[Torplexed]

One possibility for why we don't hear or see much of ET is that any advanced civilization eventually collapses due to warfare, internal strife, or environmental collapse. Or there may be an existential threat from high technology itself. Such as the familiar sci-fi trope of an AI developed to run everything deciding it doesn't need its inefficient biological predecessors around anymore. Perhaps, advanced technology proves to be a self correcting mechanism that keeps any planetary civilization from advancing very far from their home worlds.

Another more intriguing possibility is that very advanced civilizations remove themselves from our universe and create artificial universes of their own. Some cosmologists think that it may be possible to create new universes in the laboratory, and perhaps tune them to be more suitable for intelligent processes. If you can make your own paradise, why stay in this intimidating cosmos where stars and planets are so far apart? When I am feeling hopeful, I tend to favor this explanation. Perhaps these advanced civilizations in their basement universes have a way of communicating with our own world when necessary; perhaps not. A daunting thought.

But most of the time I tend towards thinking that advanced life in this galaxy or any other is just an extremely rare event and given the staggering distances involved, you're just not going to bump into many of them.