(Or go to the QuickTime animated version)
Graph of 3-Second Event
Diagram of a single three-second event; observer is at rest relative to the event
The blue line represents the passage of time from zero to three seconds. The horizontal line would represent movement through space, but in this instance, we and the event are at rest.
Velocity of observer is one-tenth the speed of light
Here, we are moving relative to the event (or the event is moving relative to us) at one-tenth the speed of light. The length of the green line shows the duration in time we will now measure for the event. Because of relativistic effects, we will measure slightly more than 3 seconds. How much more, we can see directly by comparing the lengths of the green and the blue lines.
In this case, we passed by the exact position of the event at the instant the 3-second event began. The turquoise line (at the bottom of the triangle) represents the distance--as we measure it--that we traveled during the three seconds of the event. We could also say that this is the distance the event traveled relative to us--that is, that this is the duration of the event in space.
Velocity of observer is one-half the speed of light
As we repeat our experiment at faster speeds and then plot our results, we can see that both the green and the turquoise lines eventually get quite long. If we were using the interactive version, we would see that the lengths of time we measure actually don't change very much until we get up to about half the speed of light.
Velocity of observer is 90% the speed of light
When we get close to the speed of light, say around 0.90, the lengths of time and space that we measure for the 3-second event become very huge, very fast . . .
of observer is 99% the speed of light
. . . and the angle between the green and turquoise lines approaches zero.
of observer is 100% the speed of light
If we could reach the speed of light, we would measure an infinitely long time for any event. It would seem to us as if time were passing as normal for us, but that it had stopped for all things not moving along with us. The universe would appear frozen.
Of course, it would take an infinite amount of energy to accelerate us to lightspeed. Only if we had zero mass could we get there.
Entities that exist at lightspeed have no rest mass and exhibit zero proper time.
Page created and maintained by Lynn Stephens, MALS Program, Empire State College, State University of New York. Copywrite 2004. Copyright 2004 by Lynn Stephens. Last updated March 1, 2004.