Editing 0 (section)

==Physics==
The value zero plays a special role for many physical quantities. For some quantities, the zero level is naturally distinguished from all other levels, whereas for others it is more or less arbitrarily chosen. For example, for an [[Thermodynamic temperature|absolute temperature]] (typically measured in [[kelvin]]s), [[absolute zero|zero]] is the lowest possible value. ([[Negative temperature]]s can be defined for some physical systems, but negative-temperature systems are not actually colder.) This is in contrast to temperatures on the Celsius scale, for example, where zero is arbitrarily defined to be at the [[Melting point|freezing point]] of water.<ref>{{cite book|first1=Andrew |last1=Rex |first2=C. B. P. |last2=Finn |title=Finn's Thermal Physics |edition=3rd |publisher=CRC Press |year=2017 |isbn=978-1-4987-1887-5 |pages=8–16}}</ref>{{sfn|Kardar|2007|pp=4–5,103–104}} Measuring sound intensity in [[decibel]]s or [[phon]]s, the zero level is arbitrarily set at a reference value—for example, at a value for the threshold of hearing. In [[physics]], the [[zero-point energy]] is the lowest possible energy that a [[quantum mechanics|quantum mechanical]] [[physical system]] may possess and is the energy of the [[Stationary state|ground state]] of the system.