Signal coverage approach to the detection probability of hypothetical extraterrestrial emitters in the Milky Way

Abstract

The lack of evidence for the existence of extraterrestrial life, even the simplest forms of animal life, makes it is difficult to decide whether the search for extraterrestrial intelligence (SETI) is more a high-risk, high-payoff endeavor than a futile attempt. Here we insist that even if extraterrestrial civilizations do exist and communicate, the likelihood of detecting their signals crucially depends on whether the Earth lies within a region of the galaxy covered by such signals. By considering possible populations of independent emitters in the galaxy, we build a statistical model of the domain covered by hypothetical extraterrestrial signals to derive the detection probability that the Earth is within such a domain. We show that for general distributions of the signal longevity and directionality, the mean number of detectable emitters is less than one even for detection probabilities as large as 50%, regardless of the number of emitters in the galaxy.

A History of Cosmic Habitability

“…Just to fix the idea, one can think of a radio message emitted from a location a thousand light-years from the Sun: if such communication ceased before a thousand years ago, we cannot observe it anymore. This may seem at first a trivial fact, but it has profound implications (Balbi 2017;Grimaldi 2017). For example, it implies that any technological civilization of which we might find empirical evidence must be either very long-lived or almost coeval to ours.…”

Monte Carlo estimation of the probability of causal contacts between communicating civilizations

“…Following the end of the civilization, there is still a region which is filled with the emitted signals. This approach has been also considered in other statistical models (e.g., Smith 2009;Grimaldi 2017;Grimaldi et al 2018). The trailing front, or surface of last contact (SLC) also grows from the arepresents the region R in space and time which is causally connected to the emitter (E, left vertex), following an 'A' type event ('Awakening') in which the node acquires the communication capability.…”

Artificial versus biological intelligence in the Cosmos: clues from a stochastic analysis of the Drake equation

“…It can be argued that the Fermi paradox is logically flawed because there is no compelling reason to assume that a nearby extraterrestrial intelligence would be detectable by us (Freitas, 1985). Grimaldi (2017) evaluated the probability that the earth is located in a detectable electromagnetic field emitted by an extraterrestrial emitter and concluded that the probability is less than 50% regardless of the number of emitters. Hence, this section does not set out to 'solve' the Fermi paradox as there is no paradox to solve but rather to cast the discussion in the light of the insight gained in this study.…”

“…The study of Grimaldi (2017), which concluded that the detectability of extraterrestrial signals is low, is based on several anthropomorphic assumptions. First, the duration of the signals is 100-1000 years, within the range of human civilizations.…”