Absolute zero

Absolute zero is the lowest thermodynamic temperature, defined as 0 kelvins. At this limit, a system occupies its minimum-energy state, though quantum motion can remain.

Thermodynamic temperature: A temperature scale defined by thermodynamic principles and independent of the properties of any particular substance. Absolute zero is the zero point of this fundamental temperature scale.
Laser cooling: A family of methods that uses light to reduce the kinetic energy of atoms. It cools dilute gases to temperatures extremely close to absolute zero.
Celsius: A temperature scale that assigns 0 degrees to water’s freezing point under standard pressure. Unlike Celsius zero, absolute zero is a physical lower bound on thermodynamic temperature.
Robert Boyle: A seventeenth-century natural philosopher whose gas experiments established an inverse relation between pressure and volume. Boyle’s law helped establish the quantitative study of gases that preceded absolute temperature.
Third law of thermodynamics: A thermodynamic law stating that a system’s entropy approaches a constant as temperature approaches absolute zero. It explains why cooling a system exactly to absolute zero requires an infinite sequence of operations.
Evaporative cooling: A cooling method that removes the most energetic particles from a trapped gas. It brings laser-cooled atoms closer to absolute zero.
Fahrenheit: A temperature scale that assigns 32 degrees to water’s freezing point under standard conditions. Its zero is an arbitrary scale point, not the thermodynamic limit.
Charles's law: The gas law stating that a fixed amount of gas at constant pressure has volume proportional to absolute temperature. Its extrapolation toward vanishing gas volume helped motivate the idea of a lowest temperature.
Zero-point energy: The minimum energy that a quantum system retains even in its lowest-energy state. It clarifies why reaching absolute zero does not eliminate all motion or energy.
Bose–Einstein condensate: A state of matter in which bosonic atoms collectively occupy the same quantum state at ultralow temperature. It forms only when a gas is cooled to temperatures near absolute zero.

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