# The Physics of Materials at Minus 80 Degrees Celsius

It's a hopeful sign. Pfizer announced that its Covid-19 vaccine could be 90 percent effective . That could really help us get past this darned pandemic. But there's a catch. The vaccine is based on mRNA (messenger RNA)—this reads the DNA in the nucleus of a cell and transports the instructions to the cytoplasm where proteins are produced. The problem is that the mRNA is normally short lived. It either interacts with oxygen or folds onto itself and then doesn't do its job. So if you want to use it in a vaccine, you need to make the mRNA last longer. That means you have to keep it cold. Really cold. The standard storage temperature for these types of vaccines is –80 degrees Celsius. Yup. So, that means we have to talk about cold stuff. Let's do it.

How Cold is –80 Degrees Celsius?

Maybe you aren't too familiar with temperature units in Celsius—I hear you. Honestly, there's nothing really wrong with the Fahrenheit unit of temperature (except that I can never remember how to spell it). The advantage of the Celsius unit is that it's easier to calibrate. The original method was to use the freezing point of water as 0°C and the boiling point of water as 100°C. However, the value of 1°C was later redefined to be determined from the Boltzman constant—a fundamental constant that gives a relationship between the average kinetic energy of particles and the temperature of a system.If you know two corresponding temperature values in both °C and °F, you can set up an equation that converts from Celsius to Fahrenheit. You can also use your basic algebraic skills to change this into an equation that takes the temperature in Fahrenheit and converts to Celsius. Here are those two equations.
So, if you put in a temperature of –80°C you get a temperature of –112°F. Yeah, that's pretty cold. But here is my favorite temperature: minus 40. There are two great things about –40. First, you don't have to specify if it's in Celsius or Fahrenheit since –40°C = –40°F (go ahead and check it for yourself). The second awesome thing about –40 is that it's the temperature on the surface of Hoth (from Star Wars V: The Empire Strikes Back). OK, maybe not everyone agrees about the temperature on Hoth, but this is the value used on the Star Wars episode of MythBusters so I'm going to stick with it.

How Do You Get Stuff Down to –80 Degrees Celsius?

The simplest way to get something cold is to put it in thermal contact with another object that's even colder. But you might not be able to find something colder than –80°C (although there is one option that I will get to in a little bit). That means you have to use a different cooling method. Probably the most common refrigeration method is the same one your refrigerator uses. You can understand how this works with a very simple demo using a rubber band—so go get one.