The Heat Death of the Universe

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Time's Arrow. The previous post is essential to understanding this post.

In most of the discussion of nonsense in this series, the nonsense stems from a poor understanding of physics.  This post introduces some nonsense that must be taken seriously.  Perhaps, this nonsense, also stems ultimately from a poor understanding of physics.  The people with the poor understanding this time, however, are some of the most brilliant minds in physics.

The School-Book Story

This discussion starts with the school-book story of the heat death of the universe.  By calling it the "school-book" story I do not mean to pooh-pooh it too much.  In fact, it is most likely the correct story.  Much of this post, however, will focus on caveats and complications to the story as it is usually told.

In thermodynamics, the universe is defined as the system and its surroundings.  We have seen that the second law requires that for any change the total entropy of the system and the surroundings must increase or stay the same.  As time goes by, therefore, the entropy of the universe increases.

Entropy and Information Theory

This post is part of a series,Nonsense and the Second Law of Thermodynamics The previous post is entitled  Partition Functions.

The posts in this series are primarily about the second law of thermodynamics, the concept of entropy, and the use and abuse of these ideas.  I would be remiss, however, not to mention information theory and the role that entropy plays.  This post is not intended to be a comprehensive introduction to information theory.  Readers especially  interested in this topic will want to read other sources in addition to this post.

Fluctuations

This post is part of a series,Nonsense and the Second Law of Thermodynamics The previous post is entitled Entropy and Statistical Dynamics.

The second law of thermodynamics works because of the statistics of very large numbers. Consider a bouncing ball: as it bounces, it dissipates heat and eventually does not bounce as high.  

Entropy and Statistical Thermodynamics

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Second Law and Swamp Coolers.

A previous post discusses the macroscopic thermodynamic definition of entropy, but there is another, statistical way of describing entropy.  Consider an isolated macroscopic system of interacting molecules.  Without knowing much about what is going on with the individual molecules, it is possible to measure macroscopic thermodynamic properties such as the pressure, the temperature etc.

                                                                                         (Figure Source)

Consider that the system is isolated; so that the total energy of the entire system of molecules is a constant.  Energy is free to move from one molecule to another, and each molecule has multiple electronic, vibrational, rotational, and translational energy states that it could be in.  There are many distinguishable ways that the system could be arranged to achieve the this energy.