> Do ants comprehend humans? No they don't. Ants can comprehend only other ants. By this logic we can interact only with civs that are similar or same as us.

Do ants comprehend microbes? They don't, but we comprehend (or at least apprehend) ants and microbes, which makes us qualitatively different than ants.

And is it really true that ants can't tell the difference between a forest and a house? That everything to them looks like a similar level of "wild"? I find that rather hard to believe. Ants are afraid of predators and will bite creatures which they perceive (whatever "perceive" means at the ant level) to be attacking their nest.

It may be possible for there to be an alien civilization so different in capabilities, goals, and mindset that we comprehend them no better than ants comprehend us. But I have a hard time believing that they would be so different from us that we wouldn't even be able to notice their presence if we were looking right at something they'd made or used somehow.

> How much detectable technological signature we emit for others to detect? I am not a physicist but I guess that would be next to nothing for any considerable space distance.

The basic argument is that once humans became a "colonizing" species, pretty quickly anywhere which could be lived in by humans was lived in by humans; and that once we became a species with a significant ability to transform our environment, you can't go far without finding evidence of that transformation.

Extrapolating out, we expect that our own civilization will begin to colonize the stars at some point; and then at some point our technology will become good enough to transform the galactic environment to suit our desires.

Doing the math any spacefaring civilization with what we'd consider basic level of travel could colonize the entire galaxy in 100m years or so; and so far we've had 100x that long since the universe began. So if life capable of becoming a star-faring civilization were common, we'd expect to find the galaxy already widely colonized; and we'd expect such a civilization to transform the galactic landscape as dramatically as we humans have transformed the Earth's landscape.

The lack of such a galactic civilization is what needs explaining. Where does our intuition from the extension of our own growth on planet Earth not match up to reality?

- Maybe there is a galaxy-wide civilization but either they don't see the value in transforming the environment? Or maybe there are fundamental limits to technology of which we're not aware, such that no galaxy-wide civilization would ever be able to transform the environment?

- Maybe there are loads of civilizations like ours, but they never go galactic; a Great Barrier that has stopped them and will stop us as well. But why? Are there fundamental limits of technology that make it universally impractical (which we'll hit up against soon)? Is it inevitable (or highly probable) that such civilizations become inward-focused, and spend all their time in simulations instead? Or do most civilizations end up falling prey to Moloch [1] and destroy themselves before they manage to go galactic?

- Or, maybe there's loads of life on other planets, but none of them ever become technological: that is, the Great Barrier is becoming capable of scientific discovery, and it's behind us. In 100 million years or so we'll be the first galactic civilization which everyone else finds.

- Or, maybe simple life like bacteria is common, but complex life is rare; or maybe life at all is rare.

[1] https://slatestarcodex.com/2014/07/30/meditations-on-moloch/