MadSci Network: Engineering

Re: View inside a reflecting sphere?

Area: Engineering
Posted By: Greg Billock, grad student, Caltech
Date: Thu Mar 27 17:06:13 1997
Message ID: 852234914.Eg


>View inside a reflecting sphere?

>What would one see inside a large (bigger than a house) sphere that
>had a mirrored inside surface ? How would any images produced be
>distorted ? If the only light source was, say, my cigarette lighter,
>how would any image change if the sphere were big enough for the speed
>of light to become noticeable, (eg. several light-seconds in diameter)?
>Has anyone tried this with a laser source ? Come to think of it, I bet
>the acoustics would be pretty odd too. Look forward to your answer :)

You can see some of how the objects inside a reflecting sphere would look by taking a look at these images. I made them using POV-Ray, a freeware ray tracing program.

The first is a "simple" view of the objects inside the sphere (where nothing is reflected the mirrored surface is black, just to highlight what is going on). In this image, only a couple of reflective "trips" are allowed. The brown (wooden) square is at the center of the sphere. There is a red cube, a green cube, a yellow sphere, and a blue sphere arrayed around the central point of the large enclosing mirrored surface.

The green and blue shapes are underneath the central plane defined by the brown square, and the red cube is immediately above it. The yellow sphere is quite a bit above. The camera is situated back and up a bit, fairly close to the inside surface of the big sphereical mirror.

The second image is made with 60 allowed reflections. From this, it is fairly easy to get an idea what is going on. As you can see, the reflections of the shapes are smeared out along the great circle defined by its position and the position of observation. As can be seen, it is kind of hard to pick out what exactly the shapes are inside this thing!

As the images go around the sphere, they get more and more distorted, as you can see for the cubes. If the sphere were as large a several light-seconds, in practice it would probably diminish effects, because of attenuation of the light between reflections. If we ignore this, however, then the picture would look the same if you didn't move your head. As soon as you moved your head, however, the reflections closer would move more quickly than the reflections on the opposite side of the sphere (a few light-seconds away). This would create quite a confusing effect, I'd imagine!

-Greg Billock

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