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.

Partition Functions

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

In previous posts it was shown that entropy is related to the the number of ways that a system can arrange itself subject to constraints such as constant energy.

The previous post on fluctuations showed that for very large numbers that fluctuation from the most probable distribution, are insignificant.  Most of the distribution is contained within the square root of N of the most probable result.

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.

What the Second Law Does Not Say

This post is part of a series, Nonsense and the Second Law of Thermodynamics.

The Second Law does not say it is impossible for heat to be transferred from a cold body to a hot body.  The second law does not say that "disorder" must increase on the earth or anywhere else.  Life is not a counter-example to the second law; life is an example of the second law in action.

One has to be very careful about applying statistical results to a single molecule or a few molecules and remembering that increasing entropy applies to irreversible changes, not reversible ones. The second law says nothing about disorder. The second law does not prevent evaporative coolers from operating.

The second law does not contradict radiative transfer theory or global warming. The second law does not contradict conservation of energy.  In applying the second law to  cosmology, one should tread cautiously.

Nonsense and the Second Law of Thermodynamics

Introduction

The Second Law of Thermodynamics is, perhaps, the most abused physical law of all time. It may be rivaled for that distinction by the Uncertainty Principle, Relativity, and Hawking Radiation, but I think the Second Law probably wins the contest.

There is a plethora of nonsense disseminated on the web and elsewhere that misrepresents what the law actually says. This series is an attempt to curb some of that nonsense.  Along the way, I hope to make some sense of what the second law of thermodynamics actually does say, as well as addressing some of the nonsense that people believe about it.

How To Convert To and From Wavenumbers

The question of how to convert from one set of units to another comes up from time-to-time, and I think it might be helpful to have a few short posts that simply address unit conversion.  This post addresses conversion to and from wavenumbers (cm^-1) (also called reciprocal centimeters, inverse centimeters or  Kaisers). A previous post What is Infrared Radiation (IR)? addresses the concepts behind this unit.  The unit is proportional to frequency, and can be considered a unit of frequency or of energy.

Molecules and Radiation III: Vibration, Dipoles, and Ro-Vibrational Spectra

This post is part of a primer on infrared spectroscopy and global warming. The previous post looked at the vibrational modes of several molecules including HCl and several molecules of atmospheric interest. This post discusses how these modes relate to infrared absorption and uses HCl as an example.

Molecules and Radiation II: Molecular Vibration, Rotation, and Translation

This post is part of a primer on infrared spectroscopy and global warming. The previous post  starts the process of looking at the interaction between infrared radiation and molecules and discusses the degrees of freedom of molecules and the Born-Oppenheimer approximation.  The result of the previous post is that for the purposes of IR spectroscopy, one can focus on the motion of the atomic nuclei and separate them from the electronic degrees of freedom of a molecule.

Figure Source

There are 3N nuclear degrees of freedom for a molecule that has N nuclei.  For the HCl molecule that means there are 6 degrees of freedom.

Molecules and Radiation I: Molecular Structure

This post is part of a primer on infrared spectroscopy and global warming. The previous post  starts the process of looking at the interaction between infrared radiation and matter and discusses black-bodies and relationship between temperature and infrared radiation.  This post goes further and looks at how gas phase molecules interact with infrared radiation.

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For a molecule to absorb radiation, several conditions must hold.  First, energy must be conserved: if the molecule absorbs energy from a photon, the molecule must be able to store that energy in some manner. 

Infrared Radiation, Black-bodies, and Temperature

This post is part of a primer on infrared spectroscopy and global warming. The previous post discusses the nature of  infrared radiation. This post starts the process of looking at the interaction between infrared radiation and matter and discusses black-bodies and the relationship between temperature and infrared radiation.

 

Figure source.

A Primer on Infrared Spectroscopy and Global Warming

Introduction

This post and the posts linked to it through section headers together form a primer on infrared spectroscopy and how it relates to global warming.  The purpose of the primer is not be to convince skeptics that global warming is real, but rather to explain some of the terms and issues being discussed in climate science.  My goal is not to write a super technical explanation of infrared spectroscopy.  That's been done so many times that it is hardly worth doing again.

Rather, my intent is to write something that clearly describes infrared spectroscopy and relates it to global warming that tries to explain some fairly technical concepts in reasonably plain language.  As such there is an inevitable loss of fidelity about some of the fine points of infrared spectroscopy.  Anyone interested in such detail can follow some of the sources that I will provide.  At some point one has to compromise between accessibility and technical accuracy.  I hope that the choices made in this primer are helpful to some people trying to understand this topic.  This post is an outline of the topics addressed in the linked entries.

What is Infrared Radiation (IR)?

Figure source

This first post starts with the basics.  It discusses the electromagnetic spectrum and where infrared radiation fits into it.  It discusses waves and their measures.  It introduces the idea of electric dipole radiation.  It discusses the units of radiation wavelength, frequency. It ends by discussing photons and energy quantization.