  What is a reconfigurable intelligent surface? What is a smart radio
environment? What is a metasurface? How do metasurfaces work and how to model
them? How to reconcile the mathematical theories of communication and
electromagnetism? What are the most suitable uses and applications of
reconfigurable intelligent surfaces in wireless networks? What are the most
promising smart radio environments for wireless applications? What is the
current state of research? What are the most important and challenging research
issues to tackle?
  These are a few of the many questions that we investigate in this short opus,
which has the threefold objective of introducing the emerging research field of
smart radio environments empowered by reconfigurable intelligent surfaces,
putting forth the need of reconciling and reuniting C. E. Shannon's
mathematical theory of communication with G. Green's and J. C. Maxwell's
mathematical theories of electromagnetism, and reporting pragmatic guidelines
and recipes for employing appropriate physics-based models of metasurfaces in
wireless communications.
