Irreversibility is one of the most intriguing concepts in physics. While microscopic physical laws are perfectly reversible, macroscopic average behavior (and our daily experience) has a preferred direction of time. How can irreversibility be a consequence of reversible laws, especially Schrödinger’s equation?
According to Thermodynamics, entropy of the Universe never decreases. Although this is a powerful argument in some cases, it can be generalized to stronger statements about the behaviour of systems away from equilibrium. At this point, a connection is made with Information Theory, where there is also a concept with the name ‘entropy’, with a wider meaning.
The discussion is applied to a recent experiment with Nuclear Magnetic Resonance, in which the spin 1/2 of an atomic nucles is used as a thermodynamics system. We analyse the concepts of entropy production and irreversibility in this microscopic system in a completely quantum context.
Reference: Batalhão et. al., “Irreversibility and the Arrow of Time in a Quenched Quantum System”, Physical Review Letters 115, 190601.
