Thread: WHY does light bend around obstacles?

1. Here's an example from Hubble:

Source

The two bright objects that look like squares with blobs and other stuff around them are foreground galaxies. The light from these galaxies has been diffracted by the 'tube' of the Hubble Space Telescope as the light enters it.

This is something that happens to all telescopes (IIRC google 'Diffraction limited seeing').

Nothing to do with gravity.
Nothing to do with the presence of some medium.

Pure wave mechanics.

Here, I believe, is a computer generated model of the diffraction that occurs withing the Hubble Space Telescope, whem observing a bright source:

Source

Finally, here is Sirius A showing all of the same features (albeit some of them are over exposed).

Source

2. (Very first post)
I will read every post eventually. I got to about post 10 before wanting to put this out there.

My wife and I had observed the bending of light around objects and the first thing that came to mind is how a mass warps space around it \9no matter how much mass is involved). I always figured it was light following the direct path from the source to the eye (ie. the warped space around the object, like a finger).

Now, back to the other posts.

3. Originally Posted by QuantumEntangled
(Very first post)
I will read every post eventually. I got to about post 10 before wanting to put this out there.

My wife and I had observed the bending of light around objects and the first thing that came to mind is how a mass warps space around it \9no matter how much mass is involved). I always figured it was light following the direct path from the source to the eye (ie. the warped space around the object, like a finger).

Now, back to the other posts.
I think if you calculate that warpage of space by your mass, you will find that your proximity to the warpage reduces the angle to an imperceptible amount.

To get a handle on this, you can consider the geometry of observing a star pass by the sun in eclipse, which entails a huge mass at a huge distance. This was Eddington's confirmation of Einstein's prediction that starlight bends around the sun, and would be visible in an eclipse:

The inquiry into diffraction, as explained by Trippy, is a consequence of wave mechanics. So even a water tank will demonstrate the interference resulting from a uniform wave passing through two slits:

If we were to measure gravitational bending in parsecs, and the diffraction bending in Angstroms, the difference in scale is 26 orders of magnitude. So the difference in scale is huge.

4. I'm definitely not arguing the wave mechanics explanation, which makes far more sense than the thought I came up with. It was an excuse to get my first post up . I am actually delighted to have a better explanation to what we experienced. ATM I'm trying to get my brain to translate the effect in the 2nd pic to what we actually see.

5. in space its about the atmosphere that the object gives off

6. so such as the sun gives off an atmosphere , corona

which bends the light from objects behind the sun so that then you can see what object is behind the sun ( otherwise called gravitional lensing )

7. Originally Posted by river
so such as the sun gives off an atmosphere , corona

which bends the light from objects behind the sun so that then you can see what object is behind the sun ( otherwise called gravitional lensing )
Gravitational lensing has absolutely nothing to do with the atmosphere.

8. Originally Posted by QuantumEntangled
I'm definitely not arguing the wave mechanics explanation, which makes far more sense than the thought I came up with. It was an excuse to get my first post up . I am actually delighted to have a better explanation to what we experienced. ATM I'm trying to get my brain to translate the effect in the 2nd pic to what we actually see.
Here is an idea of the projected image, demonstrating the effect of adding two sinusoidal waves that vary in phase over the length of the screen:

9. Originally Posted by lippylion
or if you call it diffraction.....there seems to be no answer in physical sense although there are mathematical theories which are based on assumptions and only explain the behaviour of light rather than explaining their origin and cause.
i have already seen many threads on this topic but none of them have answered my question and it's killing me.in case you think of replying "....because of Huygens wave theory..." or "...quantum theory...", i have looked out for them quite deep and none of them comment about the probabilistic behaviour of light seen for eg. in diffraction or interference patterns.
QED, quantum electrodynamics. 'QED The Strange Theory of Light and Matter'. A wonderful book Feynman wrote for everybody.

http://en.wikipedia.org/wiki/QED:_Th...ght_and_Matter

Prof Edwin Taylor's workbook, plus software, for studying Feynman's sum over paths method [QED]. The text would be Feynman's QED.

http://www.eftaylor.com/quantum.html

10. Okay, this may be off topic, but here is the effect I'm talking about:

Hold any two objects with rounded edges very close together, but not touching (I use the tips of my fingers). When they get close enough both edges appear to be pulled toward each other and meet as one. In reality the two edges aren't actually being pulled toward each other and the effect is purely visual.

11. Originally Posted by river
so such as the sun gives off an atmosphere , corona

which bends the light from objects behind the sun so that then you can see what object is behind the sun ( otherwise called gravitional lensing )
so . . .maybe . . . the sun's corona acts as a 'refracting' medium to light passing (from behind the sun) thru the corona??

12. Originally Posted by Aqueous Id
Here is an idea of the projected image, demonstrating the effect of adding two sinusoidal waves that vary in phase over the length of the screen:

Query: So . . . are the 'patterns' ('projected 'bands') of the same wavelength and frequency as the original, impinging source waves . . .??

13. Originally Posted by wlminex
Query: So . . . are the 'patterns' ('projected 'bands') of the same wavelength and frequency as the original, impinging source waves . . .??
I doubt it would be. Each wave has a certain amount of energy. When the waves come in contact with the slits the slits take some of that energy away from the waves. So, I would say no, the resulting waves would be diminished.

14. Originally Posted by wlminex
Query: So . . . are the 'patterns' ('projected 'bands') of the same wavelength and frequency as the original, impinging source waves . . .??
Wavelength is just the reciprocal of frequency, so consider them one thing. There is some other geometry to consider. To get it straight from the horse's mouth, I went back to the era of the Louisiana Purchase to extract this definition straight from the horse's mouth, none other than the inimitable Thomas Young:

when the two newly formed beams are received on a surface placed so as to intercept them, their light is divided by dark stripes into portions nearly equal, but becoming wider as the surface is more remote from the apertures, so as to subtend very nearly equal angles from the apertures at all distances, and wider also in the same proportion as the apertures are closer to each other. The middle of the two portions is always light, and the bright stripes on each side are at such distances, that the light coming to them from one of the apertures, must have passed through a longer space than that which comes from the other, by an interval which is equal to the breadth of one, two, three, or more of the supposed undulations, while the intervening dark spaces correspond to a difference of half a supposed undulation, of one and a half, of two and a half, or more.
So the distance between the slits changes the "beat frequency" and the projection of the spherical composite onto the planar surface introduces a nonlinearity. Here's another perspective, but don't stare at it too long if you have to operate a motor vehicle or any machinery:

15. “ Originally Posted by river
so such as the sun gives off an atmosphere , corona

which bends the light from objects behind the sun so that then you can see what object is behind the sun ( otherwise called gravitional lensing )
Originally Posted by wlminex
so . . .maybe . . . the sun's corona acts as a 'refracting' medium to light passing (from behind the sun) thru the corona??
yes

16. . . . so . . . taking this 'coronal refraction' phenomenon a bit further (beyond the current gravitational lensing interpretation) . . . perhaps 'simple' refraction due to density gradients (of coronas, or what not) around the sun, stars, galaxies, etc. is a simpler explanation than gravitational lensing?? . . . just wait 'till the SM and AE enthusiasts read this one!!

17. Originally Posted by wlminex
. . . so . . . taking this 'coronal refraction' phenomenon a bit further (beyond the current gravitational lensing interpretation) . . . perhaps 'simple' refraction due to density gradients (of coronas, or what not) around the sun, stars, galaxies, etc. is a simpler explanation than gravitational lensing?? . . . just wait 'till the SM and AE enthusiasts read this one!!
the simplicity or the possibility of greater complexity matters not

what matters is what is really happening

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