I think your sense of scale for time and distance needs recalibration.
Billions of years for structures of old to break, not just for civilisations to arrive. It's enough time for planetary atmospheres to boil off into space.
> Shouldn't civs advanced enough to build Dyson Spheres
Kessler cascade.
But, once they're actually that big, I think their only possible downfalls are fratricidal conflicts; so my thinking and comments here are mainly regarding pre-Dyson civilisations.
Further aside: on this scale, one thing I want to find out but don't know who to ask, is "how fast do iron and aluminium sublimate in a vacuum at 300 K?"
> They should at least be strong enough to withstand an asteroid hit, and those don't just disintegrate into space dust quickly.
Asteroids come in many sizes, up to "moon"; moons also disintegrate under gravity when they pass the Roche limit, and for other reasons; the rings of Saturn are young on such timescales, 10 million to 100 million years old.
Now I think about it (in favour of your position, but again I'm assuming filters other than fratricide have to happen before Dyson swarms) an expansive civilisation that Dysoned up 10 Mya inside the Milky Way should've turned the galaxy into one of red dwarfs even if the spheres have since disintegrated.
> Space Junk is already a problem for us in our present state of advancement. There's space debris from the 50s out there. Why isn't that dust?
Remember this is in the context of what we can see looking out into the cosmos.
Our space junk is indistinguishable from dust at lunar distance, let alone interstellar.
And 50 years? Every beat of your heart is to your lifetime what 8 Earth years is to the lifetime of Sol.
> civilizations don't just disappear
Yeah they do. Heck, entire species disappear.
> And if the universe is so vast and old, we should be seeing civs in transition, like ours.
Only with sufficiently good telescopes. The actual ones we've got? It's noteworthy when they've got the capacity to resolve stars as more than single pixels.
I don't ned to recalibrate anything. What I need to do is stop arguing about UFOs and electric cars in this forum. The Fermi Paradox is based precisely on the time and scale of the universe.
"he Fermi paradox can be asked in two ways.[note 1] The first is, "Why are no aliens or their artifacts found on Earth, or in the Solar System?". If interstellar travel is possible, even the "slow" kind nearly within the reach of Earth technology, then it would only take from 5 million to 50 million years to colonize the galaxy.[26] This is relatively brief on a geological scale, let alone a cosmological one. Since there are many stars older than the Sun, and since intelligent life might have evolved earlier elsewhere, the question then becomes why the galaxy has not been colonized already. Even if colonization is impractical or undesirable to all alien civilizations, large-scale exploration of the galaxy could be possible by probes. These might leave detectable artifacts in the Solar System, such as old probes or evidence of mining activity, but none of these have been observed.
The second form of the question is "Why are there no signs of intelligence elsewhere in the universe?". This version does not assume interstellar travel, but includes other galaxies as well. For distant galaxies, travel times may well explain the lack of alien visits to Earth, but a sufficiently advanced civilization could potentially be observable over a significant fraction of the size of the observable universe.[27] Even if such civilizations are rare, the scale argument indicates they should exist somewhere at some point during the history of the universe, and since they could be detected from far away over a considerable period of time, many more potential sites for their origin are within range of human observation. It is unknown whether the paradox is stronger for the Milky Way galaxy or for the universe as a whole.[28]"
Billions of years for structures of old to break, not just for civilisations to arrive. It's enough time for planetary atmospheres to boil off into space.
> Shouldn't civs advanced enough to build Dyson Spheres
Kessler cascade.
But, once they're actually that big, I think their only possible downfalls are fratricidal conflicts; so my thinking and comments here are mainly regarding pre-Dyson civilisations.
Further aside: on this scale, one thing I want to find out but don't know who to ask, is "how fast do iron and aluminium sublimate in a vacuum at 300 K?"
> They should at least be strong enough to withstand an asteroid hit, and those don't just disintegrate into space dust quickly.
Asteroids come in many sizes, up to "moon"; moons also disintegrate under gravity when they pass the Roche limit, and for other reasons; the rings of Saturn are young on such timescales, 10 million to 100 million years old.
Now I think about it (in favour of your position, but again I'm assuming filters other than fratricide have to happen before Dyson swarms) an expansive civilisation that Dysoned up 10 Mya inside the Milky Way should've turned the galaxy into one of red dwarfs even if the spheres have since disintegrated.
> Space Junk is already a problem for us in our present state of advancement. There's space debris from the 50s out there. Why isn't that dust?
Remember this is in the context of what we can see looking out into the cosmos.
Our space junk is indistinguishable from dust at lunar distance, let alone interstellar.
And 50 years? Every beat of your heart is to your lifetime what 8 Earth years is to the lifetime of Sol.
> civilizations don't just disappear
Yeah they do. Heck, entire species disappear.
> And if the universe is so vast and old, we should be seeing civs in transition, like ours.
Only with sufficiently good telescopes. The actual ones we've got? It's noteworthy when they've got the capacity to resolve stars as more than single pixels.