I thought the second law of thermodynamics was already a tautology
The article published on PRL recently reads (abstract):
The arrow-of-time dilemma states that the laws of physics are invariant for time inversion, whereas the familiar phenomena we see everyday are not (i.e., entropy increases). I show that, within a quantum mechanical framework, all phenomena which leave a trail of information behind (and hence can be studied by physics) are those where entropy necessarily increases or remains constant. All phenomena where the entropy decreases must not leave any information of their having happened. This situation is completely indistinguishable from their not having happened at all. In the light of this observation, the second law of thermodynamics is reduced to a mere tautology: physics cannot study those processes where entropy has decreased, even if they were commonplace.
I am just not seeing the paradox or brilliant new insight here, at least based on the abstract (I’ll read the full paper more carefully later). I thought the second law of thermodynamics was already a tautology. In my favorite formulation (i.e. the stat mech formulation) the law reads:
What is most likely to happen happens most of the time.
i.e. The macrostate containing the most number of microstates is the one we observe macroscopically—under the assumption of each microstates (all of equal energy) having the same probability of happening, this is self-evidently true.
So, what’s new?