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Author Topic: Light speed  (Read 1142 times)

Offline grumpy10

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Light speed
« on: 18/08/2011 00:15:55 »
If photons travel at light speed,time does not pass for them.If that is the case, how do we know how far any stars may be?
It is accepted that for any object approaching the speed of light, that time slows down & mass increases, to the point that it would have infinite mass at light speed, which would indicate that photons do not have mass, but why is light diverted by gravity. If time has stood still(regarding to light), there can be no way of telling how far away any celestial body may be !


 

Offline imatfaal

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Light speed
« Reply #1 on: 18/08/2011 10:28:07 »
If photons travel at light speed,time does not pass for them.If that is the case, how do we know how far any stars may be?
Because we measure light speed in our reference frame (the ref frame of a photon is weird, unrealistic and does not work) and in our reference frame it has a finite speed.  We only know how far stars are away by looking at red shift, comparitive luminosity, and other secondary factors.  We have no way of measuring the transit time of light from a distant star directly - we calculate how long it has travelled from our estimate of the distance.

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It is accepted that for any object approaching the speed of light, that time slows down & mass increases, to the point that it would have infinite mass at light speed, which would indicate that photons do not have mass, but why is light diverted by gravity. If time has stood still(regarding to light), there can be no way of telling how far away any celestial body may be !
Light is affected because it follows a geodesic (the equivalent of the shortest distance between two points) in curved space. 
 

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Light speed
« Reply #1 on: 18/08/2011 10:28:07 »

 

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