Drake Equation Research Articles

Frank Drake is Alive! (Rethinking the Drake Equation for the Search For Biological Life)

In 1961, astronomer Frank Drake formulated the Drake Equation as a cornerstone for scientific discourse regarding the prevalence of communicative extraterrestrial civilizations within the Milky Way galaxy. This equation, often referred to as the “Classic Drake Equation”, outlines the key factors influencing the number of potential civilizations with which we might establish communication. This article submerges into the Drake Equation and proposes a simplified version focused on the broader detection of extraterrestrial non-intelligent life. The established terms of the equation, such as the rate of stellar formation, the fraction of stars harboring planetary systems, and the probability of such systems containing habitable planets, are re-examined and discussed. Additionally, a reevaluation of other factors is presented. Based on this revised framework, various scenarios are explored. As our technological capabilities continue to advance, the detection of biosignatures on exoplanets (incorporated into the suggested new version of the equation) is anticipated to offer insights into the search for life beyond Earth. Keywords: Drake Equation, Extraterrestrial Life, Exoplanetology, Habitability, Biomarkers, Communicative Civilizations

Artificial Broadcasts as Galactic Populations. I. A Point Process Formalism for Extraterrestrial Intelligences and Their Broadcasts

Artificial broadcasts from extraterrestrial intelligences are a hypothetical class of celestial phenomena. Unlike known astrophysical objects, the societies that generate them may be able to replicate on galactic scales through interstellar travel. Different galaxies could thus have drastically different populations, with variations in abundance of many orders of magnitude. I present a probabilistic formalism to treat this shared history, in which societies and their broadcasts are described by distributions over basic properties like lifespan and energy released. The framework contains a hierarchy of objects related by a tree structure. Discrete societies, the sources of broadcasts, are organized into potentially interstellar metasocieties. The population of each type of object is represented by a random point process in an abstract parameter hyperspace, a haystack. When a selection like an observation draws a sample, the point process is thinned. Given assumptions of interchangeability and independence, observables are modeled with compound Poisson random variables. I present an example of how selection bias can favor sampling longer-lived objects. I rederive the Drake equation for societies in the limit of no expansion. When interstellar replication is present, however, the mean number of detected broadcasts can depend quadratically on stellar mass, suggesting a search strategy favoring large galaxies.

The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations

Within the uncertainties of involved astronomical and biological parameters, the Drake Equation typically predicts that there should be many exoplanets in our galaxy hosting active, communicative civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing the importance of planetary tectonic style for biological evolution. We summarize growing evidence that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated emergence and evolution of complex species. We further suggest that both continents and oceans are required for ACCs because early evolution of simple life must happen in water but late evolution of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox (1) by adding two additional terms to the Drake Equation: foc (the fraction of habitable exoplanets with significant continents and oceans) and fpt (the fraction of habitable exoplanets with significant continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by demonstrating that the product of foc and fpt is very small (< 0.00003–0.002). We propose that the lack of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on exoplanets with primitive life.

Is artificial intelligence the great filter that makes advanced technical civilisations rare in the universe?

This study examines the hypothesis that the rapid development of Artificial Intelligence (AI), culminating in the emergence of Artificial Superintelligence (ASI), could act as a "Great Filter" that is responsible for the scarcity of advanced technological civilisations in the universe. It is proposed that such a filter emerges before these civilisations can develop a stable, multiplanetary existence, suggesting the typical longevity (L) of a technical civilization is less than 200 years. Such estimates for L, when applied to optimistic versions of the Drake equation, are consistent with the null results obtained by recent SETI surveys, and other efforts to detect various technosignatures across the electromagnetic spectrum. Through the lens of SETI, we reflect on humanity's current technological trajectory – the modest projections for L suggested here, underscore the critical need to quickly establish regulatory frameworks for AI development on Earth and the advancement of a multiplanetary society to mitigate against such existential threats. The persistence of intelligent and conscious life in the universe could hinge on the timely and effective implementation of such international regulatory measures and technological endeavours.

