Phil Hobbs recently pointed out to us that, if a shiny sphere is illuminated with a plane wave, it scatters light exactly uniformly into an outer, full 4pi steradian, sphere. That seemed counterintuitive, but who's gonna argue optics with Phil?
We got a huge steel ball from a Caterpillar ball bearing and tried it. Seems to work.
John
try shining a light at it, most of the light comes back at you, not much off to the sides, negating phil.
You had a light source that was phase-coherent in a plane across the full diameter of the ball?
What did you use for a detector, the Mark I Eyeball?
Mark L. Fergerson
Does he account for the shadow by diffraction or penumbra or something?
Thanks, Rich
I can imagine it might work for a hemisphere, but won't the back be in shadow?
Not in Larkin's world ;-) ...Jim Thompson
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I love to cook with wine. Sometimes I even put it in the food.
Flashlight.
Yup.
John
No diffraction assumed, just classic ray-tracing optics.
John
"there is no dark side of the moon actually. Matter of fact it's all dark" :)
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I think that right behind the shpere (far enough away) you get a maximum, google Poisson's Spot.
You get glancing angles at the edges.
George H.
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Phil qualified his statement as assuming classical geometric ray tracing, which doesn't include diffraction. Still, it's remarkable. To me, anyhow.
John
The situation is far-field, light ultimately scattered at angles far from the sphere. Of course there's a shadow close in.
What's surprising, if you try it, is that it holds up way, way behind the ball. Well, I was impressed.
John
It didn't do that when I tried it. You see a bright spot on the surface of the ball. As you move all around, you still see a bright spot. Almost directly behind the sphere, the spot starts to stretch out into an arc (I'm using an imperfect light source; I think it'll stay a spot in the ideal case) but the total brightness stays about the same.
John
t.
=A0 =A0 =A0 ...Jim Thompson
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Yeah, I know squat about optics. Phil can trace circles around me.
George H.
We've got a silvered garden gazing ball. It's wonderful fun to hold it in your hands look into it, and walk about the house.
"John Larkin"
** Hardly an example of a plane wave.Single frequency, coherent wave front ....
.... Phil
Good enough for the eyeball experiment. Try it.
John
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When we were kids we'd look down into a mirror we were carrying and walk around the house. You really feel like you have to step over the ceiling lamps and upside-down doorways.
John
Hmmm...what about the shadow?? Would that not allow this supposed uniformity?
If true, that means one could "prove" the assertion using POV Ray program..
I'd like to try it. my first thought was a mirrored Christmas ball ornament, I think I need to inspect to see if the mirroring is inside or outside and how round is the ornament. Mikek
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