Below Absolute Zero? Gas Is Negative-Kelvin Material
For the first time, scientists have created an atomic gas that has a sub-absolute-zero temperature. Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany, and his colleagues created an ultra cold quantum gas made up of potassium atoms.
Using lasers and magnetic fields, they kept the individual atoms in a lattice arrangement. At positive temperatures, the atoms repel, making the configuration stable. The team then quickly adjusted the magnetic fields, causing the atoms to attract rather than repel each other. “This suddenly shifts the atoms from their most stable, lowest-energy state to the highest possible energy state, before they can react,” says Schneider. “It’s like walking through a valley, then instantly finding yourself on the mountain peak.”
At positive temperatures, such a reversal would be unstable and the atoms would collapse inwards. But the team also adjusted the trapping laser field to make it more energetically favourable for the atoms to stick in their positions. This result, described today in Science1, marks the gas’s transition from just above absolute zero to a few billionths of a Kelvin below absolute zero.
( Quantum gas goes below absolute zero )
(Temperature depends on the energy landscape
Ludwig Maximilian University of Munich)
Above absolute zero, adding more energy corresponds to an increase in entropy. Picture a hill next to a valley (see image above) with the height of the landscape corresponding to the energy of a particle – and the chance of finding a particle at a certain height representing entropy. At absolute zero, particles are motionless and all have no energy so are all at the bottom of the valley, giving a minimum entropy.
As the gas heats up, the average energy of the particles increases, with some gaining lots of extra energy but most just a small amount. Spread along the side of the hill, now the particles have different energies, so entropy is higher.
According to temperature's entropic definition, the highest positive temperature possible corresponds to the most disordered state of the system. This would be an equal number of particles at every point on the landscape. Increase the energy any further and you'd start to lower the entropy again, because the particles wouldn't be evenly spread. As a result, this point represents the end of the positive temperature scale.
In principle, though, it should be possible to keep heating the particles up, while driving their entropy down. Because this breaks the energy-entropy correlation, it marks the start of the negative temperature scale, where the distribution of energies is reversed – instead of most particles having a low energy and a few having a high, most have a high energy and just a few have a low energy. The end of this negative scale is reached when all particles are at the top of the energy hill.
The resulting thermometer is mind-bending with a scale that starts at zero, ramps up to plus infinity, then jumps to minus infinity before increasing through the negative numbers until it reaches negative absolute zero, which corresponds to all particles sitting at the top of the energy hill.
( Cloud of atoms goes beyond absolute zero)
Fans of sf author Alan E. Nourse may recall his description of below-absolute zero temperature materials in his 1951 story The Universe Between:
Things were going along very well until one of my men devised a radically new refrigerating pump that worked far better than anybody dreamed it could. We got our test material—a block of tungsten supported on an insulated tripod in the refrigerating vault—down closer to absolute zero than we'd ever hoped for. Maybe we hit absolute and dropped below it…I don't even know that for sure."
The phychologist blinked. "I don't follow. From absolute zero, just where can the temperature drop to?"
"A good question," McEvoy said. "I can't answer it. Below absolute zero you might speculate on some kind of negative molecular motion. Maybe that's what we did get. Certainly something changed. The test block simply evaporated. Vanished. The tripod vanished, and so did the temperature-recording device. All we could see in the vault was a small, glowing hole in the center of the room where the block had been. Nothing in it, nothing. Just a pale, blue, glowing area about six inches across that looked to some of us very strangely like a hypercube."
(Read more about Nourse's negative molecular motion)
The discovery that negative-Kelvin materials are possible has interesting implications for a variety of fields, including cosmology. The sub-absolute-zero gas mimics 'dark energy', which pushes the universe to expand against the inward pull of gravity.
Thanks to Winchell Chung of Project Rho for contributing the tip on this story, and the technovelgy reverence.
Scroll down for more stories in the same category. (Story submitted 1/4/2013)
Follow this kind of news @Technovelgy.
| Email | RSS | Blog It | Stumble | del.icio.us | Digg | Reddit |
you like to contribute a story tip?
Get the URL of the story, and the related sf author, and add
Comment/Join discussion ( 2 )
Related News Stories -
Metal That Morphs
'A mimetic poly-alloy.' John Cameron, 1991.
Invisible Drones Will (Not) Appear Over Your Town
'Light-waves are bent around it without loss or distortion.' - Doc Smith, 1939.
New Super Slippery Surface Better Than Nature's
'The water flowed off those walls without binding tension.'- Frank Herbert, 1965.
Growing Metal In The Shape You Want
What more do you need, engineers?
Technovelgy (that's tech-novel-gee!)
is devoted to the creative science inventions and ideas of sf authors. Look for
the Invention Category that interests
you, the Glossary, the Invention
Timeline, or see what's New.
Brick By Brick, Building Martian Bases
Don't try to boost everything from the surface of the Earth.
SpotMini Robot Pierson's Puppeteer-Style
Now they're kind of cute, right?
Elon Musk et. al. OpenAI Household Robot
'Any work a human being does around a house.'
BRUISE Smart Injury Detection Suit
'... Bee could see that three of them were disabled and two of them damaged.'
Tesla Model S Is Also A Boat (Sort Of)
'This Dick Dare contraption of yours...'
Promobot, The Runaway Russian Robot!
'Got yourself a runaway, Jack?'
Rowbot Small Autonomous Farm Robot
'...The tiny red glints of self-guided tractors.'
Amazon's Alexa To Recognize Emotions
Oh, Hal understood their emotions, all right.
Cool 'Single-Person Spaceships' Have Better SF Name
'A cabin so small, you couldn't stand up with the air lock closed..'
First Robot Suicide Has Science Fiction Roots
'What had happened to prevent my death?'
First US Clinical Trial For Wearable Artificial Kidney
'Wholly mechanical organs...'
Open Bionics To Produce Deus Ex Prosthetic Designs
Be a part of a science fictional future.
Human-Carrying Drone Taxi 184 Approved For Test Flights
'The cab was an egg-shaped bubble...'
Skating On Mars' Frozen Pools
'They went down, put on their skates, and started.'
Google Working On A 'Cutoff Switch' For AI
'A remote control, so you can pull the plug on Hal whenever you want to.'
Vi Artificially Intelligent Personal Trainer
More SF in the News Stories
More Beyond Technovelgy science news stories