Is the Speed of Light Really Constant?

In summary, photons travel along geodesics in a vacuum, and when they are deflected by an intermediary mass, their path is still considered "straight" along the curved surface of space-time. This does not mean that photons are accelerating, and in the theory of General Relativity, a null geodesic is the path traveled by light. This means that it is impossible for light to not follow a null geodesic, and it is only observed to vary in velocity when viewed from a stationary frame. This phenomenon is known as a gravitational lens and was first observed during a solar eclipse, providing evidence for the theory of General Relativity.
  • #1
Loren Booda
3,125
4
If photons can follow a curved trajectory, may they be considered to accelerate in a (generally) relative manner?
 
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  • #2
In a vacuum photons travel along geodesics, to be specific null-geodsics, which can be considered 'straight lines'. If the presence of an intermediary mass causes a light ray to be deflected, the path of the photon is still 'straight', it just happens to be along a surface of space-time that itself is curved by the presence of the gravitating mass.

So in this case the photon is not said to 'accelerate'.

Garth
 
  • #3
It's a theory, I don't think anyone can agree on it.

Check out this link http://van.hep.uiuc.edu/van/qa/section/Light_and_Sound/Properties_of_Light/20040223072254.htm
 
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  • #4
I believe that in GR the definition of a null Geodesic is the path traveled by light. So in that sense it is impossible for light to NOT follow a null geodesic. If you were able to travel with a photon you would never observe it to vary in its velocity. However if we consider our frame stationary and observe the path of a photon it can appear to vary its velocity. This is observed and called a gravitational lens. Also it was the supposed observation of the variation of the position of star near the limb of the sun during a solar eclipse which was the first verification of GR.
 

FAQ: Is the Speed of Light Really Constant?

1. Can photons accelerate in a vacuum?

Yes, photons can accelerate in a vacuum. According to the theory of special relativity, photons always travel at the speed of light, which is the maximum speed possible in a vacuum.

2. Do photons have mass and therefore can accelerate?

No, photons do not have mass. They are considered to be massless particles and therefore do not accelerate in the traditional sense. Instead, they can change their energy and momentum, resulting in a change in velocity.

3. How does the acceleration of photons compare to other particles?

The acceleration of photons is unique compared to other particles. Unlike massive particles, photons do not need to gain kinetic energy to accelerate. Instead, they change their frequency and wavelength to increase their energy and momentum.

4. Can photons change direction while accelerating?

Yes, photons can change direction while accelerating. This is known as refraction and occurs when photons move from one medium to another, such as from air to water. The change in the medium causes a change in the speed of the photon, which results in a change in direction.

5. Is the acceleration of photons affected by gravity?

Yes, the acceleration of photons is affected by gravity. According to the theory of general relativity, photons follow the curvature of spacetime caused by massive objects, such as planets or stars. This results in a change in the path and velocity of the photon's movement.

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