Scientists go below Absolute Zero
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It may sound less likely than hell freezing over, but physicists have created an atomic gas with a sub-absolute-zero temperature for the first time1. Their technique opens the door to generating negative-Kelvin materials and new quantum devices, and it could even help to solve a cosmological mystery.
Lord Kelvin defined the absolute temperature scale in the mid-1800s in such a way that nothing could be colder than absolute zero. Physicists later realized that the absolute temperature of a gas is related to the average energy of its particles. Absolute zero corresponds to the theoretical state in which particles have no energy at all, and higher temperatures correspond to higher average energies.
However, by the 1950s, physicists working with more exotic systems began to realise that this isn't always true: Technically, you read off the temperature of a system from a graph that plots the probabilities of its particles being found with certain energies. Normally, most particles have average or near-average energies, with only a few particles zipping around at higher energies. In theory, if the situation is reversed, with more particles having higher, rather than lower, energies, the plot would flip over and the sign of the temperature would change from a positive to a negative absolute temperature, explains Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany.
Schneider and his colleagues reached such sub-absolute-zero temperatures with an ultracold 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.
Wolfgang Ketterle, a physicist and Nobel laureate at the Massachusetts Institute of Technology in Cambridge, who has previously demonstrated negative absolute temperatures in a magnetic system2, calls the latest work an “experimental tour de force”. Exotic high-energy states that are hard to generate in the laboratory at positive temperatures become stable at negative absolute temperatures — “as though you can stand a pyramid on its head and not worry about it toppling over,” he notes — and so such techniques can allow these states to be studied in detail. “This may be a way to create new forms of matter in the laboratory,” Ketterle adds.
If built, such systems would behave in strange ways, says Achim Rosch, a theoretical physicist at the University of Cologne in Germany, who proposed the technique used by Schneider and his team3. For instance, Rosch and his colleagues have calculated that whereas clouds of atoms would normally be pulled downwards by gravity, if part of the cloud is at a negative absolute temperature, some atoms will move upwards, apparently defying gravity4.
Another peculiarity of the sub-absolute-zero gas is that it mimics 'dark energy', the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.”
It may sound less likely than hell freezing over, but physicists have created an atomic gas with a sub-absolute-zero temperature for the first time1. Their technique opens the door to generating negative-Kelvin materials and new quantum devices, and it could even help to solve a cosmological mystery.
Lord Kelvin defined the absolute temperature scale in the mid-1800s in such a way that nothing could be colder than absolute zero. Physicists later realized that the absolute temperature of a gas is related to the average energy of its particles. Absolute zero corresponds to the theoretical state in which particles have no energy at all, and higher temperatures correspond to higher average energies.
However, by the 1950s, physicists working with more exotic systems began to realise that this isn't always true: Technically, you read off the temperature of a system from a graph that plots the probabilities of its particles being found with certain energies. Normally, most particles have average or near-average energies, with only a few particles zipping around at higher energies. In theory, if the situation is reversed, with more particles having higher, rather than lower, energies, the plot would flip over and the sign of the temperature would change from a positive to a negative absolute temperature, explains Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany.
Schneider and his colleagues reached such sub-absolute-zero temperatures with an ultracold 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.
Wolfgang Ketterle, a physicist and Nobel laureate at the Massachusetts Institute of Technology in Cambridge, who has previously demonstrated negative absolute temperatures in a magnetic system2, calls the latest work an “experimental tour de force”. Exotic high-energy states that are hard to generate in the laboratory at positive temperatures become stable at negative absolute temperatures — “as though you can stand a pyramid on its head and not worry about it toppling over,” he notes — and so such techniques can allow these states to be studied in detail. “This may be a way to create new forms of matter in the laboratory,” Ketterle adds.
If built, such systems would behave in strange ways, says Achim Rosch, a theoretical physicist at the University of Cologne in Germany, who proposed the technique used by Schneider and his team3. For instance, Rosch and his colleagues have calculated that whereas clouds of atoms would normally be pulled downwards by gravity, if part of the cloud is at a negative absolute temperature, some atoms will move upwards, apparently defying gravity4.
Another peculiarity of the sub-absolute-zero gas is that it mimics 'dark energy', the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.”
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Original post by Hooj
In English please?
Temperature measures the level of energy in a molecule, they have made something have a negative level of energy. Absolute Zero = no energy at all.
