Time is a concept that has perplexed mankind for history. What is time?

We see time all around us, from the ticking of clocks, to the vibrations of a quartz crystal. However, these devices only measure time, whether in hours, minutes, seconds, or even milliseconds. They don’t answer the question of what time really is.

This question is one of the central points of the PBS show, The Fabric of the Cosmos, hosted by theoretical physicist Brian Greene. The show is a four-hour, four-part series based on Greene’s bestselling book by the same name which aired on PBS’s NOVA in July and early August, 2012 (it is also available on DVD). In the series, Greene describes time as a river that flows in one direction. At least, that’s how we perceive the concept of time. But let’s shift our view from physics, to moviemaking. A movie is made when a projector rolls several frames in a certain amount of time. For standard movies, the projector speed is 24 frames per second. But, what are those frames? Those frames, in fact, are simply still pictures. Our brains take all of the still frames and combine them into a “movie.” Brian Greene asks if time is like that: Is time really just a set of “still” moments, and do our brains perceive the “rolling” of these moments as the “flow” of time? In The Fabric of the Cosmos, Greene suggests that time is a collection of “moments,” and that the flow of time really does not exist.

Let’s think about this for a second. If time consists of “still moments,” does that mean that traveling to the future is simply traveling through thousands of “moments?” Time travel has been a dream for mankind, and it certainly was an intriguing idea for Albert Einstein. Einstein states in his Special Theory of Relativity, that the speed of light, 670 million miles per hour, is the “speed limit” of the universe. If you want to travel to the future, you would have to travel near this gargantuan speed limit. If you want to travel to the past, then 670 million miles an hour is not enough! If you traveled on a spaceship that traveled very close to the speed of light, you would have aged only a few years, while the rest of Earth aged much more. Unfortunately, Uncle Einstein doesn’t allow time travel to the past, since traveling faster than light is not possible. If that were the case, as Brian Greene puts it in his series, we should be seeing time travelers from the future in our own era!

The Fabric of the Cosmos is a thrilling show that literally stirs up one’s curiosity about the weirdest facts of the universe. Let’s face it: The universe contains 400 sextillion stars, more than the grains of sand on all the beaches on Earth. Humans have a lot to learn about nature’s mysteries!