Alien existence?

[creature386]

My take:

For the most part, the question was "Is there another civilization in our galaxy?".
I originally wanted to do this with narration, but meh. Maybe next time.

[creature386]

May 26, 2020 18:23:01 GMT 5 Infinity Blade said:

An article about the odds of life and intelligent life emerging if we reran Earth's clock. Seems to have some implications for finding life on other planets.

www.pnas.org/content/early/2020/05/12/1921655117

Bookmarked this here.

[Infinity Blade]

This is kind of going off on a tangent relative to the thread's topic, but I wonder if the finding that the evolution of intelligence may be rare supports Stephen Jay Gould's proposal that if we rewinded Earth's history, the exact life on Earth that we've familiarized ourselves with would be unlikely to evolve (i.e. "Replay the tape a million times ... and I doubt that anything like Homo sapiens would ever evolve again."). At least a bit.

But that's just me, I haven't actually read much into the whole "Is evolution more subject to contingent or deterministic forces?" debate.

[creature386]

I'm not too knowledgable on the phyletic gradualism vs punctuated equilibrium debate either, but for me, the apparent absence of sapient life besides us is more consistent with PE than with gradualism.

It's not a terribly strong argument in favor of PE at the moment because we know so little about alien life atm, but it is still an argument.

Gradualism could save itself with the rare Earth hypothesis. That being said, should it turn out that there is an abundance of planets with Earth-like conditions and about the same age as our planet, gradualism would predict at least some sapient species to exist.

[Infinity Blade]

We've got another interesting paper.

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 36 [+175 -32] 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 17,000 [+33,600 -10,000] 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.

iopscience.iop.org/article/10.3847/1538-4357/ab8225

Brackets sort of mine, in that the text they use for the plus or minus figures provided in the abstract does not translate well onto this forum.

[creature386]

I wondered if this was anything I already new, but nope, something new.

The average lightyear distance is extremely interesting. I must confess that I kinda obsessed about this when I worked on an alien story and what I ultimately came up with was a distance of 16,000 lightyears (involving a low-mass M-dwarf star, of course). Oh, the coincidence. That of course means we can forget having our SETI signals be answered in any foreseeable time.

I wonder if this average distance also has implications about the mean "radio lifespan" of a civilization, if we want to discuss the Fermi paradox. I.e., if average civilizations are tens of thousands of lightyears apart, maybe they can only send radio waves for tens of thousands of years before something happens to them?