> Personally I think the lack of visible galactic civilisations is more plausibly explained by a combination of life being rare (and probably brought to Earth via panspermia after billions of years of evolution elsewhere) and both multicellular and sentient life also being rare.
Besides these facts, space is big and the timescales of evolution are long.
Let's say there's a planet with advanced multicellular life just a dozen light years away. They're roughly the same development level as us with a post-atomic/semiconductor level of technology. We could not currently detect them unless they were beaming an extremely directional radio signal at us (accounting for proper motion between our star systems). We're not going to pick up their TV signals, those will fade below the cosmic background by about Saturn's orbit. Even high powered AM radio won't be coherent past Pluto. The odds a powerful military or weather radar beam crosses our section of their sky to be detectable by us are extremely low.
We might be able to detect spectra of industrial pollutants or biomarkers if that system is oriented such the planet transits its host star.
That assumes there's a project with the funding and appropriate telescopes to do the looking.
Space is big and terrestrial planet hunting is under-funded. It would take a lot of luck to see intelligent life next door. Postulating super AI or handwavy explanations for not finding aliens everywhere is silly. The boring answer is space is huge and aliens are almost impossible to see in the best case. We'd be very lucky to see ourselves from Alpha Centauri even knowing where to look.
Besides these facts, space is big and the timescales of evolution are long.
Let's say there's a planet with advanced multicellular life just a dozen light years away. They're roughly the same development level as us with a post-atomic/semiconductor level of technology. We could not currently detect them unless they were beaming an extremely directional radio signal at us (accounting for proper motion between our star systems). We're not going to pick up their TV signals, those will fade below the cosmic background by about Saturn's orbit. Even high powered AM radio won't be coherent past Pluto. The odds a powerful military or weather radar beam crosses our section of their sky to be detectable by us are extremely low.
We might be able to detect spectra of industrial pollutants or biomarkers if that system is oriented such the planet transits its host star.
That assumes there's a project with the funding and appropriate telescopes to do the looking.
Space is big and terrestrial planet hunting is under-funded. It would take a lot of luck to see intelligent life next door. Postulating super AI or handwavy explanations for not finding aliens everywhere is silly. The boring answer is space is huge and aliens are almost impossible to see in the best case. We'd be very lucky to see ourselves from Alpha Centauri even knowing where to look.