Researchers "Change the Laws of Physics" With Sub-Absolute Zero Quantum Gas
January 9, 2013 3:00 AM
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Lasers, magnetic fields coax lattice-arranged potassium gas into a bizarre state
Scientists have demonstrated a feat that your physics teacher may have told you was impossible -- they have created a material with a temperature below absolute zero. And the world below absolute zero is an unusual place indeed.
I. It's a Very, Very Mad World
Atoms float upwards, ignoring gravity. In a phenomenon that theoretical physicists believe mimic "dark energy", the atoms even stabilize in conditions that would normally crush inwards. It's as if gravity itself is being overridden and energetic arrangements that would normally create instability, instead stabilize. In short, we've entered the Twilight Zone of particle physics.
Massachusetts Institute of Technology
was a pioneer in the field of negative absolute temperatures. He remarks, "[With negative absolute temperatures it is] as though you can stand a pyramid on its head and not worry about it toppling over."
The MIT professor in a
lauds the new work by
of Munich, Germany's
Ludwig Maximilian University
and colleagues. In the work Professor Schneider demonstrates the first-ever peer-reviewed instance of a negative absolute temperature material breaking the absolute zero behavior.
The work began with Professor Schneider creating a peculiar quantum gas, using lasers and magnets. Composed of potassium atoms the gas was arranged into a lattice structure. A radical adjustment in the magnetic fields switches the atoms from the lowest energy state possible to the highest energy state possible.
The quantum gas is composed of potassium atoms. [Image Source: MaterialScientist]
Here is where the special behavior takes hold.
Normally the stabilizing repulsion of the original configuration would be replaced with an immense attraction, causing the system to collapse and implode. But thanks to the trapping lasers, the lattice instead remains stable in the new super-energized state. Comments Professor Schneider, "This suddenly shifts the atoms from their most stable, lowest-energy state to the highest possible energy state, before they can react. It’s like walking through a valley, then instantly finding yourself on the mountain peak."
The result is a gas that by the formal definition of the Kelvin scale is a few billionths of a degree Kelvin below absolute zero (0 K).
II. Negative Absolute Temperatures? That's Really Cold, Right?
But don't be confused. The below-absolute-zero system is not cold. It is in fact very, very hot -- hotter than any positive Kelvin system. In cooler positive temperature systems, the numbers of particles in low-energy states outnumber those in high-energy states, giving rise to the formal quantum mechanics definition of temperature. Typically entropy pushes atoms to occupy lower energy states, on average.
Lord Kelvin's temperature scale is formally based on probability, not necessarily heat.
[Image Source: Unknown]
But in certain specialized quantum mechanical systems, the entropy actually decreases as the system energy (and "heat") increase, giving rise to a negative quantum temperature.
In other words, to understand this wild breakthrough, you must abandon your traditional notions of negative being cold and positive being hot and think in quantum terms. This isn't your high school physics teacher's negative temperature. It's a bizarre exercise in inverted entropy.
Could such a state be possible for the faster-than-expected expansion of the universe (a phenomena cosmologist attribute to
so-called "dark energy"
, a poorly understood mechanism)? Professor Schneider argues the idea is worth exploring. He comments, "It’s interesting that this weird feature pops up in the Universe and also in the lab. This may be something that cosmologists should look at more closely."
Negative temperature materials could be a boon to both
theoretical particle physics
. But much work needs to be done to understand their bizarre new spin on physics.
The work by Prof. Schneider and his colleagues was
in the highly prestigious peer-reviewed journal
And if that makes your brain hurt, take a break and read the classic college urban legend of a physic professor's exam question of whether hell is exothermic or endothermic and his student's
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negative temperatures are not a new concept
1/9/2013 8:10:02 AM
I remember hearing about negative temperatures in Ising lattices over 30 years ago. It just means that entropy increases when you add energy to the system. This can occur when there are not an unlimited number of high energy states to populate. Added energy gets crowded into the highest possible energy states, making the overall energy distribution less random.
RE: negative temperatures are not a new concept
1/9/2013 8:37:22 AM
I like cheese.
RE: negative temperatures are not a new concept
1/9/2013 9:01:27 AM
Yes, over thirty years ago I assisted in several ultra low temperature experiments where a fraction of the condensate was driven to "negative" kelvin temperatures in order so that when that fraction relaxed to its "normal" state the entire condensate cooled further.
So called "negative" temperatures are nothing new. You just have to realize that it is an aberrant state.
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