What is entropy?
Entropy is the average number of yes-or-no questions it would take to say exactly which arrangement something is in. A fair coin is one bit, one question. A fair eight-sided die is three. A coin weighted nine to one comes to under half a bit, since you can usually guess. Entropy is a property of a description, of somebody's odds over the possibilities, and different odds give a different number for the same object. The same quantity turns up on five instruments built by people who did not know they were measuring one thing. An engine reads it as heat divided by temperature, a gas as Boltzmann's count of arrangements, a memory as Shannon's count of questions, a black hole as the area of its horizon, and a public record as what a settled disagreement throws away.
Also in Chapter 23: Why Does Writing Something Down Cost Heat?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 16: Why Does Time Run, and Only One Way?watch a universe make its own particles