# Gravitational Lensing : Eddington Experiment

Even I am at loss of word explaining the OP to you....
That's because you fabricate problems when there is none.
Why don't you understand, we accept that the light follows the curved path (geodesic), even though a physical straightline can be drawn but light does not follow it.......see what happens to light in BH in presence of highly curved spacetime, will we do our optics in extreme gravity (say on NS surface) on straightlines??

We accept it because that's the way it happens. Light and anything else must follow geodesics.....Similarly as a plane or a boat follows "great circle arcs" on the surface of the Earth.
The point you do not want to accept, is that the spacetime, or the fabric of the universe, is curved, and everything must follow that curvature, or geodesics. There is no straight lines.
Another analogy....Overall the universe is said to be flat within very small ranges of tolerances. What that effectively means is that two beams of light emitted parallel to each other, will remain parallel overall. [other than the odd dip/wiggle/curvature due to intervening geodesics]. If the universe was closed, the "parallel"beams would converge....If the universe was open, they would diverge.

Last edited:
Even I am at loss of word explaining the OP to you....
I fear that these concepts may be beyond your ability, but we can try once more.
The straight line shows the **APPARENT** position of the star. It is not REALLY there, space is curved around the sun, but the straight line is where it LOOKS like the star should be if there was no curvature.
I tried to find an explanation of the Eddington experiment for grade school kids but have not found one yet - if I do I will let you know.

Why don't you understand, we accept that the light follows the curved path (geodesic), even though a physical straightline can be drawn but light does not follow it.......see what happens to light in BH in presence of highly curved spacetime, will we do our optics in extreme gravity (say on NS surface) on straightlines??
I am proud of you for struggling so hard with these concepts - keep at it!
That is right the light does not go in a straight line it follows the curvature of space time! Good job! This is the hard part - the straight line is showing the APPARENT postion of the star if there was no curvature. The term apparent means that it appears to be there (but it isn't really).

Come on Origin, trolling shadowsmoke has taken heavy toll on you...
Don't get distracted, keep working on the concept of APPARENT location versus ACTUAL location. You can figure this out!
Good luck!

Gravitational Lensing in action:

http://apod.nasa.gov/apod/ap151127.html

Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 November 27

Gravity's Grin
Image Credit: X-ray - NASA / CXC / J. Irwin et al. ; Optical - NASA/STScI
Explanation: Albert Einstein's general theory of relativity, published 100 years ago this month, predicted the phenomenon of gravitational lensing. And that's what gives these distant galaxies such a whimsical appearance, seen through the looking glass of X-ray and optical image data from the Chandra and Hubble space telescopes. Nicknamed the Cheshire Cat galaxy group, the group's two large elliptical galaxies are suggestively framed by arcs. The arcs are optical images of distant background galaxies lensed by the foreground group's total distribution of gravitational mass dominated by dark matter. In fact the two large elliptical "eye" galaxies represent the brightest members of their own galaxy groups which are merging. Their relative collisional speed of nearly 1,350 kilometers/second heats gas to millions of degrees producing the X-ray glow shown in purple hues. Curiouser about galaxy group mergers? The Cheshire Cat group grins in the constellation Ursa Major, some 4.6 billion light-years away.

The point you do not want to accept, is that the spacetime, or the fabric of the universe, is curved, and everything must follow that curvature, or geodesics. There is no straight lines.

Great!
If there is no straightline then how the extrapolation can be on the straightline? Thats the point.

I fear that these concepts may be beyond your ability, but we can try once more.
The straight line shows the **APPARENT** position of the star. It is not REALLY there, space is curved around the sun, but the straight line is where it LOOKS like the star should be if there was no curvature.
I tried to find an explanation of the Eddington experiment for grade school kids but have not found one yet - if I do I will let you know.

I am proud of you for struggling so hard with these concepts - keep at it!
That is right the light does not go in a straight line it follows the curvature of space time! Good job! This is the hard part - the straight line is showing the APPARENT postion of the star if there was no curvature. The term apparent means that it appears to be there (but it isn't really).

