ETI

@article{openalexw1618666643,
    author = "Kardashëv, N. S.",
    title = "Transmission of Information by Extraterrestrial Civilizations",
    year = "1964",
    openalex = "W1618666643"
}

@article{doi1010160032063367900955,
    author = "Öpik, E.",
    title = "Intelligent life in the Universe",
    year = "1967",
    journal = "Planetary and Space Science",
    url = "https://doi.org/10.1016/0032-0633(67)90095-5",
    doi = "10.1016/0032-0633(67)90095-5",
    openalex = "W2324080478"
}

@article{openalexw3008639729,
    author = "Oliver, Bernard M. and Billingham, J.",
    title = "Project Cyclops: A Design Study of a System for Detecting Extraterrestrial Intelligent Life",
    year = "1971",
    openalex = "W3008639729"
}

The subject of extraterrestrial civilizations is relevant to astronomy in two ways. Firstly, the very existence of life outside Earth is dependent upon the picture that astronomers can draw of the Universe, and we will see how that picture allows us to be very optimistic. Then, if we think that there are intelligent beings in space, the detection of signals from them is an astronomical problem, and we will see that it most probably concerns radio astronomers.

@article{ribes1971extraterrestrial,
    author = "Ribes, J. C. and Biraud, F.",
    title = "Extraterrestrial Civilizations",
    year = "1971",
    journal = "Publications of the Astronomical Society of Australia",
    abstract = "The subject of extraterrestrial civilizations is relevant to astronomy in two ways. Firstly, the very existence of life outside Earth is dependent upon the picture that astronomers can draw of the Universe, and we will see how that picture allows us to be very optimistic. Then, if we think that there are intelligent beings in space, the detection of signals from them is an astronomical problem, and we will see that it most probably concerns radio astronomers.",
    url = "https://doi.org/10.1017/s132335800001256x",
    doi = "10.1017/s132335800001256x",
    number = "1",
    openalex = "W4237457557",
    pages = "11-13",
    volume = "2",
    references = "doi1010160032063363901041, doi1010160032063364902284, doi1010160032063367900955, doi101038228923a0, doi101038229395a0, doi101086107353, doi101086143256, doi101103physrevlett25180, doi1023071575053, openalexw3017115483"
}

@article{crossref1976six,
    title = "Six Searches for Extraterrestrial Civilizations",
    year = "1976",
    journal = "Science News",
    url = "https://doi.org/10.2307/3960660",
    doi = "10.2307/3960660",
    number = "9",
    openalex = "W4247344431",
    pages = "132",
    volume = "109"
}

@misc{asimov1979extraterrestrial1,
    author = "Asimov, I",
    title = "Extraterrestrial Civilizations",
    year = "1979",
    howpublished = "New York, Crown",
    note = "talkorigins\_source = {true}; raw\_reference = {Asimov, I., 1979, Extraterrestrial Civilizations: New York, Crown.}"
}

@article{doi1010160094576579901498,
    author = "Troitskii, V. S. and Starodubtsev, A. M. and Bondar, L. N.",
    title = "Search for radio emissions from extraterrestrial civilizations",
    year = "1979",
    journal = "Acta Astronautica",
    url = "https://doi.org/10.1016/0094-5765(79)90149-8",
    doi = "10.1016/0094-5765(79)90149-8",
    openalex = "W2033420460"
}

@misc{hendry1979the2,
    author = "Hendry, A",
    title = "The UFO Handbook",
    year = "1979",
    howpublished = "A Guide to Investigating, Evaluating and Reporting UFO Sightings: Garden City, New York, Doubleday \& Co., 297 p",
    note = "talkorigins\_source = {true}; raw\_reference = {Hendry, A., 1979, The UFO Handbook: A Guide to Investigating, Evaluating and Reporting UFO Sightings: Garden City, New York, Doubleday \& Co., 297 p.}"
}

@article{doi10106312914542,
    author = "Tipler, Frank J.",
    title = "Extraterrestrial intelligent beings do not exist",
    year = "1981",
    journal = "Physics Today",
    url = "https://doi.org/10.1063/1.2914542",
    doi = "10.1063/1.2914542",
    openalex = "W2056795477"
}

The methodology and instrumentation of a 10 yr search for extraterrestrial intelligence (SETI) program by NASA, comprising 5 yr for instrumentation development and 5 yr for observations, is described. A full sky survey in two polarizations between 1.2 and 10 GHz with resolution binwidths down to 32 Hz, and a two polarization can between 1.2-3 GHz with resolution binwidths down to 1 Hz of 700 nearby solar type stars within 20 light years of earth will extend the sensitivity of previous surveys by 300 times and cover 20,000 times more frequency space. EM signals are perceived as the only means for detecting life outside the solar system, and the SETI effort is driven by the empirical experience that once a physical process has been observed to occur, its occurrence elsewhere is assured. Further discussion is given of the history of searches for life in the Universe, the SETI search strategy, instrumentation, and signal identification.

@article{openalexw1645620773,
    author = "Wolfe, J. H. and Billingham, J. and Edelson, R. E. and Crow, R. B. and Gulkis, S. and Olsen, E. T. and Oliver, Bernard M. and Peterson, A.",
    title = "SETI - The search for extraterrestrial intelligence - Plans and rationale",
    year = "1981",
    journal = "NASCP",
    abstract = "The methodology and instrumentation of a 10 yr search for extraterrestrial intelligence (SETI) program by NASA, comprising 5 yr for instrumentation development and 5 yr for observations, is described. A full sky survey in two polarizations between 1.2 and 10 GHz with resolution binwidths down to 32 Hz, and a two polarization can between 1.2-3 GHz with resolution binwidths down to 1 Hz of 700 nearby solar type stars within 20 light years of earth will extend the sensitivity of previous surveys by 300 times and cover 20,000 times more frequency space. EM signals are perceived as the only means for detecting life outside the solar system, and the SETI effort is driven by the empirical experience that once a physical process has been observed to occur, its occurrence elsewhere is assured. Further discussion is given of the history of searches for life in the Universe, the SETI search strategy, instrumentation, and signal identification.",
    openalex = "W1645620773"
}

