In ecological systems, be it a Petri dish or a galaxy, populations evolve from some initial value (say zero) up to a steady-state equilibrium, when the mean number of births and deaths per unit time are equal. This equilibrium point is a function of the birth and death rates, as well as the carrying capacity of the ecological system itself. We show that the occupation fraction versus birth-to-death rate ratio is S-shaped, saturating at the carrying capacity for large birth-to-death rate ratios and tending to zero at the other end. We argue that our astronomical observations appear inconsistent with a cosmos saturated with extraterrestrial intelligences, and thus search for extraterrestrial intelligence optimists are left presuming that the true population is somewhere along the transitional part of this S-curve. Since the birth and death rates are a-priori unbounded, we argue that this presents a fine-tuning problem. Further, we show that if the birth-to-death rate ratio is assumed to have a log-uniform prior distribution, then the probability distribution of the ecological filling fraction is bi-modal – peaking at zero and unity. Indeed, the resulting distribution is formally the classic Haldane prior, conceived to describe the prior expectation of a Bernoulli experiment, such as a technological intelligence developing (or not) on a given world. Our results formally connect the Drake equation to the birth–death formalism, the treatment of ecological carrying capacity and their connection to the Haldane perspective.

Exopsychology is a sub-discipline of psychology concerned with how humans contemplateextraterrestrials as well as forming hypothesis about how these beings may think, feel and behave. While researching the former is undoubtedly a subject for empirical science, aspects of the latter remain uncertain. Given the contemporary scientific insight, it may still be possible to identify a set of cornerstones and eventually create a space of possible configurations of the extraterrestrial mind. Here, we identify three basic compatibility requirements: first, any form of life must navigate internal and external (environmental) demands and thus actively ensure the compatibility of its current state with the same demands. Second, any advanced cognitive development and the emergence of remotely detectable technosignatures require not only the relevant capabilities for manipulation but also compatibility with a permissive environment. Lastly, requirements also concern the compatibility of extraterrestrial thinking and behaviour with our search method. In its most basic understanding, search for extraterrestrial intelligence (SETI) searches for something done by somebody. However, the meaning of this simple formula and the psychological theory behind it is underdeveloped. Hence, psychological aid is needed to assist SETI in its effort to reveal whether galactic information indicates the presence of a mere object or activity of an identified subject with whom humans may establish contact. The fact that people believe in and search for extraterrestrials emphasizes that psychology should pay attention to this domain of phenomena. Hence, different imaginations of the extraterrestrial, ranging from benign to cruel, from superior to equally developed, are briefly discussed regarding their emergence and function as coping and motivating mechanisms for the uncertain search.

This paper introduces the SETI Post-Detection Hub, its origins, motivations, and initial undertakings, as well as the rationale for such an endeavour - to explore and develop thorough and integrated approaches in preparation for a potential discovery event in the Search for Extraterrestrial Intelligence (SETI). Officially launched at the University of St Andrews in 2022, it brings together a highly multidisciplinary international team of experts.

From the outset, our rationale has been to weave together insights from diverse fields, including governance, impact strategies, analytics, and the humanities, with particular attention to the inclusion of all humanity’s cultural voices – a vital requirement to fully understand our challenge and its solutions. So, in preparation for the discovery of extraterrestrial life, the Hub will endeavour to grow readiness for complex futures by fostering a synergistic environment that encourages imaginative, methodical preparation, to stir transformative interdisciplinary and diverse engagement.

This article examines four different points where an astrological or astrobiological discovery might propose a challenge for Christian religion. These points of contact are the size of the cosmos, human uniqueness, Christological considerations and the ultimate fate of the cosmos. I argue that the most popular interpretations of these challenges are not very serious, while there are certain issues that may genuinely push Christian religion and theology to reconsider some topics in their belief system.

The Search for Extraterrestrial Intelligence (SETI) is, at its core, a grand endeavour in communication. While we hope to detect signals from intelligent civilisations beyond our solar system, searching for cosmic company has profound implications for our species’ curiosity, technological capabilities, and innate need to connect socially. It gives pause for thought that while we focus the search and post-detection, we undervalue what evolutionary psychologists assert, neuroscientists have demonstrated, science communicators know works in connecting science with society, and journalists employ: We are hardwired for storytelling by evolution, remaining our most effective form of communication. What if the most important message is not from the stars but what the search tells about wanting to know what is in the last chapter of one of the most profound stories ever told? Should the experiment succeed, the stories of survival of intelligence from a distant civilisation may be of most interest.

On 24 May 2023, a simulated extraterrestrial message was transmitted towards Earth by the Trace Gas Orbiter, a spacecraft of the European Space Agency. The radio signal containing the message was received by several terrestrial radio antennas, as part of the interdisciplinary project “A Sign in Space”. I conceived the project in 2019, and developed it in collaboration with the SETI Institute, the Green Bank Observatory, the Italian Institute for Astrophysics and the European Space Agency. The message designed for the project required one year to be decoded by citizen scientists. The public reaction to the project provides preliminary insights into the unfolding of a concrete First-Contact scenario.