That's very interesting. Especially the part about defying gravity.
Original post by Sgany
Temperature measures the level of energy in a molecule, they have made something have a negative level of energy. Absolute Zero = no energy at all.
Interesting, but will this further mankind?
astounding
Amazing! Some possible evidence for dark matter and dark energy here too, that's what's really interested me 
Original post by Hooj
In English please?
Some scientists using a lot of energy and equipment managed to make a gas at absolute zero go a negligible amount lower, so low as to be as far as I'm aware irrelevant.
They then effectively say this will lead to awesome nebulous un-expanded on things and some sounds about pushing the frontier of human understanding of physics.
Then they finish off by throwing in an unproven link with DARK MATTER™, the Fountain of Youth, Holy Grail, etc of physics.
I'm not a quantum or energy physicist though so someone else will or already has explained it's importance.
Edit: Negged by researchers from the project.
(edited 11 years ago)
Original post by Hooj
Interesting, but will this further mankind?
Probably. The techniques used for cooling frequently open up all kinds of new types of practical technology, and cooling something below absolute zero could have multiple uses that we aren't aware of now.
But that's not why researchers do this. They do this because they're curious - they want to know how things work.
Blue sky physics research has pretty much revolutionised our lives. The internet/www, lasers (used in dvd players etc), semiconductors (used in computers, a lot) all came about from open ended physics research and every time I'm sure the general public thought it would never be useful.
If you want to hear about something that will revolutionise our lives in the future: room temperature superconductors, and quantum computers.
How much government money did they waste on this project?
It's not wasted. Science is one of the best investments a government can make. The amount that governments spend on science is virtually pennies. I read once science gives an average return of two hundred times what you invest.
(edited 11 years ago)
Original post by Studentus-anonymous
Some scientists using a lot of energy and equipment managed to make a gas at absolute zero go a negligible amount lower, so low as to be as far as I'm aware irrelevant.
I can't understand their explanation for how that is possible. Saying something is below absolute zero, by even a tiny, tiny amount, to me is like saying you have an object that is less than 0m long, or has a negative mass. I think that's why it's significant, it breaks a fundamental understanding most people have about what temperature is.
There are times when i wonder if a proportion of the human race should be cast aside as scrap but my god there's a proportion which is truly wonderfully brilliant.
Very interested in the potential anti-gravity from this which would have no end of economic benefits if it can be done cheaply.
An excellent point though we have to remember that these people are the best of best usually and so if they think something is possible it usually is (kind of like one of Dragons hiring an inventer even though his products crap because eventually one of his ideas will be golden).
Very interested in the potential anti-gravity from this which would have no end of economic benefits if it can be done cheaply.
Original post by Manitude
Probably. The techniques used for cooling frequently open up all kinds of new types of practical technology, and cooling something below absolute zero could have multiple uses that we aren't aware of now.
But that's not why researchers do this. They do this because they're curious - they want to know how things work.
Blue sky physics research has pretty much revolutionised our lives. The internet/www, lasers (used in dvd players etc), semiconductors (used in computers, a lot) all came about from open ended physics research and every time I'm sure the general public thought it would never be useful.
If you want to hear about something that will revolutionise our lives in the future: room temperature superconductors, and quantum computers.
It's not wasted. Science is one of the best investments a government can make. The amount that governments spend on science is virtually pennies. I read once science gives an average return of two hundred times what you invest.
But that's not why researchers do this. They do this because they're curious - they want to know how things work.
Blue sky physics research has pretty much revolutionised our lives. The internet/www, lasers (used in dvd players etc), semiconductors (used in computers, a lot) all came about from open ended physics research and every time I'm sure the general public thought it would never be useful.
If you want to hear about something that will revolutionise our lives in the future: room temperature superconductors, and quantum computers.
It's not wasted. Science is one of the best investments a government can make. The amount that governments spend on science is virtually pennies. I read once science gives an average return of two hundred times what you invest.
An excellent point though we have to remember that these people are the best of best usually and so if they think something is possible it usually is (kind of like one of Dragons hiring an inventer even though his products crap because eventually one of his ideas will be golden).
Original post by Hooj
How much government money did they waste on this project?
We spent more bailing out the banks in 2011 than we have spent on British science EVER.
Science is drastically underfunded, not the other way around.
(edited 11 years ago)
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