@incollection{billingham1982the,
    author = "Billingham, J. and Seeger, C.L.",
    title = "THE DEMOGRAPHY OF EXTRATERRESTRIAL CIVILIZATIONS",
    year = "1982",
    booktitle = "Space Mankind's Fourth Environment",
    url = "https://doi.org/10.1016/b978-0-08-028708-9.50032-4",
    doi = "10.1016/b978-0-08-028708-9.50032-4",
    openalex = "W1560429481",
    pages = "397-404",
    references = "doi1010079789400991156, doi1010160004698180901493, doi1010160019103581901354, doi1010160019103581901366, doi1010160032063380900240, doi101016c20130032392, doi101017cbo9780511564970003, doi101038294010a0, doi101086112121, openalexw1645620773"
}

@article{doi1023071575053,
    author = "Turner, Ralph J. and Asimov, Isaac",
    title = "Extraterrestrial Civilizations",
    year = "1983",
    journal = "Leonardo",
    url = "https://doi.org/10.2307/1575053",
    doi = "10.2307/1575053",
    openalex = "W4250150290"
}

@misc{hoyle1983the3,
    author = "Hoyle, F",
    title = "The Intelligent Universe",
    year = "1983",
    howpublished = "London, Michael Joseph, 256 p",
    note = "talkorigins\_source = {true}; raw\_reference = {Hoyle, F., 1983, The Intelligent Universe: London, Michael Joseph, 256 p.}"
}

@article{openalexw1678269282,
    author = "Brin, G. D.",
    title = "The Great Silence - the Controversy Concerning Extraterrestrial Intelligent Life",
    year = "1983",
    journal = "Quarterly journal of the Royal Astronomical Society",
    openalex = "W1678269282"
}

▪ Abstract The search for evidence of extraterrestrial intelligence is placed in the broader astronomical context of the search for extrasolar planets and biomarkers of primitive life elsewhere in the universe. A decision tree of possible search strategies is presented as well as a brief history of the search for extraterrestrial intelligence (SETI) projects since 1960. The characteristics of 14 SETI projects currently operating on telescopes are discussed and compared using one of many possible figures of merit. Plans for SETI searches in the immediate and more distant future are outlined. Plans for success, the significance of null results, and some opinions on deliberate transmission of signals (as well as listening) are also included. SETI results to date are negative, but in reality, not much searching has yet been done.

@article{doi101146annurevastro391511,
    author = "Tarter, Jill",
    title = "The Search for Extraterrestrial Intelligence (SETI)",
    year = "2001",
    journal = "Annual Review of Astronomy and Astrophysics",
    abstract = "▪ Abstract The search for evidence of extraterrestrial intelligence is placed in the broader astronomical context of the search for extrasolar planets and biomarkers of primitive life elsewhere in the universe. A decision tree of possible search strategies is presented as well as a brief history of the search for extraterrestrial intelligence (SETI) projects since 1960. The characteristics of 14 SETI projects currently operating on telescopes are discussed and compared using one of many possible figures of merit. Plans for SETI searches in the immediate and more distant future are outlined. Plans for success, the significance of null results, and some opinions on deliberate transmission of signals (as well as listening) are also included. SETI results to date are negative, but in reality, not much searching has yet been done.",
    url = "https://doi.org/10.1146/annurev.astro.39.1.511",
    doi = "10.1146/annurev.astro.39.1.511",
    openalex = "W2106184471",
    references = "doi1010160032063367900955, doi101038186670a0, doi101038scientificamerican057580"
}

The Biological Universe (Dick 1996) analysed the history of the extraterrestrial life debate, documenting how scientists have assessed the chances of life beyond Earth during the 20th century. Here I propose another option – that we may in fact live in a postbiological universe, one that has evolved beyond flesh and blood intelligence to artificial intelligence that is a product of cultural rather than biological evolution. MacGowan & Ordway (1966), Davies (1995) and Shostak (1998), among others, have broached the subject, but the argument has not been given the attention it is due, nor has it been carried to its logical conclusion. This paper argues for the necessity of long-term thinking when contemplating the problem of intelligence in the universe. It provides arguments for a postbiological universe, based on the likely age and lifetimes of technological civilizations and the overriding importance of cultural evolution as an element of cosmic evolution. And it describes the general nature of a postbiological universe and its implications for the search for extraterrestrial intelligence.

@article{doi101017s147355040300137x,
    author = "Dick, Steven J.",
    title = "Cultural evolution, the postbiological universe and SETI",
    year = "2003",
    journal = "International Journal of Astrobiology",
    abstract = "The Biological Universe (Dick 1996) analysed the history of the extraterrestrial life debate, documenting how scientists have assessed the chances of life beyond Earth during the 20th century. Here I propose another option – that we may in fact live in a postbiological universe, one that has evolved beyond flesh and blood intelligence to artificial intelligence that is a product of cultural rather than biological evolution. MacGowan \& Ordway (1966), Davies (1995) and Shostak (1998), among others, have broached the subject, but the argument has not been given the attention it is due, nor has it been carried to its logical conclusion. This paper argues for the necessity of long-term thinking when contemplating the problem of intelligence in the universe. It provides arguments for a postbiological universe, based on the likely age and lifetimes of technological civilizations and the overriding importance of cultural evolution as an element of cosmic evolution. And it describes the general nature of a postbiological universe and its implications for the search for extraterrestrial intelligence.",
    url = "https://doi.org/10.1017/s147355040300137x",
    doi = "10.1017/s147355040300137x",
    openalex = "W2163357830"
}

Given the fact that there are perhaps 400 billion stars in our Galaxy alone, and perhaps 400 billion galaxies in the Universe, it stands to reason that somewhere out there, in the 14-billion-year-old cosmos, there is or once was a civilization at least as advanced as our own. The sheer enormity of the numbers almost demands that we accept the truth of this hypothesis. Why, then, have we encountered no evidence, no messages, no artifacts of these extraterrestrials? In this second, significantly revised and expanded edition of his widely popular book, Webb discusses in detail the (for now!) 75 most cogent and intriguing solutions to Fermi's famous paradox: If the numbers strongly point to the existence of extraterrestrial civilizations, why have we found no evidence of them?

