Why are action and entropy unrelated?

[Suekdccia]

Although I've read many papers that propose a relation between action and entropy, I've been told that there is no generally accepted relation in physics.

But how/why are these concepts unrelated?

What about nobel laureate Frank Wilczek? He proposes that entropy and action are closely related. Is he using some framework not used in mainstream physics? (He mentions this here, in page 17: arxiv.org/abs/1503.07735). Also, usually physics theories have some kind of action. There are informational-based models in physics like the holographic principle (en.wikipedia.org/wiki/Holographic_principle) which proposes that the information (entropy) of a universe in a bulk can be encoded in its boundary.

If entropy and action are unrelated, how can the holographic principle that the information (entropy) from a theory (and thus, its action) can be encoded in a boundary?

Also, I've read that action has dimensions of [energy]⋅[time] or [momentum]⋅[length] and its SI unit is the Joule-second. This suggest that energy and action are related. If so, since energy is also related with entropy, wouldn't that mean that after all, action and entropy are also related?

 

[tkyoung75]

Entropy is a thermodynamic property best introduced with the Clausius inequality. Clausius also provides one of the statements that describes the second law of thermodynamics. There is no one single statement for the second law of thermodynamics. The second law is born of whose observation that a perfectly efficient process (perpetual motion) cannot be achieved.

Action, it appears, is an abstract quantity used in theoretical physics to describe the overall motion of a system (britannica.com/science/action-physics).

The reference paper (Wilczek, 2015) shows that theoretical physicists have realized a strong connection between these two independently developed parameters, and that this connection may be a motivator for the reinterpretation of the laws of physics from "action principles" to "statements of information".

A relationship implies that changing one parameter will affect a change in the other, and its typically expressed as a mathematical formula. Rather, the paper describes an identity, "in that framework the expectation value of the Euclideanized action essentially is the entropy", that is not inherently recognised in the current definition of entropy:

(Moran and Shapiro)

To be clear, one could remain quite functional, yet ignorant of this identity in the current (state of the art) application of theoretical physics (at least at many levels). However, over time, the presentation of the laws of physics may change to accommodate the new learnings, as required to further our understanding of the universe, and improve the definition of physical models.

 

[PeterDonis]

What about nobel laureate Frank Wilczek? He proposes that entropy and action are closely related.

In a paper which clearly states that it's speculation. Which means that, even though it's written by a Nobel laureate, it's out of bounds for discussion here, since it's admittedly not mainstream physics, just one physicist's speculation.

Thread closed.