Where did they all go?

Respected scientist Dr. Frank Drake sat down many years ago to look at how many other planets might have intelligent life on them. He created the famous Drake Equation, devised in the 1960s in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of extraterrestrial civilizations. It was cited by Gene Roddenberry as supporting the multiplicity of starfaring civilizations shown in Star Trek, the television show he created.
Problems arose almost immediately, however. No matter what the reasonable guesses you plugged into the Drake equation, it always showed a lot of life in the universe. Some people have estimated millions of intelligent civilizations in our galaxy alone. Another great scientist, Enrico Fermi, had a very natural question.
He asked that if there were a multitude of advanced extraterrestrial civilizations in our galaxy, the Milky Way, then, "Where are they? Why haven't we seen any traces of intelligent extraterrestrial life, such as probes, spacecraft or transmissions?" Those who adhere to the premise behind the Fermi paradox often refer to that premise as the Fermi principle.
The paradox can therefore be summed up as follows: The commonly held belief that the universe has many technologically advanced civilizations, combined with our observations that suggest otherwise, is paradoxical, suggesting that either our understanding or our observations are flawed or incomplete.
There are some general answers to Fermi:
- They exist, but cannot technically reach us
- They exist and have arrived—but most people have yet to see them
- They exist—but we have missed them
- They exist—but do not communicate with us
- They exist and communicate—but we are not listening or dismiss the evidence
- They no longer exist—or we do not exist for long enough
- They do not exist – yet
- They never existed
Note that these solutions are not necessarily mutually exclusive.
I think there is an implicit assumption in all of these answers. The assumption is that the time scales involved are easily comprehensible to the oberserver -- ie, us. I believe that for any civilization to even be considered a "beginner" the population must live, on average, ten thousand years or more. The size of the galaxy, and of the larger universe, means that even assuming superluminal travel (warp drive) unless you are alive for many eons there is nothing much for you to do.
So yes, they're here, and yes, they contact us all the time. They probably send us a radio beaon every couple thousand years or so -- other than that, it is more probable that their communication system would appear as noise (or not appear at all) to our primitive equipment. They probably visit us when they are "in the neighborhood" -- maybe even once every couple hundred years or so. But every time they show up, it's like visiting a jar of fruit flies: we are simply too ephemeral for any sort of meaningful exchange. Perhaps a couple times in the last ten thousand years they even stopped to try to explain themselves. But the information they gave was so beyond the comprehension of the average man that all we have now are myths and legends.
In short, it's not that we haven't "grown up" enough. Heck, we're so short-lived that it's impossible to communicate meaningfully to us at all. Let's say a Zeta Reiticulian lands on the White House lawn, gets out, and makes a treaty with the US and the rest of the world nations. He gets back in his ship and says an ambassador will be coming along in 3 thousand years or so. It would be a pointless exercise. From the ZR standpoint, the nations he negotiated with are unlikely to still be around when he returns. For that matter, it may be very unlikely that any of these monkey-like creatures will still be around. Likewise, collecting any humans to take back would be stupid as well, as they would never live to see even the beginning of the trip.
If you live to be 50 or 100 thousand years old, surely you can wait around a few more thousand years to see how these earthlings turn out. If we are getting close to a "transition point" in our technology, I'm sure we are quite entertaining to our neighbors!