@article{doi105860choice403987,
    title = "If the universe is teeming with aliens... where is everybody?: fifty solutions to the Fermi paradox and the problem of extraterrestrial life",
    year = "2003",
    journal = "Choice Reviews Online",
    abstract = "Given the fact that there are perhaps 400 billion stars in our Galaxy alone, and perhaps 400 billion galaxies in the Universe, it stands to reason that somewhere out there, in the 14-billion-year-old cosmos, there is or once was a civilization at least as advanced as our own. The sheer enormity of the numbers almost demands that we accept the truth of this hypothesis. Why, then, have we encountered no evidence, no messages, no artifacts of these extraterrestrials? In this second, significantly revised and expanded edition of his widely popular book, Webb discusses in detail the (for now!) 75 most cogent and intriguing solutions to Fermi's famous paradox: If the numbers strongly point to the existence of extraterrestrial civilizations, why have we found no evidence of them?",
    url = "https://doi.org/10.5860/choice.40-3987",
    doi = "10.5860/choice.40-3987",
    openalex = "W560908667"
}

We speculate about possible cosmic exploration by extraterrestrial civilizations using interstellar smart probes. We call attention to some emerging technologies that may be used for interstellar exploration. We estimate that advanced civilizations may already have these technologies and may be using them to contact their galactic neighbors. We explore some observational consequences of these contacting strategies.

@article{doi101017s0074180900193763,
    author = "Tough, Allen and Lemarchand, Guillermo A.",
    title = "Searching for Extraterrestrial Technologies Within Our Solar System",
    year = "2004",
    journal = "Symposium - International Astronomical Union",
    abstract = "We speculate about possible cosmic exploration by extraterrestrial civilizations using interstellar smart probes. We call attention to some emerging technologies that may be used for interstellar exploration. We estimate that advanced civilizations may already have these technologies and may be using them to contact their galactic neighbors. We explore some observational consequences of these contacting strategies.",
    url = "https://doi.org/10.1017/s0074180900193763",
    doi = "10.1017/s0074180900193763",
    openalex = "W1670370822",
    references = "doi1010160019103569900840, doi101016s0308596199000646, doi101038186670a0, doi101038scientificamerican057580, doi10106312811219, doi10230720049291, openalexw1489050524"
}

▪ Abstract Astrobiology is the study of the living universe. Astronomy provides the context for the origin and evolution of life on Earth. Conversely, discoveries about the terrestrial biosphere—from extremophilic microbes to the evolution of intelligence—inform our thinking about prospects for life elsewhere. Astrobiology includes the search for extraterrestrial life via in situ exploration, spectroscopy of solar and extrasolar planetary atmospheres, and the search for extraterrestrial intelligence. This review situates astrobiology within philosophical issues of the definition of life and the biological compatibility of the universe. It reviews the habitability of the Galaxy in general and of planets and moons in particular, and summarizes current controversies in origins-of-life research and in evidence for the earliest life on Earth. It critiques certain “rare Earth” and “anthropic” arguments, and considers four approaches to deciding whether intelligent life exists elsewhere in the Galaxy. It concludes that astrobiology must also speak to the future of human civilization.

@article{doi101146annurevastro43051804102202,
    author = "Chyba, Christopher F. and Hand, K. P.",
    title = "Astrobiology: The Study of the Living Universe",
    year = "2005",
    journal = "Annual Review of Astronomy and Astrophysics",
    abstract = "▪ Abstract Astrobiology is the study of the living universe. Astronomy provides the context for the origin and evolution of life on Earth. Conversely, discoveries about the terrestrial biosphere—from extremophilic microbes to the evolution of intelligence—inform our thinking about prospects for life elsewhere. Astrobiology includes the search for extraterrestrial life via in situ exploration, spectroscopy of solar and extrasolar planetary atmospheres, and the search for extraterrestrial intelligence. This review situates astrobiology within philosophical issues of the definition of life and the biological compatibility of the universe. It reviews the habitability of the Galaxy in general and of planets and moons in particular, and summarizes current controversies in origins-of-life research and in evidence for the earliest life on Earth. It critiques certain “rare Earth” and “anthropic” arguments, and considers four approaches to deciding whether intelligent life exists elsewhere in the Galaxy. It concludes that astrobiology must also speak to the future of human civilization.",
    url = "https://doi.org/10.1146/annurev.astro.43.051804.102202",
    doi = "10.1146/annurev.astro.43.051804.102202",
    openalex = "W2106694690",
    references = "doi1010160032063367900955, doi10106311325239"
}

@book{doi1010073540328386,
    author = "Ulmschneider, P.",
    title = "Intelligent Life in the Universe",
    year = "2006",
    booktitle = "Advances in astrobiology and biogeophysics",
    url = "https://doi.org/10.1007/3-540-32838-6",
    doi = "10.1007/3-540-32838-6",
    openalex = "W1503632359"
}

@article{crossref2009life,
    title = "Life in the universe: the abundance of extraterrestrial civilizations",
    year = "2009",
    journal = "Choice Reviews Online",
    url = "https://doi.org/10.5860/choice.46-6176",
    doi = "10.5860/choice.46-6176",
    number = "11",
    openalex = "W4229823969",
    pages = "46-6176-46-6176",
    volume = "46"
}

