Is this physically impossible concept visually coherent?

Okay, I know that this idea couldn’t happen in the real world; that’s not my question. My question is whether it’s possible to visualize this concept.

The concept is simple. It’s a sphere, with a perfectly mirrored-looking surface, except that nothing is reflected in it. It’s shiny silver, but the silver is unbroken by any sort of reflection.

I’m imagining it sort of like it’s sitting in a featureless room, in which the walls of the room radiate steady ambient light. The viewer into the room is viewing through a one-way wall.

I think I can visualize this image, and so I included it in a recent roleplaying game, as an object that defied physics; a far more visual player than myself, however, was frustrated, saying that what I described was visually incoherent, that a silvery surface that reflected nothing would appear gray, not silver.


Can’t you just claim that your sphere reflects light from a parallel timestream of ultimate nothingness?

I’d agree with your friend. I can’t visualize an object such as this. The thing that makes silvery things silvery is their reflection of objects around them, especially light sources (which is what makes them shiny). If this sphere is reflecting a perfectly uniform ambient light, then it’s going to appear white or grey.

I can’t visualize it either. “Shiny” means it shines, i.e. have specular reflection. If there were no localized light source or object to reflect, it wouldn’t be shiny. Say you are trying to make an image of a shiny sphere (any medium - pencil, paint, CGI, whatever) - how can you make it look shiny without using reflections?

I can imagine a shiny silver sphere that doesn’t reflect me, though. I’d just imagine myself as being invisible (transparent) or infinitely small.

Okay, so it sounds like maybe I’m wrong here :). Squink, you must be a gamer, right? That idea will work well: the sphere is a device for travelling between dimensions, and so altering my description such that it reflects rippling light from some vague interdimensional space might be just what I need.

Thanks, all!

It should be possible to visualise the concept, since computer rendering programs make it possible to place a non-visible camera inside the construct (so the reflection of the camera or viewer isn’t an issue).

So we’re talking about a perfectly smooth, 100% efficient mirrored sphere at the centre of a uniformly-lit (or uniformly-radiant) spherical room? I would imagine it will not be possible to see the mirrored sphere, but I might be wrong because of angles and edge effects. I’ll try modelling it tonight and let you know what it looks like.

Awesome! I was hoping someone would be able to do this; I don’t know anything about graphics modelling, though, and wasn’t sure.


And if you (or anyone else) manages to do this, if you could try one last thing, I think it would really help me understand this once and for all:

After creating the reflective sphere in the lit room, could you cut and paste the sphere’s graphic (not its properties, but its image) from the spherical lit room and stick it in a regular-looking boxy gray room with directional light? That’s what I’m trying to imagine: something that is reflective, but not of anything around it or of anything specific.


I would have thought that a sufrace that reflected nothing would not appear silver in the first place, nor gray, but black ?

What I mean is that it reflects nothing specific, and certainly not anything you can see in the area. Remember that I’m not asking whether the device could exist within the laws of physics: I know that it can’t. I’m just asking whether it can be visualized.


Lets simplify this a bit with a thought experiment; a flat mirror looks like a window into a room that is the other way around to the one in which you’re standing; a flat mirror that was magically reflecting something else would be indistiguishable from a window looking into somewhere else.

A spherical mirror looks like a fisheye lens view of a room that is the other way around to the one in which you’re standing; a spherical mirror that was magically reflecting something else would be indistiguishable from a fisheye lens view, looking into somewhere else.

Could we make a model of this doing the following:

Create a hollow 6’ sphere made of white opaque plastic that allows light through. On the inside is the suspended 2’ ball with the smooth mirrored surface. Put a pinhole through the 6’ opaque sphere to look inside. I’d wager to guess the mirrored sphere looks like a white ball.

Here’s an idea:

Render it to reflect what is at the other side of the gate. That almost physically makes sense. The light hits the gate at the far end, and gets transmitted through the tunnel to reappear at the close end of the tunnel. It also give observant players some idea of what is on the other end.

If the other end is in darkness, then your gate is rendered as a shiny, dark sphere and the player can consider getting his flashlight ready.

The reflection is of course distorted as all get out (this is a sphere, after all) but that is to the good. You want to give them hints, not give the game away.

Say, like, the biggest, baddest monster in the whole game has a distinctive color. One is waitng beyond the far side of the gate. An observant player sees a splotch of the correct color, and goes off to find a big, bad monster killing weapon before he goes through. Mr. Numbnuts doesn’t see the splotch, and goes through to get immediately graunched by the big, bad monster.

Or in other words, what it will look like is very much dependent on your definition of what ‘nothing specific’ looks like.

