The Spin-Echo Experiments and the Second Law of Thermodynamics

Ping-Xing, Chen, Jianming +5 more

Fernando G. S. L. Brandão, Martin Bodo Plenio

Peter Mark Ainsworth

Fernanda Samaniego Bañuelos

In the so-called "Spin-Echo Experiments" the behaviour of a spin's system seems to violate the second law of thermodynamics. For this reason the "Spin-Echo Experiments" are considered of particular interest for the Foundations of Physics. Interventionists have provided a classical explanation (Blatt, 1959; Ridderbos & Redhead, 1998) and a quantum-based explanation (Hemmo & Shenker, 2005) of these experiments. Here both interventionist explanations are assessed by means of the Manipulability Theory of Causal Explanation (Woodward, 2003). It is argued that interventionism would gain explanatory depth by providing functional relations and predicting relaxation times.

Charis Anastopoulos, Ntina Savvidou

Spin-echo experiments are often said to constitute an instant of antithermodynamic behavior in a concrete physical system that violates the second law of thermodynamics. We argue that a proper thermodynamic treatment of the effect should take into account the correlations between the spin and the translational degrees of freedom of the molecules. To this end, we construct an entropy functional using Boltzmann macrostates that incorporate both spin and translational degrees of freedom. With this definition there is nothing special in the thermodynamics of spin echoes: dephasing corresponds to Hamiltonian evolution and leaves the entropy unchanged; dissipation increases the entropy. In particular, there is no phase of entropy decrease in the echo. We also discuss the definition of macrostates from the underlying quantum theory and we show that the decay of net magnetization provides a faithful measure of entropy change.