@article{doi101016jactaastro201111006,
    author = "Smart, John M.",
    title = "The transcension hypothesis: Sufficiently advanced civilizations invariably leave our universe, and implications for METI and SETI",
    year = "2011",
    journal = "Acta Astronautica",
    url = "https://doi.org/10.1016/j.actaastro.2011.11.006",
    doi = "10.1016/j.actaastro.2011.11.006",
    openalex = "W2050361934",
    references = "doi101017cbo9780511790881, doi101017cbo9781139164245, doi101073pnas0507655102, doi10114510818701081893, doi1023071425268, doi10230720031996, doi1048550arxiv08031087, doi105860choice275886, doi105860choice396411, doi105860choice495144, openalexw1618666643, openalexw2340966270"
}

We motivate the \^G infrared search for extraterrestrial civilizations with large energy supplies. We discuss some philosophical difficulties of SETI, and how communication SETI circumvents them. We review "Dysonian SETI", the search for artifacts of alien civilizations, and find that it is highly complementary to traditional communication SETI; the two together might succeed where either one, alone, has not. We discuss the argument of Hart (1975) that spacefaring life in the Milky Way should be either galaxy-spanning or non-existent, and examine a portion of his argument that we dub the "monocultural fallacy". We discuss some rebuttals to Hart that invoke sustainability and predict long Galaxy colonization timescales. We find that the maximum Galaxy colonization timescale is actually much shorter than previous work has found ($< 10^9$ yr), and that many "sustainability" counter-arguments to Hart's thesis suffer from the monocultural fallacy. We extend Hart's argument to alien energy supplies, and argue that detectably large energy supplies can plausibly be expected to exist because life has potential for exponential growth until checked by resource or other limitations, and intelligence implies the ability to overcome such limitations. As such, if Hart's thesis is correct then searches for large alien civilizations in other galaxies may be fruitful; if it is incorrect, then searches for civilizations within the Milky Way are more likely to succeed than Hart argued. We review some past Dysonian SETI efforts, and discuss the promise of new mid-infrared surveys, such as that of WISE.

@article{doi1010880004637x792126,
    author = "Wright, J. T. and Mullan, B. and Sigurdsson, S. and Povich, M. S.",
    title = "THE Ĝ INFRARED SEARCH FOR EXTRATERRESTRIAL CIVILIZATIONS WITH LARGE ENERGY SUPPLIES. I. BACKGROUND AND JUSTIFICATION",
    year = "2014",
    journal = "The Astrophysical Journal",
    abstract = {We motivate the \^G infrared search for extraterrestrial civilizations with large energy supplies. We discuss some philosophical difficulties of SETI, and how communication SETI circumvents them. We review "Dysonian SETI", the search for artifacts of alien civilizations, and find that it is highly complementary to traditional communication SETI; the two together might succeed where either one, alone, has not. We discuss the argument of Hart (1975) that spacefaring life in the Milky Way should be either galaxy-spanning or non-existent, and examine a portion of his argument that we dub the "monocultural fallacy". We discuss some rebuttals to Hart that invoke sustainability and predict long Galaxy colonization timescales. We find that the maximum Galaxy colonization timescale is actually much shorter than previous work has found ($< 10^9$ yr), and that many "sustainability" counter-arguments to Hart's thesis suffer from the monocultural fallacy. We extend Hart's argument to alien energy supplies, and argue that detectably large energy supplies can plausibly be expected to exist because life has potential for exponential growth until checked by resource or other limitations, and intelligence implies the ability to overcome such limitations. As such, if Hart's thesis is correct then searches for large alien civilizations in other galaxies may be fruitful; if it is incorrect, then searches for civilizations within the Milky Way are more likely to succeed than Hart argued. We review some past Dysonian SETI efforts, and discuss the promise of new mid-infrared surveys, such as that of WISE.},
    url = "https://doi.org/10.1088/0004-637x/792/1/26",
    doi = "10.1088/0004-637x/792/1/26",
    openalex = "W2061889550"
}

Abstract Pulsars have at least two impressive applications. First, they can be used as highly accurate clocks, comparable in stability to atomic clocks; secondly, a small subset of pulsars, millisecond X-ray pulsars, provide all the necessary ingredients for a passive galactic positioning system. This is known in astronautics as X-ray pulsar-based navigation (XNAV). XNAV is comparable to GPS, except that it operates on a galactic scale. I propose a SETI-XNAV research program to test the hypothesis that this pulsar positioning system might be an instance of galactic-scale engineering by extraterrestrial beings. The paper starts by exposing the basics of pulsar navigation, continues with a critique of the rejection of the extraterrestrial hypothesis when pulsars were first discovered. The core section of the paper proposes lines of inquiry for SETI-XNAV, related to the pulsar distribution and power in the galaxy; their population; their evolution; possible pulse synchronizations; pulsar usability when navigating near the speed of light; decoding galactic coordinates; directed panspermia; and information content in pulses. Even if pulsars are natural, they are likely to be used as standards by ETIs in the galaxy. I discuss possible objections and potential benefits for humanity, whether the research program succeeds or not.

@article{doi101017s147355041700043x,
    author = "Vidal, Clément",
    title = "Pulsar positioning system: a quest for evidence of extraterrestrial engineering",
    year = "2017",
    journal = "International Journal of Astrobiology",
    abstract = "Abstract Pulsars have at least two impressive applications. First, they can be used as highly accurate clocks, comparable in stability to atomic clocks; secondly, a small subset of pulsars, millisecond X-ray pulsars, provide all the necessary ingredients for a passive galactic positioning system. This is known in astronautics as X-ray pulsar-based navigation (XNAV). XNAV is comparable to GPS, except that it operates on a galactic scale. I propose a SETI-XNAV research program to test the hypothesis that this pulsar positioning system might be an instance of galactic-scale engineering by extraterrestrial beings. The paper starts by exposing the basics of pulsar navigation, continues with a critique of the rejection of the extraterrestrial hypothesis when pulsars were first discovered. The core section of the paper proposes lines of inquiry for SETI-XNAV, related to the pulsar distribution and power in the galaxy; their population; their evolution; possible pulse synchronizations; pulsar usability when navigating near the speed of light; decoding galactic coordinates; directed panspermia; and information content in pulses. Even if pulsars are natural, they are likely to be used as standards by ETIs in the galaxy. I discuss possible objections and potential benefits for humanity, whether the research program succeeds or not.",
    url = "https://doi.org/10.1017/s147355041700043x",
    doi = "10.1017/s147355041700043x",
    openalex = "W2608353587",
    references = "doi1010079783319050621, doi101016001910357390050x, doi101016037015739190064s, doi101017s147355041700043x, doi101038216567a0, doi101038218731a0, doi101038300615a0, doi101038nphoton2012138, doi101093mnras2343477, doi101109mcom20031204759, doi101111j13652966200509087x, doi101126scienceaaj2038, doi1012942lrr20088"
}

