#### Star One

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« Reply #180 on: 04/23/2018 07:52 PM »
Could an Industrial Prehuman Civilization Have Existed on Earth Before Ours?

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Today, less than 1 percent of Earth’s surface is urbanized, and the chance that any of our great cities would remain over tens of millions of years is vanishingly low, says Jan Zalasiewicz, a geologist at the University of Leicester in England. A metropolis’s ultimate fate, he notes, mostly depends on whether the surrounding surface is subsiding (to be locked in rock) or rising (to be eroded away by rain and wind). “New Orleans is sinking; San Francisco is rising,” he says. The French Quarter, it seems, has much better chances of entering the geologic record than Haight–Ashbury.

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“After a couple of million years,” Frank says, “the chances are that any physical reminder of your civilization has vanished, so you have to search for things like sedimentary anomalies or isotopic ratios that look off.” The shadows of many prehuman civilizations could, in principle, lurk hidden in such subtleties.

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Taking all this into consideration, what remains is a menu of diffuse long-lived tracers including fossil fuel combustion residues (carbon, primarily), evidence of mass extinctions, plastic pollutants, synthetic chemical compounds not found in nature and even transuranic isotopes from nuclear fission. In other words, what we would need to look for in the geologic record are the same distinctive signals that humans are laying down right now.

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“I find it amazing that no one had worked all this out before, and I’m really glad that somebody has taken a closer look at it,” says Pennsylvania State University astronomer Jason Wright, who last year published “a fluffy little paper” exploring the counterintuitive notion that the best place to find evidence of any of Earth’s putative prehuman civilizations may well be off-world. If, for instance, dinosaurs built interplanetary rockets, presumably some remnants of that activity might remain preserved in stable orbits or on the surfaces of more geologically inert celestial bodies such as the moon.

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Wright also acknowledges the potential for this work to be misinterpreted. “Of course, no matter what, this is going to be interpreted as ‘Astronomers Say Silurians Might Have Existed,’ even though the premise of this work is that there is no such evidence,” he says. “Then again, absence of evidence is not evidence of absence.”

https://www.scientificamerican.com/article/could-an-industrial-prehuman-civilization-have-existed-on-earth-before-ours/

#### Star One

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« Reply #181 on: 04/24/2018 08:55 PM »
SETI with Gaia: The observational signatures of nearly complete Dyson spheres

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A star enshrouded in a Dyson sphere with high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson-sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson-sphere candidates in the sample of stars common to Gaia Data Release 1 and RAVE Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M⊙). This scenario can be further tested through upcoming Gaia data releases.

https://arxiv.org/abs/1804.08351

#### jebbo

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« Reply #182 on: 04/26/2018 05:33 PM »
Don't think the discrepancy for TYC 6111-1162-1 holds up given Gaia DR2, which has a significantly lower parallax. The spectroscopic and astrometric are now only ~1.5 sigma apart.

#### Star One

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« Reply #183 on: 04/27/2018 08:14 PM »
Another fascinating article on the Silurian Hypothesis.

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Ancient aliens. Devious dinosaurs. Benevolent Atlanteans. Could such legendary civilisations have left any trace behind that would survive the eons? Archaeologists are certain: we have … so why not them?

« Last Edit: 04/27/2018 08:16 PM by Star One »

#### Star One

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« Reply #184 on: 05/09/2018 07:32 PM »
Congress Is Quietly Nudging NASA to Look for Aliens

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That could soon change. Lawmakers in the House of Representatives recently proposed legislation for nasa’s future that includes some intriguing language. The space agency, the bill recommends, should spend $10 million on the “search for technosignatures, such as radio transmissions” in the next two fiscal years. The House bill—should it survive a vote in the House and passage in the Senate—can only make recommendations for how agencies should use federal funding. But for seti researchers like Tarter, the fact that it even exists is thrilling. It’s the first time congressional lawmakers have proposed using federal cash to fund seti in 25 years. https://www.theatlantic.com/amp/article/558512/ #### Star One • Senior Member • Posts: 9395 • UK • Liked: 1689 • Likes Given: 183 ##### Re: General SETI Thread « Reply #185 on: 05/10/2018 07:22 PM » NASA Awards Grants for Research into Life in Universe NASA has awarded five-year grants, each approximately$8 million, to three research teams that will study the origins, evolution, distribution and future of life in the universe.

