The coolness of cold
Some scientists embrace extremely low temperatures while others just learn cope with them
By: Kevin Ma
| Posted: Wednesday, Jan 16, 2013 06:00 am
Researchers often use the Kelvin scale instead of the Centigrade scale when dealing with extreme temperatures. The Kelvin scale starts at 0 K, which is absolute zero or -273.15 C. To convert from kelvins to Celcius, simply add Kelvins to -273.15.
Cold out there, isn’t it?
It’s winter in St. Albert, which means ice, snow and temperatures in the minus 20s. It also means a lot of bellyaching about how darn cold it is outside.
Bah! Back in my day (which wasn’t long ago), we hit -30 C on a regular basis, and we liked it! Edmonton got down to -49.4 C as recently as 1893, says Environment Canada meteorologist Dan Kulak.
These temperatures are balmy compared to the ones physicist John P. Davis cooks up in his lab at the University of Alberta, where the frazzle-haired, fun-loving researcher regularly flirts with liquid helium, absolute zero and really bad puns.
“Edmonton is a hotbed of low-temperature physics,” he says, with a dry laugh, as we make our way to his underground lab where he plans to show us some “cool demos” of cold. “There are these beautiful, interesting physical phenomena that only occur when you get colder.”
“This is 77 Kelvin (-196.15 C),” he says, pointing to a gorilla-sized steel jug of liquid nitrogen, “and it’s the warmest thing in the lab.”
Using a vacuum on a flask of liquid nitrogen (which, he casually admits, could cause an explosion), he’s able to cool it to 65 K and cause a foamy, white solid to mushroom out of the liquid.
That’s solid air, he explains.
“Pretty cool, right?”
Cold, colder, coldest
Davis’s underground lab is reputedly the coldest in Canada. Using various arcane methods, he can cool stuff down to about -273 C, which is about as cold as is physically possible.
The lab itself is a concrete bunker filled with compressors, tubes and tanks. Pumps cough and wheeze constantly, as liquid helium and nitrogen boil silently in huge steel jugs.
“Cold is the absence of energy,” Davis explains, specifically heat, which is the kinetic energy of particles. Less energy means more cold.
Earth gets most of its energy from the sun. Since our planet is tilted away from its heat source during the winter, we get less energy and colder weather.
“All the water molecules in the air that used to be zipping around are now locked up in snow,” Davis says. “There’s much less energy.”
Temperature has a big impact on city operations, says St. Albert public works operations manager Bruce Thompson. When the air dips below the dew point, for example (which varies based on atmospheric conditions), it spits out any moisture that’s in it, creating black ice and a pressing need to sand streets.
Crews can scrape roads down to the pavement until it gets to about -15 C outside, Thompson says. Salt water freezes below that, and ice becomes so firm that it damages the blades on trucks. Crews stop scraping ice at this point and put down chipped rock to provide traction.
Anything below -20 C is very hard on people and machinery.
“Everything is so brittle,” Thompson says, and engine blocks freeze solid.
Winter coveralls and balaclavas are a must, and workers have to watch each other carefully for signs of frostbite.
Everyone packs it in when it’s under -30 C, he continues.
“Physically, that’s just dangerous.”
When it’s that cold, crews head indoors and start on paperwork.
University of Alberta biologist Andrew Derocher is often still out in the field under those conditions, chasing polar bears up north.
“Below minus 30, it gets really hard to operate,” he says, especially since he has to do most of his work with bare hands.
Derocher says he encounters temperatures of around -50 C with wind chill, when he flies around the Arctic in a helicopter with its door open. When he spots a polar bear, he and his crew have to tranquilize it, examine it and get back in the air before the chopper’s engine – and their fingers – freeze.
“My fingertips certainly don’t have the sensitivity they did 30 years ago,” he said.
Conditions this cold can lead to ice mirages as the light refracts through different layers of air.
“It’s the most bizarre thing,” Derocher says. “I’ve seen whole cities on the horizon.”
Polar bears, of course, have little trouble with Arctic cold, which often dips into the minus 40s. Look at them in infrared, and you’ll find that they only lose heat through their nose, eyes, belly and paws – everything else is super insulated. They can also use their arteries to re-heat blood coming back from their feet, allowing them to keep their core at 38 C while their feet are at zero.
If it’s really cold and blowing, a polar bear will camp out behind a ridge and let the snow blanket over it.
“It’s kind of the disappearing bear scenario,” Derocher says.
The arctic fox is the king of cold resistance, Derocher says. With dense fur and fat stores, tiny ears, a bushy tail and plenty of cached food, it’s able to weather minus 50 conditions with nary a shiver.
The coldest natural temperature ever recorded on Earth was -89 C at Vostok, Antarctica back in 1983, Kulak says.
To get below that, as Davis does in his lab, you need to use physics. Create a vacuum, as he did with that flask of liquid nitrogen, and you can pull off the most energetic atoms in a substance, lowering its temperature.
If you force atoms to stay still through compression, you cause them to shed energy to their surroundings and cool. Let them move again by lowering the pressure, and the atoms speed up, sucking in energy as they do so. Refrigerators use this principle to expel heat, cooling the food inside. Davis uses it to produce liquid helium (-269 C).
Using very powerful magnets and ultra-low temperatures, Davis can cool substances down to about 0.000006 K, which is pretty close to absolute zero (0 K or -273.15 C).
“You cannot get to absolute zero,” Davis adds.
Getting there would mean having something with zero energy in it, which our understanding of quantum physics suggests is impossible, he says.
You can, however, skip over and get below absolute zero, he notes – a feat researchers pulled off for the first time earlier this month, reports Science, using lasers, magnets and other quantum techniques. No one’s sure what happens when you get this cold, but some researchers think you could end up with stuff that defies gravity.
Why cold matters
Why would you want to get this cold anyways? Two words: hover trains.
“This is actually a pellet of superconductor,” Davis says, as he brings out a thumbnail-sized black hockey puck.
Superconductors are materials that do weird stuff when they get cold enough. Plop a magnet on this puck at room temperature, and nothing happens. Douse the puck in liquid nitrogen beforehand and the magnet levitates.
When you get superconductors really cold (about -196 C in this case), there’s so little movement amongst their electrons that they smear together into one big particle, making them perfect transmitters of electricity. This could lead to the development of electricity networks that are far more efficient than current ones.
Manhattan is already using a superconducting line to save on transmission losses.
“The energy saved is enormous,” Davis says.
Superconductors also “expel” magnetic fields applied to them at these temperatures, Davis says, which is why magnets are repelled from them – useful if you want a hover-train.
“Imagine you lived on a planet that never got below 0 C,” Davis says – you’d never know that water could solidify into ice (and, by association, ice cream). Just as we can peer into creation by making stuff really hot (in particle accelerators, for example), we can learn more about the world by cooling it down.
So if you think it’s cold now, take heart: it could be worse.