Number of habitable worlds within170 light years?

[Tom Mazanec]

Of course after we go extinct maybe raccoons evolve radi, then after some more megayears the mongooses, then rats…

[Johnny1A.2]

Originally Posted by ericthered

So life shows up on earth pretty quickly, which gives hope for finding life most times you get what space calls an "Ocean world". I don't think that the oxygen energy storage loop is particularly unlikely: oxygen is the third or fourth most common element in the universe, and its energy storage properties are amazing. It did take 2 billion years (roughly) to show up on earth though, and that could be slow, or it could fast. Sample sizes of one are tricky.

This^^^. When you have only one data point to work from, almost anything you conclude inevitably contains large elements of WAG.

We just don't know.

Originally Posted by Pursuivant

Decades of wishful thinking to the contrary, while ocean-dwelling life might develop sapience it's unlikely to develop extensive tool use. (Consider that there species of cetaceans and octopi which are very smart, and sometimes demonstrate tool-using behaviors, but haven't shown much inclination towards tool making.)

Nor do the huge majority of land-based life forms. Tool use, esp. general-purpose tool use, is super-rare. (Yes, crows, chimps, elephants, etc. They display a very, very limited tool-using tendency. But it's still not even a shadow of the human tendency that way, and that's still a tiny handful of species out of millions.)

We only have the example of one world to judge from, so we really can't assign a meaningful probability to things like oceanic tool use (or land-based tool use, or technological sapience, for that matter). We can observe that there appears to have been life on Earth for over 3 billion years, complex multicellular life for at least hundreds of millions, vertebrates for almost that long, land-based vertebrates since the Devonian (or thereabouts), mammals since at least the middle Mesozoic, but AFAWK human style high-tool sapience only goes back at most a megayear or so, or 1/4500 of Earth's existence.

That would seem to hint that life might be easy, complex life not much worse, but full-on technological sapience hard and rare. Which would be one of the standard 'solutions' to the Fermi Paradox, 'technological aliens are rare'.

But it's still a tissue of assumptions based on one data sample. Based on the data available, it would be just about as plausible that techno-sapience is easy and Earth is the exception. One data point, no way to judge.

"x chance of a lucky planetary collision which doesn't destroy the planet, but which does provide an Earth-like moon to "keep the pot boiling."" (Alternately, the presence of other gravitational forces which generate vulcanism.)

"x chance that terrestrial life evolves."

That's the 'intelligent tool using life is rare' explanation, which has always been one of the possible explanations, as Fermi noted. Fermi's observed paradox is based on what was received scientific wisdom at the time, which was that life and intelligence ought to be common, and interstellar travel relatively easy (relatively!). That combination, together with the lack of any evidence of the presence of said aliens, is the Paradox.

The scientific community has oscillated back and forth for over a century on the subject of alien life, it goes back and forth from 'life is probably common' to 'life is probably exceedingly unlikely and rare', it's cycled back and forth probably at last three times in the last two centuries. We have absolutely no idea which is true, because we have no data other than to generalize from Earth.

Originally Posted by SydneyFreedberg

What Malloyd said. Also, my personal guess for the Fermi Paradox solution is that, even if all life-bearing worlds evolve intelligence, they're very unlikely to evolve it at the same time. Modern humans have been around for, what, 100,000 years, at most, and transmitting radio waves for 100; even if you round that way up to a 1 million year lifespan for our species (before we go extinct/transcend/whatever), that's 1/500th of the time since the Cambrian Explosion (ca. 500 mya). So figure a planet with macroscopic (i.e. big enough to see) multi-cellular life has a 1/500 or 0.2% chance of having intelligent life on it right now.

That's the infamous final factor in the Drake Equation, the typical lifespan of a technological civilization. It usually gets mentioned in context of self-destruction, but in practice it doesn't matter what the agency of destruction is, what matters for the Paradox is the WAG you apply for that typical duration period. If it's very short, the Paradox evaporates. If it's long, the Paradox reappears.

We have precisely zero data to plug into that final component of the Drake Equation. The only known high-tech civilization continues to exist, with no guarantee of either longevity or imminent demise. Absolutely any figure you slot in the final factor is a total, 100% WAG.

[Pursuivant]

Originally Posted by Johnny1A.2

Tool use, esp. general-purpose tool use, is super-rare. (Yes, crows, chimps, elephants, etc. They display a very, very limited tool-using tendency. But it's still not even a shadow of the human tendency that way, and that's still a tiny handful of species out of millions.)

