This is an EXPANDED and UPDATED version (in 1080p) of our Cosmic Journeys episode. The answer to this question may depend on whether Stephen Hawking was right in his theory that describes how black holes shed mass and eventually decay. Time is flying by on this busy, crowded planet as life changes and evolves from second to second. At the same time, the arc of the human lifespan is getting longer: 67 years is the global average, up from just 20 years in the Stone Age.

Modern science provides a humbling perspective. Our lives, indeed even that of the human species, are just a blip compared to the Earth, at 4.5 billion years and counting, and the universe, at 13.7 billion years.

It now appears the entire cosmos is living on borrowed time. It may be a blip within a much grander sweep of time. When, we now ask, will time end?

Our lives are governed by cycles of waking and sleeping, the seasons, birth and death. Understanding time in cyclical terms connects us to the natural world, but it does not answer the questions of science.

What explains Earth's past, its geological eras and its ancient creatures? And where did our world come from? How and when will it end? In the revolutions spawned by Copernicus and Darwin, we began to see time as an arrow, in a universe that's always changing.

The 19th century physicist, Ludwig Boltzmann, found a law he believed governed the flight of Time's arrow. Entropy, based on the 2nd law of thermodynamics, holds that states of disorder tend to increase.

From neat, orderly starting points, the elements, living things, the earth, the sun, the galaxy. are all headed eventually to states of high entropy or disorder. Nature fights this inevitable disintegration by constantly reassembling matter and energy into lower states of entropy in cycles of death and rebirth.

Will entropy someday win the battle and put the breaks on time's arrow? Or will time, stubbornly, keep moving forward?

We are observers, and pawns, in this cosmic conflict. We seek mastery of time's workings, even as the clock ticks down to our own certain end. Our windows into the nature of time are the mechanisms we use to chart and measure a changing universe, from the mechanical clocks of old, to the decay of radioactive elements, or telescopes that measure the speed of distant objects.

Our lives move in sync with the 24-hour day, the time it takes the Earth to rotate once. Well, it's actually 23 hours, 56 minutes and 4.1 seconds if you're judging by the stars, not the sun. Earth got its spin at the time of its birth, from the bombardment of rocks and dust that formed it. But it's gradually losing it to drag from the moon's gravity.