The Fermi Paradox, the Drake Equation, and Stars: Maybe a galactic civ is expanding through the Milky Way but they don't like the Sun.
By using different variables to answer each of those questions, we get different estimates of how many technological civilizations there might be. It’s a thought experiment, but one informed by evidence, though the evidence is rudimentary.
The authors point to one of the most famous analyses of the Fermi Paradox. It came from American astrophysicist Michael Hart in 1975. Hart’s paper was “,” and it was published in the Quarterly Journal of the Royal Astronomical Society. It’s considered to be the first rigorous analysis of the paradox. In his paper, Hart showed how a civilization could expand through the galaxy in a period of time shorter than the galaxy’s age.
Artist’s conception of the exoplanet system orbiting Gliese 581. The authors say low-mass, long-lived stars like Gliese 581 might be desirable expansion targets for alien civilizations. Credit: ESO/L. Calçada With greater travel capabilities, the civilization could dramatically reduce the two billion-year time span. “Even more rapid expansion could occur within 2 Myr, with travel requirements of about10 ly to settle all M-dwarfs and about 50 ly to settle all K-dwarfs.”
The authors think that there could be a low-mass star, Galactic Club spreading through the Milky Way right now, and we can’t rule it out just because we haven’t noticed it. The absence of evidence isn’t evidence of absence, as the adage goes. “In particular, we note that a low-mass Galactic Club, originating from a parent G-dwarf system, would have had plenty of time to develop in the history of the galaxy without us taking any notice of its activities,” they write.