Linked Questions

5
votes
2answers
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?
3
votes
2answers
213 views

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. ...
3
votes
2answers
178 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 ...
2
votes
2answers
120 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 ...
0
votes
2answers
81 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 ...
-1
votes
2answers
61 views

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 ...
2
votes
1answer
211 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 ...
1
vote
1answer
54 views

Spatial variation in velocity of light or curved space-time?

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{...
1
vote
1answer
164 views

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 ...
1
vote
1answer
135 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 ...
1
vote
1answer
85 views

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 $$ds^{2}=-\left(1+k^{2}r^{2}\right)dt^{2}+\left(1+k^{2}r^{2}\right)^{-1}dr^{2}+r^{2}d\Omega ^{2}.$$ ...
0
votes
1answer
47 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 ...
0
votes
1answer
41 views

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?
0
votes
1answer
545 views

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 ...
0
votes
0answers
105 views

Can you outrun light in general relativity?

The top answer on this question explains that the speed of light can change with distance from an accelerated observer. Is there then in any meaningful sense a way to outrun light emitted from a ...

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