Complex sentence: Thus, much scientifically based speculation might convince one (or many) that the hypothesis that other intelligent species exist is true, but there being not experiment now known which can test this hypothesis, science itself can have little to say about the possibility.
Split into simpler sentences: Thus, much scientifically based speculation might convince one (or many) that the hypothesis that other intelligent species exist is true. But since there no experiment now known which can test this hypothesis, science itself can have little to say about the possibility.