B Gravitational Lensing: Gravity's Effect on Light

[Rigel84]

This is my first (well second if we exclude introduction forums) topic here. I just want to make clear that I am not professional nor involved in field in any way. I am just regular Joe who wants to know more about nature.
I could say that I understand fact that mass distorts space but there is one thing that is unclear to me.

Maybe I understood it wrong but it seems to me that mass effects objects such as asteroids for example and light in different manner.
Gravity "attracts" objects with mass, they get pulled down to planet/star or get slingshoted.
On the other hand light behaves differently, it gets slightly pushed(?) and this is why we can see stars behind certain massive objects in space.

Am I getting something wrong here?

 

[PeroK]

This is my first (well second if we exclude introduction forums) topic here. I just want to make clear that I am not professional nor involved in field in any way. I am just regular Joe who wants to know more about nature.
I could say that I understand fact that mass distorts space but there is one thing that is unclear to me.

Maybe I understood it wrong but it seems to me that mass effects objects such as asteroids for example and light in different manner.
Gravity "attracts" objects with mass, they get pulled down to planet/star or get slingshoted.
On the other hand light behaves differently, it gets slightly pushed(?) and this is why we can see stars behind certain massive objects in space.

Am I getting something wrong here?

Unfortunately, most of what you said is not correct. Light is deflected around a massive object in a similar way that a fast moving particle would be. Try this, for example:

https://oneminuteastronomer.com/9237/gravitational-lens/

http://www.spacetelescope.org/images/heic1106c/

 

[A.T.]

...it seems to me that mass effects objects such as asteroids for example and light in different manner...

Actually the local effect (acceleration relative to the big mass) is the same for everything.

 

[DrStupid]

Actually the local effect (acceleration relative to the big mass) is the same for everything.

At least for everything with the same relative velocity.

 

[Rigel84]

Unfortunately, most of what you said is not correct. Light is deflected around a massive object in a similar way that a fast moving particle would be. Try this, for example:

https://oneminuteastronomer.com/9237/gravitational-lens/

http://www.spacetelescope.org/images/heic1106c/

This is what I was referring to. Maybe I wasn't clear enough with my question. To simplify, is light effected by gravity in same manner as objects with mass regardless of speed? Photons do not have mass but they do have energy.
Everything follows curvature of space?

Physics I learned back in school didn't have much to do with this. As electric technician I learned mostly what is important for that field.

It's kinda hard to wrap mind around this, that's why I find it fascinating.

 

[PeroK]

This is what I was referring to. Maybe I wasn't clear enough with my question. To simplify, is light effected by gravity in same manner as objects with mass regardless of speed? Photons do not have mass but they do have energy.
Everything follows curvature of space?

Physics I learned back in school didn't have much to do with this. As electric technician I learned mostly what is important for that field.

It's kinda hard to wrap mind around this, that's why I find it fascinating.

The paths of light rays differ from, but are similar to, those of particles with mass, but not in the way you suggested in your OP. Where, I think you suggested light was repelled by a massive object.

The path taken by a particle depends on its velocity relative to the massive object. So, there is no single path. Compare a particle falling to Earth and one in orbit.

The path taken by light also depends on its initial velocity relative to the massive object. A light ray moving directly towards an object will continue on that course and hit the object. But, one moving past the object will be deflected - perhaps only slightly - towards it.

 

[DrStupid]

To simplify, is light effected by gravity in same manner as objects with mass regardless of speed?

No, but light is effected by gravity in a similar manner as objects with mass and similar speed and the mechanism is identical.

 

[Rigel84]

Thanks, it bit clearer. At least I think it is.

 

[Tracer]

Would it be correct to say that in Eddington's solar eclipse experiment, the suns's gravitational field existed with or without photons moving through it and
(A) photons would follow a geodesic as they moved past the sun?
and
(B) Photons would also experience a separate acceleration toward the CG of the sun based on the distance between the photons and the CG of the sun
Therefore
The total deflection would be the sum of effects A and B?
Or are A and B the same thing?

 

[DrStupid]

No, there is no separate acceleration.

 

[Ibix]

Would it be correct to say that in Eddington's solar eclipse experiment, the suns's gravitational field existed with or without photons moving through it and
(A) photons would follow a geodesic as they moved past the sun?
and
(B) Photons would also experience a separate acceleration toward the CG of the sun based on the distance between the photons and the CG of the sun
Therefore
The total deflection would be the sum of effects A and B?
Or are A and B the same thing?

Particles in free-fall follow geodesics. There is no other effect here. In particular, gravity as modeled by GR doesn't cause an acceleration in most senses of the word. It just modifies the meaning of "straight line" in Newton's first law.

 

[Yukterez]

The paths of light in the observer's frame of reference are



as you can see the speed of light is not constant, but shapiro-delayed (infinitely, at the horizon; only the local velocity is constant). If you took high velocity particles instead of photons, for example with 0.99999c local initial velocity, you would see no difference on the plot because the deflection and shapiro-delay would be almost the same.