Absolute Zero
The lowest possible temperature, at which particles retain only their irreducible quantum zero-point motion.
Formula / equation
0 K = −273.15 °C
Unit
K
In depth
Extrapolating the volume or pressure of any ideal gas to zero gives the same intercept, which defines the kelvin scale's origin. The third law of thermodynamics shows that absolute zero can be approached indefinitely closely but never actually attained in a finite number of steps.
Examples in the real world
Laser-cooled atoms have reached below a nanokelvin, and helium becomes a frictionless superfluid near 2 K.