Much of his science fiction is thoroughly grounded in science (with the addition of unscientific but standard speculations such as faster-than-light travel).
He has proposed an absurd and inconclusive experiment to test a perfectly ridiculous and unscientific hypothesis that ignores virtually the entire body of geological knowledge.
This work was criticized for unscientific methods, but today it is commonly accepted that he contributed significantly to the preservation of the traditional ballads.