Monday, July 2, 2012

Methodological Monday: Fun with Cryogenic Temperatures

Due to a budgeting snafu, I'm moving Food Week to next week, to coincide with actually having fresh  ingredients of the sort needed to do the projects I had planned. We now return to what was intended to be regularly scheduled programming.

I'd mentioned on the last Methodological Monday that one of the SI units I have a fondness for is the Kelvin, a measure of thermodynamic temperature. I also believe I mentioned that thermodynamics treats 0 Kelvin as Absolute Zero, the lower-bound temperature limit for the universe. As you might expect, physics becomes nearly an arcane science at the very low, and very high, temperatures.

At 0K, the universe has reached its limit. Objects and areas cooled to absolute zero are entirely still across all scales. Thermodynamic exchange stops. To reach this temperature, it is necessary to have a perfectly closed system. Scientists have only ever approached this limit.

At 10e-18 K, or 1aK, matter behaves very strangely. Macroscopic matter teleports through a process known properly as Quantum Tunnelling. This makes it possible for matter, in some form, to proceed through an otherwise insurmountable barrier. In fact, in some extreme cases, quantum tunnelling has been observed to violate the otherwise hard-and-fast rule of the speed limit of the universe (that being the transmission of electromagnetic energy through vacuum). These temperatures currently only exist in our universe in supermassive blackholes.

Scale up to a temperature 1,000,000,000,000,000 times as high, and we reach the microKelvin stage, or thousandths of a kelvin. 1.7 mK is the temperature record for dilution refrigeration using helium-3 and helium-4, which is considered to be the coldest maintainable temperature. Lower temperatures have been (extremely impractically) reached by the University of Helsink, about one ten-millionth of a microkelvin. Temperatures of the microkelvin range are extremely useful for physics. We begin to see microwave and radio emissions spontaneously.

Kelvin-range temperatures are also very useful. We know that the average temperature of the Cosmic Microwave Background is about 2.8 K. At temperatures below 10K, we start seeing metals like lead, niobium, and mercury becoming superconductors - extremely useful materials with bizarre electric and magnetic properties such as the ability to levitate magnets and an apparent lack of electromagnetic resistance.

For those wondering, 77 K is the boiling point of nitrogen. Liquid nitrogen costs you about as much as milk per unit volume and is considerably more fun, assuming you exhibit a proper respect for it. It's also surprisingly easy to find and available at many industrial gas/welding supply shops. You're going to need a Dewar Flask (do NOT use a thermos) and a safe way to transport it. I mention nitrogen specifically for two reasons. The first is Ben Krasnow's Astoundingly Understandable Homebrew Liquid Nitrogen Generator, and the second is that there are some compounds, such as YBa2Cu3O7, are actually superconductors above this temperature, the so-called High Temperature Superconductors. That means that you can actually tinker with superconductivity at home! Levitate things!

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