Near the end of the summer, my fiancé was tearing through a book about an American surgeon in Paris. Every so often, he’d make an incredulous comment towards the pages. Finally, I asked him to explain the plot since he was clearly enjoying it.
“It’s about a surgeon who’s chasing his father’s murderer,” he said.
“That sounds interesting,” I answered dismissively.
“No, no! That’s just the background. The real story involves severed heads.”
“Severed heads?”
“Yup. And other people’s bodies. Wait until you read the ending.”
Well, okay then. Turns out, the crazies in the book are reattaching heads on other people’s bodies at the extremely low temperature of absolute zero. (Oh, and there’s a twenty year old murder mystery plus an all encompassing love story in there, as well. There’s a lot going on. Throw some Nazis in, too.)
Why absolute zero? The theory of cryopreservation is that you are hitting a “pause” button on a person’s life. All the biological processes that are currently occurring in our bodies will abruptly stop if we are dipped into a super-cold environment. In theory, we could stay that way indefinitely. Our food would sit in our stomach waiting to be digested, our last thought would be held in our mind, our heart would remain mid-beat. Once warmed, those processes could continue as if they were never interrupted. It would be as if waking from a long sleep. (But, unlike Austin Powers’ experience, we wouldn’t need to pee for five minutes.)
Biological processes occur within cells and are driven by proteins (and metabolites, nucleic acids, etc). These components are all comprised of atoms. More specifically, they rely on an atom’s ability to move. Within any molecule, bound by their bonds and environment, atoms writhe around in space. As the temperature is cooled, an atom will move less and less. Eventually, you will reach a temperature where all atomic movements are as slow as they can be. This number goes by many names: -273°C, 0 K, -459.7 °F, or absolute zero.
In the early 19th century, several scientists were heavily studying gases, particularly the relationships between volume, pressure, mass, and temperature. Much of this work lead to the creation of the Ideal Gas Law, but we are going to focus on one particular relationship known as Charles’ Law. Named for Jacques Charles, the work was published by Joseph Louis Gay-Lussac. He carefully measured the volume of a particular amount (mass) of gas at different temperatures and found that as the temperature increased, so did the volume of the gas.
Let’s pretend you are Charles; what did you actually do? First, you would have procured a specific mass of a specific gas (let’s say 1 gram of Gas A). You then measured the volume of 1 gram of Gas A at 32°F, 70°F and 100°F. Then, you graphed your data (temperature on the x axis and volume on the y axis) and would have been happy to see that your points made a straight line. Mathematically, this means that the temperature of Gas A and volume of Gas A have a direct relationship.
Now, you’d repeat your experiment with 1 gram of Gas B or 1 gram of Gas C (Figure 1.1). You would be showing over and over that, no matter the gas, this direct relationship is always seen. All the gases would expand and contract at their own pace (the lines don’t all slope the same, some are steeper than others), but the points for each gas always fell on a straight line.
What does this have to do with absolute zero? Ah, we’re getting there!
Since you are smart, you decide to put all this data into one mega-graph and draw lines through the points (Figure 1.2). Look carefully at the lines. What do you see…?
Each line, no matter what gas we’re talking about, all hit the x axis in the same place.
As a gas gets cooler, a gas gets smaller. If the gas becomes very very cold, its volume must become very very small. In terms of Charles’ Law, this point where our lines cross the x axis is telling us what temperature the gas is when its volume is zero*. Each gas will hit a volume of zero at the exact same temperature. In other words, you can’t seem to get any gas colder than -459.7°F.
This is quite extraordinary! All gases have the same, inherent, lowest possible temperature! Neat.
On the Celsius scale of temperature, -459.7°F is -273°C. The Kelvin scale shifts all Celsius temperatures up 273 degrees so that 0 K is representing the coldest temperature anything can be.
-273°C = 0 K; -272°C = 1 K; 100°C = 373 K
Far more intelligent people than me in the field of physics and mathematics proved and defined absolute zero using thermodynamics. The explanations of them go far beyond what this chemist knows, but should you like to read more about it, I suggest looking up the works of the ever impressive William Thomson (aka Lord Kelvin) and the slightly crazy, but definitely genius Ludwig Boltzmann.
Meanwhile, our Frankenstein surgeons are performing their operations at absolute zero because it’s the coldest, slowest, and most paused atoms (and, in turn, proteins, cells and biological processes) can get. Of course, the book doesn’t describe how their machines can still work at such cold temperatures given that the atoms within them are governed by the same natural rules…
* A gas can never have a volume of zero because the atoms that comprise the gas have size. The idea of a gas being at volume zero is purely theoretical. I’ll discuss this more in another topic on gases!
References
Zumdahl, Steven S. “Chemical Principles, 4th Edition” (2002) Houghton Mifflin Company, Boston, MA.
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