The “Drake Equation” of Exomoons—A Cascade of Formation, Stability and Detection

After 25 years of the prediction of the possibility of observations, and despite the many hundreds of well-studied transiting exoplanet systems, we are still waiting for the announcement of the first confirmed exomoon. We follow the “cascade” structure of the Drake equation but apply it to the chain of events leading to a successful detection of an exomoon. The scope of this paper is to reveal the structure of the problem, rather than to give a quantitative solution. We identify three important steps that can lead us to discovery. The steps are the formation, the orbital dynamics and long-term stability, and the observability of a given exomoon in a given system. This way, the question will be closely related to questions of star formation, planet formation, five possible pathways of moon formation; long-term dynamics of evolved planet systems involving stellar and planetary rotation and internal structure; and the proper evaluation of the observed data, taking the correlated noise of stellar and instrumental origin and the sampling function also into account. We highlight how a successful exomoon observation and the interpretations of the expected further measurements prove to be among the most complex and interdisciplinary questions in astrophysics.

Research repertoires and boundary work in the search for extra-terrestrial intelligence (SETI)

ABSTRACT The idea of scouting the sky in search of extra-terrestrial signals (SETI) was first proposed in the late 1950s; soon afterwards, its scope was formalised in the so-called Drake Equation, a probabilistic argument to gauge the number of ‘civilisations’ capable of radio communication on the basis of astronomical, biological and cultural factors. Since then, radio telescopes around the world have been searching for an artificial signal from elsewhere in the universe, a sign of extraterrestrial communication. How have SETI practitioners claimed scientific legitimacy and epistemic authority over the search for extra-terrestrial life, a matter often regarded to be at the very periphery of science? And how have they succeeded (or failed) in maintaining them over time? The historical trajectory of SETI offers the opportunity to investigate how, over time, an interdisciplinary community coalesced around a research repertoire and navigated ebbs and flows of interest by rearticulating the methods and scope of their research. The ‘probability repertoire’ around which the SETI community coalesced is an evolving entity, entailing significant boundary work. As with every successful repertoire, it is a flexible but always entailing a recognisable alignment of material, social and epistemic components instrumental for a research community in gaining recognition and negotiating its epistemic positioning within the always shifting boundaries of science.

The Fermi paradox and the Drake equation

The Fermi paradox and the Drake equation seem to be incompatible. Here we shall show that is not so, and the paradox actually justifies the assumptions made in formulating this equation.

Drake equation of search for extraterrestrial intelligence: A proposal for modification in the light of Dirac’s large number hypothesis

In the light of Dirac’s Large Number Hypothesis (LNH), we try to relate the Drake equation with the extra-terrestrial intelligence (ETI), specifically in terms of cognitive science. This argument has been drawn from the ratio of smallest time scale (i.e. 40[Formula: see text]Hz oscillation in neuronal system of brain) to the smallest timescale (i.e. the Planck time in the present universe) which provides a very large dimensionless number [Formula: see text]. Under this LNH, we emphasize on the issue of the alien equation of Drake and provide a modified version of it by considering consciousness of the ETI. Thus, the Drake equation, which basically represents a statistical conjecture with random and arbitrary values, can be related with a feasible as well as applicable background philosophy.

Beyond the Drake Equation: A Time-dependent Inventory of Habitable Planets and Life-bearing Worlds in the Solar Neighborhood

We introduce a mathematical framework for statistical exoplanet population and astrobiology studies that may help direct future observational efforts and experiments. The approach is based on a set of differential equations and provides a time-dependent mapping between star formation, metal enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemo-population history of the solar neighborhood. Our results are summarized as follows: (1) the formation of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about 11 Gyr ago; (2) within 100 pc from the Sun, there are as many as 11,000(η ⊕/0.24) Earth-size planets in the habitable zone (“temperate terrestrial planets” or TTPs) of K-type stars. The solar system is younger than the median TTP, and was created in a star formation surge that peaked 5.5 Gyr ago and was triggered by an external agent; (3) the metallicity modulation of the giant planet occurrence rate results in a later typical formation time, with TTPs outnumbering giant planets at early times; and (4) the closest, life-harboring Earth-like planet would be ≲20 pc away if microbial life arose as soon as it did on Earth in ≳1% of the TTPs around K stars. If simple life is abundant (fast abiogenesis), it is also old, as it would have emerged more than 8 Gyr ago in about one-third of all life-bearing planets today. Older Earth analogs are more likely to have developed sufficiently complex life capable of altering their environment and producing detectable oxygenic biosignatures.