We report on a search for engineered signals from a sample of 692 nearby stars using the Robert C. Byrd Green Bank Telescope, undertaken as part of the Breakthrough Listen Initiative search for extraterrestrial intelligence. Observations were made over 1.1-1.9 GHz (L band), with three sets of five-minute observations of the 692 primary targets, interspersed with five-minute observations of secondary targets. By comparing the "ON" and "OFF" observations, we are able to identify terrestrial interference and place limits on the presence of engineered signals from putative extraterrestrial civilizations inhabiting the environs of the target stars. During the analysis, 11 events passed our thresholding algorithm, but a detailed analysis of their properties indicates that they are consistent with known examples of anthropogenic radio-frequency interference. We conclude that, at the time of our observations, none of the observed systems host high-duty-cycle radio transmitters emitting between 1.1 and 1.9 GHz with an Equivalent Isotropic Radiated Power of similar to 10(13) W, which is readily achievable by our own civilization. Our results suggest that fewer than similar to 0.1% of the stellar systems within 50 pc possess the type of transmitters searched in this survey.

@article{doi10384715384357aa8d1b,
    author = "Enriquez, J. Emilio and Siemion, Andrew and Foster, Griffin and Gajjar, Vishal and Hellbourg, Greg and Hickish, J. and Isaacson, Howard and Price, Danny C. and Croft, S. and DeBoer, David R. and Lebofsky, Matt and MacMahon, David H. E. and Werthimer, Dan",
    title = "The Breakthrough Listen Search for Intelligent Life: 1.1–1.9 GHz Observations of 692 Nearby Stars",
    year = "2017",
    journal = "The Astrophysical Journal",
    abstract = {We report on a search for engineered signals from a sample of 692 nearby stars using the Robert C. Byrd Green Bank Telescope, undertaken as part of the Breakthrough Listen Initiative search for extraterrestrial intelligence. Observations were made over 1.1-1.9 GHz (L band), with three sets of five-minute observations of the 692 primary targets, interspersed with five-minute observations of secondary targets. By comparing the "ON" and "OFF" observations, we are able to identify terrestrial interference and place limits on the presence of engineered signals from putative extraterrestrial civilizations inhabiting the environs of the target stars. During the analysis, 11 events passed our thresholding algorithm, but a detailed analysis of their properties indicates that they are consistent with known examples of anthropogenic radio-frequency interference. We conclude that, at the time of our observations, none of the observed systems host high-duty-cycle radio transmitters emitting between 1.1 and 1.9 GHz with an Equivalent Isotropic Radiated Power of similar to 10(13) W, which is readily achievable by our own civilization. Our results suggest that fewer than similar to 0.1\% of the stellar systems within 50 pc possess the type of transmitters searched in this survey.},
    url = "https://doi.org/10.3847/1538-4357/aa8d1b",
    doi = "10.3847/1538-4357/aa8d1b",
    openalex = "W2755790435"
}

Abstract We present a cosmic perspective on the search for life and examine the likely number of Communicating Extra-Terrestrial Intelligent (CETI) civilizations in our Galaxy by utilizing the latest astrophysical information. Our calculation involves Galactic star formation histories, metallicity distributions, and the likelihood of stars hosting Earth-like planets in their habitable zones, under specific assumptions which we describe as the Astrobiological Copernican Weak and Strong conditions. These assumptions are based on the one situation in which intelligent, communicative life is known to exist—on our own planet. This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so. We investigate the possible number of CETI civilizations based on different scenarios. At one extreme is the Weak Astrobiological Copernican scenario—such that a planet forms intelligent life sometime after 5 Gyr, but not earlier. The other is the Strong Astrobiological Copernican scenario in which life must form between 4.5 and 5.5 Gyr, as on Earth. In the Strong scenario (under the strictest set of assumptions), we find there should be at least civilizations within our Galaxy: this is a lower limit, based on the assumption that the average lifetime, L, of a communicating civilization is 100 yr (since we know that our own civilization has had radio communications for this time). If spread uniformly throughout the Galaxy this would imply that the nearest CETI is at most lt-yr away and most likely hosted by a low-mass M-dwarf star, likely far surpassing our ability to detect it for the foreseeable future, and making interstellar communication impossible. Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within the Galaxy based on variations of our assumptions.

@article{doi10384715384357ab8225,
    author = "Westby, Tom and Conselice, Christopher J.",
    title = "The Astrobiological Copernican Weak and Strong Limits for Intelligent Life",
    year = "2020",
    journal = "The Astrophysical Journal",
    abstract = "Abstract We present a cosmic perspective on the search for life and examine the likely number of Communicating Extra-Terrestrial Intelligent (CETI) civilizations in our Galaxy by utilizing the latest astrophysical information. Our calculation involves Galactic star formation histories, metallicity distributions, and the likelihood of stars hosting Earth-like planets in their habitable zones, under specific assumptions which we describe as the Astrobiological Copernican Weak and Strong conditions. These assumptions are based on the one situation in which intelligent, communicative life is known to exist—on our own planet. This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so. We investigate the possible number of CETI civilizations based on different scenarios. At one extreme is the Weak Astrobiological Copernican scenario—such that a planet forms intelligent life sometime after 5 Gyr, but not earlier. The other is the Strong Astrobiological Copernican scenario in which life must form between 4.5 and 5.5 Gyr, as on Earth. In the Strong scenario (under the strictest set of assumptions), we find there should be at least civilizations within our Galaxy: this is a lower limit, based on the assumption that the average lifetime, L, of a communicating civilization is 100 yr (since we know that our own civilization has had radio communications for this time). If spread uniformly throughout the Galaxy this would imply that the nearest CETI is at most lt-yr away and most likely hosted by a low-mass M-dwarf star, likely far surpassing our ability to detect it for the foreseeable future, and making interstellar communication impossible. Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within the Galaxy based on variations of our assumptions.",
    url = "https://doi.org/10.3847/1538-4357/ab8225",
    doi = "10.3847/1538-4357/ab8225",
    openalex = "W3015792756",
    references = "doi101086145971, doi101086376392, doi101086506610, doi1010880004637x766281, doi1010880004637x807145, doi1010880004637x8082132, doi101146annurevastro081811125615, doi101146annurevastro081915023441, openalexw2900548288, openalexw3100024326"
}

