“Gee Thug… What have you been up to!?!”

What follows is an email I drafted for a friend of mine who wanted to better understand entropy. For whatever reason, exactly what I’m not sure, she said she hoped the 2nd law of thermo would support her anti-creationist position in a debate with her sci-fi authoring pop.

******,

Whoa. You and your dad have deep convos. My dad and I restrict our topics of discussion to cars, trucks and sometimes planes. Please excuse the tone of the lecture that follows. It is as much for me (as practice for explaining physiology to nursing students) as it is for you:

Entropy is the tendency of all physical systems, over time, to assume configurations that maximize the number of different possible states that they may assume at a given energy level. For a particular energy, the number of available configuration states is greatest when that system is most “disordered” as popular science authors rightly call it. (Yeah that definition is definitely opaque – let me try to explain. By the way, “Energy”, basically, is the potential to perform “work” (the amount of force exerted over a given amount of time) or generate heat; both heat and work are forms of energy). Examples of ordered vs. disordered states are respectively: an intact teacup (ordered state) before it shatters (disordered state of equivalent energy), a cold glass of water in a hot room that when left by itself in the heat, warms up to room temperature, even a living person before that person dies is an example of an ordered configuration state and the corresponding disordered state that is inevitable with time. In our world, as time passes, entropy drives structures to erode, forces objects of initially different temperatures, to reach an equivalent temperature after they are brought into thermal contact, what causes certain elements to spontaneously decay, and what ensures that different gases, kept in the same container, will always mix.

Entropy increases as the number of available states increase. Interestingly though, as the number of available states, hence entropy, increases, the likelihood that the system will return to a configuration of fewer available states diminishes exponentially. This is why entropy always increases rather than decreases; why we never observe sand spontaneously organizing itself into a ceramic teacup, why one never finds water, after having been left in a room by itself for any length of time, to have heated up to a higher temperature than the room and why dead bodies never form themselves back into living people (at least we don’t think so, maybe they will for Armageddon). Some physicists believe, I’m not sure if what follows is an accepted theory to the origins of entropy, that entropy stems from the fact that our universe is presently expanding; that is, ALL galaxies are ALL moving away from each other.

Boltzmann, using Einstein’s principle of quantum states, devised the concept of entropy to characterize how microscopic states of gases determine their macroscopic properties, such as pressure, temperature, volume etc. The observed tendency for the entropy of physical systems to always increase is the second law of thermodynamics. Entropy drives many other processes in physical systems, above are just some common examples that I borrowed.

The second law of thermo is based from a science called Statistical Mechanics (the bane of physics students everywhere) which simply finds that it is extremely statistically unlikely that a given system (i.e. a contained gas) will spontaneously assume a higher energy state (different particles will confine themselves to separate spatial locations in the container and not mix) at the macroscopic level. Statistical mechanics, like quantum mechanics, describes applicable phenomena (i.e. behavior of gasses, contraction/expansion of solids with temperature, states of fluids etc.) in terms of quantum states. Quantum states refer to the discrete, as opposed to continuous, configurations that constituents of the system are allowed to occupy; for example, electrons can occupy a given orbital in an atom or it can’t, an electron cannot partially occupy an orbital and partially occupy another. An example of a quantum state in statistical mechanics would be the ways in which poly-atomic gas particles are able to vibrate, there are only a finite amount of ways depending upon the number of constituent sub-particles and the geometry of how they bond together. This concept of “quantum states” to describe microscopic phenomena has only been around for about a century and a half.

Quantum Mechanics, like Statistical Mechanics, explains the behavior of phenomena statistically. Quantum phenomena, like everything else physical in our universe, must obey the second law of thermodynamics. However, Quantum mechanics, because of its statistical framework can account for some strange behaviors that can seem to contradict the 2nd law of thermo based on our expectations of everyday phenomena, but actually do not. One of those is the phenomenon of “particle tunneling” where particles can traverse barriers that we would intuitively expect to completely contain them. According to quantum mechanics, it’s a statistical possibility that if a person throws a baseball at a steel plate it can “tunnel” through it because the baseball’s absolute location and absolute momentum cannot both be known at the same time. We don’t observe this because tunneling is extremely improbable for large particles, it’s less improbable, though, for small particles and we would not have semi-conductors, hence, any modern electronics if tunneling didn’t actually happen.

Here’s a tasty tidbit to talk about with your pop that relates both the 2nd law of thermo and quantum mechanics: tell him that protons, the building blocks of all stable matter in our world, are themselves, believed to be unstable. That is, that they are likely to spontaneously break down into smaller subatomic particles after a long enough amount of time passes. Now, granted this length of time is much greater than the longevity of our universe if it is to end in the “cosmic crunch” so we would really not have anything to worry about if we humans can manage to live that long. We’d happily be fused together like all the rest of our matter family before we’d fall to pieces due to failing proton integrity.

Happy father-daughter bonding!!!