Don't get distracted, keep working on the concept of APPARENT location versus ACTUAL location. You can figure this out!
Good luck!

You are being unnecessarily rude. If you are attempting to tell me that I do not understand what is actual and what is apparent, then so be it. You are not able to get beyond the straighline extrapolation which is done in optics in normal almost flat spacetime...try visulaizing the optics in extremally curved spacetime, you will get the point.

Great!
If there is no straightline then how the extrapolation can be on the straightline? Thats the point.
The line of sight simply follows the geodesic path of curved spacetime and we see the illusionary concept of a straight line. :shrug:
You are unable to accept a logical explanation due to your previously closeted agenda.
But as always if you believe you have something concrete, follow the tried and true scientific methodology and get appropriate peer review.
Might see you at next years Nobel awards...
You are being unnecessarily rude. If you are attempting to tell me that I do not understand what is actual and what is apparent, then so be it. You are not able to get beyond the straighline extrapolation which is done in optics in normal almost flat spacetime...try visulaizing the optics in extremally curved spacetime, you will get the point.
I fail to see any rudeness in that post at all...In fact its style and mannerisms actually reflect on the many if not all, posts that you burden us with.

The line of sight simply follows the geodesic path of curved spacetime and we see the illusionary concept of a straight line. :shrug:

You have written something.
Imagine yourself at the surface of a Neutron Star as an observer (Extreme Gravity). Imagine an object with a lamp some 100 meters away from you (100 meters is taken supposing that it can give an appreciable curved geodesic around NS surface, this is an arbitray figure and can be adjusted). Now the light which comes to you from the object will not be on a straight path, it will be a somewhat curved (bow like) path. So where do you see the object? Hanging in the sky?

If you are attempting to tell me that I do not understand what is actual and what is apparent, then so be it.
That is certainly the way it seem.
You are not able to get beyond the straighline extrapolation which is done in optics in normal almost flat spacetime...try visulaizing the optics in extremally curved spacetime, you will get the point.
Huh? You asked about the straight line extrapolation and I am trying help you figure it out, remember? Did you forget your question? As I feared, it seems that you still can't seem to understand what the significance of the straight line is in diagram. Maybe science is just not you thing.

That is certainly the way it seem.

Huh? You asked about the straight line extrapolation and I am trying help you figure it out, remember? Did you forget your question? As I feared, it seems that you still can't seem to understand what the significance of the straight line is in diagram. Maybe science is just not you thing.

Sorry, you are just trying to act smart and have no substance in your response...

Sorry, you are just trying to act smart and have no substance in your response...
I'm sure it seems that way to you. I tried to help but you are unwilling or unable to figure this out. Well, good luck.

Even I am at loss of word explaining the OP to you....

We are used to extrapolating in straightline, but in curved spacetime straightline is non existent....

Why don't you understand, we accept that the light follows the curved path (geodesic), even though a physical straightline can be drawn but light does not follow it.......see what happens to light in BH in presence of highly curved spacetime, will we do our optics in extreme gravity (say on NS surface) on straightlines??

Come on Origin, trolling shadowsmoke has taken heavy toll on you...

Consider the following image.

The path the light from the viewed star is curved, but by the time it reaches the Earth it is traveling in a straight line for all practical purposes. Thus the light see see coming from this star strikes our eyes/sensors from the same direction as it would as if was coming in on a straight line from the star's apparent position in the diagram. In other words, the image we see is the same as if the if the star was in the apparent position and there was no bending of the light path. This is in contrast to the direction the light would come from if the light did come directly from the star with no bending. We do not extrapolate the lensed image, the lensed image is what we directly see and what we extrapolate is true position of the star. ( the direction the light would come from if it it hadn't been bent by the intervening mass.) With the Sun this is easy because we can compare the image of that part of the sky when there is no Sun to bend the light to the image of the same section of the sky when the Sun is in it during a total eclipse.

