IIRC Carl Sagan speculated the persecution of those teaching such things as irrational numbers may have set us back 500 to 1000 years. We're talking Jetsons on space coke.
As a civilization we have littered our solar system with space probes. Many that have gone to other planets and many more that will exit our system and continue on theoretically forever.
To think we are it, all there is in the vastness of space is arrogant and foolish at best, there are others out there.
Even if a given race is only 100, 200 or 300 years older than we are. Or let's say they are 200 years younger than we. Yet during our Roman Empire days instead of destroying each other they were busy making technological leaps. What's to say they, while being slightly younger than our civilization are a few hundred years ahead of us.
Now my point is, they might have created propulsion that would enable them to send deep space probes, possible artificially intelligent deep space probes which can sense and respond to other intelligent life, visit planets, gather data and relaunch themselves back into space.
Its not far fetched at all, my guess is that in about 100 to 300 years we will have the same capability.
I kinda wonder if the truly unexplained UFO's are infact space probes from another civilization. If our .gov is infact in possession of an alien space craft, its almost surely an unmanned space probe. Not ET's corvette.
IIRC Carl Sagan speculated the persecution of those teaching such things as irrational numbers may have set us back 500 to 1000 years. We're talking Jetsons on space coke.