Absolute zero

Absolute zero is the lowest limit of the thermodynamic temperature scale; a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as −273.15 degrees on the Celsius scale (International System of Units),^[1]^[2] which equals −459.67 degrees on the Fahrenheit scale (United States customary units or imperial units).^[3] The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.

It is commonly thought of as the lowest temperature possible, but it is not the lowest enthalpy state possible, because all real substances begin to depart from the ideal gas when cooled as they approach the change of state to liquid, and then to solid; and the sum of the enthalpy of vaporization (gas to liquid) and enthalpy of fusion (liquid to solid) exceeds the ideal gas's change in enthalpy to absolute zero. In the quantum-mechanical description, matter at absolute zero is in its ground state, the point of lowest internal energy.

The laws of thermodynamics indicate that absolute zero cannot be reached using only thermodynamic means, because the temperature of the substance being cooled approaches the temperature of the cooling agent asymptotically.^[4] Even a system at absolute zero, if it could somehow be achieved, would still possess quantum mechanical zero-point energy, the energy of its ground state at absolute zero; the kinetic energy of the ground state cannot be removed.

Scientists and technologists routinely achieve temperatures close to absolute zero, where matter exhibits quantum effects such as Bose–Einstein condensate, superconductivity and superfluidity.

^ "SI Brochure: The International System of Units (SI) – 9th edition (updated in 2022)". BIPM. p. 133. Retrieved 7 September 2022. [...], it remains common practice to express a thermodynamic temperature, symbol T, in terms of its difference from the reference temperature T₀ = 273.15 K, close to the ice point. This difference is called the Celsius temperature
^ Arora, C. P. (2001). Thermodynamics. Tata McGraw-Hill. Table 2.4 page 43. ISBN 978-0-07-462014-4.
^ Zielinski, Sarah (1 January 2008). "Absolute Zero". Smithsonian Institution. Archived from the original on 1 April 2013. Retrieved 26 January 2012.
^ Masanes, Lluís; Oppenheim, Jonathan (14 March 2017), "A general derivation and quantification of the third law of thermodynamics", Nature Communications, 8 (14538): 14538, arXiv:1412.3828, Bibcode:2017NatCo...814538M, doi:10.1038/ncomms14538, PMC 5355879, PMID 28290452

[sib2115-1] "SI Brochure: The International System of Units (SI) – 9th edition (updated in 2022)". BIPM. p. 133. Retrieved 7 September 2022. [...], it remains common practice to express a thermodynamic temperature, symbol T, in terms of its difference from the reference temperature T₀ = 273.15 K, close to the ice point. This difference is called the Celsius temperature

[arora-2] Arora, C. P. (2001). Thermodynamics. Tata McGraw-Hill. Table 2.4 page 43. ISBN 978-0-07-462014-4.

[3] Zielinski, Sarah (1 January 2008). "Absolute Zero". Smithsonian Institution. Archived from the original on 1 April 2013. Retrieved 26 January 2012.

[4] Masanes, Lluís; Oppenheim, Jonathan (14 March 2017), "A general derivation and quantification of the third law of thermodynamics", Nature Communications, 8 (14538): 14538, arXiv:1412.3828, Bibcode:2017NatCo...814538M, doi:10.1038/ncomms14538, PMC 5355879, PMID 28290452

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