Light has no mass because gravity and light travel at the same speed, true or false?

[Jalopy]

I discovered on google that the speed of light and the speed of gravity are the same.

Does that mean that gravity fails to have any effect on light, because gravity and light travel at the same speed?

i.e is that why light has no mass?

 

Edited March 3, 2022 by Jalopy

[Sensei]

18 minutes ago, Jalopy said:

i.e is that why light has no mass?

When a scientist says that "light has no mass", he or she, means to say that "light has no rest-mass" and "light has no valid frame-of-reference in which the photon is at rest"..

19 minutes ago, Jalopy said:

Does that mean that gravity fails to have any effect on light, because gravity and light travel at the same speed?

Did not you hear about Gravitational lens?

https://en.wikipedia.org/wiki/Gravitational_lens

Edited March 3, 2022 by Sensei

[beecee]

3 hours ago, Jalopy said:

I discovered on google that the speed of light and the speed of gravity are the same.

Does that mean that gravity fails to have any effect on light, because gravity and light travel at the same speed?

i.e is that why light has no mass?

 

Light has no rest mass, but then again, it is never at rest. And yes light/photons do actually warp spacetime ever so slightlydue to momentum. Gravity of course is spacetime warpage/geometry.

1 minute ago, beecee said:

Light has no rest mass, but then again, it is never at rest. And yes light/photons do actually warp spacetime ever so slightlydue to momentum. Gravity of course is spacetime warpage/geometry.

Light also travels in geodesics in curved/warped spacetime. eg: gravitational lensing.

[swansont]

14 hours ago, Jalopy said:

I discovered on google that the speed of light and the speed of gravity are the same.

Does that mean that gravity fails to have any effect on light, because gravity and light travel at the same speed?

i.e is that why light has no mass?

 

Light moves at the same speed as gravity because photons have no mass. Massless things move at c. Massive things move at speeds slower than c.

[Janus]

18 hours ago, Jalopy said:

I discovered on google that the speed of light and the speed of gravity are the same.

Does that mean that gravity fails to have any effect on light, because gravity and light travel at the same speed?

i.e is that why light has no mass?

 

What are the same are the speed of light (in a vacuum) and the speed of gravity waves.  Gravity waves are not gravity itself, but more like ripples traveling through the gravitational field. Put another way, you can't have gravitational waves without there already being a gravitational field, but you can have a gravitational field without gravitational waves.

Light interacts with the gravitational field, which is "already there"

As already mentioned, light has no "rest mass".  However, it still can interact gravitationally.  While in Newtonian physics you need mass to do so, under our more recent understanding of gravity(General Relativity), mass is just one factor that can contribute to gravity. Energy is another, and light does have energy.

[johnsankey]

e=mc²

light is energy

Gravity does indeed have an effect on light: search 'gravitational lensing'

[MigL]

38 minutes ago, johnsankey said:

e=mc²

light is energy

Is your claim supposed o follow from he equality ?

I read that as energy is equivalent to mass; and don't see 'light' in that equation at all.

[exchemist]

1 hour ago, johnsankey said:

e=mc²

light is energy

Gravity does indeed have an effect on light: search 'gravitational lensing'

That doesn't make a lot of sense. E=mc² returns a result of zero for a massless entity like a photon. You need the full formula including momentum, which for a massless entity reduces to E=pc, which in turn, via de Broglie's relation, gives you Planck's formula E=hν.

More fundamentally, "light is energy" is just wrong. Energy is one of many properties of light. You seem to have watched too much Star Trek.😀 

[johnsankey]

A photon does not have rest mass, but it's energy gives it a mass in general relativity. That's why it's affected by gravitation.

Light is energy in e=mc² ; of course it has other properties too.

[Bufofrog]

32 minutes ago, johnsankey said:

A photon does not have rest mass, but it's energy gives it a mass in general relativity.

No, energy does not give mass to a photon.  You are making a lot of unsupported claims.  

[exchemist]

8 hours ago, johnsankey said:

A photon does not have rest mass, but it's energy gives it a mass in general relativity. That's why it's affected by gravitation.

Light is energy in e=mc² ; of course it has other properties too.

No. E=mc² is just a special case of the full formula: E² = (mc²)² + p²c², p being momentum and m the rest mass, repeat rest mass.

In the case of objects at rest relative to the observer that reduces to E=mc², as p is zero in such cases. In the case of light, that is obviously untrue. As photons have zero rest mass, you get E=pc.

De Broglie's relation tells you that p=h/λ, so E= hc/λ , but since c=νλ, i.e. c/λ=ν,  then voila, E=hν, Planck's relation. 

 

[joigus]

14 hours ago, johnsankey said:

e=mc²

Yes.

14 hours ago, johnsankey said:

light is energy

 

No.

14 hours ago, johnsankey said:

Gravity does indeed have an effect on light: search 'gravitational lensing'

Yes.

66.6 % right as to the sheer number of assertions.

And, as pointed out to you, 100 % wrong as to the logic. You could have a world in which e=mc² (the world of special relativity), and it is conceivable that photons didn't couple to the gravitational field. So those are independent assertions.

[Tutoroot]

Thank you for sharing this information.