A lot is happening on tonight episode of the CW’s The Flash. One development that will send the fans shivering is the introduction of Killer Frost. The winter powered Earth-2 version of Dr. Caitlin Snow (Danielle Panabaker) is sliding onto the scene and just might freeze the Flash in his tracks. Ok I’ll chill it with the frosty puns, but if one more skates by you’ll just have to Let it Go.
Joking aside, characters with ice based powers regularly appear in pop culture. Is the basic science behind these powers accurate? Let’s start with some thermodynamic basics. Temperature, refers to the measurement of internal energy inside something. This energy can change or be transferred between different forms. According to the First Law of Thermodynamics energy is not created or destroyed, but can be changed from one form to another.
When we talk about heat or heat energy, we are referring to the transfer of energy between two systems, because of a temperature difference. Most of the time energy moves from something hot to something cold. This is because of entropy, the measurement of disorder in a system. Think of how a room naturally gets messy over time, or your headphones get tangled when you put them in your pocket. The Second Law of Thermodynamics says the entropy of a system will always increase. Think of the Second Law as saying heat will always move in a direction where it can be evenly shared amongst the most people or objects. A hot pan of cookies will burn you because heat moves from the hotter pan, to the colder cells in our hands. Whereas, holding an ice cube feels cold because heat moves from our warmer hands to the colder ice. If something feels hot, then you are absorbing heat, while if something is cold, you are releasing heat.
Now let’s look at what we know about Killer Frost’s powers from the comics. Dr. Caitlin Snow became Killer Frost after an accident changed her cellular makeup. Her body is
made of ice-like cells and she feeds on heat from external sources. She actually fights Firestorm primarily because his powers generate energy for her to absorb. If she is made of ice-like cells, we can assume that her body is going to be naturally colder than normal. Thus she can logically absorb heat from other people, but what about the ice? Water can exist in different states of matter, and one way to move between states is to change the amount of energy of the water molecules. Liquid water can become solid ice by removing heat, or vapor by adding heat. On Earth, the air contains about 1- 5% water vapor. When Killer Frost removes heat from water vapor, the water molecules contain less energy and change into solid ice.
At this point, some of you Flash fans are probably thinking about Captain Cold (Wentworth Miller), the other ice themed character on The Flash and Legends of Tomorrow, who can freeze things with his cold gun. This actually introduces the Third Law of Thermodynamics. One way this can be stated is that as temperature approaches 0 degrees Kelvin (-459.7 degrees Fahrenheit), or absolute zero, the entropy will approach a constant. What does this mean? Solid ice is made of water molecules packed tightly together, however they still have some entropy because they can vibrate in place. At absolute zero, the molecules vibrate as slow as possible, and thus have the lowest entropy. Since the temperature of an object depends on how fast its atoms and molecules are moving, absolute zero is the coldest temperature possible. Scientists have tried to reach it, and have gotten very close, but no one has thus far.
Captain Cold’s cold gun works by generating a “field of absolute zero” that slows down the atomic motion of what it hits. Once again, it creates ice by freezing the water molecules in the air. As part of the Flash’s powers involves his molecules vibrating faster than normal (he contains more energy) it is considered a dangerous weapon. In the real world, while we don’t have guns that can generate beams of absolute zero, scientists can use lasers under controlled conditions to remove the heat from atoms by slowing them down (molecular cooling).
So, not all the science of these characters is accurate. However, when you watch our ice-based villains on The Flash and Legends of Tomorrow you can know that their powers and weapons do follow three laws of thermodynamics.