Editing Loschmidt's paradox (section)

{{Short description|Conflict between known physical principles (time symmetry and entropy)}}

In [[physics]], '''Loschmidt's paradox''' (named for [[Josef Loschmidt]]), also known as the '''reversibility paradox''', '''irreversibility paradox''', or '''''{{lang|de|Umkehreinwand}}''''' ({{ety|de||reversal objection}}),<ref>{{cite journal |title=Boltzmann's ''H'' theorem and the Loschmidt and the Zermelo paradoxes |author-last=Wu |author-first=Ta-You |author-link=Wu Ta-You |journal=[[International Journal of Theoretical Physics]] |date=December 1975 |volume=14 |issue=5 |page=289 |doi=10.1007/BF01807856 |bibcode=1975IJTP...14..289W |s2cid=119792996 }}</ref> is the objection that it should not be possible to deduce an [[irreversible process]] from time-symmetric dynamics. This puts the [[time reversal symmetry]] of (almost) all known low-level fundamental physical processes at odds with any attempt to infer from them the [[second law of thermodynamics]], which describes the behaviour of macroscopic systems. Both of these are well-accepted principles in physics, with sound observational and theoretical support, yet they seem to be in conflict, hence the [[paradox]].