Absolute Zero

Absolute zero is the temperature at which all motion within molecules completely stops.  Below absolute zero temperature does not exist.  At this temperature nothing is in motion.   Absolute zero is the lowest possible temperature that can be theoretically reached, at which the particles of matter have the least possible kinetic energy.  The lowest temperature possible is \(-273.15^\circ\)C, or \(0^\circ\) on the absolute Kekvin scale.  The idea that it is impossible, through any physical process, to lower temperature of a system to zero is known as the Third Law of Thermodynamics.

At absolute zero, all substances would be completely solid, since there would be no thermal energy to keep the molecules moving.  This theoretical state has never been achieved in a laboratory, but scientists have come close to reaching it by cooling gases to a few billionths of a degree above absolute zero using methods such as laser cooling and evaporative cooling.

Absolute zero has important implications for many areas of physics, including thermodynamics, quantum mechanics, and the behavior of materials at low temperatures.  For example, the laws of thermodynamics predict that it is impossible to reach absolute zero in a finite number of steps, since the efficiency of any cooling process must decrease as the temperature approaches absolute zero.