Absolute zero is defined as the lowest temperature possible on the Kelvin scale, but in early 2013, scientists were able to create an atomic gas in a laboratory that actually reached sub-absolute zero temperatures. This temperature is equivalent to -459.67° Fahrenheit (-273.15° Celsius). Physicists in Germany cooled quantum gas in a chamber and used magnetic fields and lasers to rearrange its atomic particles. At positive temperatures on the Kelvin scale, atoms attract each other and remain stable, but with these changes to the atomic arrangements, the particles repelled each other and thus were theoretically considered to be at a negative temperature on the Kelvin scale.
More about temperatures:
The average temperature of ice cream is about 272.65 on the Kelvin scale, and the average safe refrigerator temperature is 277.59 Kelvin degrees.
Sub-absolute zero gas has been found to behave similarly to dark energy, or the mysterious force that makes the universe expand even as gravity pulls it inward.
Learning about sub-zero temperatures might help physicists create combustion engines that have a thermodynamic efficiency of more than 100%. Rocket engines typically have a 70% thermodynamic efficiency.