Reaction to Schwartz & Townes 1961

Following the theme of last week’s papers which took a look at alternatives to radio searches, this week’s papers focus on laser SETI in the optical and near-infrared. The first paper to discuss this possibility was Schwarz & Townes 1961, which was published just two years after Cocconi & Morrison motivated the radio SETI search in 1959. In an act of sheer clairvoyance (probably afforded by the fact that Townes won the Nobel prize for the discovery of lasers), the authors predicted a time when “maser apparati near the optical” technology would exist and be a viable alternative method of interstellar communication.

Notably, in our timeline, the discovery of lasers followed the development of radio communications; however, it seems that there is no necessary reason why this ought to be the case. One could imagine an ETI developing proficiency with lasers first, and hence use those as the primary means to signal to other ETI. Therefore, the abilty to detect a optical beams is an important addition in the ensemble of SETI search avenues.

To detect such a beam, the authors set two criteria: 1) that it produces enough photons per unit of area on the r eceiving end to be detectable (given the design of the detector and telescope), and 2) that it is distinguishable from the background. Given those criteria, they examined the possibility of whether or not an optical beam can be used to establish interstellar communications by testing two systems: 1) one which consists of a continuous 10kW beam at 5000A with a bandwith of 1Mhz and assuming a 200in reflector telescope, and 2) an array of 25 lasers like in part (1), but with an effective aperture of 4in. They conclude that in both cases that a signal carried on such a beam ought to be detectable to a distance 10ly given c. Earth 1960 technology. Of course, the technology of today is significantly more advanced than sixty years ago, so probably this estimate is highly underrated.

This paper is important because it was one of the first to offer a novel approach to the SETI problem (I believe the second after the Dyson 1960 paper). This paper’s predictions were vindicated by papers such as the other one for this week (Wright 2014) and others which actually conducted optical and NIR SETI searches. This paper laid the groundwork on which these subsequent additions build and helped frame our thinking about how a laser search ought to be conducted. Indeed, as we move further into the 21st century (only the second century of electronic technology on Earth) we are fastly transitioning to fiberoptical communication. Could it be that other societies also inevitably reach this conclusion as well (or at least transition through such a phase on a path of development to some even more advanced communication scheme)? Only a dedicated laser SETI search can attempt to answer those questions!

Author: Alan

Hi, I'm a first year graduate student in the Penn State Department of Astronomy and Astrophysics and the Center for Exoplanets and Habitable Worlds.