mechanics is weakly emergent

In Search of the Holy Grail: How to Reduce the Second Law of Thermodynamics

The search for the statistical mechanical underpinning of thermodynamic irreversibility has so far focussed on the spontaneous approach to equilibrium. But this is the search for the underpinning of what Brown and Uffink (2001) have dubbed the ‘minus first law’ of thermodynamics. In contrast, the second law tells us that certain interventions on equilibrium states render the initial state ‘irrecoverable’. In this paper, I discuss the unusual nature of processes in thermodynamics, and the type of irreversibility that the second law embodies. I then search for the microscopic underpinning or statistical mechanical ‘reductive basis’ of the second law of thermodynamics by taking a functionalist strategy. First, I outline the functional role of the thermodynamic entropy: for a thermally isolated system, the thermodynamic entropy is constant in quasi-static processes, but increasing in non-quasi-static processes. I then search for the statistical mechanical quantity that plays this role — rather than the role of the traditional ‘holy grail’ as described by Callender (1999). I argue that in statistical mechanics, the Gibbs entropy plays this role

Asymmetry, abstraction and autonomy: justifying coarse-graining in statistical mechanics

Whilst the fundamental laws of physics are time-reversal invariant, most macroscopic processes are irreversible. Given that the fundamental laws are taken to underpin all other processes, how can the fundamental time-symmetry be reconciled with the asymmetry manifest elsewhere? In statistical mechanics, progress can be made with this question; what I dub the Zwanzig-Zeh-Wallace framework can be used to construct the irreversible equations of statistical mechanics from the underlying microdynamics. Yet this framework uses coarse-graining, a procedure that has faced much criticism. I focus on two objections in the literature: claims that coarse-graining makes time-asymmetry (i) `illusory' and (ii) `anthropocentric'. I argue that these objections arise from an unsatisfactory justi�fication of coarse-graining prevalent in the literature, rather than from coarse-graining itself. This justification relies on the idea of measurement imprecision. By considering the role that abstraction and autonomy play, I provide an alternative justi�fication and o�er replies to the illusory and anthropocentric objections. Finally I consider the broader consequences of this alternative justi�fication: the connection to debates about inter-theoretic reduction and further, the implication that the time-asymmetry in statistical mechanics is weakly emergent

Landauer Defended: Reply to Norton

Ladyman et al (2007) proposed a model of the implementation of logical operations by physical processes in order to clarify the exact statement of Landauer's Principle, and then ordered a new proof of the latter based on the construction of a thermodynamic cycle, arguing that if Landauer's Principle were false it would be possible to harness a machine that violated it to produce a violation of the second law of thermodynamics. In a recent paper in this journal, John Norton (2011) directly challenges the consistency of that proof. In the present paper we defend the proof given by Ladyman et al against his critique. In particular, contrary to what Norton claims, we argue that the pro- cesses used in the proof cannot be used to construct a cycle that enacts erasure in a thermodynamically reversible way, and that he does not show that the processes used in the proof violate the Second Law of Thermodynamics

Landauer Defended: Reply to Norton

Ladyman et al (2007) proposed a model of the implementation of logical operations by physical processes in order to clarify the exact statement of Landauer's Principle, and then ordered a new proof of the latter based on the construction of a thermodynamic cycle, arguing that if Landauer's Principle were false it would be possible to harness a machine that violated it to produce a violation of the second law of thermodynamics. In a recent paper in this journal, John Norton (2011) directly challenges the consistency of that proof. In the present paper we defend the proof given by Ladyman et al against his critique. In particular, contrary to what Norton claims, we argue that the pro- cesses used in the proof cannot be used to construct a cycle that enacts erasure in a thermodynamically reversible way, and that he does not show that the processes used in the proof violate the Second Law of Thermodynamics

Is Thermodynamics Subjective?

Thermodynamics is an unusual theory. Prominent figures, including J. C. Maxwell and E. T. Jaynes, have suggested that thermodynamics is anthropocentric, and contemporary approaches label thermodynamics a “subjective theory.” Here, we evaluate the arguments for anthropocentrism but conclude that instead of pointing to an anthropocentric view, they point towards a resource-relative understanding of thermodynamics which can be shorn of the “subjective gloss.

Stars and steam engines: to what extent do thermodynamics and statistical mechanics apply to self-gravitating systems?

Foundational puzzles surround (Newtonian) gravitational thermal physics — a realm in which stars are treated as akin to molecules in a gas. Whether such an enterprise is successful and the domain of thermal physics extends beyond our terrestrial sphere is disputed. There are successes (such as the collisionless Boltzmann equation) and paradoxical features (such as the ‘gravothermal catastrophe’). Callender (2011) advocates reconciling the two sides of the dispute by taking a broader view of thermodynamics. Here I argue for an alternative position: if we are careful in distinguishing statistical mechanics and thermodynamics, then no reconciliation is required. Both sides can live in harmony because whilst statistical mechanics applies, thermodynamics does not. This state of affairs — the applicability of statistical mechanics with- out the emergence of thermodynamic behaviour — can be explained in terms of an infamous infinite idealisation: the thermodynamic limit