hypothetical optics question

[RobWard]

Could someone perhaps answer a question that has caused some debate amongst some colleagues and myself please?
(We have NO connection with optics at all, this is just for fun and we are just curious...)

IF you were suspended inside a perfect, mirrored sphere and you turned on a torch, what would you see?

Our answers range from a "totally white wall", through a "distorted image of yourself, like at a fairground hall of mirrors" to "it would stay totally black."

Me? No idea!

It seems like a standard sort of hypothetical question that people who understand optics should just know the answer to, and apologies to anyone who thinks I'm missusing this forum.

Rob Ward.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[cev]

Probably a better question for "ask the experts" sort of web site, or sci.physics newsgroup.

The problem with this sort of hypothetical question is that you have created an imaginary construct ("the perfect mirror"), but you have not specified the rest of the question specifically enough to generate a unique answer. Since you started out in an imaginary universe, how many of your other constraints are physical, and how many are imaginary?

Any of the potential answers you have provided could be true, depending on those specifications. For instance, what is a "torch?" Are you English (Americans call it a flashlight), or do you mean a flame? The type of light makes a huge difference.

Best,
CV

 

[RobWard]

Oh dear.
I seem to have stumbled into a "Life, The Universe and Everything = 42" situation here, in that we probably don't fully understand the question ourselves!

You are quite correct that this probably isn't the place for this sort of question anyway, but I do appreciate you taking the time to reply.

In our scenario "perfect mirror" implies a perfect sphere, reflecting 100% of the light from the torch (flashlight).

The debate here has also now started to encompass the the "observer's" position in the sphere and what effect that would have.

My favourite suggestion (not that I neccessarily agree with it) is that the sphere would be totally dark until the focal point of the reflector of the torch (flashlight) was coincident with the exact center of the sphere. At this point the sphere would be totally filled with light. (Or as someone else suggested "you'll probably achieve cold fusion")

We had thought that this would be a "standard" question, but I'm starting to think that the question is as complex as the answer.
And it's starting to make my brain hurt.

Still, at least it has got my colleagues thinking.
I shall try to find a more suitable place to ask this question...


Rob



"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[IRstuff]

if by torch, you are refering to a bulb with a nominally parabolic reflector, then the answer is not as stated, since the parabolic reflector results in a point source at infinity, at best, and a fuzzy source at infinity nominally. In either case, the virtual source is not the center of the sphere, so there will not be a perfect retroreflection.

Only a perfect point source at the precise center will result in a perfect retroreflection on the first bounce. Then the question becomes, "what is the reflective properties of the source itself?"

TTFN

 

[nbucska]

If you use a laser, you may have interaction with the reflected light...

<nbucska@pcperipherals DOT com> subj: eng-tips

 

[stuff]

In the design of light condensing optics for a slide projector, we use standard practise of placing a shallow spherical mirror behind the lamp filament. The filament is a 1:2 ratio rectangle and the filament tip is concentric to the spherical mirror. This creates a mirror image of the filament to produce a square object+image filament for condensing onto the square slide frame.

So, does that illustrate it for you? Just pretend to be the burning observer above the lamp filament.

I don't expect this to help!

Matt