I should have clarified. Not only do few aquatic species demonstrate tool use, none, other than sea otters and octopi show signs of modifying tools. Furthermore, the fundamental conditions which make it possible to store tools or harness basic natural forces (e.g., fire, gravity, wind) are less likely to be present underwater than on land.

Obviously, that's a terrestrial-biased point of view, but I just don't see how you get from paleolithic technology to neolithic technology without fire and the ability to safely use it.

Aquatic creatures could conceivably use geothermal vents to heat things, but they would need to lower whatever it is they wanted to heat into the vent using long ropes to avoid being boiled themselves.

My take is that purely aquatic species might be sapient, but they aren't likely to become highly technologically advanced without going onto land. If that is inherently lethal due to radiation by high energy UV and cosmic rays, it's going to be a huge drag technological development.

Furthermore, constant bombardment of a planet's surface by radiation is going to make it much harder for terrestrial plants and terrestrial or amphibious animals to evolve.

Originally Posted by Johnny1A.2

The scientific community has oscillated back and forth for over a century on the subject of alien life, it goes back and forth from 'life is probably common' to 'life is probably exceedingly unlikely and rare', it's cycled back and forth probably at last three times in the last two centuries.

Agreed, but these days is that we're starting to get real data rather than pure speculation for a number of variables in the Drake Equation. The past ~25 years have given us a decent estimate on the number of star systems that might harbor Earth-like planets and for the number of star systems that might have Earth-sized planets in the habitable zone. The next 10-20 years will give us (some) answers as to how many of those star systems have planets with Earth-like gravities, temperatures, and atmospheres.

[ericthered]

Originally Posted by Johnny1A.2

This^^^. When you have only one data point to work from, almost anything you conclude inevitably contains large elements of WAG.

We just don't know.

The scientific community has oscillated back and forth for over a century on the subject of alien life, it goes back and forth from 'life is probably common' to 'life is probably exceedingly unlikely and rare', it's cycled back and forth probably at last three times in the last two centuries. We have absolutely no idea which is true, because we have no data other than to generalize from Earth.

Originally Posted by Pursuivant

Agreed, but these days is that we're starting to get real data rather than pure speculation for a number of variables in the Drake Equation. The past ~25 years have given us a decent estimate on the number of star systems that might harbor Earth-like planets and for the number of star systems that might have Earth-sized planets in the habitable zone. The next 10-20 years will give us (some) answers as to how many of those star systems have planets with Earth-like gravities, temperatures, and atmospheres.

I suspect we'll see some dramatic movement in the next five years. Now is a terrible time to be making real guesses, and a wonderful time to be making bets, because JWST is going to start analyzing exoplanet atmospheres.

[Infornific]

Regarding the Fermi paradox, there was an interesting recent take that argued revious estimates of the Drake equation made hard assumptions about each probability. If on the other hand you modelled the uncertainty of each factor it suggested we're probably alone in the galaxy. It's an interesting take.

If I've got my math right, this should determine the average distance between habitable worlds:

D=R/((N*0.75)/pi)^(⅓)

Where

pi is pi
R=Radius of inhabited space
N=Number of habitable worlds
D=average distance between habitable worlds

So if the territory has a radius of 175 light years and 1,000 habitable worlds, there's typically 28 light years between each habitable world.

[agentdenton]

If you want to add some weird worlds that stretch the definition of habitable then you could read Niven's known space series. He had a few worlds that were only partially habitable. Plateau was more or less Venus like, with a hufe plateau that rose above the dense toxic atmosphere into a habitable layer where the air was breathable.

A planet called warhead was more like mars but had a deep fissure in it that had atmosphere dense enough to breath.

Wemadeit (we made it!) had breathable atmosphere but due to orbital mechanics was scoured by 1000mph winds during parts of it's orbit making underground cities the only way to survive on it.

Jinx was a heavy planet that was habhitable only in two bands that were above the equator and below the poles, the equator region's atmosphere was too dense to breath, the poles had very thin atmosphere.

Another variant on habitable might be worlds with livable gravity, radiation, etc and have things like oxygen, carbon, nitrogen, etcbut are not habitable as is. Such worlds could be lived on in dome type cities that process basic atmosphere from local elements.

If you stretch 'habitable' to cover worlds that are possible to live on under some conditions or only in some parts, you could end up with a lot more than just 'earth clones'.