I was watching Discovery channel the other night, they were telling that time slows down when you travel at a higher speed. This means there is a difference between the actual speed you travel at, and the perceived speed.
Does anybody know what the perceived speed is, the speed it seems you're travelling at?
What does this imply? Does it have any meaning, in some theories perhaps, that the perceived speed is lower? Does this mean that you can never actually travel close to the speed of light?
I'm also not into physics, so try to keep it simple.
Best Answer
Your perceived speed is the same as the speed you travel at. That is, if you travel at 0.8c past the earth, people on the earth will measure your speed as 0.8c, and you will measure the speed of the earth going past you also as 0.8c. Thus you will conclude that you are traveling at 0.8c. So there is no difference between the speed you travel at and the speed you perceive that you travel at.
On the other hand, the people on the earth will see you as slowed down (relative to themselves). Similarly, you will see the people on the earth as slowed down. The two of you can't come to agreement on this because you don't have a consistent way of comparing your watches. Whichever one of you does the comparison will conclude that the other is slowed down. This is related to the fact that in relativity there is no way to determine time in an absolute fashion. It's always relative. There's no way to figure out which of you is moving and which is standing still. It is only when you get back to the earth that you might decide that it was you who was moving and it was you who was experiencing a slowing in time.
The fact that when you get back to the earth you determine that you were the one that was slowed down is only due to the fact that you were the one who changed course and returned to the earth. If instead the earth were somehow sped up and caught up with you, everything would be reversed. It would you who grew older than the people on earth.