Speed of light around a (massive) object in space ...(i.e.sun

[tma73]

Just wondering how a photon reacts when it is affected by gravity of an object in space like a star.
Does the gravity actually bend the light/photons?
Say you have a series of photons in a perfect line, all travelling, well, at the speed of light toward a massive object(x).
The photons in the objects direct path will collide with that object. The photons that will 'barely' avoid this massive object will be bent?
Photons further away with no gravitational influence of this massive object...of course keep their 'speed of light'.

So, I guess what I'm asking the photons being 'warped' by object(x)'s gravity will be (slightly) behind the photons who were not affected by the gravity?
The photons/light that were 'bent' by gravity still traveled at the speed of light? it's just maybe they traveled a little further than photons that were not affect by Object(x)?

I understand that gravity does not bend light/photons it's already the 'curvature of space time created by Object(x) (correct?)

tma73

btw, I read this in the FAQ section:

In general relativity, gravitation is a manifestation of the curvature of spacetime. The motion of all objects is affected by this curvature, regardless of whether they have mass or not. Light follows geodesic paths in spacetime, which are straight lines in flat spacetime, and curved paths in curved spacetime.

Note that by "mass" above I mean "invariant mass" as discussed in the following FAQ:

https://www.physicsforums.com/showthread.php?t=511175

because it is the invariant mass that is zero for a photon. If you prefer to think in terms of "relativistic mass" (which is related to energy via E=mrelc2" role="presentation" style="display: inline-block; line-height: 0; font-size: 18.08px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; font-family: "PT Sans", san-serif; position: relative;">E=mrelc2E=mrelc2, note that all photons (as far as we know) follow the same geodesics, regardless of their energy. This has been verified, for example, by comparing the deflection of visible light as it passes close to the sun, with the deflection of radio waves from distant sources.

The following forum members have contributed to this FAQ:
jtbell

 

[Ibix]

First of all, it's best not to think of photons in this context. They're rather complicated quantum entities and their interaction with curved spacetime is way beyond my level of understanding. Instead think of a pulse of light, like a short flash from a lamp.

Light does indeed follow a curved path near a massive body (as does everything else), and detection of the deflection of star light passing close to the sun by Eddington was one of the early triumphs of general relativity. The effect is sometimes called gravitational lensing, because the massive body acts like a (very poorly made) lens.

It's a bit difficult to know what you mean by some of the light being a bit behind. Light passing near the body leaves in a different direction to light further away, so "behind" isn't the right word. It is true that light takes longer to travel near the Sun than a naive calculation would suggest - this is called Shapiro delay.

Hope that helps.

 

[tma73]

Thanks Ibix,
Sorry about the confusion.
I guess what I was asking is that this light (pulse..) following this curved path or b/c of the Shapiro delay, these photons don't slow down at all. I think you answered my question in your response here:
"It is true that light takes longer to travel near the Sun than a naive calculation would suggest - this is called Shapiro delay."
There's nothing that can slow down light or a photon pulse?
Can photons/light/photon pulse actually achieve a speed greater than c (speed of light) from some (?) phenomena?
I remember I had a professor in college that said (can't recall the particles name) could travel faster than photons/light...but not slower, can't recall the name..

thanks :)

 

[Nugatory]

"It is true that light takes longer to travel near the Sun than a naive calculation would suggest - this is called Shapiro delay."

It is easy to misinterpret this statement though, so you have to be careful here. If we were to position a measuring device at any point along the path followed by the light beam, we would measure its speed at that point to be $c$ - no slowing down at all. Only when we choose two widely separated points do we find that when we divide the distance between the two points by the travel time (the natural way of calculating the speed of light between the two points) we get something slightly less than $c$. The explanation, loosely speaking, is that there is a bit more distance between the two points than our naive calculation suggests.

 

[Grinkle]

Can photons/light/photon pulse actually achieve a speed greater than c (speed of light) from some (?) phenomena?

c is the speed of light in a vacuum. The speed lof light in a non-vacuum transparent medium is slower than c. I'm not sure if this applies to your question or not.

 

[tma73]

It is easy to misinterpret this statement though, so you have to be careful here. If we were to position a measuring device at any point along the path followed by the light beam, we would measure its speed at that point to be c - no slowing down at all. Only when we choose two widely separated points do we find that when we divide the distance between the two points by the travel time (the natural way of calculating the speed of light between the two points) we get something slightly less than c. The explanation, loosely speaking, is that there is a bit more distance between the two points than our naive calculation suggests.

Thanks Nugatory...I kind of understand what you're saying hehe
Appreciate the replies, time and help

t

 

[tma73]

c is the speed of light in a vacuum. The speed lof light in a non-vacuum transparent medium is slower than c. I'm not sure if this applies to your question or not.

I meant a speed in a vacuum (I didn't want complicate things)
Yeah I do remember this from Physics :) I guess if that object(X) I talked about above had an atmosphere...would then affect things/ outcome would be different... but sorry for my question(s) seemed to have created more of a mess than I meant to :)