What is the lowest possible temperature and why?

Answer 1

It depends whether you are referring to the lowest theoretic temperature possible, or the lower temperature ever actually achieved. Absolute zero is a temperature marked by a 0 entropy configuration. It is the coldest temperature theoretically possible and cannot be reached by artificial or natural means. Temperature is an entropically defined quantity that effectively determines the number of thermodynamically accessible states of a system within an energy range. Absolute zero physically possesses quantum mechanical zero-point energy. Having a limited temperature has several thermodynamic consequences; for example, at absolute zero all molecular motion does not cease but does not have enough energy for transference to other systems, it is therefore correct to say that at 0 kelvin molecular energy is minimal. In addition, any particle with zero energy would violate Heisenberg's Uncertainty Principle, which states that the location and momentum of a particle cannot be known at the same time. A particle at absolute zero would be at rest, so both its position, and momentum (0), would be known simultaneously.

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° on the Celsius scale. Absolute zero is also precisely equivalent to −459.67° on the Fahrenheit scale. Though it is not theoretically possible to cool any substance to 0 K, scientists have made great advancements in achieving temperatures close to absolute zero, where matter exhibits quantum effects such as superconductivity and superfluidity.

The lowest temperature ever produced in a lab is 100 pK (picoKelvins), which is 10-10 or 0.0000000001 K. This world record was set during the nuclear magnetic ordering at Helsinki University of Technology's Low Temperature Lab. It is currently the lowest possible temperature ever attempted.