The idea of ‘nothing’ has been tackled by a number of SF writers (most often it is what you see (or rather don’t see) when you look out of the window of your FTL spaceship - not empty space, not blackness, nothing.

A reflective sphere has to reflect something, otherwise, it’s not very reflective, now innit? :slight_smile:

That said, I can probably whip up a 3D render of the sort of thing you’re looking for. I’ve played around with ray tracing in 3DS Max, and it’s true- if you don’t actually have something to reflect, the object will just appear black or gray, depending on the lighting and base material properties. One option is to use a kind of generic reflection map- an image that is being “reflected” by the sphere, which is different from the actual environment. I use this technique every now and then- it looks generically reflective, without being dependant upon the environment (and it’s a lot faster to render).

If you can give me an expanded description of the scene, I’ll try to render it out for you.

That would be fantastic. This generic reflection map sounds like what I’m looking for, although I know I’m not describing it correctly: I want it to look reflective, but people looking in it won’t be able to get any useful information out of what it’s reflecting.

If you feel like doing an expanded scene and earning my eternal gratitude, you could show this sphere sitting on a low, crumbling gray stone dais, in a dark room that looks vaguely like an Egyptian ruin – brownstone, possibly hieroglyphs etched into the walls, a few columns to support it, etc. (Obviously I’m not saying there have to be hieroglyphs for the scene to work–anything you wanted to whip up would be great–but that’s how I’ll be describing the locale to the players). None of the surroundings should be reflected in the sphere’s surface, but nonetheless I’d love it if the sphere could convey the idea of reflectivity.

Mort, that’s an interesting idea, but this device isn’t so much a gate as it is a ship. As such, its destination is only determined once folks are inside.

Mangetout, the “nothing” is a good analogy. The player that didn’t like my description loves The Neverending Story; maybe next time I talk with him, I’ll say, “It’s like the Neverending Story’s Nothing, only shiny!”

You folks rock!


Lefty, why not just have the sphere emit an intense internal light? That’ll give you uniform brightness around the sphere without reflections or point of contact-light glares?

The proper answer to this is “You’re right, it is visually incoherent. But that’s what you see, and it’s still sitting there in the next room.”. Sometimes, “Because I’m the DM and I say so” is the best answer. Usually, in fact. This thing is supposed to be bizzare, after all. If it’s so bizarre that the player can’t even visualize it, so much the better.

That’s kind of the approach I took, and it made several players very unhappy (one of them downright angry), so I’m backing off of it :). If I can give them a way to imagine it, even if it makes their heads hurt, I’ll stick with it; otherwise, I’ll modify it just enough so that they can imagine it.

It was, all told, a pretty trippy session.


Let’s look at this from a thermodynamics perspective. Energy incident on the surface will equal to the energy output of the surface. There will be energy absorbed, energy radiated, energy transmitted, and energy reflected.

Energy transmitted: this is the “clearness” of the surface.
Energy absorbed: this is the color of the surface. Actually, it’s the inverse of the color of the surface.
Energy radiated: this is not any energy generated from the surface, it’s the energy that’s been absorbed that has been released in a different form. From our perspective, it’s photons in the infrared, so we can pretty much forget about them, and pretend that energy absorbed by the surface goes into a black hole or something.

Energy reflected: this is the meat of the problem. For this, we need the BRDF, the bidirectional reflectance distribution function.[sup]1[/sup] This is a mapping, for any given point on the surface, and given incident direction of an energy source, and the direction from that point to an observer, what is the percentage chance of that energy being transmitted to the observer. Technically, we should also take into account the frequency of the energy and the polarization, but for most surfaces we can throw the former into the absorbtion and ignore the latter.

So, for this perfectly shiny object, all energy incident on the surface is perfectly reflected. No light is absorbed, and all incoming light coming in from any given angle goes out in exactly one other angle, with the angle of incidence – the angle between the incoming ray and the surface’s normal (the “up” direction at that point) – equal to the angle of reflectance between the surface’s normal and the outgoing ray. For this perfect room, the walls are exactly the same color at all points from all directions, including the direction that the observer is in, because of some strange one-way surface’s properties.

So, for this setup, if you trace a ray from the observer to a point on the sphere, and then trace the ray from that point to the point on the wall that would be seen by that observer, then the color that the observer sees in the direction of the point on the sphere is exactly the same color as the point on the wall viewed directly.

This means that, since every point on a wall is exactly the same color, and all six walls’ colors are identical, so that an observer looking at any point on the sphere will see the same color as if the sphere wasn’t there at all. So, looking through the one-way wall they will see this vast field of a single color, with no apparent floor, ceiling, or walls.

[sup]1[/sup]Some people call this the BDRF, "bi-directional reflectance function. Just ignore them, they’re wrong.