Oct 26, 2022 10:54 PM
(This post was last modified: Oct 27, 2022 04:54 AM by C C.)
Maybe we don't see aliens because nobody wants to come here
https://www.universetoday.com/158287/may...come-here/
EXCERPTS: . . . A new paper addresses the Fermi Paradox by focusing on star types. It says that not all types of stars are desirable to an expanding technological civilization. Low-mass stars, particularly K-dwarf stars, are the best migration targets for long-lived civilizations.
The paper is “Galactic settlement of low-mass stars as a resolution to the Fermi paradox,” and the Astrophysical Journal has accepted it for publication...
[...] 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 “An Explanation for the Absence of Extraterrestrials on Earth” [...] 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. Hart explained what would happen if a civilization sent out colony ships to the nearest 100 stars. They could colonize those star systems, then each of those colonies could do the same, and the process could keep repeating.
“If there were no pause between trips, the frontier of space exploration would then lie roughly on the surface of a sphere whose radius was increasing at a speed of 0.10c,” Hart wrote. “At that rate, most of our Galaxy would be traversed within 650,000 years.” Hart pointed out that a technological civilization would’ve had ample time to reach us unless they had started less than two million years ago. For Hart, the only explanation for the lack of evidence of alien civilizations is that there are none.
[...] The authors of this paper disagree. An underlying assumption for many people who contemplate the Fermi Paradox is that stars are uniformly attractive to a spacefaring civilization, and the civilization would spread everywhere equally. But is that true?
The authors of this new paper don’t think so. “We suggest, following the hypothesis of Hansen & Zuckerman (2021), that an expanding civilization will preferentially settle on low-mass K- or M-dwarf systems, avoiding higher-mass stars, in order to maximize their longevity in the galaxy,” they write.
Gauging stars by their longevity isn’t intuitive to humans. If one type of star lasts 10 billion years and another lasts 10 trillion, what difference does it make to anyone but an astrophysicist? But now, imagine you’re part of a decision-making body for a civilization that is a million years old—or even older—and has expanded to different solar systems. Then, a star’s age matters to you.
[...] The authors of this new paper calculated a new estimate for the time a galactic civilization needs to colonize the galaxy if that civilization only targeted K dwarfs and M dwarfs. They say it would take two billion years for a galactic civ to reach all low-mass stars. “This would require interstellar travel capabilities of no more than about 0.3 ly to settle all M-dwarfs and about 2 ly to settle all K-dwarfs,” they write.
With greater travel capabilities, the civilization could dramatically reduce the two billion-year time span. [...But...] the authors say that the [vastly lower] 2 Myr settlement scenario can safely be rejected...
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... (MORE - missing details)
https://www.universetoday.com/158287/may...come-here/
EXCERPTS: . . . A new paper addresses the Fermi Paradox by focusing on star types. It says that not all types of stars are desirable to an expanding technological civilization. Low-mass stars, particularly K-dwarf stars, are the best migration targets for long-lived civilizations.
The paper is “Galactic settlement of low-mass stars as a resolution to the Fermi paradox,” and the Astrophysical Journal has accepted it for publication...
[...] 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 “An Explanation for the Absence of Extraterrestrials on Earth” [...] 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. Hart explained what would happen if a civilization sent out colony ships to the nearest 100 stars. They could colonize those star systems, then each of those colonies could do the same, and the process could keep repeating.
“If there were no pause between trips, the frontier of space exploration would then lie roughly on the surface of a sphere whose radius was increasing at a speed of 0.10c,” Hart wrote. “At that rate, most of our Galaxy would be traversed within 650,000 years.” Hart pointed out that a technological civilization would’ve had ample time to reach us unless they had started less than two million years ago. For Hart, the only explanation for the lack of evidence of alien civilizations is that there are none.
[...] The authors of this paper disagree. An underlying assumption for many people who contemplate the Fermi Paradox is that stars are uniformly attractive to a spacefaring civilization, and the civilization would spread everywhere equally. But is that true?
The authors of this new paper don’t think so. “We suggest, following the hypothesis of Hansen & Zuckerman (2021), that an expanding civilization will preferentially settle on low-mass K- or M-dwarf systems, avoiding higher-mass stars, in order to maximize their longevity in the galaxy,” they write.
Gauging stars by their longevity isn’t intuitive to humans. If one type of star lasts 10 billion years and another lasts 10 trillion, what difference does it make to anyone but an astrophysicist? But now, imagine you’re part of a decision-making body for a civilization that is a million years old—or even older—and has expanded to different solar systems. Then, a star’s age matters to you.
[...] The authors of this new paper calculated a new estimate for the time a galactic civilization needs to colonize the galaxy if that civilization only targeted K dwarfs and M dwarfs. They say it would take two billion years for a galactic civ to reach all low-mass stars. “This would require interstellar travel capabilities of no more than about 0.3 ly to settle all M-dwarfs and about 2 ly to settle all K-dwarfs,” they write.
With greater travel capabilities, the civilization could dramatically reduce the two billion-year time span. [...But...] the authors say that the [vastly lower] 2 Myr settlement scenario can safely be rejected...
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... (MORE - missing details)