Understanding Space-Time

Understanding Space-Time Part I:
What Exactly *is* the Speed of Light?

One of the hardest concepts to grasp about space-time theory is that time is relative to the observer and is not absolute. The universe as a whole does not follow some "master clock" that encompasses everything.

The speed of light has been measured using various means with significant accuracy. That speed is 186,282 miles per second in a vaccuum. However, that speed is relative to a stationary observer on Earth. How fast would the speed of light appear to be if you trailed behind it at 99% of its speed? It would still appear to leave you at the same speed.

Take another example using the classic unit of measurement to find the distance to a star -- the light year. Suppose that a star was said to be 15 light-years away from Earth. What exactly does that mean? Well, it could mean several things depending on your frame of reference. To the observer on Earth, if a spaceship were to leave and head towards this star at the speed of light, the observer on Earth would notice 15 years later that the spaceship finally made it to that star. What about from the perspective of someone on that ship?

Well, the person on that ship would notice that the trip was instantaneous. How is this possible? How could the ship take both 15 years and, at the same time, get their instantaneously?

The answer lies in something called "relativity."

To be continued ...