Everything we now know about the universe-from the behaviour of quarks to the birth of entire galaxies-has stemmed from scientists who've been willing to ponder the unanswerable.

Everything we now know about the universe-from the behaviour of quarks to the birth of entire galaxies-has stemmed from scientists who've been willing to ponder the unanswerable. And with the advent of modern science, great minds have turned to testing and experimentation rather than mere thought as a way of approaching and grappling with some of the universe's most pressing and vexing dilemmas.—Hans Sprenkel