reply to post by fiftyfifty
Hi FiftyFifty, (found a better diagram. seemed more clear.)
You're not the only one whose confused. When Einstein developed his special and general theories of relativity many scientists were as perplexed by
the results as you are. Space-time, and it's measurement, is relative to a particular viewer/measurer. Mathematically this is easy to see, but the
math can be difficult. One model to help us understand the nature of time dilation is the light clock:
Imagine you are beside a train track, and you see a train approach you. On this train is a strange clock. A single pulse of light moves from the
floor of the train to the roof of the train. To make this easier to picture, imagine it takes one second for the pulse of light to move from the
floor of the train, reflect off the roof, and hit the floor of the train again. (Even though in reality it will seem instantaneous.)
As the train moves at normal speeds, the light will appear both to a person on the train, and an observer outside the train, to take one second to
complete its round trip from floor to roof to floor. This is what our common sense would seem is right. But something weird happens as the train
approaches the speed of light.
As the train moves faster and faster, the light clock will take longer and longer to complete its journey, but only from the perspective of someone
outside the train. From this outside perspective, the light no longer looks like it is moving straight up and down from floor to ceiling, but rather
is moving at an angle. Because the light appears to be taking this angle, it also appears to take a longer amount of time to complete it's trip from
the floor of the train, to the ceiling, back to the floor again. Hopefully the diagram in the link will make my description clearer.
The really weird part about all this is that from the perspective of the person on the train, the light clock is working as it should, taking one
second to make it's journey from floor to ceiling to floor.
The big question is, so whose perspective is the correct one, the outside observer or the train observer? Well, weirdly enough, they are both right.
The measurement of space-time is relative to the observer, and both readings are perfectly correct.
So, a space traveler, going the speed of light, from the perspective of someone on earth, will seem like they are taking a long time, but from the
perspective of someone on the spaceship, they are not taking any extra time at all.
Hope this helps. It's definitely weird, fascinating stuff.
[edit on 9/21/2007 by Toromos]