Is there anybody out there? Can individual loneliness, need for closure, and religiosity predict the belief in extraterrestrial life and intelligence?

AbstractThinking about the universe also includes thinking about hypothetical extraterrestrial intelligence. Two key questions arise: Why are we thinking about them in the first place? And why are we anthropomorphizing them? One possible explanation may be that the belief in extraterrestrials results from a subjective feeling of loneliness or the need for closure. Results of an online questionnaire (N = 130) did not reveal a confident and consistent correlation between personal feelings of aloneness or need for closure and belief in extraterrestrial life or intelligence. The same was true for the anthropomorphic representation of extraterrestrial intelligence. The belief in extraterrestrial life was negatively linked to frequent religious activity, and to a lesser and more uncertain extent, to the belief in extraterrestrial intelligence. As evidenced by their parameter estimates, participants demonstrated an intuitive grasp of the probabilities inherent in the Drake equation. However, there was significant variability in the solutions provided. When asked to describe hypothetical extraterrestrials, participants mainly assessed them in terms connoted with physical appearance, neutral to humans, and partially influenced by anthropomorphism. Given the severe limitations, we conservatively conclude that individual loneliness is indeed individual and does not break the final frontier, that is, space.

Astrobiology: resolution of the statistical Drake equation by Maccone's lognormal method in 50 steps

AbstractThe authors use the mathematical tool of Maccone's lognormal distribution to further factor the Drake equation, which calculates the number of advanced civilizations in the galaxy, from the seven original levels of the Drake equation to 49 levels of overall analysis. The Maccone approach, in fact, supported by the central limit theorem, becomes more reliable the more levels are introduced. The resulting study necessarily draws upon an array of disciplines ranging from astronomy, chemistry and geology to biology, palaeontology and futurology. The final result calculates the number of planetary systems suitable for life in its various stages of development: those which have probably hosted life in the past and those which still host it at its various evolutionary levels. The final evolutionary level is the so-called galactic civilization (often called ETC, or extraterrestrial civilizations). The number of resulting galactic civilizations is divided between static civilizations, which do not move around the galaxy and whose Kardašëv rating is still low (&lt;1.4), of which we find three examples (we ourselves plus, perhaps, two others), and potentially dynamic civilizations, which move around the galaxy and have a sufficiently high Kardašëv rating (≥1.4), of which we find 2000.

Is Biological Death Final? Recomputing the Drake-S Equation for Postmortem Survival of Consciousness

This participatory team science project extended Laythe and Houran’s (2022) prior application of a famous probabilistic argument known as the "Drake equation" to the question of postmortem survival. Specifically, we evaluated effect sizes from peer-reviewed, empirical studies to determine the maximum average percentage effect that ostensibly supports (i.e., "anomalous effects") or refutes (i.e., "known confounds") the survival hypothesis. But unlike the earlier application, this research included a study-specific estimate of the hypothesized variable of "living agent psi" via a new meta-analysis of empirical studies (N = 17) with exceptional subjects vs participants from the general population. Our updated analysis found that putative psi was a meaningful variable, although it along with other known confounds still did not account for 30.3% of survival-related phenomena that appear to attest directly to human consciousness continuing after physical (biological) death. Thus, the popular conventional variables that we measured here are seemingly insufficient to account for a sizable portion of the purported empirical data that has been interpreted as evidence of survival. Our conclusion is nonetheless tempered by several assumptions and limitations of our speculative exercise, which ultimately does not affirm the existence of an ‘afterlife’ but rather highlights the need for measurements with greater precision and/ or a more comprehensive set of quantifiable variables. Therefore, we discuss how our probabilistic approach provides important heuristics to guide future research in this highly controversial domain that touches both parapsychology and transpersonal psychology.

