Linked Questions

0 votes
0 answers
199 views

What is the speed of light at the photon sphere? [duplicate]

At the photon sphere (where photon exhibit circular orbit around a black hole), the radius is given by $r={\frac {3}{2}}r_{\rm {s}}$, and the angular velocity is $({\frac {d\phi }{dt})^{2}=\frac {c^{2}...
Jim RF's user avatar
  • 1
-1 votes
2 answers
118 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 ...
Sam Cottle's user avatar
  • 1,544
0 votes
2 answers
181 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 ...
Philipp's user avatar
  • 41
0 votes
1 answer
101 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 ...
PiggyChu001's user avatar
0 votes
2 answers
64 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 ...
Patrick Szalapski's user avatar
1 vote
0 answers
35 views

If a black hole bends light what does to a beam that arrives at a zero degree angle directly towards the singularity? [duplicate]

We can only speculate what is going on but does the black hole singularity make the light arrive faster than it would in space not affected by gravity?
Janko Bradvica's user avatar
0 votes
1 answer
51 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?
user avatar
59 votes
6 answers
10k 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 ...
Sharon Salmon's user avatar
4 votes
5 answers
4k 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 ...
Harsh Kumar's user avatar
13 votes
2 answers
7k 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 ...
math and mountains's user avatar
6 votes
3 answers
627 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 ...
Muze's user avatar
  • 1
5 votes
2 answers
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?
Peter4075's user avatar
  • 3,029
0 votes
1 answer
725 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 ...
sequence's user avatar
  • 568
3 votes
2 answers
259 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 ...
Derb's user avatar
  • 65
2 votes
1 answer
420 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 ...
user2299067's user avatar

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