If aliens exist, why are they not here?
The speed of light limit is NOT the answer to this question - you see, an intelligent species can colonize the entire Milky Way in a few tens of millions of years and the galaxy is BILLIONS of years old.
As I see it, it may be a case that life (if it exists anywhere besides here) is not evenly distributed throughout the universe. I mean, look at the Earth, life is not evenly distributed whatsoever, though life can survive in the most unusual (from our perspective) locations. What's to say that Earth is one of the few outposts of life in our galactic/universal neck of the woods.
I find the assertation that an intelligent species can colonize the entire Milky Way in the timeframe available somewhat...unhelpful, since it implies it's the only thing that will happen with an intelligent spacefaring race. A timeframe of billions of years for the Milky Way's existance is enough time for a galaxy spanning civilization to collapse and all evidence wiped out by the passages of time. (see the amount of sci-fis with this concept of resurgences of intelligent species and it happening in cycles?)
It could be perfectly reasonable to suppose that we could be at any point in this 'cycle' where intelligent life is only restarting it's journey across the stars, and hence there is either:
-no one yet to meet out there, humanity could be the 'first', this time round.
-intelligent life is out there, we're just in a bit of a backwater and yet to be found.
The worst bit could be finding out that humanity is the first species to be hitting the stars out of this galaxy, and it's a sparsely populated, or totally uninhabited, and everywhere else is teeming with life.
It's a big place, the universe, anything is
About Milky way colonization and the cycles of alien civilizations:
Let's say you have an alien species that just learned to travel close to light speed (and let's assume lightspeed is an absolute speed limit).
This species now has ships that can reach the nearest stars in a few decades. Also, this species will be composed from various factions with various motivations (if it's anything like humanity). This means that some of the factions will have motivations that include sending colonizing ships to the nearest inhabitable systems.
These inhabitable systems will be inhabited in ~100 years, and the colonies will thrive in, let's say, ~500 years. These colonies will send their own ships (in addition to the ones being sent by the home system) around this time.
In another 600 years, the colonies created by this new colonizing wave will begin to send heir own ships - which will be added to the ships being sent by the home system and the first established colonies.
And so forth - the rate of exploration/colonization will increase exponentially as new colonies are established/the alien species expands.
In a few million years, this alien species will have colonies EVERYWHERE in the galaxy - Milky way is 100.000 in diameter!
And these colonies will be only very tenuously linked with the home system; in a few million years they will be completely different civilizations! Their values and perhaps their biology will be different - think star trek humanoids, at the very least.
Let's say the original alien civilization collapses - this will have NO EFFECT on the civilizations fathered by it! There can be no such thing as a "galactic middle age" when the galaxy is filled with thousands of different civilizations! Some will collapse, but some will be at their peak!
And I'm assuming that, at the beginning, there existed only one alien species - anywhere in the galaxy!
What if there are hundreds/thousands of alien species! Even if one assumes that a species is completely unlike humanity/has no desire to colonize the galaxy, a few of hundreds/thousands will do it.
About humanity being the first intelligent species in the Milky Way:
Milky Way has been having the ability to nurture life for ~6 BILLION YEARS. We're the first species to develop intelligence/civilization/technology? Why is intelligent life so scarce?