Absolute zero describes a theoretical system that neither emits nor absorbs energy. The Absolute zero temperature is known to be 0 K (–273.15 °C). While it is possible to cool any substance to near absolute zero, it may never actually be achieved.
Absolute zero is the point at which particles have a minimum energy, determined by quantum mechanical effects, which is called the zero-point energy.
By international agreement, absolute zero is defined as precisely 0 K on the Kelvin scale, which is a thermodynamic (absolute) temperature scale, and –273.15 °C on the Celsius scale. Absolute zero is also precisely equivalent to 0 °R on the Rankine scale (also a thermodynamic temperature scale), and –459.67 °F on the Fahrenheit scale.
While scientists cannot fully achieve a state of “zero” heat energy in a substance, they have made great advancements in achieving temperatures ever closer to absolute zero (where matter exhibits odd quantum effects). In 1994, the NIST achieved a record cold temperature of 700 nK (billionths of a kelvin). In 2003, researchers at MIT eclipsed this with a new record of 450 pK (0.45 nK).