I Don't Know

Voltaire wrote in The Philosophical Dictionary under the entry "Limits of the Human Mind"

"SOMEONE asked Newton one day why he walked when he wanted to, and how his arm and his hand moved at his will. He answered manfully that he had no idea. 'But at least,' his interlocutor said to him, 'you who understand so well the gravitation of the planets will tell me why they turn in one direction rather than in another!' And he again confessed that he had no idea." 

Voltaire's point: we should find where the limits of our knowledge stops and then refuse to go further. Instead of offering some intuitively appealing, but unproven explanation, Newton is willing to just say, "I don't know." 

This is the difference between empirical science and speculative explanations of all sorts from astrology, to ancient aliens, to conspiracy theories.