NASA Home Page JPL Home Page Caltech Home Page
NASA - Jet Propulstion Laboratory + View the NASA Portal  
Shell image/ Home button Fundamental Physics in Space
The Story of Our Search
Shell image / home button
The Story of our Search
Fundamental Physics
Sensational Symmetry
Big Bang and Beyond
It's About Time
Quantum Questions
Adventures in Science
Technical Details



different time pieces "Time!" The coach of the Lakers has just called time out after the Blazers player has made only one of his two free throws. The TV breaks for commercials. There's 2:05 left on the game clock, so there's plenty of time to go make a sandwich, grab a cold drink, and still get back to see the end of the game. With all the time-outs and free throws, the game will likely last another 20 minutes or so, and many plays will be squeezed into the 2 minutes and 5 seconds left on the game clock. Coaches and players are often criticized or praised for how well they manage the clock in those last few minutes of a game.

This is one of the distortions of modern timekeeping: There's game time; and there's the actual time elapsing on your wristwatch. A new statistic is even kept comparing the time a star sits on the bench for a rest with the time run off the game clock.

So which is the 'real' time? To the players and the coach, the time on your watch is irrelevant. The only time that counts to them is that which gives them more opportunities to score. If you are at the game, you may be fretting about the time you're going to have to pay for the babysitter. These are two very different concepts of the passage of time for two people in nearly the same place.

Picture another scene: A toddler has ventured off the curb into the street. A passing jogger sees the child, and also sees a large truck approaching him at 40 miles per hour. The jogger veers into the street, grabs the child, and dives out of the way of the truck as it brushes past with its tires screeching. Afterwards the jogger says that time stood still for her - everything seemed to go in slow motion. There was never any doubt that she could get the child safely out of danger. The truck driver, on the other hand, says it all happened so fast that she can't recall any of it. She saw the child in front of the truck and slammed on the brakes, but she knew she couldn't stop in time.

Again two people involved in the same event have two very different experiences regarding the time that elapsed during the event. And the actual time involved was only a few seconds.

What is time? How real is it? Can it be so variable as these subjective experiences suggest? Can we control how we experience time? Is time travel possible? If so, can we go back to ...?

Let's call on the bards for some hint of the essence of time. Take Shakespeare's Sonnet 64:

"Ruine hath taught me thus to ruminate:
That Time will come and take my love away.
This thought is as a death which cannot choose
But weepe to have that which it fears to lose."

Or perhaps Omar Khayam's Rubaiyat can spell it out for us:

"The Moving Finger writes; and having writ,
Moves on: nor all your Piety nor Wit
Shall lure it back to cancel half a Line,
Nor shall your Tears wash out a Word of it."

The one expresses the onward rush of events, with no holding them back. The other says that history is immutable, there's no going back to rewrite it. One says that time flows uniformly on; the other says this flow is only one direction.

Maybe there's some light on this subject in the writings of the Greek philosophers. Aristotle believed that time is cyclic, that what has passed will occur again. Writing in his Physics, he states "there is a circle in all other things that have a natural movement and coming into being and passing away. This is because all other things are discriminated by time and end and begin as though conforming to a cycle; for even time itself is thought to be a circle." To modern Western concepts this notion of repeating events seems unacceptable.

Plato, who taught Aristotle, distinguished two aspects of time, Being and Becoming. Being is a real, intelligible concept, always the same; Becoming is the state of coming to be, never fully real, and is completely unintelligible. These concepts seem separated from the real world; this realm of ideas is the favorite area of study of the Greek Golden Age.

So not much help from the Greek philosophers. Maybe the great Isaac Newton can enlighten us. In 1666 he wrote in his Principia that time "... flows equably without relation to anything external." Therefore, time is just part of the background of events, as is the space in which events occur. Given some initial state of a body and the forces acting on it, one can calculate both the history and the future of its motions.

Let's leave it there for now. We'll get back to some concepts of varying time frames in future discussions. You can learn some more about the development of clocks.

Check back soon for the Complete Story!

Last Updated:

link to First Gov NASA logo