Abstract The 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.

@article{doi101017s1473550422000404,
    author = "Smith, Reginald D.",
    title = "Communicating extraterrestrial intelligence (CETI) interaction models based on the Drake equation",
    year = "2022",
    journal = "International Journal of Astrobiology",
    abstract = "Abstract The 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.",
    url = "https://doi.org/10.1017/s1473550422000404",
    doi = "10.1017/s1473550422000404",
    openalex = "W4311106122",
    references = "doi101093mnrasstaa512"
}

@incollection{anton2023protosociology,
    author = "Anton, Andreas and Schetsche, Michael",
    title = "Proto-Sociology of Extraterrestrial Civilizations",
    year = "2023",
    booktitle = "Meeting the Alien",
    url = "https://doi.org/10.1007/978-3-658-41317-0\_10",
    doi = "10.1007/978-3-658-41317-0\_10",
    openalex = "W4381623246",
    pages = "199-228",
    references = "doi1010079783319620459, doi1010079783642328367, doi101007s1160900901023, doi101016jactaastro201111006, doi101017s147355040300137x, doi101017s1473550417000349, doi101017s1473550417000362, doi101023a1020503324273, doi101038415023a, openalexw1598213472"
}

@article{doi101038s41550023021342,
    author = "Crawford, Ian and Schulze‐Makuch, Dirk",
    title = "Is the apparent absence of extraterrestrial technological civilizations down to the zoo hypothesis or nothing?",
    year = "2023",
    journal = "Nature Astronomy",
    url = "https://doi.org/10.1038/s41550-023-02134-2",
    doi = "10.1038/s41550-023-02134-2",
    openalex = "W4390345558",
    references = "doi1010160019103573901103, doi1010160019103573901115, doi101017cbo9780511614736, doi101038s41586022044965, doi1010880004637x792126, doi101089ast20151387, doi101093mnrasstaa512, doi101093oso97801985029440010001, doi101146annurevearth031208100209, doi101146annurevecolsys36102403114735, doi10384715383881abc418"
}

ABSTRACT The Search for Extra-Terrestrial Intelligence (SETI) has been conducted for over 60 yr, yet no technosignatures have been identified. Previous studies have focused on stars in our Galaxy, with few searches in the extragalactic Universe despite a larger volume being available. Civilizations capable of harvesting energy from a star or a galaxy are classified as KII or KIII on the Kardashev scale, respectively. Technosignatures from such advanced civilizations would be extremely luminous and detectable by current radio telescopes, even from distant galaxies. To explore the frontier of extragalactic SETI, we investigate the likely prevalence of extragalactic civilizations possessing a radio transmitter, known as the transmitter rate, based on observational results from the Breakthrough Listen (BL) observations. We calculated the transmitter rate by considering the background galaxies in the field of view of target stars in BL observations. We used a statistical method to derive the total mass of stars in those background galaxies from a galaxy stellar mass function. Our statistical method suggests that less than one in hundreds of trillions of extragalactic civilizations within 969 Mpc possess a radio transmitter above 7.7 × 1026 W of power, assuming one civilization per one-solar-mass stellar system. Additionally, we cross-matched the BL survey fields with the WISE × SuperCOSMOS Photometric Redshift Catalogue and compared with the statistical method. Our result sets the strictest limits to date on the transmitter rate at such high-power levels, emphasizing the high efficiency of searching for radio transmitters in galaxies and the rarity of technologically advanced civilizations in our Universe.

@article{doi101093mnrasstad993,
    author = "Uno, Yuri and Hashimoto, T. and Goto, Tomotsugu and Ho, Simon C-C and Hsu, Tzu-Yin and Burns, Ross A.",
    title = "Upper limits on transmitter rate of extragalactic civilizations placed by Breakthrough Listen observations",
    year = "2023",
    journal = "Monthly Notices of the Royal Astronomical Society",
    abstract = "ABSTRACT The Search for Extra-Terrestrial Intelligence (SETI) has been conducted for over 60 yr, yet no technosignatures have been identified. Previous studies have focused on stars in our Galaxy, with few searches in the extragalactic Universe despite a larger volume being available. Civilizations capable of harvesting energy from a star or a galaxy are classified as KII or KIII on the Kardashev scale, respectively. Technosignatures from such advanced civilizations would be extremely luminous and detectable by current radio telescopes, even from distant galaxies. To explore the frontier of extragalactic SETI, we investigate the likely prevalence of extragalactic civilizations possessing a radio transmitter, known as the transmitter rate, based on observational results from the Breakthrough Listen (BL) observations. We calculated the transmitter rate by considering the background galaxies in the field of view of target stars in BL observations. We used a statistical method to derive the total mass of stars in those background galaxies from a galaxy stellar mass function. Our statistical method suggests that less than one in hundreds of trillions of extragalactic civilizations within 969 Mpc possess a radio transmitter above 7.7 × 1026 W of power, assuming one civilization per one-solar-mass stellar system. Additionally, we cross-matched the BL survey fields with the WISE × SuperCOSMOS Photometric Redshift Catalogue and compared with the statistical method. Our result sets the strictest limits to date on the transmitter rate at such high-power levels, emphasizing the high efficiency of searching for radio transmitters in galaxies and the rarity of technologically advanced civilizations in our Universe.",
    url = "https://doi.org/10.1093/mnras/stad993",
    doi = "10.1093/mnras/stad993",
    openalex = "W4362568660",
    references = "doi101038184844a0, doi101046j13658711200104022x, doi10106313057500, doi101086145971, doi101086376392, doi1010880004637x782290, doi101093mnrasstac472, doi101111j13652966201220340x, doi101146annurevastro081811125615, doi10384715383881aabc4f"
}

