Editing Optical isolator (section)

==Optical isolators and thermodynamics==
It might seem at first glance that a device that allows light to flow in only one direction would violate [[Kirchhoff's law of thermal radiation|Kirchhoff's law]] and the [[second law of thermodynamics]], by allowing light energy to flow from a cold object to a hot object and blocking it in the other direction, but the violation is avoided because the isolator must absorb (not reflect) the light from the hot object and will eventually reradiate it to the cold one. Attempts to re-route the photons back to their source unavoidably involve creating a route by which other photons can travel from the hot body to the cold one, avoiding the paradox.<ref>{{cite web|url=http://www.usna.edu/Users/physics/mungan/_files/documents/Scholarship/FaradayIsolators.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.usna.edu/Users/physics/mungan/_files/documents/Scholarship/FaradayIsolators.pdf |archive-date=2022-10-09 |url-status=live |title=Faraday Isolators and Kirchhoff's Law: A Puzzle |access-date=2006-07-18 |last=Mungan |first=C.E. |year=1999 }}</ref><ref>{{cite journal|doi=10.1038/064577e0|title=On the Magnetic Rotation of Light and the Second Law of Thermo-Dynamics|journal=Nature|volume=64|issue=1667|pages=577–578|year=1901|last1=Rayleigh|doi-access=free}}</ref>