Reaction to Townes (1983) and Hippke & Forgan (2017): Alternative Frequencies for SETI

The theme between the Townes (1983) and Hippke & Forgan (2017) papers is that our SETI efforts should not be solely focused on searches in microwave and radio frequencies. These papers make the case that there are in fact equally viable if not superior alternatives to radio in both the infrared (IR) and X-ray portions of the electromagnetic spectrum, respectively. SETI experiments have been influenced by the precedent set by the earliest ideas in the field, which emphasized the radio search (and often near the 1.2-1.67GHz water hole). In fact, it was Cocconi and Morrison who gave us the idea that the most important factor when imagining interstellar communication systems is their efficiency in terms of photons per watt, which led them to pursue the radio search. However, with the development of new technologies and perspectives, it is clear that this narrow viewpoint misses out on a greater variety of possibilities.

These are examples of quality SETI papers because they attempt to expand our perspective and push boundaries. They remind us that we should be ever aware of falling into narrow-minded modes of thinking, and that when dealing with the perplexity of trying to predict the motivations and strategies of an ETI, we should stoically expect that we are wrong. They are also remarkable in their approach to the question. In the case of Townes, he thinks critically about the observational challenges of moving to the infrared and quantitatively compares the pros and cons of IR methods with those of microwave/radio. He is also cognizant of the fact that there are a lot of assumptions (which he makes explicit) made about the strategy of a transmitting ETI which we can only speculate about and limit the effectiveness of the IR search. On the other hand, Hippke & Forgan are motivated by the search of the global optimum for interstellar communication, which they decide ought to be in the X-ray near 1nm. In pursuit of this grail frequency, they examine a variety of astrophysical and observational difficulties which complicate communication, such as diffractive photon loss, interstellar extinction, and atmospheric transmission. In this way, both papers are firmly rooted in taking a classically quantitative and astronomical approach to SETI. This places these papers a tier higher than those which solely offer speculation on search strategies unsubstantiated by rigorous examinations of the merits of the alternative. Overall, the field benefits when scientists take SETI seriously and improve it by contributing to it with quality papers.

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.