It seemed that we were closing in on a vision of our universe in which everything to be calculated, predicted, understood. However two theories eternal inflation and string theory now suggest that the same fundamental principles from which the laws of nature derive may lead to many different self consistent universes with many different properties.
paradox by definition is:
statement or situation that appear illogical or contradictory but that may reveal an underlying truth.
It seems to me that the sentence starting from "however" is perfectly a contradiction to the sentence before it. But according to my answer key, "speculation" is a better answer as to which rhetorical strategy the author uses.
Source (where I found it): My SAT Critical Reading Preparatory Book