You have written something.
Imagine yourself at the surface of a Neutron Star as an observer (Extreme Gravity). Imagine an object with a lamp some 100 meters away from you (100 meters is taken supposing that it can give an appreciable curved geodesic around NS surface, this is an arbitray figure and can be adjusted). Now the light which comes to you from the object will not be on a straight path, it will be a somewhat curved (bow like) path. So where do you see the object? Hanging in the sky?
The line of sight simply follows the geodesic path of curved spacetime and we see the illusionary concept of a straight line. :shrug:
And of course again, gravitational lensing is really a simple concept tied to the warpage and curvature of spacetime. The eye of course is unable to discertain any curve or bend in the geodesic path of that light.
You seem to be the only one with any problems envisaging this observationally verified concept. :shrug: again.
Which suggests an agenda.

Consider the following image.

The path the light from the viewed star is curved, but by the time it reaches the Earth it is traveling in a straight line for all practical purposes. Thus the light see see coming from this star strikes our eyes/sensors from the same direction as it would as if was coming in on a straight line from the star's apparent position in the diagram. In other words, the image we see is the same as if the if the star was in the apparent position and there was no bending of the light path. This is in contrast to the direction the light would come from if the light did come directly from the star with no bending. We do not extrapolate the lensed image, the lensed image is what we directly see and what we extrapolate is true position of the star. ( the direction the light would come from if it it hadn't been bent by the intervening mass.) With the Sun this is easy because we can compare the image of that part of the sky when there is no Sun to bend the light to the image of the same section of the sky when the Sun is in it during a total eclipse.

You are defining the Gravitational Lensing, I have already given the link to image and the definition in my earlier post as quoted below. The question is not what is Gravitational Lensing, the question is correctness of extrapolation in a straightline on a curved spacetime around Sun (Star).

A reference is drawn to a paper..

http://www.astro.ubc.ca/people/newbury/siam/gravlens.pdf

At page #2 Fig 2.1, shows the geomtery of lensing.

Now consider the image pasted by you. Say S1, S1' (Image of S1), S2 (Top one) as the stars and S as the lensing Star (Sun) and O as the observer. S2 is different and OS2 line of sight is the direct straightline as curving effect by S is negligible.

The light from S1 is deflected due to curved spacetime around S and as per definition 'O' will see the same at S1'. Thats the lensing definition. My question is how can we make OS1' extrapolation when the OS1' straightline is non existent in the curved spacetime around S?

This picture gives rise to one more observation, say OS2 is the closest straightline path with almost negligible deflection, anything inside OS2 will have some deflection, Now draw a tangential line from O to S (Lensing Star) extended till infinity, so any source between this tangential line OS and OS2 (Extended) will not be visibile to O, because deflected light will not be focussed at O. And whatever we see on the envelop of OS and OS2 will actually be images of stars below OS.

You may also like to consider a situation wherein source and observer are both at the surface of a Neutron Star (Extreme Gravity and curved spacetime), as we increase the distance between the observer and the source, the observer sees the object slowly lifting up in the air (towards sky) due to this straightline extrapolation. My argument is that you can only make the extrapolation on the path of light, a straightline is not the path of light in the curved spacetime.

Last edited:
The line of sight simply follows the geodesic path of curved spacetime and we see the illusionary concept of a straight line. :shrug:
And of course again, gravitational lensing is really a simple concept tied to the warpage and curvature of spacetime. The eye of course is unable to discertain any curve or bend in the geodesic path of that light.
You seem to be the only one with any problems envisaging this observationally verified concept. :shrug: again.
Which suggests an agenda.

Did you pick up this shruging from AI Krash661? Be careful it may dislocate your shoulders.

Thanks MODs, for correcting the spelling of 'Eddington' in the thread title.....

Did you pick up this shruging from AI Krash661? Be careful it may dislocate your shoulders.
It's either shrug at the futility of your claims, or laugh at the stupidity.

My argument is that you can only make the extrapolation on the path of light, a straightline is not the path of light in the curved spacetime.