Traditionally the search for extraterrestrial intelligence (SETI) has been mostly a kind of engineering task, based on two assumptions: the existence of other technological culture somewhere in our Galaxy and that this culture is using radiotechnology that can be detected with our receivers. However, SETI endeavors could benefit more by expanding its scope into two-folded interdisciplinary research program, one exploring the nature of human, other animals, and artificial cognition, and the another exploring all possible and hypothetical ways and channels that potential ETI could use to manifest itself. This kind of new research program could be named cognitive astrobiology in order to better describe its research areas.

The search for extraterrestrial life, especially intelligent life, is among the most profound scientific endeavors. Although the international community achieved consensus within a few years of the launch of Sputnik on legal principles fundamental to the peaceful exploration of outer space, including the Moon and other celestial bodies, those principles did not directly address the subject of SETI. Nevertheless, principles relevant to SETI are expressed in the law of outer space, including treaties in force as well as non-binding forms of international instruments. As the search for extraterrestrial intelligent beings has developed and a myriad of issues has arisen, the relevance of many of these legal principles has become apparent.

The growing international public attention to astrobiology and SETI, combined with the immense costs of space exploration and the potential outcome, the discovery of extraterrestrial life, will likely increase the pressure for public justification and the need to address societal concerns about the risks of searching for, finding, or being found by extraterrestrial life. Understanding these perceptions and concerns warrants a more systematic inclusion of risk communication research in studying pre- and post-detection scenarios. In this chapter, we review the state of the art in risk perception/communication research related to astrobiology and detection. Based on three major challenges (social risk amplification/attenuation, misguided risk information seeking, ineffective risk message design), we explore the contribution of risk communication theory (SARF, RISP, EPPM, IDEA) to future research and institutional preparedness for potential detections of extraterrestrial life.

The question of whether extraterrestrials exist has driven both the search for extraterrestrial intelligence (SETI) and some attempts of messaging to extraterrestrial intelligence (METI). Nevertheless, no data-driven or theory-based behavioural policy has been suggested. Here we simulate a comprehensive set of human–extraterrestrial strategic interactions, modelled as two-by-two game-theoretic matrices. We examine a sample of possible outcomes by relying on the theory of subjective expected relative similarity (SERS), which takes into account both the expected payoffs and the extent of strategic similarity – the prospects of the opponent making identical choices. Simulation results suggest: focusing messaging efforts on signalling of complete strategic similarity, monitoring potential alien communications for similarity-indicating signals, and using risk-averse decision rules for policy planning and decision-making. The discussion puts forward three guidelines for METI initiatives and addresses the relevance of the findings to human conflict management.

The Fermi paradox points to the apparent contradiction between the idea that the emergence of life and civilization on Earth is an objective process following the general rules of Nature and that there are no visible signs of other civilizations beyond Earth. The Fermi paradox is widely discussed in astronomical, biological and other natural sciences but almost totally ignored by social sciences, even though more than half of known explanations deal with intentions and behaviours of extraterrestrial civilizations (ETCs) or social aspects of the evolution of technological civilizations. The article analyses the problem and possible solutions to the Fermi paradox from the perspective of social sciences. In this article I argue that the Fermi paradox is primarily a social science problem, and the most plausible solutions have to contain some form of social science explanations. Three types of explanations are discussed, namely, those related to ETCs’ intentions, capacities and the consequences of their decisions and activities. I argue that attempts to explain the paradox by referring to specific goals and motives of ETCs are the least plausible. Arguments related to the capacities and consequences are more solid but do not convincingly solve the paradox. I conclude that the Fermi paradox is an important problem for social sciences whether ETCs exist or not, and it should attract greater attention from social scientists.

Of all species on Earth, only one – Homo sapiens – has developed a technological civilization. As a consequence, estimates of the number of similar civilizations beyond Earth often treat the emergence of human-like intelligence or ‘sophonce’ as an evolutionary unicum: a contingent event unlikely to repeat itself even in biospheres harbouring complex brains, tool use, socially transmitted behaviours and high general intelligence. Here, attention is drawn to the unexpected recency and temporal clustering of these evolutionary preconditions to sophonce, which are shown to be confined to the last ≤102 million years. I argue that this pattern can be explained by the exponential biotic diversification dynamics suggested by the fossil record, which translated into a nonlinearly expanding range of cognitive and behavioural outcomes over the course of Earth's history. As a result, the probability of sophonce arising out of a buildup of its enabling preconditions has been escalating throughout the Phanerozoic. The implications for the Silurian hypothesis and the search for extraterrestrial intelligence (SETI) are discussed. I conclude that the transition from animal-grade multicellularity to sophonce is likely not a rate-limiting step in the evolution of extraterrestrial technological intelligences, and that while H. sapiens is probably the first sophont to evolve on Earth, on macroevolutionary grounds it is unlikely to be the last.