“With NASA’s Transiting Exoplanet Survey Satellite on its way to discover new worlds around our nearest stellar neighbors, Cassini’s discovery of the ingredients necessary for life in Enceladus’s plumes, and with Europa Clipper and Mars 2020 on the horizon, these research teams will provide the critical interdisciplinary expertise needed to help interpret data from these missions and future astrobiology-focused missions,” said NASA Chief Scientist Jim Green.

The interdisciplinary teams will become members of the NASA Astrobiology Institute (NAI), headquartered at the agency’s Ames Research Center in Silicon Valley, California.

The selected teams are:

Evolution of Nanomachines in Geospheres and Microbial Ancestors (ENIGMA)

Rutgers University

New Brunswick, New Jersey

Led by Professor Paul Falkowski, the ENIGMA team will investigate how proteins evolved to become the catalysts of life on Earth by looking at prebiotic molecules and enzymes that are ancestral and common across many types of microbes.

The Astrobiology Center for Isotopologue Research (ACIR)

Pennsylvania State University, University Park

ACIR, led by Professor Kate Freeman, will address how the features of elements within molecules reveal the origins and history of organic compounds, from compounds that arrived from planetary environments to those that were derived from metabolic systems, using cutting-edge observational and computational tools.

NASA’s Jet Propulsion Laboratory (JPL)

Dr. Rosaly Lopes will lead research at JPL focusing on Saturn’s largest moon, Titan, to address what habitable environments may exist on the moon and what potential signatures of life would be expected, using data from the Cassini-Huygens mission. These data cover a wide swath of the moon, from beneath its surface all the way up through its thick atmosphere.

“The intellectual scope of astrobiology is vast, from understanding how our planet became habitable and inhabited, to understanding how life has adapted to Earth’s harshest environments, to exploring other worlds with the most advanced technologies to search for signs of life,” said Mary Voytek, director of the Astrobiology Program at NASA Headquarters. “The new teams will complement our existing teams to cover breadth of astrobiology, and by coming together in the NAI, they will make the connections between disciplines and organizations that stimulate fundamental scientific advances.”

“We are delighted to welcome these three new NAI teams into the Institute family and look forward to the important work that they will accomplish over the time of their awards,” said NAI Director Penelope Boston. “Our existing teams are waiting to explore overlapping interests with the new project teams and the potential for even greater exchange of information, inspiration, and synergy.”

The NAI serves a vital role in advancing the goals of the NASA Astrobiology Program, with a focus on seeking the answers to these fundamental questions: How does life begin and evolve? Is there life beyond Earth and, if so, how can we detect it? What is the future of life on Earth and beyond?

https://nai.nasa.gov/

#### Star One

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« Reply #186 on: 05/18/2018 03:28 PM »

#### Star One

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« Reply #187 on: 05/20/2018 08:24 PM »

Expanding cosmological civilizations on the back of an envelope

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We present a simplified description of expansionistic life in the standard relativistic cosmology. The resulting model is exactly integrable, yielding a simple set of predictive formulas. This allows one to quickly propose new scenarios for the life appearance rate and the dominant expansion speed and evaluate the observable consequences. These include the expected number and angular size of visible expanding domains, the total eclipsed fraction of the sky, and the life-saturated fraction of the universe. We also propose a simple anthropic bound on observable quantities, as a function of the dominant expansion velocity alone. The goal is to create a simple and intuition-building tool for use in the context of cosmology, extragalactic SETI, and futures studies. We discuss the general predictions of this framework, including conditions giving rise to an "extragalactic Fermi paradox," in which zero civilizations are visible beyond the Milky Way. This can occur even if a substantial fraction of the universe is already saturated with ambitious life.

https://arxiv.org/abs/1805.06329

#### Star One

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« Reply #188 on: 06/13/2018 07:41 PM »

Anders Sandberg, Eric Drexler, Toby Ord

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

https://arxiv.org/abs/1806.02404

I like the way they try and find a way to supplant an equation that has a lot of guesses but using a whole other bunch of guesses. Because at the end that’s all any of it is.
« Last Edit: 06/13/2018 09:40 PM by Star One »

#### RotoSequence

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« Reply #189 on: 06/13/2018 09:38 PM »

Quote from: Jason Wright
Wow, PAGB and supergiant stars have *very* Dyson-spherey spectra. Check out this one. @ESAGaia puts it at 370 pc, but it's spectroscopically a supergiant and the GAIA fit is *terrible*. Probably at 3.7kpc.

#### Star One

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