- Sep 23, 2011
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There aren't that many things set in stone in science, but Absolute Zero, the lowest possible temperature at which atomic movement stops altogether was one of them. But you can thank quantum physics, the ultimate troll of the physics world, for ruining this as well.
Scientists have been able to go below zero Kelvin, -460°F or -273°C, something that was previously thought impossible. It is still impossible, you can't get any cooler than zero Kelvin, all movement has already stopped.
But that hasn't stopped scientists from adding a negative side to the Kelvin scale, making it possible to get negative temperatures.
Negative temperatures on the Kelvin scale aren't colder than positive ones, in fact, they're hotter than any possible positive temperature.
To try to understand negative temperatures, think of the Kelvin scale not as a straight line but as a loop.
Temperatures approach zero Kelvin and then go below into negative territory. At the same time, infinite Kelvin is not the end of the scale, beyond it are very high negative temperature.
At the atom level, temperature has a direct link to the energy level distribution of atoms. The cooler a gas is, the more likely it is that atoms will occupy lower energy states. As it heats up, more atoms occupy higher energy states, but most still tend to stay at the lower ones.
This is known as the Boltzmann distribution. Eventually, at infinite temperature, all energy states are equally probable, meaning atoms will occupy any of them.
As we push into the negative temperature range, things get strange, here atoms tend to occupy the higher energy states rather than the lower ones, the exact opposite of positive temperatures.
Negative temperatures are not possible in all systems as they would require infinite energy. However, some systems have an upper limit to the amount of energy they can absorb and get hotter.
Once the limit is reached, energy can still be pushed into the system, but it won't get any hotter, rather it will move over to the negative temperature range.
Temperature is directly linked to the movement of atoms, the less movement the cooler a system is. But temperature is also linked to the amount of energy in a system. Normally, increasing the total energy increases the movement, i.e. kinetic energy.
But if you manage to increase the amount of energy without increasing kinetic energy, you can push a system into negative temperatures. Researchers were able to devise an experiment that created such a system.
They cooled a gas of a few hundred thousand atoms to a few nanokelvin, a billionth of a Kelvin, very close to absolute zero.
At this temperature, virtually all movement stops. The scientists then immobilized the atoms using a laser lattice limiting their movement, therefore creating an upper bound to the kinetic energy. The atoms could still change position via quantum tunneling.
The potential energy and interaction were also limited in the experiment. This way, the scientists were able to push the system to negative temperatures of a few nanokelvin. What's more, that state was actually stable.
A system at a very low temperature is stable, isolated from outside factors, the balls are all in the valley in the image to the left.
http://news.softpedia.com/news/Quan...o-Negative-Temperatures-Achieved-318623.shtml
Scientists have been able to go below zero Kelvin, -460°F or -273°C, something that was previously thought impossible. It is still impossible, you can't get any cooler than zero Kelvin, all movement has already stopped.
But that hasn't stopped scientists from adding a negative side to the Kelvin scale, making it possible to get negative temperatures.
Negative temperatures on the Kelvin scale aren't colder than positive ones, in fact, they're hotter than any possible positive temperature.
To try to understand negative temperatures, think of the Kelvin scale not as a straight line but as a loop.
Temperatures approach zero Kelvin and then go below into negative territory. At the same time, infinite Kelvin is not the end of the scale, beyond it are very high negative temperature.
At the atom level, temperature has a direct link to the energy level distribution of atoms. The cooler a gas is, the more likely it is that atoms will occupy lower energy states. As it heats up, more atoms occupy higher energy states, but most still tend to stay at the lower ones.
This is known as the Boltzmann distribution. Eventually, at infinite temperature, all energy states are equally probable, meaning atoms will occupy any of them.
As we push into the negative temperature range, things get strange, here atoms tend to occupy the higher energy states rather than the lower ones, the exact opposite of positive temperatures.
Negative temperatures are not possible in all systems as they would require infinite energy. However, some systems have an upper limit to the amount of energy they can absorb and get hotter.
Once the limit is reached, energy can still be pushed into the system, but it won't get any hotter, rather it will move over to the negative temperature range.
Temperature is directly linked to the movement of atoms, the less movement the cooler a system is. But temperature is also linked to the amount of energy in a system. Normally, increasing the total energy increases the movement, i.e. kinetic energy.
But if you manage to increase the amount of energy without increasing kinetic energy, you can push a system into negative temperatures. Researchers were able to devise an experiment that created such a system.
They cooled a gas of a few hundred thousand atoms to a few nanokelvin, a billionth of a Kelvin, very close to absolute zero.
At this temperature, virtually all movement stops. The scientists then immobilized the atoms using a laser lattice limiting their movement, therefore creating an upper bound to the kinetic energy. The atoms could still change position via quantum tunneling.
The potential energy and interaction were also limited in the experiment. This way, the scientists were able to push the system to negative temperatures of a few nanokelvin. What's more, that state was actually stable.
A system at a very low temperature is stable, isolated from outside factors, the balls are all in the valley in the image to the left.
http://news.softpedia.com/news/Quan...o-Negative-Temperatures-Achieved-318623.shtml
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