# WHY does light bend around obstacles?

Discussion in 'General Science & Technology' started by lippylion, Dec 3, 2009.

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1. ### lippylionRegistered Member

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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.

3. ### StryderKeeper of "good" ideas.Valued Senior Member

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Perhaps the simplest thought could aid you. How much force does it require to move something with zero mass? Then perhaps you'll start to reason why light bends.

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First you need to clarify what you're talking about.

In the title, you say "light bending AROUND obstacles", yet in the first sentence of the post you say "diffraction" which occurs when light passes THROUGH an object or at the interface in a change in media. So which is it??

7. ### Uno HooRegistered Senior Member

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My WAG guess is that OP might mean "the bending of waves when they pass near the edge of an obstacle or through small openings."

Another WAG guess is that you have completely amnesiacally forgotten such definition since the time long ago when you last read your physics textbook.

I took the OP to be writing of a subject that I also have wondered about but have unfortunately not yet given a good study to. We have the very edge of a solid object, consisting of its outermost layer of molecules/lattice atoms. Of course, at such a location there is a ponderable electric field associated with the atoms. Along comes a photon, or, if you wish, a light wave. As the photon passes by the electric field, what is the description of the interaction between the passerby photon and the virtual photons mediating the field?

8. ### James RJust this guy, you know?Staff Member

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Light bends around obstacles for the same reason that water waves bend around obstacles. Think about what happens when water waves hit the pylons of a jetty, or when the waves go through a gap that is of a similar size to the wavelength.

In short, light is a wave phenomenon, and waves diffract. The reason is that they interact with the sides of holes they pass through, and they interact with obstacles they pass around.

9. ### Uno HooRegistered Senior Member

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So, to repetitively redundantly repeat again my above post twice; when the passerby photon approaches the electric field of the edge of the object causing the diffraction, what is the description of the interaction between the passerby photon and the electric field of the "side"?

10. ### raggamaxBannedBanned

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There is actually an other theory of light if you want to bother. Its called extinction shift effect. This simple principle states that a wave of light interacting with any interfering medium is immediately extinguished and replaced by a new wave. Thus when a ray of light enters a continuous medium it will be continuously absorbed and re emitted. The diffraction phenomenon can be seen in terms of extinction shift as follows. When the ray of light encounters a slit like opening the atoms on the edges of opening absorb and re emit the light wave in the form of a cylindrical wave front.
Here check this out
http://www.extinctionshift.com/DOUBLE_SLIT_Topic/DOUBLE_SLIT_topic.htm

11. ### Uno HooRegistered Senior Member

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At real small micro level: Here comes a photon. Incoming! Side,or, edge, depending on your proclivity, has virtual photons out on patrol mediating its electric field.

Describe activity between incoming photon and virtual photons belonging to side or edge.

12. ### madanthonywayneMorning in AmericaRegistered Senior Member

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But a single photon doesn't behave the same as light does normally. As demonstrated by the double slit experiment.. Sometimes light behaves as predicted by particle physics, other times it behaves like a wave. So trying to explain the behavior of waves of light in terms of individual photons is often quite frustrating.

Last edited: Dec 6, 2009
13. ### Uno HooRegistered Senior Member

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Please choose your own favorite model of light, be it photon or wave, MAW, BTM, JR, Funkster,(oops, already accounted for) et al. And please gut it out and step up to the plate and take a healthy swing to explain it.

The side or edge has an electric field. The incoming light wave has an electromagnetic field. The side or edge can be modeled a number of ways in physics. The incoming light wave can be modeled a number of ways in physics. The diffraction can be written of as an interaction between an incoming photon and the virtual photons populating the side or edge's electric field. The diffraction can be written of as the interaction between the incoming light electromagnetic wave and the side or edge electric field. Or, perhaps there are other ways also to model the interaction.

It is amusing that the resident genius experts have done no better to explain the subject at the micro level than to say "it is frustrating".

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thank the copenhagen meetings

as now most everything is physics is based on the speed (of a particle)

you can oooosually tell who is walking the planck; their farts are lumpy

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16. ### scifesIn withdrawal.Valued Senior Member

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when water molecules squeeze through an edge, the edge applies a force on the stream of molecules, the stream "replies" by a reaction force, when the water leaves the edge or the place of pressure, its reaction force somehow persists, making it "bend" around the edge after it leaves it..
water molecules have a mass and take up space, that's why you can squeeze them and crowd them up to get forces and reaction forces, photons and waves don't.
if the edge indeed has an electric field that can and does affect the photon's magnetic field, then it's kinda solved i guess, the photons are under an external flux when [assing by the edge, i assume there is some sort of reaction from the photons, when they leave the edge it's waht deflects the ones on the outer rim of the stream.

does that make any sense?

17. ### jonoghueRegistered Member

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well my guess is that since anything with mass has gravity, and since photons have so little mass (they do have mass though), light is moved around objects by gravity.

18. ### wlminexBannedBanned

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Is this the Almond Joy - Mounds (candy bar) analogy for light? . . . "Sometimes you feel like a nut . . . sometimes you don't" . . . .
(<--humor here). BTW, I have posted elsewhere on Sciforums . . . in October 2011, I think . . . . about light diffraction. Might be in Alternate Theories . . or maybe just on my webpage (request a link via PM, if interested).

19. ### river

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on Earth , because air diffracts light

20. ### wlminexBannedBanned

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IMO . . . air refracts light . . . the atmosphere is kind of like a huge prism . . . . that's one reason that sunrises and sunsets tend toward the 'red' end of the visible spectrum . . . sunlight (assume white) passes through a thick atmospheric wedge (read: prism) . . . shorter wavelengths are 'bent' (i.e., refracted) skyward.

21. ### river

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its not about atmosphere , its about bending " around obstacles "

22. ### wlminexBannedBanned

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Air? . . . Atmosphere? . . are they not the same in the context of your post? BTW: atmosphere is made-up of 'air' components, is it not?

23. ### TrippyALEA IACTA ESTStaff Member

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It has nothing to do with the medium the wave is travelling through. It is simply an example of wave mechanics.

The same behaviour can be seen in water waves in the ocean: