And about the colonisation paradox, why should aliens colonise everything that comes to their path?Surely they are not invasive insects without reasoning about what planets should they colonise and what they shouldn't, because without mind you don't have spaceships.My speculation is that even if they decided to colonise most of the lifeless planets of pur galaxy, they are interested in living worlds so much that they don't want to disrupt them by any means, but probe them, maybe experiment a bit, and do not reveal themselves to their observation/test subjects.
And what meaned "colonise" for Fermi?, sending a probe to a world is one thing building entire civilizations on planets is another.

Btw really read my previous post [the long one], I explained my toughts more there.

Or there's even another possibility; that they've colonised Earth in the past and erased all traces to not reveal themselves when they observed that intelligent life is going to bud on Earth.
Civilization building rocket ships capable of 0.1 c or even more should surely conduct their colonisation and subsequent trace erasure quietly using maybe nanobots, picobots, plancktech or some another unknown technology.

I am not claiming any of these hypotheses as fact, they are just possibilities, just and much more probable that that there is noone other than us in a galaxy with around 400 billion stars.

And the notion that there is no civilisation that decided to colonise the whole galaxy is still much more probable than "we are alone"/
What if they developed superior intelligence that told them it's better to improve what you made than needlessly expand and devour?
Or maybe they ended up in a conclusion that fast space expansion would cost more resources than it will bring, be too dangerous and so it's needless to colonise when there's enough resource avilable?Utilitarianism, simple.

Or I have a wild idea that eventually all sapient/transapient beings would be contained in nano pico or plancktech dust dense substrate and so it would be uneeded to go far if you can have trillions of human equivalents in a moon or bigger size superbrain, like the archialect computronium structures in Orion's Arm SCI-FI?

I think that an advanced more than human equivalent intelligence would eventually go for the most efficient and design and resource saving alternative, energy and resorces are limited, remember?