How Much SETI Has Been Done? Finding Needles in the n-dimensional Cosmic Haystack

Abstract

Many articulations of the Fermi Paradox have as a premise, implicitly or explicitly, that humanity has searched for signs of extraterrestrial radio transmissions and concluded that there are few or no obvious ones to be found. Tarter et al. (2010) and others have argued strongly to the contrary: bright and obvious radio beacons might be quite common in the sky, but we would not know it yet because our search completeness to date is so low, akin to having searched a drinking glass's worth of seawater for evidence of fish in all of Earth's oceans. Here, we develop the metaphor of the multidimensional "Cosmic Haystack" through which SETI hunts for alien "needles" into a quantitative, eight-dimensional model, and perform an analytic integral to compute the fraction of this haystack that several large radio SETI programs have collectively examined. Although this model haystack has many qualitative differences from the Tarter et al. (2010) haystack, we conclude that the fraction of it searched to date is also very small: similar to the ratio of the volume of a large hot tub or small swimming pool to that of the Earth's oceans. With this article, we provide a Python script to calculate haystack volumes for future searches and for similar haystacks with different boundaries. We hope this formalism will aid in the development of a common parameter space for the computation of upper limits and completeness fractions of search programs for radio and other technosignatures.

A SETI survey of the Vela region using the Murchison Widefield Array: Orders of magnitude expansion in search space

“…assumptions. We find the haystack fraction to be ∼ 2 × 10 −16 , which is almost two orders of magnitude higher than the highest previous fraction listed in Wright et al (2018), which was for our previous observations of the Orion Molecular Cloud (Galactic Anticentre) field. Our new result yields the haystack fraction almost three orders of magnitude higher than the largest non-MWA survey listed by Wright et al (2018).…”

“…Overall, our MWA surveys show the rapid progress that can currently be made in SETI at radio frequencies, using wide field and sensitive facilities, but also show that SETI surveys have a long way to go. The continued use of the MWA, and the future similar use of the SKA at much higher sensitivities, offers a mechanism to make significant cuts into the haystack fraction of Wright et al (2018), while maintaining a primary focus on astrophysical investigations, making excellent commensal use of these large-scale facilities.…”

“…We also consider a different metric, utilising the method of Wright et al (2018) in order to calculate the 'haystack fraction' accessible to our observations of the Vela region. This metric takes into account the observational parameters without significant Figure 5 from Price et al (2020) with our results for the Gaia catalogue survey (Section 3.2) shown for comparison.…”

“…In their analysis of 'How Much SETI Has Been Done? Finding Needles in the n-dimensional Cosmic Haystack', Wright et al (2018) examine an eight-dimensional parameter space for radio SETI and find our two previous surveys to have the highest searched fractions for this parameter space for single surveys, factors of approximately 2 and 10 greater than the next highest, respectively. However, the highest −18 , indicating that only a vanishingly small fraction of the SETI parameter space has been covered thus far.…”

First SETI Observations with China’s Five-hundred-meter Aperture Spherical Radio Telescope (FAST)

“…We've only had radio technology for a century; that's a blink of the eye in the history of the universe and life on this planet. We are beginning to explore tiny regions of the large parameter space of possible technosignatures from potential extraterrestrial civilizations (Wright et al 2018a). Even though we are in an infant stage, SETI science and technology is growing exponentially.…”