Astrobiology: New calculations on intelligent civilizations in the Milky Way

Woollybear · Jun 15, 2020

2020 needed a little good news.

The Astrobiological Copernican Weak and Strong Limits for Intelligent Life

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 ${36}_{-32}^{+175}$ 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 ${17,000}_{-10,000}^{+33,600}$ 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.

It's behind a paywall, but here's the more conversational version which is just a click away:

There Are At Least 36 Intelligent Alien Civilizations In Our Galaxy, Say Scientists

Chris P · Jun 15, 2020

Thanks for linking! I'll give it a read later.

I think of two things when this subject comes up:

1) The Fermi Paradox

And

2) Calvin and Hobbes

Woollybear · Jun 16, 2020

My guess is that contact mathematically fails because of (all of the other small probabilities plus) the mere blink of geological time that allows civilization.

My guess (just an envelope musing) is that for a civilization to establish requires enormous stores of energy like fossil fuels. Here on Earth, the rate at which we burn that fuel is 1,000,000 times faster than it forms (that's a very rough statement). Globally, we Earthlings at least show no sign of slowing down that rate of burn. Any improvements in fuels and efficiency is easily offset by population growth year over year.

So, we burn out. Civilization ends up being barely a blip in the geological record.

So... still musing here... a planet that can allow civilization to form requires time to store fuel to power that civilization, and the civilization will consume said fuel in a blink.

We won't overlap, so we won't find anyone.

~~

Oh here's a thought: if it takes 300,000,000 years to restore the oil reserves that we've burned, back to their circa 1800 volumes, then that means the animals (species) currently sitting on the cusp of language, art, and so on... (the ones who could evolve tools and agriculture and whatnot in the next 100,000 years or so, you know, after humans are gone) are SOL in terms of finding easy ways to build a civilization on our ashes. There's no good energy for them.

Suckers! Ha. We beat them to it.

~~

I also wonder if the paper accounted for the ('need') for tectonics (rifts and deep-ocean thermal/sulfur chimneys) and/or tides (necessitating moons?) to get life started, or if it brought in other ways to create the extreme gradients that most OOL models use to envision formation of the first complex molecules. I believe lightning etc (the Miller Urey thing) can only take you so far.

Chris P · Jun 16, 2020

Woollybear said:
So, we burn out. Civilization ends up being barely a blip in the geological record.

Snip

We won't overlap, so we won't find anyone.

I found your entire post thought provoking--energy must be considered--but the "we won't overlap" is the resolution to the Fermi Paradox I find most compelling. The Earth is 4.5 billion years old, with all life (as far as we know) evolving within 1 billion of those years. Of that, we have only been able to send and receive radio signals into and from space for about 100 years.

So if life only takes 1 billion years to go from proto-ooze to a society capable of sending and receiving signals, in the 15 billion years of the universe it is likely to have happened multiple times. Trouble is, the signals from another planet might have been streaming past us while T. rex was stomping around, when the cockroaches were squiggling in the swamps of the Carboniferous, or even when Ben Franklin was flying his kites. By the time we as humans developed the ability to listen, the society sending the signals might have long since stopped broadcasting and the signals passed us by.

All that also assumes we can detect the signals sent by the other society. If they had discovered something other than electromagnetic waves to communicate we could have the signals all around us now and not know it.

Introversion · Jun 16, 2020

I think we probably can transition away from fossil fuels to more sustainable sources, even if cheap practical fusion never appears. And, maybe we can do so soon enough to avoid cooking the planet?

I suspect our bigger barrier to not crashing & dying out is ourselves; how we treat eachother, and how shortsighted we are. If there’s a World War 3, it may be our last, and not in a good way.

MaeZe · Jun 16, 2020

Don't forget the huge distances in addition to the time a society might have and survive with technology. The biggest problem contacting other intelligent life is how far away it is likely to be. Something that is 80,000 light years away means we'd have to travel at the speed of light for 80,000 years to get there.

It will take a breakthrough in manipulating space-time or something like that to really travel around the galaxy. And communicating with other advanced lifeforms would require another mega-breakthrough in the speed to send and receive messages.

I don't think running out of fuel is going to be an issue. The Sun has plenty for a few billion more years.

Doesn't mean we won't go extinct for any number of other possibilities.

I think for the foreseeable future all of our contact with intelligent life is going to be in our fiction. Probably better than some super advanced life coming here to enslave us.

BTW, it's not logical they would need slaves, food, or batteries (Matrix) if they were that advanced. So maybe a few of us would end up in their zoos or they'd come here as tourists. :tongue

Astrobiology: New calculations on intelligent civilizations in the Milky Way

Woollybear

Chris P

Likes metaphors mixed, not stirred

Woollybear

Chris P

Likes metaphors mixed, not stirred

Introversion

Pie aren't squared, pie are round!

MaeZe