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### Speed of light in general relativity [duplicate]

My question has a few parts concerning the speed of light in general relativity. Firstly, time changes in response to gravity and speed. Therefore, as gravity effects time in an area of space, should ...
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### Time dilation due to gravity [duplicate]

I'm getting conflicting statements when it comes to time dilation due to gravity. Some sites say time slows down near the source of gravity and some say it's faster. Can anyone she'd some light on ...
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### Do black holes slow down photons? [duplicate]

If a photon was moving directly away from a black hole, would the gravitational pull force it to change it's linear velocity (thus causing it at one point to have a velocity of 0)?
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### Is there a mathematical equivalence between gravitational optics and quantum optics or are they mathematically incompatible theories?

I know that massive gravitational bodies will curve the path that light travels. I think that quantum optical mediums also bend light. I am still confused of whether quantum optical mediums actually ...
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### Acceleration and its effect on the speed of light

One of Einstein's thought experiments involved a rocket and two light sensors inside the rocket, one at the top, and one at the bottom. When the rocket was at rest, a pulse of light from the bottom ...
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### The Michelson-Morley experiment

A fundamental assumption in special relativity is that the speed of light is constant in all inertial reference frames, which was first established empirically via the Michelson-Morley experiment. ...
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### What is the age of planet Earth, if we are not looking for the age at sea level?

I remember to learn at school that our planet is approximately 4.543 billion years old. But since the time is affected by mass of an object, this number is actually the age on the sea level, where ...
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### We all accept/believe in $c$. But what happens when light travels away from the center of gravity of a heavy star? Does it slow down?

I'm basically trying to understand a mysterious characteristic of the universe. Why light has to travel at $c$? I understand and accept that from experiment. Not arguing that it does not. Just saying ...
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### Why speed of light in vacuum remains constant over space and time?

Imagine a Pulse of light traveling through space at $c$, coming towards an observer on Earth, while at the same time, Space-time fabric (metric) is continuously changing (expanding), then why is the ...
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### Do photons have absolute motion?

Absolute rest is not possible as the concept of motion is relative. But can we assert that photons have absolute motion as the observers in all the frames of reference would agree to the same value of ...