Space | Time

According to Einstein's theory of relativity space and time are two sides of the same coin. Einstein made a description of movement in space, thus involving time. Surprisingly, he blurred the distinction between space and time.
To describe the movement of a body in space, time is normally included as a forth axis to the three dimensions length, width and height. Einstein claimed that the four dimensions were without essential difference to one another. He described the universe as a space-time-continuum based upon these four dimensions. This was not in opposition to classical mechanics. The divergence was that Einstein considered the dimensions to be relative.
Let's say we make an observation from the earth of a comet passing by in orbit. We can calculate its speed in relation to the earth. If our observation-point was on the comet, the earth would seem to pass by with the same speed. As we know from our daily life (e.g. when we go by a train) movement is relative: "Didn't Slagelse just pass by?"
It is harder to understand that movement can influence dimensions as distance and time.
Einstein focussed on a specific coherence between space and time: the speed of light, which has a constant value (300.000 kms per second) all over the universe. If we travel close to the speed of light, we can clearly experience the relativity of time.
You probably know of science-fiction stories about close-to-light-speed travellings. People returning from space and finding themselves less aged than their earthly relatives. If the velocity could reach the speed of light, time onboard would stop completely. Most likely the crew would make the following comment as they took a glance out of the window: "Didn't year 3000 just pass by?"

Steen Juhler   Comments are welcome: ny@tid.nu