Epilogue

Abstract

Astronomical maser research had an intriguing history. The masers were discovered shortly after the construction of the very first laboratory lasers, when population inversion was a novelty, still regarded as something of a mysterious, exotic process. Many of the intricate, unique properties of coherent radiation were studied by astronomers almost at the same time they were being unraveled by laboratory physicists. Reading through the early literature on astronomical masers, one can sense a prevalent feeling that maser radiation is such a spectacular effect, that it alone ought to teach us a great deal about the emitting sources. As evident from much of the discussion presented here, this expectation was unfounded. Population inversion is easily produced in the low-density environment of interstellar space and although maser radiation carries valuable information about its source of origin, its interpretation usually must be supplemented by other observations. The backlash to the early unfulfilled anticipation led to the opposite extreme view that nothing can be learned from masers, an opinion that prevailed in some quarters through much of the 70’s.