We explain that black holes are the most efficient capacitors of quantum information. It is thereby expected that all sufficiently advanced civilizations ultimately employ black holes in their quantum computers. The accompanying Hawking radiation is democratic in particle species. Due to this, the alien quantum computers will radiate in ordinary particles such as neutrinos and photons within the range of potential sensitivity of our detectors. This offers a new avenue for search for extraterrestrial intelligence, including the civilizations entirely composed of hidden particles species interacting with our world exclusively through gravity.

This paper provides an overview of recent historical research regarding scientifically-informed challenges to the idea that the stars are other suns orbited by other inhabited earths – an idea that came to be known as ‘the Plurality of Worlds’. Johannes Kepler in the 17th century, Jacques Cassini in the 18th and William Whewell in the 19th each argued against ‘pluralism’ based on what in their respective times was solid science. Nevertheless, pluralism remained popular despite these and other scientific challenges. This history will be of interest to the astronomical community so that it is better positioned to avoid difficulties should the historical trajectory of pluralism continue, especially as it persists in the popular imagination.

In a recent refreshing paper, Cowie (2022, The Philosophical Quarterly) analyses the hypothesis of artificial origin of the mysterious interstellar object 1I/2017 U1 ʻOumuamua, as well as the wider question of justification of the artefactual origin explanation for anomalous astronomical phenomena. This highly commendable philosophical project should be further developed in order to establish more general methodology for dealing with traces and manifestations of extraterrestrial intentional actors. In the present note, I demonstrate a couple of weaknesses of the standard account, mainly dealing with philosophy of technology, and suggest ways of improving upon it.

The self-replicating machine has high utility by virtue of its universal construction properties and its productive capacity for exponential growth. Their capacity is unrivalled. They can be deployed to the Moon to industrialize it using local in-situ resources in the short term to open up the solar system and thence deployed on interstellar spacecraft to explore the entire Galaxy by exploiting in-situ stellar system resources. Nevertheless, there are significant concerns regarding the inherent safety of self-replicating machines. We consider the general problem of runaway population growth in physical self-replicating machines to prevent the grey goo problem, the number of offspring spawned by self-replicating machines may be controlled at a genetic level. We adopt a biologically-inspired approach based on telomeres, DNA endcaps that are progressively shortened during cellular replication. This acts as a counter that imposes a limit to the number of replication cycles (Hayflick limit). By examining the biological process in detail, we can obtain some insights in implementing similar mechanisms in self-replicating machines. In particular, we find that counting mechanisms are vulnerable to cancerous runaway.

In this paper it is analysed which of the thousands of stars in the WOW! Signal region could have the highest chance of being the real source of the signal, providing that it came from a star system similar to ours. A total of 66 G and K-type stars are sampled, but only one of them is identified as a potential Sun-like star considering the available information in the Gaia Archive. This candidate source, which is named 2MASS 19281982-2640123, therefore becomes an ideal target to conduct observations in the search for techno-signatures. Another two candidate stars have a luminosity error interval that includes the luminosity of the Sun, and 14 candidates more are also identified as potential Sun-like stars, but the estimations on their luminosity were unknown.

Advanced extraterrestrial civilizations may produce observable technosignatures when they migrate inside their planetary systems and to other planetary systems. Collectively, the search for technosignatures produced by migrating extraterrestrial civilizations can be described as the search for migrating extraterrestrial intelligence (SMETI). I propose that extraterrestrial civilizations may use free-floating planets as interstellar transportation to reach, explore and colonize planetary systems. I propose possible technosignatures and artefacts that may be produced by extraterrestrial civilizations using free-floating planets for interstellar migration and interstellar colonization, as well as strategies for the search for their technosignatures and artefacts. I discuss technosignatures that may be produced by extraterrestrial civilizations using other methods of interstellar migration and colonization. As an example, I discuss the star GJ 433, which experienced a close flyby a few thousand years ago. I divide possible technosignatures of migrating civilizations into groups to highlight similarities and differences among technosignatures produced by civilizations using different methods of migration and interstellar colonization. It follows from the comparison, for example, that interstellar migration using flybys of stars can blend with interstellar migration using free-floating planets.

Solutions to the Fermi paradox either deny the existence of extraterrestrials or offer alternative reasons to explain the non-occurrence of a first contact. While the latter, more optimistic approaches generally assume the existence of extraterrestrials, they simultaneously hint to limited future detectability. If solutions to the Fermi paradox are accepted as true, they must be evaluated in terms of how they affect the likelihood of success of future SETI efforts. Some solutions may lead to the so-called Fermi constraint: in order to explain why there has not been any contact so far, optimistic solutions to the Fermi paradox have to accept assumptions that, if the solution is assumed to be correct, indicate a very low probability of future contact. In other words: they are not here, and that is why they may never appear.