Below Absolute Zero temperature

Researchers have achieved the record “negative temperature”, i.e. below absolute zero that was considered to be the lowest possible temperature.

This research has been published online in the journal Science.

This is a paradoxical temperature as the temperature below zero is referred to as cold but this “negative absolute temperature” can also be considered as hotter than infinity and it has “motional degrees of freedom” while at colder temperatures atoms show decreased motion or stop moving.

With positive temperatures (blue), atoms more likely occupy low-energy states than high-energy states, while the opposite is true for negative temperatures (red). (Credit: LMU / MPQ Munich)

With positive temperatures (blue), atoms more likely occupy low-energy states than high-energy states, while the opposite is true for negative temperatures (red). (Credit: LMU / MPQ Munich)

“We have created the first negative absolute temperature state for moving particles,” said researcher Simon Braun at the University of Munich in Germany.

Usually atoms like to occupy the lower energy state at positive temperatures that is known as Boltzmann distribution in physics. However, atoms can go to the higher energy states after heating. At absolute zero, atoms occupy the lowest energy state and at an infinite temperature, atoms would occupy all energy states. On the other hand, negative temperatures are opposite to the positive temperatures i.e. atoms would like to occupy high energy states than low energy states that could be considered as the “inverted Boltzmann distribution.”

“The inverted Boltzmann distribution is the hallmark of negative absolute temperature, and this is what we have achieved,” said researcher Ulrich Schneider, a physicist at the University of Munich in Germany. “Yet the gas is not colder than zero kelvin, but hotter. It is even hotter than at any positive temperature — the temperature scale simply does not end at infinity, but jumps to negative values instead.”

One of the oddities of the negative temperature is that the energy flows from the objects with the negative temperatures to the objects with positive temperatures i.e. negative temperatures are hotter than the positive ones. Another weird finding is that the entropy, i.e. the measure of the disorderliness of a system, is absorbed by the objects in the negative temperature, when they release energy.

The cold gas will also have the negative pressure created by researchers, which would result in collision of the atoms but the negative temperature is avoiding such happening.

This research paves the way to develop new engines with more than 100% efficiency. Those new types of engines would not only absorb energy from the hotter substances but also from the colder substances helping them to work with more than 100% efficiency.

This research could also help to understand the mysterious dark energy that is thought to be involved in the expansion of the universe.

Reference:

Braun, S., Ronzheimer, J., Schreiber, M., Hodgman, S., Rom, T., Bloch, I., & Schneider, U. (2013). Negative Absolute Temperature for Motional Degrees of Freedom Science, 339 (6115), 52-55 DOI: 10.1126/science.1227831