The Milky Way is probably full of dead civilizations • Hacker News Board

Re: The Milky Way is probably full of dead civilizations

#11

Post by kstrauser » Sat, Nov 08, 2025, 5:27 AM UTC

amanaplanacanal wrote: post #3

Looks like a bullshit paper. This big question mark is: assuming life evolves on a suitable planet, what are the odds that something like an intelligent technological species would ever evolve? We only have one example: us. You can't extrapolate from that, so they just made up numbers.

Define "technological". We've recently accepted that there are several tool-using species other than us.

We have a head start on other apes, but they might catch up if we weren't in the picture. If octopi stopped dying so young, they might give us a run for our money. Orcas have fashion trends ("did you see Becky's dead salmon hat? I'm getting one of those!"). Mess with corvids at your own risk.

Re: The Milky Way is probably full of dead civilizations

#12

Post by intended » Sat, Nov 08, 2025, 5:31 AM UTC

amanaplanacanal wrote: post #3

Looks like a bullshit paper. This big question mark is: assuming life evolves on a suitable planet, what are the odds that something like an intelligent technological species would ever evolve? We only have one example: us. You can't extrapolate from that, so they just made up numbers.

By this criteria - all papers that extrapolate are BS papers.

There’s a ridiculous number of stars in the sky - no matter how low you put the odds of intelligent life, you will still end up with more than 1 civilized species in the universe.

This is, at least for me, the primary utility of such extrapolations. And eventually - extrapolations will be tested.

Re: The Milky Way is probably full of dead civilizations

#13

Post by vikingerik » Sat, Nov 08, 2025, 5:45 AM UTC

thomassmith65 wrote: post #2

It seems equally likely to me that conditions in the Universe just weren't amenable to life until relatively recently. Radio waves take time to travel; there could be many civilisations out there whose signals haven't had time to reach us. If that's the case, we're just the first intelligent civilisation to evolve in our immediate vicinity.

This isn't likely. The Milky Way is 100k light years in diameter. That's tiny relative to the age of life. Animals comparable to humans in complexity have existed for something like 250 million years on Earth, and could have on planets of stars that formed billions of years before our sun. The possible timespan for signal-emitting life to have developed is many multiples of the timespan that signals take to cross the galaxy.

It's far more likely that signal-emitting life is so rare (or short-lived) so that they are separated by distances where their signals weaken to undetectability, than that we are the one fantastically lucky star to be the first among a hundred billion.

Star Trek showing all the rival civilizations exploring the galaxy at the same time makes no sense at all. It's far more likely that civilizations would arise separated by time of millions or billions of years, than that they would all be concentrated within a few centuries. (Trek does hint strongly that the explanation is panspermia, that life was seeded everywhere at the same time to account for the time-concentrated development.)

What we don't know is what makes signal-emitting civilizations cease to do so. But (if we aren't the fantastically unlikely first one) either something must, or they're so far apart that signals can't be detected between them.

Re: The Milky Way is probably full of dead civilizations

#14

Post by thomassmith65 » Sat, Nov 08, 2025, 6:08 AM UTC

vikingerik wrote: post #13

thomassmith65 wrote: post #2

It seems equally likely to me that conditions in the Universe just weren't amenable to life until relatively recently. Radio waves take time to travel; there could be many civilisations out there whose signals haven't had time to reach us. If that's the case, we're just the first intelligent civilisation to evolve in our immediate vicinity.

This isn't likely. The Milky Way is 100k light years in diameter. That's tiny relative to the age of life. Animals comparable to humans in complexity have existed for something like 250 million years on Earth, and could have on planets of stars that formed billions of years before our sun. The possible timespan for signal-emitting life to have developed is many multiples of the timespan that signals take to cross the…

The radius of the observable universe is 45.7 billion light-years.

The universe is approximately 13.8 billion years old. Primates evolved only six million years ago. So let's be charitable and say it took only 13 billion years for a lifeform capable of transmitting radio waves to evolve.

Unless I'm missing something, if we're listening for ETs, we would only have visibility into a sphere with a radius around 1/45th the radius of what is out there?

My point is, if the Universe is such that it takes a minimum of, say, 10 billion years for planetary conditions to make evolution possible and evolution to wind up at intelligent life, then there could be hundreds or thousands of civilisations out there, at this very moment, whose earliest signals won't reach us for millions of years.

Re: The Milky Way is probably full of dead civilizations

#15

Post by Madmallard » Sat, Nov 08, 2025, 6:10 AM UTC

thomassmith65 wrote: post #2

It seems equally likely to me that conditions in the Universe just weren't amenable to life until relatively recently. Radio waves take time to travel; there could be many civilisations out there whose signals haven't had time to reach us. If that's the case, we're just the first intelligent civilisation to evolve in our immediate vicinity.

Isn’t it likely that radio waves beyond a certain distance will just become indistinguishable from background noise? They’re travelling hundreds of thousands if not more light years

Re: The Milky Way is probably full of dead civilizations

#16

Post by adrian_b » Sat, Nov 08, 2025, 6:20 AM UTC

kstrauser wrote: post #11

amanaplanacanal wrote: post #3

Looks like a bullshit paper. This big question mark is: assuming life evolves on a suitable planet, what are the odds that something like an intelligent technological species would ever evolve? We only have one example: us. You can't extrapolate from that, so they just made up numbers.

