**Author**: Giovanni Gallavotti

**Title**
* Irreversibility time scale*:
(version 1.1: 26 Mar 2006 )

**Abstract:** We introduce the entropy creation rate for a
system interacting with thermostats ({\it i.e.}, in the usual language, for a
subsystem subject to internal conservative forces interacting with the
``outside'' thermostats via conservative forces) and prove a fluctuation
theorem for it. As an application a time scale is introduced, to be interpreted
as the time over which irreversibility becomes manifest in a process leading
from an initial to a final stationary state of a mechanical system in a general
nonequilibrium context. The time scale is evaluated in a few examples,
including the classical Joule-Thompson process (gas expansion in a vacuum).

**Key words: **
Nonequilibrium Themodynamics, Statistical mechanics, Chaos,
Fluctuation Theorem, Entropy, Irreversibility, Thermostats

**PACS: **
47.52.+j, 05.45.-a, 05.70.Ln, 05.20.-y

Giovanni Gallavotti

Fisica, Universita' di Roma 1

P.le Moro 2

00185 Roma, Italia

tel +39-06-4991-4370

fax +39-06-4957697

em: giovanni.gallavotti@roma1.infn.it

http://ipparco.roma1.infn.it