"It is really quite amazing by what margins competent but conservative scientists and engineers can miss the mark, when they start with the preconceived idea that what they are investigating is impossible. When this happens, the most well-informed men become blinded by their prejudices and are unable to see what lies directly ahead of them." - Arthur C. Clarke.
"Modern science should indeed arouse in all of us a humility before the immensity of the unexplored and a tolerance for crazy hypotheses." - Martin Gardner.
"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." - Arthur C. Clarke's First Law
At one time we thought human flight was impossible. Leonardo Da Vinci speculated about it, and the Wright brothers proved it was possible. Before the era of "flying machines", who ever dreamed that one day humans would land on the moon?
Rolling out the "caveman" image, what would a "caveman" think of modern computers? What would someone even living in the 19th century think of them? Although experimental at the time, what would "the man in the street" in 1950 think of "email"?
What ever happened to telephone boxes? Did you notice that they're all gone? This is why they're all gone.
But what about almost bizarre theories that tax our wildest imagination? Like the possibility of there being a billion other universes, some, or maybe all of which have different "laws" of physics than our universe?
Although the video is a bit blurry, Michio Kaku was one of the first physicists to speculate about a Multiverse.
The World is Not Enough: A New Theory of Parallel Universes is Proposed.
5 Reasons We May Live in a Multiverse.