Good, Bad, or Not-Even-Wrong Science and Mathematics in Transpersonal Psychology: Comment on Rock et al.'s "Is Biological Death Final?"

Rock et al. (this issue) used a Drake-like equation to provide an estimate of the mathematical likelihood of survival of consciousness after death based on combining a number of probability guestimates. Although it is refreshing to see a mathematical paper within transpersonal psychology, as this subdiscipline of psychology suffers from a shortage of quantitative research, it is uncertain whether this contribution is good, bad, or not-even-wrong science. The original Drake equation, and its derivative Drake-like equation spinoffs, have been criticized for combining numbers that produce results that lack meaning and thereby perhaps can be seen as using pseudomathematics. This concern is discussed in relationship to problems related to romantic scientism within transpersonal science, including methodolatry involved in privileging qualitative over quantitative approaches. Self-expansiveness is discussed as an example of transpersonal psychology appropriately using good science, while the critical positivity ratio is discussed as an example of bad science, and astrology is discussed as an example of pseudoscience that is not-even-wrong. Questions are raised about the proper use and the misuse of mathematics within the transpersonal area, and comment is made about advances in mathematics that might become useful within transpersonal psychology.

Is Everyone Probably Elsewhere?

AbstractIt has been widely discussed whether the existence of other universes than the known universe is a purely metaphysical consideration. This paper argues to the contrary that the existence of other universes is a meaningful hypothesis, which can be tested based on observable data. The paper applies the perspective of observer bias as an approach for assigning probabilities to the mutually excluding hypotheses of universe vs. multiverse, i.e., whether the known universe is the only universe, or just one universe in an ensemble of universes, a so-called multiverse. The basic idea of the paper relies on the following consideration. In a multiverse, the vast majority of observers would live in universes that are more life friendly. Thus, conditional on there being a multiverse, we should expect to find ourselves in a universe with values of the fundamental parameters that provide particularly fertile grounds for life. In contrast, if there is only a single universe, it may well be the case that there is still a few observers even if the parameters are far from ideal for life, and in that case, those observers will find values of the parameters that are not ideal for intelligent life. It may well be the case that, among all parameter configurations that allow life at least somewhere, those that are not ideal for life far outnumber those that are ideal for life. Based on this elementary consideration, the paper proceeds to propose a quantitative framework to determine probabilities for either hypothesis. In particular, it is described how a future ab initio determination of some of the factors in the Drake equation may be used to infer which one of the two hypotheses is the more likely. A quantitative approach to this end is proposed. Expressing these factors of the Drake equation in the context of the two hypotheses, a general likelihood approach is first described. Then, to support intuition, example computations are provided, illustrating how an actual hypothesis test would work in practice.

Frank Drake, “The Father of SETI”, May 28, 1930, to September 2, 2022

Frank Drake was a hero, a legend, an icon. His eponymous Drake Equation was the catalyst forSETI—the search for extraterrestrial intelligence. It is often called the second most famousequation in physics, right up there with E = mc2. His name is recognized by highschoolstudents—a pantheon that includes names such as Newton, Einstein, Gauss, Maxwell, Planck,Boltzmann.

Philosophical and Scientific Implications of Astrobiology and Palaeontology in the Light of Hypothesising the Existence of Intelligent Pre-human Civilisations on Earth: Empiricist, Rationalist, and Positivist Approaches

In this paper, the scientific and philosophical implications of the theory that suggests the existence of an intelligent civilisation on Earth prior to mankind is discussed. All available scientific evidence which would constrain such theory is brought into discussion. Therefore, we first review the Drake Equation regarding this hypothesis. We summarily appraise the Shadow Biosphere within the scope of the theory. Subsequently, we thoroughly analyse important geochemical and sedimentological constraints of the proposal, mainly in the context of some Fossillagerstätten. This leads us to discuss the philosophical implications this theory may have for the fields of Astrobiology and Palaeontology, analysing them under empiricist, rationalist, and positivist approaches. We contextually examine the concepts of technological species, intelligence, and industrialisation, taking into account the scope of the theory. Furthermore, we debate on the validity of this hypothesis, considering all constraints it presents regarding the analysed concepts. Finally, we propose to appraise the hypothesis under an epistemological/positivist point of view.

