Example

Dress Rehearsal

A new riddle of the sphinx: You know it passes. You know it can be measured. You know you are ruled by it. You know you want more of it when you’re having fun, and less of it when you’re in school. What is it? Time, of course, but what is time really?

The dictionary defines time as “the indefinite continued progress of existence and events in the past, present, and future regarded as a whole.” Furthermore, it is “a non-spatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. “ At first glance, these definitions seem quite reasonable.

Your physics book takes this a step further. It contradicts the second description. It boldly suggests that “motion through space is related to motion in time.” You can thank that wacky genius, Albert Einstein, for this theory. Einstein theorized that by moving through space, including just taking a walk, we alter time itself since the movement speeds up the future. He called this his special theory of relativity.

When studying the concept of time, you’ll notice that none of it seems to make any sense. None. Nill. Zip. Zero. But don’t let being a little human keep you from having fun with time. Newton and his friends questioned whether the universe exists in time and insisted that time moved in a linear fashion. Today, most of us see time as a product of the past, the present, and the future, always moving in one direction.

But Einstein said time does not exist as we see it. He states that there is no time just as there is no space outside the universe. Um...what? Einstein argued that space and time are two parts of one element called space-time. We all live in space-time. If you’re standing still, you’re moving solely through time. If you’re taking that walk, you’re traveling through space but mainly time.

Here comes the amazing thing. If you could travel at the speed of light, you would be traveling through space only… no time at all. Crazy, huh? No wonder Einstein’s hair always seemed to be standing up! There’s more.

Motion in space always affects time, whether that motion is slow or fast. Movement, then, changes time…in the future. That stretching of time is barely noticeable as we move slowly on earth, but future travelers moving close to the speed of light in outer space will be able to move so quickly in time that they can be centuries ahead of the rest of us. Maybe there was something to all those Back to the Future movies after all, though I think Einstein is talking about speeds far greater than 88 miles per hour.

Hard to believe, isn’t it? Your textbook goes on to give this idea a little boost by explaining the theory of the relativity of motion. Motion is relative in that speed depends upon the position from which the movement is being observed. Imagine you and a truck are stationary. The driver throws a ball at you, and it travels 60km per hour.

Now, imagine that the truck is driving toward you at 40km per hour while someone is throwing the ball at 60km per hour. The ball now travels at a speed of 100km per hour. Inversely, imagine the truck traveling away from you 40km per hour while throwing the ball at the same speed. The ball is traveling just 20km per hour. So, motion is relative.

While a thrown ball and moving truck might react this way, light does not. In empty space, or a vacuum, its speed is constant no matter the speed of source or receiver: ALWAYS about 300 000km per second, the maximum speed anything can move. Think of it this way: the light of some of the stars in the universe has already left them long ago, but we can still see the light. Unbelievable?

Let’s let another source, a documentary called The Fabric of the Cosmos: The Illusion of Time, take it from here. You learn that there is, in fact, no distinction between past, present, or future. Time has been measured with reference to the earth’s rotation, creating the concept of the 24-hour day, 60-minute hours, 60-second minutes… and so on. Yet Einstein proposed that time could run at different rates and be different for each person.

Motion through space affects the passage of time, slowing it down. On earth, we don’t notice this because our movements are so slow that motion’s impact on time is unremarkable. But it is measureable. An experiment involving a jet flying around the world with an atomic clock showed that, upon landing, that clock was no longer in sync with a clock on the ground.

Thus, the distinctions we make among past, present, and future, might only be an illusion. As you continue to view the documentary, you learn that past, present, and future according to the laws of physics all exist and are equally real. This renders the flow of time as an illusion. To put a wrinkle in this idea, just know that gravity can exert a pull on time slowing it down as well. But, we’ll save that explanation for another time.

For now, you’ve collected a great deal of information from a dictionary, a textbook, and a documentary film. Putting it all together, you can better explain the concept of time in a more knowledgeable fashion.

Sources:

Hewitt, Paul G. Conceptual Physics, 3rd edition. California: Addison-Wesley Publishing Company, 1997.

“Time.” The Free Dictionary. 2012. Farlex, Inc. 10 May 2012.
< http://www.thefreedictionary.com/time>.

Greene, Brian, et al. The Fabric of the Cosmos: The Illusion of Time. Dir: Randall MacLowry. Perf: David Albert, Randall MacLowry, and Peter Galison. Nova, 2011.

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