Naked Science Forum
General Science => General Science => Topic started by: Dorian on 18/03/2009 00:30:02
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Dorian asked the Naked Scientists:
A couple of questions, here, closely related:
What would you see if you were centred inside of a large mirrored sphere (presuming you didn't have to worry about a light source blinding you at every angle)?
I know that when you put a flat mirror across from a flat mirror, you see an infinite regression inside each mirror. But a sphere has no sides to differentiate one mirror from the other in the reflection! It's blowing my mind trying to figure out the resulting image.
And why wouldn't a mirrored sphere be a suitable container for light? I believe intuitively that as soon as any light source goes out, the light inside the sphere would also go out, but I don't know why. It seems it should keep reflecting virtually forever until someone "pours" it out through an aperture, and I know that can't work, I just don't know why!
Thanks for your insight.
Dorian Greer
PS: Love the podcast! (http://www.thenakedscientists.com/HTML/podcasts/)
What do you think?
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the same as you see when u get ut hair cut at a barber who has parallel mirrors it will just be in a spherical setting rather than a linear one mirror in front of another.
you will be looking at yourself from everywhere to everywhere for eternity to come. well ofcourse you would need a light source with u.
as for the container part, it won't work because it would ultimately absord the light as heat. you would need a superconducting surface/material. one that does not loose energy, to this day there exits none. WEll you could also attain the same result by cooling ur container to 0 degrees kalvin which again is unatainable so far.
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rex789, a superconductor conducts electricity without resistance. It really has nothing to do with light reflectivity. Your thinking is correct, though. An imperfect mirror with absorb or transmit some percentage of the light that falls on it instead of reflecting it away. A light beam would be reflected millions or maybe even billions of times per second inside of a reflective sphere (depending on its size). The energy of the beam would be quickly transformed into heat.
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rex789, a superconductor conducts electricity without resistance. It really has nothing to do with light reflectivity.
Reflection of em waves can be due to two mechanisms.
1. Total internal reflection - at the boundary between materials of low and high refractive indices. There will be losses because of the conductive component of a real refractive index.
2. Due to conduction on the reflecting surface. This applies to any frequency of em. The currents induced by the fields of the incident wave generate a reflected field which follows the normal laws of reflection and cause a 'ray' in the appropriate direction. It is a straightforward (?!?) bit of classical em theory which doesn't conflict with the quantum approach. The finite resistance of all real surfaces causes loss. Superconductivity would make a difference.
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thanks sophiecentaur, my thinking exactly.
superconductors are the holly grail of all that uses, heat, electricity any kind or energy that is.
superconductors are not limited to electricity, we just hear more about them in that case.
and light you 'see' is a wave and a particle so in order to box it you would need a material that does two things.
bounce back the wave in the same wavelength and energy state that it hit it
not absorb any energy from the particle at collision
i guess you could do an experiment where you have bulb in a sphere with a camera. if you still see something after the bulb goes out then there is some light that is being trapped by your system if not then well try again. mabye ask the Puppeteer Hindmost to give u a piece of his superconducting cloth (for ringworld readers)
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To go back to the original question. It depends how big the sphere is and where you are placed in it. Let us assume that the sphere is quite large say about the size of a room and you are near to one of the walls if you looked towards the wall close to you you would see a slightly enlarged image of yourself a bit like looking in a magnifying shaving mirror. If then you turned round and looked at the other wall you would see an upside down image of yourself some distance away (actually just a bit closer to you than twice the diameter of the sphere) you would also see this upside down image also if you turned back to face the wall and looked into the distance behind your image. There would be a continuing regression of these images but like with flat mirrors they would become distorted and fade.
Now lets assume you move slowly towards the centre of the sphere these normal and upside down images towards and away from the wall would both gradually get larger and larger and more distorted until they became a blur. Just like when you move too far away from a magnifying shaving mirror.
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If you had your eye (pupil) at the centre of the sphere, the only thing you would see would be your pupil. The only light that would enter you eye would be traveling along a radius from your pupil and be reflected (normal to the surface) right back into your pupil. It would be pupil all the way around - within your field of vision, at least.
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The last superconductor I saw was black.
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It clearly didn't superconduct at high frequencies, then!
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I believe even if you had a light source and were in the absolute center. You will see complete darkness as if in a Black Hole.
Light bounces off the inner surface to other areas of the sphere, but not the center. So light would in effect travel completely around the inner surface of the mirror unable to escape to the inner volume. You can look at the original light source and perceive it as a star or a single point of light, the same as any additional light source. You could look at yourself (not your head of course) and see yourself floating in a void, but not reflected off the inner surface.
Another concept is, you might see yourself as a hologram at the very center of the volume of the sphere (no matter where you were in the volume of the sphere) but the light might overpower the hologram.
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My thought was that your pupil would scatter light (non specular reflections of light direct from the light source) and that would be what you would see.
Why a hologram? Unless there was coherent source you would not get any holography. You would, as always, be seeing a diffraction pattern but there would be no appreciable peaks and troughs because of the lack of coherence of the light source.
It is true to say that a lens or curved mirror will produce the Fourier transform of the original image in the focal plane. That's sort of what you may be getting at.
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You would see a bunch of people in costumes dancing around with a few Muppets to a song by an aging but still awesome British rocker...
(I wonder who will get this obscure reference...I couldn't help myself)
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Are there resources to test this? I mean, get a camera, LED light, two mirrored hemispheres... Put the camera on a black thin stick. Post it in the inner space enclose the sphere around the camera with the LED and see what the effect might be like?
I don't think the size of the sphere or light matters, but the size of the camera does.
The main thing, can this tell us something about our Universe? Why not?
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It would tell you something about mirrors.