NEIL deGRASSE TYSON: And now for some final thoughts from the "dark side."

Consider all we've learned about the size, age and contents of the universe, from its fiery birth in the Big Bang, through 14 billion years of cosmic expansion that has followed. Even better, consider the powerful laws of physics we've discovered that account for it all. Kind of makes you stand with pride for being human.

So we're clueless about that one too, with no idea about what occupies the remaining 96 percent.

We call these two entities "dark matter" and "dark energy." What are they? Maybe they're exotic never-before-seen forms of matter and energy, or maybe they reveal a hidden flaw in our understanding of how the universe works. But really, the two terms are placeholders for our abject ignorance. We could just as easily have labeled them "Bert" and "Ernie" or "Without-a-Clue A" and "Without-a-Clue B."

So we are left in a curious situation. What we know of the universe, we know well. Yet a larger cosmic truth lies undiscovered before us, a humbling yet thrilling prospect for the scientist driven not only by the search for answers, but by the love of questions themselves.

And that is the cosmic perspective.