Number of alien life forms
how many intelligent life forms
This is an interesting report, estimating the number of intelligent life forms based on the number of known exoplanets, and based on whether (a)life is difficult to arise but easy to evolve to intelligence, or (b) life is easy to evolve but intelligence difficult to achieve. The calculations put the number of intelligent life forms between 360 and 36000. Of course, just because a life form is intelligent doesn’t mean we would be able to communicate with it, or that it would be technological. It is a fairly safe bet that Plato or Shakespeare were a good deal more intelligent than I am, but neither of them could even conceive of radiowaves.