Even if the likelihood of intelligent life is .001%, there are over a billion stars with planets surrounding them, which makes the odds of there being at least ONE other intelligent life actually VERY high.
First of all, let's narrow-mindedly assume that all life needs exactly the same things we need in order to survive. The number of earth-like planets is actually not as small as you may think. But regardless of that, let's now assume that life can exist under different circumstances, not just those needed by humans and Earth surface species. I specify surface species due to the link
, which can live under circumstances humans and even most fish cannot, and yet would die at lower pressures. Even just the odds of there being the general conditions needed to support life of some sort have to be at least existent, as we know for a fact it happened at least once.
Actually, the odds of life (in some way, shape or form) is obscenely high. The odds of intelligent life aren't unreasonable. But the odds of intelligent life having reached earth-- highly improbable.
But where am I getting my facts? OK, let me explain.
The age of the universe is link
, give or take .2 billion years. Now, to give an idea of relativity, earth is fairly young, only 4.5 billion years old. The oldest human civilization is only 9,500 years old. That is VERY YOUNG in terms of the universe.
For relativity's sake, say that human civilization has existed for a second, and that earth has been around for 131.6 hours (about 5 and a half days) (YES that is to scale). And if Earth has been around 131.6 hours, then the universe has been around for 450.7 hours (18.8 days).
One second, versus 18.8 days.
In 18.8 days-- that's a lot of seconds, folks-- you don't think that it's possible, nay, even PROBABLE, that in ALL those seconds, there wasn't at least ONE other civilization that existed on a planet on a distant star? Or, even more, not even one species of life at all? Even if you're willing to admit there is a .001% of a chance-- there are 1624320 seconds in 18.8 days. .001% of 1624320 is 1624.32
That, in my opinion, is a lot of seconds.
Now, consider other extra terrestrial civilizations exist for about one second as well. However, they are millions-- if not billions-- of light years away from us (in our time scale, a billion light years is 1.4 "light days").
Therefore, it is literally IMPOSSIBLE for a civilization who has only existed for one second to cross a distance it takes light 1.4 DAYS to travel (a speed impossible to break without shattering the rules of physics, another discussion entirely).
This thought experiment has been made into what's called (by me at least) "The Christmas Tree Scenario."
Consider all the intelligent civilizations in the universe-- light years apart, like lights on a Christmas tree, since the beginning of time. Obviously, civilizations don't evolve and exist simultaneously. Now remember-- according to our scale, a civilization only exists for a second.
One light flashes on and remains on for one whole second while another at the bottom of the tree flashes on .75 seconds into time itself. They have a .25 second period where the two civilizations overlap in existence, but the first civilization swiftly dies out. Another flashlight blinks into existence for a second, then blinks out.
All in all, the lights are blinking too fast to have any time to send ships out searching for life. And, by the time their probes find a planet that HAD life, it would have long since died out (as would the host civilization, most likely).
And that, my friends, is my scientific theory on why life (even intelligent life) exists, but why we as a species will never get the chance to know it.