The Laws of Thermodynamics

 

1. Energy is neither created nor destroyed. (The Law of Conservation of Energy)
2. Entropy never decreases.

The First Law: Energy is neither created nor destroyed

Energy, in case you've forgotten, is the ability to do work. Work is defined as moving something. So wood has energy, since I can burn the wood and use the heat to boil water and drive a steam engine which lifts something. The wood provided the energy that moves the system.

The First Law can be stated in a variety of ways; I picked one that's simple and intuitive. It depends on your "system," though, in an obvious way. If your system is smaller than the universe, you may have the appearance of energy being created or destroyed. Imagine a wind-up toy that you see moving. How did it get the energy to move? Was energy created? Of course not. Something outside of the wind-up toy system - a person - wound it up ("performed work on it") and let it go.

The First Law of Thermodynamics tends to come up in discussions of Evocation spells. Where does the heat of a fireball come from? When a mage creates cold, where is the extra heat dumped? The standard GM answer is that the needed heat is taken from (or dumped into) the surrounding area, but over a large enough area that the temperature change isn't noticeable. So when the mage casts a fireball, the lands for a three mile radius around him experience a 0.1 degree cooling effect.

What if your players actually want you to peg down the temperature of the fireball, its energy, the temperature drop in the surrounding area and over what radius? Tell them that they just don't know. They don't have the equipment to measure both the interior temperature of the fireball and the tiny change in temperature ten miles away. They could, conceivably, come up with a "Detect Temperature" spell, but I have a hard time imagining a PC who really cared that much.

Another interesting implication of the First Law is that all the energy that goes into creating spell effects has to come from somewhere. What is that energy source? And is it renewable? The AD&D 2e "Dark Sun" setting was based around the idea that magical energy could be drained from living plants. Mages destroyed their ecology exploiting this non-renewable resource.

If you don't want your mages to run out of energy, then what? Maybe mana (or the Weave, or ley lines, or whatever you like to call your magical energy source) is like solar power: limited, but with a limit so large it might as well be infinite. After all, one day the sun will stop shining. It's just not likely that we'll still be around when that happens.

The Second Law: Entropy never decreases.

Entropy is a sort of fuzzy idea that represents "disorder" in the universe. Energy can't be destroyed, but it can be "lost" to entropy - it becomes "waste heat" that can't be harnessed to do any useful work anymore. When I burned the wood in the example above, only some of the heat was transferred to the boiling water. Some of it drifted off with the smoke and was lost to entropy. If I could transfer all of the wood's energy to the water, and all of the steam's energy to the engine, and all of the engine's energy to the thing I'm moving, I'd have an ideal system with no losses to entropy. This is the absolute best I can do; I can never reverse entropy.

The other classic entropy example involves chocolate milk. To make chocolate milk, you add chocolate syrup into a glass of milk. The syrup sits in a lump at the bottom of the glass until you stir it up. But once it's stirred, no amount of stirring or not stirring will cause the syrup to re-congeal at the bottom of the glass. Once the particles of chocolate syrup are disturbed from their ordered lump at the bottom of the glass and scattered randomly throughout the milk, they won't go back. That's entropy never decreasing.

The Second Law of Thermodynamics is usually invoked in discussions about the nature of magic. I have played with a GM who declared that magic was a "zero-entropy phenomenom" - that is, an ideal system with no losses. This still doesn't explain how magic works. It says you can summon the heat for your fireball with no energy lost to entropy - but it doesn't say how you summon that heat, or focus it, or release it. It's an interesting idea, but it doesn't really explain anything about magic. But it does guarantee that you'll never run out of magical energy. If you're not losing energy to entropy, then it stays in the system and can eventually be converted to a usable form later.

The Second Law, by the way, implies the "heat death" of the universe - that point in the far future when all the stars burn out and all matter hovers at just above absolute zero. All of the energy in the universe is uniformly and thinly distributed everywhere. If magic is "zero entropy," then it isn't speeding the world toward this eventuality. But what if magic is a high entropy phenomenon? Bending and breaking all those physical laws might result in a lot of energy being lost. Does anyone know? Does anyone care?

Entropy makes a great bad guy. Diane Duane's "Book of Night with Moon" deals with some of these issues; in it, wizards fight the very heat death of the universe itself.

Law and Chaos

While entropy and chaos can be said to be close cousins, the reverse can't really be said about energy and law without some creative stretching. Entropy is defined as a measure of randomness in a system, at a molecular level. It's a fair synonym for chaos. Energy is just the ability to do work. One could do useful, organizing work, or one could do chaotic, destructive work. And even if "lawful" work is chosen, the very act of working will, in any nonideal case, result in an increase in entropy!

How is that? Let us say there is a bookshelf crammed full of books. I take several hours and put the books in alphabetical order. I congratulate myself on increasing order in the world and decreasing entropy.

Unfortunately, as I moved and shifted the books, I converted my lunch into muscular motion. As I did that, I generated extra body heat - waste heat. That energy flitted away into the heat sink of entropy. And the harder I worked, the more waste heat I generated!

Depressing? Well, as it's been said about entropy: You can't win, you can't draw, and you can't even quit the game.

The Positive and Negative Energy Planes

These are elements of the D&D cosmology that lend a certain symmetry to the Inner Planes. The Positive Energy Plane is a sort of source of life energy, while the Negative Energy Plane is some sort of anti-energy that animates the undead and drains life away from normal creatures.

Now, while there is matter and anti-matter, no one's ever found an anti-energy. The Negative Energy Plane doesn't make a whole lot of sense from a physical standpoint defined that way. But you could make a fairly good argument for the Negative Plane to be the source of entropy in the world.

Assume for the moment that undead are actually animated by regular magical energy. (There are, after all, spells for creating them). Their effects - level draining, ability draining, life draining - could reasonably be taken as a manifestation of decay and disorder. Imagine, if you will, a lost Strength point ripped out and scattered into the universe like chocolate syrup.

Your Prime Material Planes, then, are physically composed of Fire, Air, Earth and Water. Life is started by Positive Energy and ends because of the influence of Negative Energy. And as long as the Positive Energy Plane keeps creating energy (in total violation of normal physics), the world will never end - at least, not from the heat death of the universe.