Light from atoms falling into a black hole
General relativity as originally developed by Einstein is based on the union of geometry and gravity. Half a century later the union of general relativity and thermodynamics was found to yield surprising results such as Bekenstein-Hawking black hole entropy and Hawking radiation.
In their seminal works, Hawking, Unruh and others showed how quantum effects in curved space yield a blend of thermodynamics, quantum field theory and gravity which continues to intrigue and stimulate. It has been shown  that virtual processes in which atoms jump to an excited state while emitting a photon is an alternative way to view Unruh acceleration radiation. The present work  is an extension of that logic by considering what happens when atoms fall into a black hole. This problem also shows a new way to arrive at Einstein’s equivalence principle. Connection with the “temperature as an imaginary time” paradigm of many-body theory is also illustrated by this problem. In general, the quantum optics – black hole physics interface is a rich field.