Saturday, January 5, 2013

Temperatures below absolute zero are possible

One of the fundamental laws of physics is that it is not possible to achieve temperatures lower than absolute zero, which is defined as 0 Kelvin. This equals to -273.15 degrees Celcius and attaining this temperature will cause particles to come at an absolute stand still. Temperature can be regarded as the 'tremblings' of atoms and molecules, and movements less than zero are therefore considered impossible. Scientists have already achieved near zero temperatures, and have shown that all kinds of weird behaviour occurs at that level. Now it appears that scientists have actually managed to let the temperature drop below absolute zero, thereby defying what was thought to be an absolute constant in the realm of physics, and revealing all kinds of interesting phenomena in the process.

Breaching the barrier
A gaseous system was used in order to achieve these incredibly low temperatures, eventually resulting in a few billionths of a degree below absolute zero. While that may not sound like much of an achievement, it is actually quite amazing, if you realise that the absolute zero was long thought to be impossible to achieve, let alone breach it. The study was conducted by the Ludwig Maximilian University in Germany.

As said, the scientists used gases to achieve their extremely low temperatures. It mainly consisted of potassium atoms in an enclosed system. To achieve the sub-zero Kelvin temperature, lasers and rapidly switching magnetic fields were used. Switching refers to the direction of the magnetic field, which can be compared with an electric charge that is either positive or negative. What this setup achieves is that the atoms stay in their place, while adopting a certain energy state that is known as a Bose-Einstein condensate.

A Bose-Einstein condensate describes matter in which the atoms stop behaving as individuals, but instead function as a single 'state' with quantum mechanical properties. Such a condensate is known to arise when atoms or molecules reach temperatures near absolute zero. Because of this particular energetic state, matter behaves differently than what we have come to expect, and this seems to be especially true when the temperature dips below what was originally thought to be the absolute zero.

In their experimental setup, the German scientists saw that their atoms adopted all kinds of strange properties. This includes the effects of pressure and viscosity: normally we observe positive values, but in the experimental setup, the scientists measured negative values. Negative pressure and negative viscosity already reveal that a gaseous system in Bose-Einstein condensate conditions behaves quite weird, but the German experiment revealed something that is even more peculiar. Apparently, the effect of gravity in the experiment was found to be negative as well, which means matter doesn't pull together, but instead repels each other.

Dark energy
Perhaps the negative values of gravity in the experimental setup are the most interesting in terms of future research. Astronomers believe that a mysterious force, known as dark energy, counters the effects of gravity and is responsible for expansion of the universe. The proposition of dark energy yielded a Nobel prize in 2011. We currently do not know what this anti-gravity force is, but the German experiment shows that matter can have properties that are similar to the proposed dark energy. It may help us to elucidate what this mysterious force consists of. Obviously, it is also very interesting to find out why the laws of physics appear to switch from positive to negative (or the other way around, depending on your point of view) when dipping below the absolute zero.
Atomic behaviour around 0 Kelvin.

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