Is the Milky Way a boneyard of long-dead civilizations?

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I tend to be biased on this perspective. I think likely in terms of species even on the path to becoming interstellar I think it’s likely we’re among the first. I say that only because of the incredible fact that we’ve not yet encountered a single instance of a technological signature. Based on even just a no FTL scenario (being the most likely) it would only take about a few million years for a species to just litter the galaxy with probes. We don’t even need to consider colonization on this front because that is a great deal harder but making robots that can make themselves is basically a logical first step to exploring your galactic neighborhood especially since it would become self sufficient after the first generation of probes.


If they’re alive by the time we see them, they’re probably dead now.


Earth exceptionalism! We are also probably the only allegedly sentient beings in the galaxy to argue over whether wearing masks during an epidemic is a good idea.


That does call the whole concept of “sentience” into question, now, doesn’t it.


Isaac Arthur covers this concept in some detail on his channel. Basically, seems likely that we are alone in our chunk of the galaxy or maybe the whole galaxy. Any civilization even a few million years ahead of us, and having the ability and desire to escape their gravity well (not a given), should be very very visible by now.


I also think that we are more likely to see other civilizations in the denser regions of the galaxy, and because of the great distances, they didn’t litter our area. We are essentially in a backwater in the Orion arm, halfway to the furthest extent, well away from the galactic center.


What scares me is that maybe the others have reason to be very, very quiet. Meanwhile, we’re effectively screaming our heads off and flinging tourist pamphlets out into space.


Yup, we would be the West Virginia of our galaxy, convinced that we are the peak of all possible civilizations! However, while absence of evidence is not evidence of absence, there should be visible evidence of any Kardaschev type 2’s or close. If they are anywhere near on our level, of course, they would be damn near invisible even if we were looking right at them.


The “Dark Forest” scenario. The first message we receive is “Be quiet, you fools!” Just ahead of the relativistic kill missiles, of course.


If a civilisation desired to escape it’s gravity well and then spray it’s tag on every possible planet, and maybe go back every thousand years or so to see in anything cool has evolved while their backs were turned. We would see them alright. But what is a million-year old civilisation like? Do they have kings or emperors? What wars to they have? What gods do they worship?

My personal feeling is anything that has lasted for a million years is likely to be a lot more mellow than that. They may say ‘hello’ someday but there is no rush.


I’m sure the cosmic death rays are already headed our way, disguised by a bright star directly behind it.


I’m not sure I agree with the “we’d have seen something by now if we weren’t alone” hypothesis. Forget about radio signals- with the distances involved and assuming a high power transmitting capability existing for 10k years before a civilization collapses (probably generous) it’s likely impossible to receive a signal within the lifetime of a civilization, even if anyone was transmitting at the incredible power levels that would be required to reach us. They would also have to be transmitting at us, again incredibly unlikely given how many good options they would have to transmit to.

It’s a myth, by the way, that all our radio signals are blanketing the galaxy. Power matters. Very soon after leaving earth, the signal strength vanishes into the noise. It’s still there, but you’d never pick it out of the background after a handful of light years. So for a signal to reach us, it has to be intentional- a high power transmission directly at us, like we have done a few times. Since we now know there are trillions of planets out there, the odds of someone choosing to beam at us is basically zero.

So that leaves physical detritus- the probes and such. They would be silent, since no power source or mechanical/electrical device that we know of comes even close to surviving 10k years. So we’re talking about spotting tiny dark objects in infinitely immense open space. Think about how hard it is to find a ship lost in the ocean. This is trillions of magnitudes harder than that. There could be millions of dead probes floating around out there and we’d never see one. We can barely detect asteroids big enough to destroy our planet that are within our own system. People way way way underestimate the size of outer space, generally. It’s so much more vast than our imaginations can conceive of.

I think the most likely scenario is that we’re all ships with no lights, passing in the night. There’s lots of us out here, but the speed of light is a cruel mistress and it has likely trapped us all in isolation from each other.

Of course, the fundamental problem with all such speculation is that our n=1. We’re all extrapolating from our own single data point, so almost certainly we’re all wrong in ways we can’t even imagine.


Correct. I am an alien and I like hanging out on the internet anonymously.


The evidence we could and should see are stars that radiate largely or almost exclusively in the IR spectrum due to the energy-harvesting Dyson spheres/swarms surrounding them. That kind of “free” energy should be irresistible to any civilization with the space faring capability to make use of it. Also the reason for the excitement of “Tabby’s Star” with the small possibility that we were seeing such a megastructure under construction. Further study says unlikely, but that is what we would see.

ETA: Since I mentioned him upthread, only fair to link to his channel. I have wasted a lot of hours listening to him explain deep space and far future stuff. He takes a bit of getting used to, but no one else seems to cover this stuff as well.


Came here to say that but you did it more elegantly than I could. Thanks.


An interesting premise! That presumes a very long lived civilization though- likely millions of years to build and maintain such infrastructure (and to have need of it- a handful of fusion reactors would power our entire civilization). Again, we only have one data point so who can say, but there’s no evidence to suggest civilizations ever last that long. The longer you live, the more likely your number comes up for a gamma ray burst or other planet killer event. That’s before even getting into internal strife and environmental degradation. Since it happens to us, it seems likely to be a big problem for others as well. Will we ever grow out if it? Hard to say.

Another possibility that hasn’t been mentioned yet- we may be early to the party. We got a big boost in evolution from the asteroid that killed the dinosaurs. The evolutionary road to higher intelligence was pretty stalled with the dinosaurs- they weren’t getting much smarter, because there was little pressure to do so. The rise of the mammals created such competitive pressure that intelligence was needed to win. It’s entirely plausible that, because of that asteroid, we’re a few million years ahead of the curve.

It may be that most life-supporting planets just kinda settle into equilibrium at large fauna but never get to primate equivalents unless something forces them out of that local maximum.


Or we are not, and that accounts for what happened to all the others.


I suspect that if we can get to a multiplanetary civilization we could be functionally immortal. Although the inhabitants of distant planets would rapidly become aliens as far as we are concerned, simply due to limitations of contact and communication, barring FTL. This all assumes there is not some highly xenophobic elder race out there that periodically sterilizes fertile solar systems to eliminate competition. (Dark Forest) I am of a more optimistic bent, and think that any interplanetary and certainly any interstellar civilization has the means to exterminate any other and therefore homicidal/genocidal would be held somewhat in check. Maybe…


Yah, I’ve been presuming single planet civilizations in my speculations, simply because the likelihood of any race having two inhabitable planets near enough to each other to be colonizable and act coherently as one civilization seems remote. Your species would be protected from asteroids and such by virtue of the decentralization, but you may cease to be one people any longer. Our closest opportunity is Alpha Centauri, and even if there is a habitable planet there, maintaining the most basic communication and trade is functionally impossible. The people who went there would be on their own and starting over, civilization-wise. They’d be subsistence farmers for a few hundred years, at least (assuming they survive, which is unlikely given the survival rate of human colonies on Earth in the earlier days- which is a much easier task).