Special Relativity Question

PoBoy321 · #1 06-03-2006, 03:53 PM

OK, I just started reading The Elegant Universe and the first few chapters deal largely with special relativity. Here's my question, and I'm sure it's pretty basicc, but I'm dense and I'm not sure who to ask.

I understand that if I tried to follow a beam of light, travelling at 670 million mph, at a speed of 570 million mph, the light would still appear to be travelling away form me at 670 million mph, not 100 million mph as Newtonian physics would imply.

So if I followed the light for one hour, after an hour it would appear to be 670 million miles away from me, and I would be 570 million miles away from the starting point, so the light would be 1240 million miles away from the starting point, so shouldn't the light have appeared to have travelled faster than 670 million mph from the vantage point of an observer at the starting point?

ChromePony · #2 06-03-2006, 04:30 PM

The catch is that the time you experience is different than the time an observer experinces from a static location. Its only an hour for you, for them its close to two, so the light still travels at c in their reference frame. Dealing with relativity you gotta start thinking in terms spacetime not space/time.

atrifix · #3 06-03-2006, 04:45 PM

[ QUOTE ]
So if I followed the light for one hour, after an hour it would appear to be 670 million miles away from me, and I would be 570 million miles away from the starting point, so the light would be 1240 million miles away from the starting point, so shouldn't the light have appeared to have travelled faster than 670 million mph from the vantage point of an observer at the starting point?

[/ QUOTE ]

The speed of light is what is held constant, not the distance. The distance is variable.

surftheiop · #4 06-03-2006, 05:05 PM

The Elegant Universe - is that the string theory book?

"I understand that if I tried to follow a beam of light, travelling at 670 million mph, at a speed of 570 million mph, the light would still appear to be travelling away form me at 670 million mph, not 100 million mph as Newtonian physics would imply."

From a third person perspective it would appear he is going 100 million mph less correct?

PoBoy321 · #5 06-03-2006, 07:01 PM

[ QUOTE ]
The Elegant Universe - is that the string theory book?

[/ QUOTE ]

Yeah.

surftheiop · #6 06-03-2006, 07:03 PM

We watched a 3 part PBS nova special in Physics that was done by the guy who wrote that book, really interesting stuff

poincaraux · #7 06-05-2006, 11:28 PM

[ QUOTE ]
We watched a 3 part PBS nova special in Physics that was done by the guy who wrote that book, really interesting stuff

[/ QUOTE ]
The book is way better than the PBS special. You should read it if this stuff is interesting to you .. the author is a world leader in string theory, so you know it's not quack science.