Finding Needles in a Cosmic Haystack

How much Search for Extra Terrestrial Intelligence (SETI) has been done? According to Jason T. Wright and coworkers of Pennsylvania State University, our search to date is akin to having searched a drinking glass’s worth of seawater for evidence of fish in all of Earth’s oceans. They think the “needle in a haystack” metaphor is especially appropriate in a SETI context because it emphasises the vastness of the space to be searched(1):

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.

Here is Bayesian approach to SETI published in PNAS(2) last week which reinforces the idea that the effort required to live up to the challenge will be commensurate to the size of the Haystack:

The datum of non-detection has however a moderate informative value unless the sampled region contains a significant fraction of the Galaxy. The possibility that galactic, non-natural EM emissions as powerful as the Arecibo radar cross our planet can be reasonably ruled out only if no signals are observed within a radius of at least ~ 40 kly for Earth.

In a previous preprint, “Dissolving the Fermi Paradox,” Anders Sandberg et. al. of Future of Humanity Institute at Oxford University Oxford University argue, after reviewing the premises used to estimate prior probabilities, that there might be no needle in the haystack after all(3):

The Fermi paradox is the conflict between an expectation of a high ex ante probability of intelligent life elsewhere in the universe and the apparently lifeless universe we in fact observe. The expectation that the universe should be teeming with intelligent life is linked to models like the Drake equation, which suggest that even if the probability of intelligent life developing at a given site is small, the sheer multitude of possible sites should nonetheless yield a large number of potentially observable civilizations. We show that this conflict arises from the use of Drake-like equations, which implicitly assume certainty regarding highly uncertain parameters. We examine these parameters, incorporating models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude. This makes a stark difference. When the model is recast to represent realistic distributions of uncertainty, we find a substantial ex ante probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it. This result dissolves the Fermi paradox, and in doing so removes any need to invoke speculative mechanisms by which civilizations would inevitably fail to have observable effects upon the universe.

This is actually throwing Wright et al.’s glass of cold seawater on years of speculation around the Fermi Paradox.

Let’s face it. Searching for a needle in a haystack is adventurous, to put it mildly.


(1) Wright, Jason T., et al. ‘How Much SETI Has Been Done? Finding Needles in the n-Dimensional Cosmic Haystack’. ArXiv:1809.07252 [Astro-Ph], Sept. 2018.,

(2) Grimaldi, Claudio, and Geoffrey W. Marcy. ‘Bayesian Approach to SETI’. Proceedings of the National Academy of Sciences, vol. 115, no. 42, Oct. 2018, pp. E9755–64., doi:10.1073/pnas.1808578115.

(3) Sandberg, Anders, et al. ‘Dissolving the Fermi Paradox’. ArXiv:1806.02404 [Physics], June 2018.,

Feature Image: Hubble eXtreme Deep Field (XDF)

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