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### Is there variation in the speed of light? [duplicate]

I read recently that there may be (very slight) variations in the speed of light due to the nature of spacetime itself, I had the idea that this may be due to the photon having mass, but that's ...
88 views

### Speed of light in gravitational field [duplicate]

Why has the speed of light in a gravitational field always the same value $c$ when measured locally? More precise: When you are far away from any masses, that means when the spacetime is flat, and ...
48 views

### Gravitational Time Dilation and Speed of Light [duplicate]

From what I'm understanding, the Speed of Light is roughly 186k MPS NO MATTER WHAT! Then say if a bean of light shoot pass near a Black Hole (Outside the Event Horizon of course) 1k lightyear away to ...
42 views

### Is the light escaping from a massive star held back a bit by the pull of gravity, or by the warping of spacetime near it? [duplicate]

In The Universe in a Nutshell chapter 4, Hawking explains the warping of spacetime according to general relativity. Near a massive but ordinary star, spacetime is warped such that the light emitted ...
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### Can I change the speed of light in vacuum? [duplicate]

General theory of relativity proved that gravity does attract light ( photons ), what if I project a beam of light radially towards a black holes will it increases it's speed or not?
7k views

### What is the connection between special and general relativity?

What is the connection between special and general relativity? As I understand general relativity does not need the assumption on speed of light constant. It is about the relation between mass and ...
2k views

### Why is the speed of light said to be constant when we know it slows down in a medium? [duplicate]

If we ask someone what the speed of light is, they will say that it is constant and its value is $3\times 10^{8}\ \mathrm{m/s}$. But if we recall refraction of light, we say that when the light ...
4k views

### 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 ...
532 views

### Can a photon that is emitted from a denser part of the universe to a less dense part appear redshifted?

Galaxy one is located in a dense area of the universe and galaxy two is located in a less dense part of the universe. Would galaxy one appear red-shifted to galaxy two? Is the mass density at our ...
2k views

### Is speed of gravitational waves constant? [duplicate]

Is the speed of gravitational waves constant in all inertial frames? If so, why isn't this included as one of the postulates of special relativity?
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### Wrong statements in Special Relativity [closed]

In my lecture notes on General Relativity, I have the following statements that are said to be wrong in Special Relativity: Every physical observer measures a speed of light equal to $c$. Every ...
181 views

### Does the speed of light change? [duplicate]

I know that there is a similar questions, but I think mine is a bit different. I wonder if with the expansion of the universe the speed of light changes. It seems that the speed of light is very ...
136 views

### What will the results be of this experiment to measure the trajectory of light?

I imagined a theoretical experiment about gravity. First of all, I know that it is very hard to build such sensitive test apparatus with our current technology but it is just theoretical experiment ...
220 views

### Is there a difference between what Schwarzschild vs Gullstrand-Painleve predict for c?

When we set the interval(ds) for a given coordinate(i.e. Schwarzschild coordinates) to 0 to calculate for the velocity of light in a gravitational field, we can arrive at an equation such as the one ...
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### Speed of light in a perfect vacuum

Lets' say that something is in a universe with a perfect vacuum, where nothing exists but that object. This universe has an infinite amount of space and time. Now that object emits a single photon. ...
130 views

### Does the equivalence principle imply that light must move slower when moving away from a massive object?

Thought experiment: Elevator going up at an extreme acceleration, pulse of light bouncing up, and down between mirrors on the floor, and the ceiling. Won't it take light longer to travel from the ...
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### Metric in spacetime

From the flat spacetime metric, we can see that the line element corresponding to null geodesic predicts that photon travel at speed $c$, but when we make a generalized coordinate transformation can ...
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### Velocity of massless particles in $\mathrm{AdS}_4$ space-time

In spherical coordinates in a $(1+3)$-dimensional space-time one has the $\mathrm{AdS}_4$ metric $$ds^{2}=-\left(1+k^{2}r^{2}\right)dt^{2}+\left(1+k^{2}r^{2}\right)^{-1}dr^{2}+r^{2}d\Omega ^{2}.$$ ...
In the case of spherical symmetry you can say that the velocity of light (in coordinate time) goes as: $v_{light}=c(1-\frac{2GM}{rc^2})$ in the radial direction and as: \$v_{light}=c\sqrt{(1-\frac{...