Where are all the alien species? Why can’t we detect them?
If there are space-faring civilisations, they have to be social. Solitary animals, passing on skills to their offspring, might not even learn to make flint axes, leave alone smelt iron. Ironwork requires specialisation. Even reaching the moon involved more than 300,000 people. Rocket science is not particularly complicated, unlike brain surgery; rocket engineering is extremely complex.
They also have to be altruistic. We are destroying the environment because enough people care more about their own short term gains. We may destroy our species, or even our biosphere, before we have been transmitting radio waves for two hundred years. From the start of life to the end of intelligence takes perhaps 3.8bn years, and two hundred is a tiny part of that. Alternatively, we are increasingly transmitting information by cable rather than broadcast, so we may stop emitting radio waves because of improving technology.
This is not certainty. The Singularity, in transhumanism, is the moment when intelligent machines start to program themselves, and their intelligence starts to increase exponentially. Possibly before the biosphere is destroyed, such machines will have been created, operating automated plant to reproduce. With unfettered neoliberalism, they could inherit paranoid selfishness from their creators, and seek to destroy any other civilisation which they would perceive as a threat.
However, I hope that the spacefaring civilisation would see the galaxy as a place of abundance rather than scarce resources needing conquest to avoid competition. We would certainly not be slaves in mines, as any civilisation which could travel through space could mine with automation more efficiently.
I hope that we have two things they might want to preserve. We have our culture. If we were contacted by a more advanced civilisation, our culture might become a pale imitation of theirs. They want us to develop without contamination, to benefit from our unique way of seeing the universe, and relating to one another. We have our genetic diversity. Considering that bacteria are as different from archaea as eukaryotes are, possibly there are unique genetic solutions on Earth, never seen elsewhere.
Though as humans are destroying the biosphere’s genetic diversity, they might want to conquer us in order to preserve it.
Intelligent life may not be common. If it evolves in aquatic species, it will not lead to technology, leave alone space travel. Life here may need the Moon, which keeps our axial tilt stable: Mars’ axial tilt varies from 0° to 60°, which could cause climate change too rapid for species to adapt, preventing complex evolution. Life may need Jupiter, whose gravity captures rocks like the Chicxulub impactor, or we would have had more mass extinctions from such impacts.
They have not come yet.
And now what shall become of us without aliens?
These people were in sooth some sort of settlement.