Man, it’s been a looooong time since I put up a new post. That was not intentional. It was part lack of motivation (or inspiration, as the case may be), and part being too busy doing science to sit down and write about it. But, I’ve given myself a New Year’s resolution of sorts to give this blog the love that it deserves, so here it goes…
It’s cold outside. Super cold, thanks to the ridiculous amount of wind that is accompanying our cold front. Walking across campus to my office has made me feel like David Attenborough traversing Greenland. In the grand scheme of things, however, it’s not even that cold. I mean, it’s certainly outside my comfort zone, but it’s not even the coldest it’s been here. While pumping liquid helium, I have experienced true, unholy cold. You think -10 °F is unpleasant, try -451 °F. Just being in proximity to something that cold feels like it is drawing the soul out of the body, not unlike the Dementors of Harry Potter fame.
Temperature is an interesting thing when you think about it. What exactly is it that we’re talking about when we refer to an object being “hot” or “cold”? It all seems so arbitrary; hot or cold with respect to what? Further, think about the fact that, unlike most other physical properties, we don’t directly measure temperature. Instead, we are always measuring the response of some other physical quantity to a change in temperature. In a mercury thermometer, for example, we are measuring the change in the volume of the mercury as the temperature changes. In a fancier electric thermometer, like the one you put in your mouth when you’re sick, you’re measuring the change in electrical resistance of some component. Sometimes, the concept of temperature isn’t even defined. Think about a rod of metal being heated by a torch where there is a significant gradient of heat across the length. What “temperature” would you say that rod is at? Point is, temperature is wacky and we really take the concept for granted. So, let’s think about it for a little bit!
The Concept of Temperature
Imagine two objects, say two cubes of metal, one “warm” and one “cool”. You bring them together so that they touch and then observe what happens to their physical properties over time. We know, for instance, that materials shrink when cooled and expand when warmed. When the cubes are brought together, you will observe that one begins to contract slightly while the other expands. After some time, however, these changes will stop. When this happens, we say that the objects have reached equilibrium, more specifically thermal equilibrium. Being in equilibrium doesn’t mean that the volumes are equal, just that they are no longer changing. Things want to be in equilibrium.
The idea of temperature is this: it’s the physical thing that tells you if you are in thermal equilibrium. All physical systems have some sort of internal energy. The air around you is comprised of molecules buzzing about with some amount of kinetic energy. So, in fact, is your body. If you are in thermal equilibrium with your surroundings, life is great. If, however, the air has more internal energy than you do, Nature does what it needs to do to balance the equation by dumping excess energy into you to try an achieve thermal equilibrium. Of course, you perceive this as “getting hot”. Unfortunately, your surroundings are much larger than you, so the amount of energy it has to give is nigh infinite and it’s probably best to seek air conditioning. The same goes for surroundings that are colder than you, only this time, you are the one giving the energy and you perceive this reverse flow as “being cold”.
Back in the day (i.e., the mid 19th century), distinguished gentlemen such as William Thompson …
thought that this transfer was due to the flow of some unseen fluid they called “caloric”. It was later established, much to Kelvin’s credit, that this idea was false and ultimately led to the idea that heat was transferred by atomic collisions, the kinetic theory of gases. He also gave us the important concept of an absolute temperature scale, one upon which “absolute zero” was the lowest temperature possible and got the SI unit of temperature named after him. Well played, Lord Kelvin.
I should point out that Victorian-era science was big on the weird fluids. There was the caloric that transferred heat, the frigoric (seriously) that transferred cold, the phlogiston that was released during combustions, and let’s not forget the fantastic luminiferous æther through which light propagated. But, I digress…
Chaos
We are, of course, not just simple blocks of metal. Our temperature is regulated by a process called homeostasis which ensures a constant body temperature, one optimized for the processes of life. In both the above cases, you are perceiving a disruption in your body’s “normal state of affairs”. But we don’t get this feature for free. We are fantastically ordered machines and it takes a lot of energy to create and maintain that order. Nature is always looking to extract its tax.
Over the years, there have been a great many rules which scientists have claimed Nature must adhere to, but the one that truly seems like it must be followed is the Second Law of Thermodynamics. This law can be stated in many ways, but the one most applicable to this discussion is that “the entropy of the Universe (a closed system) tends towards maximization”. Well, cool…what’s entropy?
Entropy is a deep subject, but the most popular way to describe it involves the idea of chaos. When frozen, water molecules take on a rigid crystal structure which has a great deal of order. As energy is added, the molecules become agitated until they break their crystalline bonds, becoming less ordered. They still weakly interact, however, and so maintain a specific volume and form a liquid. Heat that liquid even more and the molecules overcome this interaction, becoming even less ordered still, and turn into a gas. A physicist would say that the water vapor has more entropy than liquid water which, in turn, has more entropy than ice. The second law determines the direction in which this process occurs. Increase the internal energy, that increases the temperature, and you increase the entropy. We expect ice to melt when it is warm. How strange it would be to see a glass of water in a warm kitchen spontaneously freeze! It’s the transfer of energy towards thermal equilibrium, from hot to cold, that prevents this from happening. And that flow of energy increases, ever so slightly, the total entropy of the Universe.
What about a refrigerator? Doesn’t it lower the entropy of the stuff inside? It does indeed, by pumping the heat out into the surroundings through some process which itself generates heat. The net result is an increase of the surrounding entropy that is greater than the decrease inside. Your frozen peas don’t upset the order of the Universe.
Back to our homeostasis. Based on this idea of order, we have fantastically low entropy. Our surroundings are constantly pushing and pulling, but we keep the machine running with the energy we get from food, constantly trying to maintain order. But the Universe is relentless.
It keeps chipping away at our thermodynamic integrity until something finally breaks, homeostasis fails, and death occurs. All of our complexity disintegrates and the second law is maintained. Death is losing the battle against entropy.
One consolation is that we are, ever so slightly, sticking it to man. Like the refrigerator, we radiate large amounts of heat back into the environment over our lives, increasing the Universe’s entropy, driving everything towards thermal equilibrium. At some point in the very distant future, everything will become a dark, near-absolute-zero soup and, with heat ceasing to flow, entropy will finally be maximized. The inevitable heat death of the Universe. The joke’s on you, Nature. A bleak outcome, perhaps, but at least my face won’t hurt when I go outside.