– Ecology leads to a simplified equation and a solution of the problem
In 1995 mankind discovered the first extrasolar planet and since then we have detected thousands of them. We have also detected planet candidates that seem to be within a certain distance to their home stars so that liquid water should exist on their surface. We have detected enough of those worlds to get into statistic ranges, where extrapolations normally are quite good (significant). Meanwhile we can predict with a high certainty that our galaxy owns at least millions of planets with conditions that allow life as we know it. But where are the aliens?
Actually, if there are so many worlds with conditions that are similar to planet Earth, there should be an agile traffic between all that planets. Aliens should regularly visit us, one might expect. Why don’t they? Where are they? Do they actually exist? At least these alien civilizations should be capable to send radio signals into the surrounding universe, as we do. We are searching for that alien radio signals since decades now but never found anything. Why is space void if there are so many planets with possible life conditions? We call this discrepancy the Fermi Paradox.