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Whos frame of reference? 
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#1
Dec2911, 11:59 PM

P: 4

I found out that Proxima Centauri is 4.2 light years away from earth. If someone was on a voyage to this star via space ship, would this person measure the time to be shorter than 4.2 years if their space ship was traveling 99.99999 percent the speed of light, assuming that the 4.2 years is measured on earth? Wouldn't this make the voyage a lot less daunting for the traveler?
Doesn't a moving clock move slower? 


#3
Dec3011, 01:02 AM

P: 4

What if he shines a laser pointer out of the front windshield? Does he see it escaping him at the speed of light? I think yes. However the observer sees it just overtaking the ship barely. This seems too bizarre...



#4
Dec3011, 01:55 AM

P: 784

Whos frame of reference?
Everyone always agrees, regardless of reference frame, that light is always going the same speed, the speed of light. It is from this single postulate (and one other smaller one) that all of Special Relativity is derived.
I would suggest this as a place to read up on special relativity and its implications: http://en.wikipedia.org/wiki/Introdu...ial_relativity 


#5
Dec3011, 02:55 AM

PF Gold
P: 4,743

The second postulate of Special Relativity defines those two times to be equal for any inertial measurement and this is the basis for a Frame of Reference. So when we say that the light propagates away from a high speed spacecraft at c, we mean that it is defined to be traveling at that speed according to the rest frame of the spacecraft and according to the same definition of a different rest frame for the earth, it is also traveling at c. It's not the least bit bizarre once you grasp what a Frame of Reference is. Einstein's 1905 paper introducing relativity is a good place to learn about this. 


#6
Dec3011, 11:22 AM

P: 5,632

Time on earth passes as normal...but is not observed (measured) as such from the fast moving spaceship. Only when earth clocks are compared with space ship clocks upon return would observers recognize different elapsed times. 


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