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 -
Laser Etching Makes Metal Super-Hydrophobic
'The water flowed off those walls without binding tension.'- Frank Herbert, 1965.
3D Printing Your Science-Fictional Metals
I love science-fictional materials!
Self-Healing Plastic Fixes Even Big Holes
'The room had been strained and healed faultily....'- JG Ballard, 1962.
Living Root Bridges Of India
Grow your own infrastructure and housing using ecologically sound materials.
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.
Autonomous Cars Will Own Themselves
'The robot drew his cab up before Eric's modest six-room bungalow.'
World's First 3D Printed Villa
'It makes drawings in the air following drawings...'
Hyperloop Track Starts Next Year
Brainflight Brain-Controlled Drone
'Mr Gant, you must think in Russian. Can you do that?'
Students Control Lab Experiments Remotely Via App
'Hello, Europa... Is this your robot I'm looking at, in sector 94?'
ROBEAR Nursing Care Robot
What other robots are strong enough to carry you? Do you want them to do so?
Testing New Spacesuits In 1929 And 2015
'I'm going to pump the air from this room... so that the interior will be like airless and pressure-less space.'
Space Station Kitchens 1929 and 2015
'Plates and cups ... slowly floated down to the floor and were not broken.'
Volvo's 'Drive Me' Program Offers Autonomous Cars In 2017
'She woke just before the signal from the car which would have called her...'
Squad X Core Technologies For Infantry
'You can flip through your several types of radar displays quicker than you can change channels to avoid a commercial...'
Neptune Duo Smartwatch Wearable Wristband
'[He] pressed several buttons on the wide bracelet he wore upon his left wrist...'
FAA Drone Rules Beta Ready For Comments
Drones, big and small, you're going to like them all.
'Cortical Modem' Latest On DARPA's Wishlist
'...inside his skull... is a little cylinder, that neuronic receptor-transmitter.'
The Martians Are On Their Way!
'Dense clouds of smoke or dust, visible through a powerful telescope on earth...'
GuardBot Robotic Sphere Of War
Much more ominous looking when they come after you.
Sony Aibo Robotic Dog Now With No Repairmen
'...they break down and then everyone in the building knows.'
More SF in the News Stories
More Beyond Technovelgy science news stories