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Q & A: general relativity, gravity, and light speed

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Most recent answer: 04/22/2015
If every planet has different gravity.. That means every planet has different time speed around moon has faster time speed rather then earth due to their mass.....( light speed is constant in entire universe . ) so what will happen if I measure the light speed at moon and light speed on earth.. Due to their different speeds of time moon and different data of light speed measurements..... But actually it not seen... Everywhere in universe the speed of light is same in journal measuring experiment. Whatever the mass whatever the position whatsoever the time speed
- Dinesh (age 22)
udaipur,Rajasthan, India

Yes, each observer will measure the usual local speed of light using local clocks and meter sticks. A local clock could be, for example, based on oscillations of light emitted from a specific atom. A local meter stick might consist of a crystal with a specified number of platinum atoms in one direction. Any other type of local clock and meter stick will give the same results.

But what happens when someone at another location, up in a gravitational field, looks at the same light? They will say that it's traveling slowly. So the constancy of the speed of light in general relativity applies to local light, not light somewhere else.

Mike W.

(published on 04/22/2015)

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