What is the relation between gravity and light?

In summary, the speed of light is not a rarity as it is also the speed at which a hypothetical particle responsible for carrying gravity, called a graviton, propagates. This is based on the theory of general relativity, which sets a universal speed limit on communication between objects in the universe. The reason why gravity propagates at the speed of light is still a question, but it is expected due to dimensional analysis. Additionally, the possibility of instantaneous speed of gravity has been disproven.
  • #1
phy_freak
32
0
why did they have to be the same speed? do you think that this speed was somehow set as a standard speed for such things, i don't know maybe there are other things that are also in the speed of light.. so the speed of light isn't so rare..
 
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  • #2
GR sets a universal speed limit on 'communication' between objects in the universe. That limit happens to be the speed of light.
 
  • #3
phy_freak said:
why did they have to be the same speed? do you think that this speed was somehow set as a standard speed for such things, i don't know maybe there are other things that are also in the speed of light.. so the speed of light isn't so rare..

Hipothetical particle responsible for carrying gravity is massless boson called graviton. Massless particles propagate at speed of light.

If graviton is never confirmed to be real, then your question - why gravity propagates at speed of light - is very good question. Simply stating that GR forbids FTL communication, doesn't explain anything, because question is why speed of gravity propagation is exactly same as the speed of light propagation, not why gravity is not faster then light.
 
  • #4
I think the "speed of gravity" can be worked out using GR...and it turns out to be c...but I've no idea how. :P
 
  • #5
Matterwave said:
I think the "speed of gravity" can be worked out using GR...and it turns out to be c...but I've no idea how. :P
Related thread:

https://www.physicsforums.com/showthread.php?t=369420

Edit: Also, on the grounds of dimensional analysis, we expect to get c. The only other really conceivable option would be for gravity to propagate instantaneously.
 
Last edited:
  • #6
If graviton is never confirmed to be real, then your question - why gravity propagates at speed of light - is very good question.
A graviton simply inherits its properties from the classical wave it is meant to quantize. Whether or not there is a graviton is irrelevant, the speed is derived from linearized gravity, i.e. the wave solution in the weak field approximation.
 
  • #7
Instantaneous speed of gravity has been thoroughly debunked AFAIK.
 
  • #8
S.Vasojevic said:
Hipothetical particle responsible for carrying gravity is massless boson called graviton. Massless particles propagate at speed of light.

If graviton is never confirmed to be real, then your question - why gravity propagates at speed of light - is very good question. Simply stating that GR forbids FTL communication, doesn't explain anything, because question is why speed of gravity propagation is exactly same as the speed of light propagation, not why gravity is not faster then light.


could you please explain what you meant by "GR" and "FTL" ? :confused:
 
  • #9
phy_freak said:
could you please explain what you meant by "GR" and "FTL" ? :confused:
GR = general relativity, Einstein's law of gravity
FTL = faster than light
 

1. What is gravity?

Gravity is a force that exists between any two objects with mass. It is the force that pulls objects towards each other. The strength of gravity depends on the mass of the objects and the distance between them.

2. What is light?

Light is a form of electromagnetic radiation that can be detected by the human eye. It travels in the form of waves and can also behave like particles called photons. Light is essential for vision and plays a crucial role in many other natural phenomena.

3. How are gravity and light related?

Gravity and light are related in several ways. First, according to Einstein's theory of general relativity, gravity is caused by the curvature of space and time, and this curvature can also affect the path of light. Second, the mass of an object can also affect the speed of light, as seen in the phenomenon of gravitational lensing.

4. Can gravity bend light?

Yes, gravity can bend light. This is known as gravitational lensing. When light passes near a massive object, such as a star or a galaxy, the gravitational pull of the object can bend the path of the light, causing it to appear distorted or magnified to an observer.

5. How does gravity affect the speed of light?

Gravity can affect the speed of light in two ways. First, as mentioned before, the mass of an object can affect the speed of light, causing it to slow down or speed up. Second, the gravitational field can also cause the path of light to be curved, which can affect the perceived speed of light.

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