I feel there is little consensus in the physics community about the origins of the arrow of time. This would suggest that we really know little about the nature of time. So most of them merely display their points of view and interpretations but fall short of providing proofs.

The Wikipedia article on the arrow of time already mentions a couple of different conceptions of the arrow of time, It is not always clear which one is being talked about, and there are at least a couple of different dilemmas, as none of them is perfectly understood.

In this situation, the best I can do is to express my personal views.

So I think Loschmidt's paradox (for the thermodynamic arrow of time) can be resolved by purely statistical arguments. Referring to the improbability of spontaneous entropy reduction, I think the thermodynamic arrow is explained well enough by the fact the low entropy state of the universe (which remains unresolved).

In quantum mechanics, there is a different arrow of time, defined by the collapse of the wave function. But in recent years, some researchers have arrived at a quite good understanding what causes the impression of the collapse of the wave function in a macroscopic world, using quantum thermodynamics. So basically you split your quantum world into the small system you consider and the rest which is the reservoir. Then you analyze the time evolution of the projection of the wave function of the small system to quantum states of the reservoir. And you get the collapse of the wavefunction which happens on an extremely short time scale, related to the size of the small system an the coupling between the two. The effect is called disentanglement. It turns out that it is notoriously hard to avoid disentanglement. This fact is being experienced by the folks trying to build a quantum computer, for which you need to keep your qbits entangled.

So the twist to the story is, that in this particular view of the affairs, Statistical arguments and concepts from classical thermodynamics lead to the explanation of the arrow of time in quantum mechanics. Furthermore it tells us something about the relation between quantum mechanics and thermodynamics.

This, on a first read of the Simons Foundation article you are citing, seems to strongly contradict the findings of Lloyd, who claims, entanglement would emerge in accord with thermal equilibrium. Further he claims that entanglement is what **causes** equilibration. Yet, the effect of disentanglement described above happen on vastly different time scales and scale completely differently with the number of particles. So Lloyd's view is greatly incompatible with mine.

In contrast, the paper by Maccone seems to highlight a fairly interesting fact about the consequences of quantum mechanics. But I think his view is quite consistent with what others say who are being cited in that same article. The way how Maccone presents the claims of the other papers grossly overexaggerates the importance of his own work. (But I think there is no serious scientist who would not do that.) I do not think Maccone does explain thermodynamics arrow of time, rather he already uses it in the step with the wave function collapse. So it would be evident that he gets it back.

As a result, I would not be concerned too much about those claims. Time remains a mystery for the time being, while Loschmidt's paradox is not a paradox at all if you take into account probabilities, I think.

This post imported from StackExchange Physics at 2014-05-25 06:50 (UCT), posted by SE-user ilmiacs