Various messages have been sent out to potentially existing intelligent extraterrestrial life since the 1960s. Considering the significance of such messages as a medium of first contact and representation of humankind, it is surprising that they have received no attention from sociology. What is their purpose? Who speaks for earth? What is their content and has it changed over time? This work seeks to answer these questions by analyzing all relevant messages (N = 14) sent to outer space as well as related press coverage and official statements from the period 1962–2018. Analyses find a striking shift in purpose, authorship, and content, from political and scientific elites celebrating nation, science and (high) culture to, more recently, for-profits and science facilitating commercial exploitation but also individual agency and planetary awareness. However, such plurality makes global consensus and oversight on whether and what kind of messages should be sent even more difficult.

@article{doi1030884jogs20230110,
    author = "Zapp, Mike",
    title = "Speaking Out to Outer Space – An Analysis of the Humanity's Messages to Extraterrestrial Intelligent Life, 1962–2018",
    year = "2023",
    journal = "Journal of Globalization Studies",
    abstract = "Various messages have been sent out to potentially existing intelligent extraterrestrial life since the 1960s. Considering the significance of such messages as a medium of first contact and representation of humankind, it is surprising that they have received no attention from sociology. What is their purpose? Who speaks for earth? What is their content and has it changed over time? This work seeks to answer these questions by analyzing all relevant messages (N = 14) sent to outer space as well as related press coverage and official statements from the period 1962–2018. Analyses find a striking shift in purpose, authorship, and content, from political and scientific elites celebrating nation, science and (high) culture to, more recently, for-profits and science facilitating commercial exploitation but also individual agency and planetary awareness. However, such plurality makes global consensus and oversight on whether and what kind of messages should be sent even more difficult.",
    url = "https://doi.org/10.30884/jogs/2023.01.10",
    doi = "10.30884/jogs/2023.01.10",
    openalex = "W4390730917",
    references = "doi101007978303033730814, doi101007s111860079035z, doi1010801369118x20151020824, doi10111915053112, doi101162002081897550474, doi1011770263276403020002001, doi1011771749975507082052, doi1015159783110240450, doi1023073172751, doi105860choice463820"
}

Abstract The Breakthrough Listen search for intelligent life is, to date, the most extensive technosignature search of nearby celestial objects. We present a radio technosignature search of the centers of 97 nearby galaxies, observed by Breakthrough Listen at the Robert C. Byrd Green Bank Telescope. We performed a narrowband Doppler drift search using the turboSETI pipeline with a minimum signal-to-noise parameter threshold of 10, across a drift rate range of ±4 Hz s −1, with a spectral resolution of 3 Hz and a time resolution of ∼18.25 s. We removed radio frequency interference (RFI) by using an on-source/off-source cadence pattern of six observations and discarding signals with Doppler drift rates of 0. We assess factors affecting the sensitivity of the Breakthrough Listen data reduction and search pipeline using signal injection and recovery techniques and apply new methods for the investigation of the RFI environment. We present results in four frequency bands covering 1–11 GHz, and place constraints on the presence of transmitters with equivalent isotropic radiated power on the order of 10 26 W, corresponding to the theoretical power consumption of Kardashev Type II civilizations.

@article{doi10384715383881acf576,
    author = "Choza, Carmen and Bautista, Daniel and Croft, S. and Siemion, Andrew and Brzycki, Bryan and Bhattaram, Krishnakumar and Czech, Daniel and de Pater, Imke and Gajjar, Vishal and Isaacson, Howard and Lacker, Kevin and Lacki, Brian C. and Lebofsky, Matt and MacMahon, David H. E. and Price, Danny C. and Schoultz, Sarah and Sheikh, Sofia Z. and Varghese, S. S. and Morgan, L.N.C. and Drew, Jamie and Worden, S. Pete",
    title = "The Breakthrough Listen Search for Intelligent Life: Technosignature Search of 97 Nearby Galaxies",
    year = "2023",
    journal = "The Astronomical Journal",
    abstract = "Abstract The Breakthrough Listen search for intelligent life is, to date, the most extensive technosignature search of nearby celestial objects. We present a radio technosignature search of the centers of 97 nearby galaxies, observed by Breakthrough Listen at the Robert C. Byrd Green Bank Telescope. We performed a narrowband Doppler drift search using the turboSETI pipeline with a minimum signal-to-noise parameter threshold of 10, across a drift rate range of ±4 Hz s −1, with a spectral resolution of 3 Hz and a time resolution of ∼18.25 s. We removed radio frequency interference (RFI) by using an on-source/off-source cadence pattern of six observations and discarding signals with Doppler drift rates of 0. We assess factors affecting the sensitivity of the Breakthrough Listen data reduction and search pipeline using signal injection and recovery techniques and apply new methods for the investigation of the RFI environment. We present results in four frequency bands covering 1–11 GHz, and place constraints on the presence of transmitters with equivalent isotropic radiated power on the order of 10 26 W, corresponding to the theoretical power consumption of Kardashev Type II civilizations.",
    url = "https://doi.org/10.3847/1538-3881/acf576",
    doi = "10.3847/1538-3881/acf576",
    openalex = "W4389391084",
    references = "doi101038184844a0, doi101038s4158602026492, doi10106313057500, doi101086164079, doi1010880004637x7952158, doi10108817551315311012012, doi101089ast20171729, doi101093mnrasstad993, doi10384715384357aa8d1b, openalexw3099878876, openalexw3124069841"
}

Whether intelligent species exist in our galaxy has long remained an unresolved question withinthe Fermi Paradox. While numerous theories have been proposed to address the Fermi Paradoxand theories and estimates as to the possible number of intelligent civilizations in our galaxy hasbeen proposed. The Fermi paradox also has hidden implications which may be explored utilizingthe interrelationship between astrophysics, neurobiology, and complex network theory and whichprovides a deeper understanding of the mathematical implications behind the origin and evolutionof life in the universe.