You have no argument....you have an agenda.
The line of sight simply follows the geodesic path of curved spacetime and we see the illusionary concept of a straight line. :shrug:

The light from S1 is deflected due to curved spacetime around S and as per definition 'O' will see the same at S1'. Thats the lensing definition. My question is how can we make OS1' extrapolation when the OS1' straightline is non existent in the curved spacetime around S?
My question is, "how in the name of God is this so confusing for you"?

Lets try an analogy. Lets say you look into a mirror and see a table. The table is behind you because what you are seeing is a reflection; the path of the light is from the table to the mirror and from the mirror to your eye. But you could draw a straight line from your eye to where it looks like the table is. It is that simple.

If you are going on about this to make so sort of point, I think you should realize that this point is lost to all of us and you just sound like you have some rather glaring mental defect.

My question is, "how in the name of God is this so confusing for you"?

Lets try an analogy. Lets say you look into a mirror and see a table. The table is behind you because what you are seeing is a reflection; the path of the light is from the table to the mirror and from the mirror to your eye. But you could draw a straight line from your eye to where it looks like the table is. It is that simple.

If you are going on about this to make so sort of point, I think you should realize that this point is lost to all of us and you just sound like you have some rather glaring mental defect.

there is no confusion, you also understand what i am talking about, but you are carefully stearing away from it, and attempting to teach me the basics of mirror/lense optics in flat spacetime, which mostly high school kids do. please see the OP thats the prereq for this thread, suggesting that at least I know the basics of optics.

i will clarify once more.....the spacetime around lensing star (S) is curved, whether the actual light site path or apparent light path, both of them must lie on geodesics, if so how can the apparent path extrapolated to S1' be a straightline ? please understand OS1' is non existent in GR curved spacetime..

your answer (and all others, even including me till yesterday) is that light shall follow the geodesics, but apparent extrapolations can be on straightline......this appears to me incorrect. your analogy of mirror or lense in the lab or room, will have straightline extrapolation because no appreciable or detectable curvature present.

[You are forgetting that there are no Eucleadian straight lines in curved spacetime, which light can follow].

If what I am saying is right, and I pray that i am not, then the conclusion is very sinister.

there is no confusion,
Your confusion is so profound it is as if you have lost your mind!
you also understand what i am talking about, but you are carefully stearing away from it,
No, I really don't know what in the hell you are talking about.
and attempting to teach me the basics of mirror/lense optics in flat spacetime, which mostly high school kids do. please see the OP thats the prereq for this thread, suggesting that at least I know the basics of optics.
This is not really about optics, it is just about why a diagram is drawn the way that it is.
i will clarify once more.....the spacetime around lensing star (S) is curved, whether the actual light site path or apparent light path, both of them must lie on geodesics, if so how can the apparent path extrapolated to S1' be a straightline ?
Wrong! The apparent path does not follow the geodesic. That is the whole point. It is just like the mirror example I gave, the apparent light path does not follow the reflected light path! How can this be so difficult for you?
please understand OS1' is non existent in GR curved spacetime.
No shit! That is the point, the apparent position of the star and the straight line of sight is based on the old notion of gravity not warping space.
your answer (and all others, even including me till yesterday) is that light shall follow the geodesics, but apparent extrapolations can be on straightline......this appears to me incorrect. your analogy of mirror or lense in the lab or room, will have straightline extrapolation because no appreciable or detectable curvature present.
No, no, no! The straight line extrapolation for the mirror is wrong because the table in not in front of you, it is behind you, the extrapolation is showing the apparent light path not the actual light path. Just like the straight line extrapolation in the diagram shows the apparent light path of the star not the actual light path.
[You are forgetting that there are no Eucleadian straight lines in curved spacetime, which light can follow].
No, I am not, the light is not really following the straight line extrapolation
If what I am saying is right, and I pray that i am not, then the conclusion is very sinister.
Basically you are wrong because - well, I don't know why this incredibly simple concept has blown your mind.