Communicating extraterrestrial intelligence (CETI) interaction models based on the Drake equation

AbstractThe Drake equation has proven fertile ground for speculation about the abundance, or lack thereof, of communicating extraterrestrial intelligences (CETIs) for decades. It has been augmented by subsequent authors to include random variables in order to understand its probabilistic behaviour. However, in most cases, the emergence and lifetime of CETIs are assumed to be independent of each other. In this paper, we will derive several expressions that can demonstrate how CETIs may relate to each other in technological age as well as how the dynamics of the concurrent CETI population change under basic models of interaction, such as the Allee effect. By defining interaction as the change in the expected communication lifetime with respect to the density of CETI in a region of space, we can use models and simulation to understand how the CETI density can promote or inhibit the longevity and overall population of interstellar technological civilizations.

Galactic Settlement of Low-mass Stars as a Resolution to the Fermi Paradox

An expanding civilization could spread rapidly through the Galaxy, so the absence of extraterrestrial settlement in the solar system implies that such expansionist civilizations do not exist. This argument, often referred to as the Fermi paradox, typically assumes that expansion would proceed uniformly through the Galaxy, but not all stellar types may be equally useful for a long-lived civilization. We suggest that low-mass stars, and K-dwarf stars in particular, would be ideal migration locations for civilizations that originate in a G-dwarf system. We use a modified form of the Drake equation to show that expansion across all low-mass stars could be accomplished in 2 Gyr, which includes waiting time between expansion waves to allow for a close approach to a suitable destination star. This would require interstellar travel capabilities of no more than ∼0.3 lt-yr to settle all M-dwarfs and ∼2 lt-yr to settle all K-dwarfs. Even more rapid expansion could occur within 2 Myr, with travel requirements of ∼10 lt-yr to settle all M-dwarfs and ∼50 lt-yr to settle all K-dwarfs. The search for technosignatures in exoplanetary systems can help to place constraints on the presence of such a “low-mass Galactic Club” in the Galaxy today.

The Case for Technosignatures: Why They May Be Abundant, Long-lived, Highly Detectable, and Unambiguous

Abstract The intuition suggested by the Drake equation implies that technology should be less prevalent than biology in the galaxy. However, it has been appreciated for decades in the SETI community that technosignatures could be more abundant, longer-lived, more detectable, and less ambiguous than biosignatures. We collect the arguments for and against technosignatures’ ubiquity and discuss the implications of some properties of technological life that fundamentally differ from nontechnological life in the context of modern astrobiology: It can spread among the stars to many sites, it can be more easily detected at large distances, and it can produce signs that are unambiguously technological. As an illustration in terms of the Drake equation, we consider two Drake-like equations, for technosignatures (calculating N(tech)) and biosignatures (calculating N(bio)). We argue that Earth and humanity may be poor guides to the longevity term L and that its maximum value could be very large, in that technology can outlive its creators and even its host star. We conclude that while the Drake equation implies that N(bio) ≫ N(tech), it is also plausible that N(tech) ≫ N(bio). As a consequence, as we seek possible indicators of extraterrestrial life, for instance, via characterization of the atmospheres of habitable exoplanets, we should search for both biosignatures and technosignatures. This exercise also illustrates ways in which biosignature and technosignature searches can complement and supplement each other and how methods of technosignature search, including old ideas from SETI, can inform the search for biosignatures and life generally.

Cosmic Queries: StarTalk's Guide to Who We Are, How We Got Here, and Where We’re Going

Cosmic Queries: StarTalk's Guide to Who We Are, How We Got Here, and Where We’re Going