@misc{chou2024the,
    author = "Chou, Chung-Pin",
    title = "The Fermi Paradox and the Emergence of Intelligent Extraterrestrial Civilizations",
    year = "2024",
    abstract = "Whether intelligent species exist in our galaxy has long remained an unresolved question withinthe Fermi Paradox. While numerous theories have been proposed to address the Fermi Paradoxand theories and estimates as to the possible number of intelligent civilizations in our galaxy hasbeen proposed. The Fermi paradox also has hidden implications which may be explored utilizingthe interrelationship between astrophysics, neurobiology, and complex network theory and whichprovides a deeper understanding of the mathematical implications behind the origin and evolutionof life in the universe.",
    url = "https://doi.org/10.31219/osf.io/84rwq",
    doi = "10.31219/osf.io/84rwq",
    openalex = "W4401555709",
    references = "doi101093mnrasstaa512, doi101093mnrasstad993, doi103389neuro090312009, doi10384715383881acf576, doi10384715384357aa961c, doi10384715384357ab8225, doi104236oalib1108154, openalexw1618666643, openalexw3045218883"
}

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.

@article{doi101016jactaastro202403052,
    author = "Garrett, M. A.",
    title = "Is artificial intelligence the great filter that makes advanced technical civilisations rare in the universe?",
    year = "2024",
    journal = "Acta Astronautica",
    abstract = {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.},
    url = "https://doi.org/10.1016/j.actaastro.2024.03.052",
    doi = "10.1016/j.actaastro.2024.03.052",
    openalex = "W4393930779",
    references = "doi101093mnrasstaa512, doi10384715383881acf576"
}

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.

@article{doi101038s4159802454700x,
    author = "Stern, Robert J. and Gerya, Taras",
    title = "The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations",
    year = "2024",
    journal = "Scientific Reports",
    abstract = "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.",
    url = "https://doi.org/10.1038/s41598-024-54700-x",
    doi = "10.1038/s41598-024-54700-x",
    openalex = "W4394747096",
    references = "doi101007s120520110357y, doi101093mnrasstaa512"
}

We introduce the concept of a one-way, broadband information package, the Cosmic Illuminating Gift, intended to provide distant intelligences with fundamental empirical data about the Universe. Unlike previous messaging to extraterrestrial intelligences (METI) that emphasized greetings or cultural identity, the Gift aims to transmit unbiased, universally interpretable information that recipients could not otherwise obtain due to their distinct spacetime position and epoch. By emphasizing raw observations, rather than human interpretations or cosmological models, the Gift aspires to serve as a neutral and enduring resource. A central assumption of the project is that any potential recipients are likely to possess a level of intelligence and technological sophistication far beyond our own. Accordingly, the content and encoding of the Gift are not designed to “teach” fundamentals, but to deliver compact, logically structured packets that such civilizations could decode even at extremely low signal-to-noise levels. This perspective shifts the challenge from brute-force transmission to ensuring that photons arrive in spectrally quiet windows and that the format is unmistakably artificial and distinguishable from astrophysical backgrounds. We outline strategies for content selection, encoding, and transmission that reflect this assumption. Practical implementation is feasible with current or near-term infrastructure, and future advances will only improve the quality of subsequent Gifts. Ultimately, the endeavor is unique among scientific projects in that it anticipates no feedback or measurable result within the span of our civilization’s timeline. Its significance lies instead in the act of contribution itself: offering a durable, universal dataset as a gesture of intellectual solidarity across cosmic distances.

@article{doi103390universe12040115,
    author = "Shafieloo, Arman",
    title = "Cosmic Illuminating Gift: A One-Way Information Box for Extraterrestrial Intelligences",
    year = "2026",
    journal = "Universe",
    abstract = "We introduce the concept of a one-way, broadband information package, the Cosmic Illuminating Gift, intended to provide distant intelligences with fundamental empirical data about the Universe. Unlike previous messaging to extraterrestrial intelligences (METI) that emphasized greetings or cultural identity, the Gift aims to transmit unbiased, universally interpretable information that recipients could not otherwise obtain due to their distinct spacetime position and epoch. By emphasizing raw observations, rather than human interpretations or cosmological models, the Gift aspires to serve as a neutral and enduring resource. A central assumption of the project is that any potential recipients are likely to possess a level of intelligence and technological sophistication far beyond our own. Accordingly, the content and encoding of the Gift are not designed to “teach” fundamentals, but to deliver compact, logically structured packets that such civilizations could decode even at extremely low signal-to-noise levels. This perspective shifts the challenge from brute-force transmission to ensuring that photons arrive in spectrally quiet windows and that the format is unmistakably artificial and distinguishable from astrophysical backgrounds. We outline strategies for content selection, encoding, and transmission that reflect this assumption. Practical implementation is feasible with current or near-term infrastructure, and future advances will only improve the quality of subsequent Gifts. Ultimately, the endeavor is unique among scientific projects in that it anticipates no feedback or measurable result within the span of our civilization’s timeline. Its significance lies instead in the act of contribution itself: offering a durable, universal dataset as a gesture of intellectual solidarity across cosmic distances.",
    url = "https://doi.org/10.3390/universe12040115",
    doi = "10.3390/universe12040115",
    openalex = "W7154243848",
    references = "doi101017s147355041700043x"
}