Define "technological". We've recently accepted that there are several tool-using species other than us. We have a head start on other apes, but they might catch up if we weren't in the picture. If octopi stopped dying so young, they might give us a run for our money. Orcas have fashion trends ("did you see Becky's dead salmon hat? I'm getting one of those!"). Mess with corvids at your own risk.

From a technological point of view, the main distinctive feature of humans has not been the use of tools, which is relatively widespread among animals, but the control of fire.

The control of fire is what has enabled humans to produce and use new classes of materials that all other living beings are unable to make, e.g. ceramics, metals, glasses, cements, thermoplastics and thermosets, various kinds of crystals, including semiconductors, etc.

These materials have been essential in the development of human technology during the last twenty thousand years.

All the other living beings can use only a limited range of materials, consisting of polymers that can be synthesized at ambient temperature and pressure (e.g. wood or horn or chitin), adhesives and the equivalent of sedimentary rocks (in various kinds of skeletons, most commonly made from composites of proteins or chitin with insoluble salts of calcium, strontium or barium, but also including those made of sedimentary glass, i.e. opal, like in sponges and diatoms). (Natural glass is either volcanic, made by rapid cooling, like most artificial glass, or sedimentary, i.e. opal deposited from a solution of silicic acid in water. Living beings can catalyze the latter reaction in order to make siliceous skeletons.)

So the myth of Prometheus was actually quite wise in comparison with many later attempts to define essential features of humans.

Any living beings that have remained confined to a water environment, like cephalopods, do not have any chance to develop a technology comparable to that of humans, because without being able to use fire they could not make metals and the other materials required for that. Being unable to create an advanced technology is not an obstacle to reaching a high intelligence, as high as that of humans. The humans of fifty thousand years ago were as intelligent as those of today (perhaps on average even more, as all the dumb ones died quickly), even if they did not have yet any technologies that could not have been developed by something like an octopus.

Re: The Milky Way is probably full of dead civilizations

#17

Post by Panzerschrek » Sat, Nov 08, 2025, 6:23 AM UTC

This paper doesn't account the possibility of a civilization to spread itself and to fill eventually the whole galaxy. But in such case it's practically impossible for such civilization to extinct. Since we see no intelligent signatures everywhere, it's certain that no such civilization was formed in our galaxy.

Re: The Milky Way is probably full of dead civilizations

#18

Post by vikingerik » Sat, Nov 08, 2025, 6:59 AM UTC

thomassmith65 wrote: post #14

vikingerik wrote: post #13

Earlier quoted context omitted.

This isn't likely. The Milky Way is 100k light years in diameter. That's tiny relative to the age of life. Animals comparable to humans in complexity have existed for something like 250 million years on Earth, and could have on planets of stars that formed billions of years before our sun. The possible timespan for signal-emitting life to have developed is many multiples of the timespan that signals take to cross the…

The radius of the observable universe is 45.7 billion light-years. The universe is approximately 13.8 billion years old. Primates evolved only six million years ago. So let's be charitable and say it took only 13 billion years for a lifeform capable of transmitting radio waves to evolve. Unless I'm missing something, if we're listening for ETs, we would only have visibility into a sphere with a radius around 1/45th t…

Primates evolved six million years ago here. There are plenty of stars billions of years older than our sun (and still sufficiently enriched with heavy elements from prior stellar generations) where they could have, so that their signals would have reached us by now. The past light cone is everything you see in the sky. Even a million light-years from neighboring galaxies is small compared to the time scale of possibilities on the order of multiple billions of years.

Re: The Milky Way is probably full of dead civilizations

#19

Post by ayaros » Sat, Nov 08, 2025, 7:12 AM UTC

vikingerik wrote: post #13

thomassmith65 wrote: post #2

It seems equally likely to me that conditions in the Universe just weren't amenable to life until relatively recently. Radio waves take time to travel; there could be many civilisations out there whose signals haven't had time to reach us. If that's the case, we're just the first intelligent civilisation to evolve in our immediate vicinity.

This isn't likely. The Milky Way is 100k light years in diameter. That's tiny relative to the age of life. Animals comparable to humans in complexity have existed for something like 250 million years on Earth, and could have on planets of stars that formed billions of years before our sun. The possible timespan for signal-emitting life to have developed is many multiples of the timespan that signals take to cross the…

It is panspermia. See TNG season 6 episode 20, The Chase.

Re: The Milky Way is probably full of dead civilizations

#20

Post by eszed » Sat, Nov 08, 2025, 7:17 AM UTC

adrian_b wrote: post #16

kstrauser wrote: post #11

Earlier quoted context omitted.

Define "technological". We've recently accepted that there are several tool-using species other than us. We have a head start on other apes, but they might catch up if we weren't in the picture. If octopi stopped dying so young, they might give us a run for our money. Orcas have fashion trends ("did you see Becky's dead salmon hat? I'm getting one of those!"). Mess with corvids at your own risk.

From a technological point of view, the main distinctive feature of humans has not been the use of tools, which is relatively widespread among animals, but the control of fire. The control of fire is what has enabled humans to produce and use new classes of materials that all other living beings are unable to make, e.g. ceramics, metals, glasses, cements, thermoplastics and thermosets, various kinds of crystals, incl…

I'm trying to decide whether it would be possible for super-intelligent cephalopods to use underwater lava vents to refine metals. Would make a fun SF premise, but I take your point.