On the anniversary of Greenwich, England’s designation as the Universal Time meridian (Oct. 13, 1844), now seems as fine a moment as any to ask, in the simplest possible terms, a question that has bedeviled great minds for millennia: what is time, anyway?

Ask 20 random people, “What is the nature of time?” and chances are pretty good that you’ll get 20 disparate answers born of a thousand different factors, from a respondent’s cultural background to the mood he or she happens to be in when asked the question. Time is an arrow, says one. Time is a circle, suggests another. Time is relative. Time is an illusion. Time is whatever we imagine it to be.

But no matter how assured or unhesitating the reply, most people would be hard-pressed to offer a single, definitive method for illustrating time. A clock face is too prosaic; a pendulum is too arbitrary; a gravestone is too … gravestoney. How on earth can we capture what is essentially a philosophical concept like time (or, if you prefer, Time, with a capital T) using a purely practical method or mechanism like, say, photography?

Pablo Picasso “draws” with light, 1949

Fully aware that the true nature of time remains, and will likely always remain, an unknowable mystery, LIFE.com offers a selection of marvelous photographs, stroboscopic and otherwise, by the great Gjon Mili. (At left: Mili’s famous 1949 portrait of Pablo Picasso creating what LIFE magazine called a “distorted spatial centaur” in midair with a small flashlight.) Here are technically brilliant pictures that fiddle with moments, junctures, sequences—and in the process offer a playful commentary on the slippery relationship between mere mortals and the temporal.

“To see a world in a grain of sand,” William Blake famously wrote, “and a heaven in a wild flower, hold infinity in the palm of your hand and eternity in an hour.” At their best, Gjon Mili’s stroboscopic photographs not only mirror Blake’s vision, but celebrate—with an unsentimental, clear-eyed wonder—the reality of sentient beings moving through both space and time.

Seen 60 and even 70 years after they were made, they also remain incredibly cool.