That question will be for our great-grandchildren to answer. If you'd asked someone in 1906 who would be the man of the 20th century, who would have even guessed the potential contenders? (and to them, it would very much have been "man"--making history was considered a male-only activity back then). Who would have named an obscure mathematician who had developed some outlandish concept named "relativity" just the year before?
The people back then lived with confidence that their world would stay that way forever. A world of ruling upper-class white men, convinced of their moral and racial superiority, with everyone in their rightful place; the women at home, the lower classes in the factories and the darkies in the colonies. We're no longer that complacent, but we have traded their certainties for new ones that we may not even be aware of.