Invisible talking, or physical philosophical nonsense

[Marinus]

Continued from: http://pcpuzzle.com/forum/viewtopic.php?p=194585#194585

How about the fact that you can see the sky is blue?

Yes, actually that's what I meant with "air is visible". Also when you see a picture of Earth from a space shuttle you see the atmosphere.

I think I didn't give a definition of tranparency. I only asked the question:

Does transparant only mean, not absorbing or reflecting light, or also not changing the direction of lightbeams?

which implicates that I believe it means at least "not absorbing or reflecting light".

Your first two examples say: "a material could absorb ...." so I think they are not fully transparent.

About the third example; I have to admit, I don't fully understand what's exactly polarization. I don't understand some of the English jargon on Wikipedia, and in the Dutch Wikipedia is not that much explanation about it.

...... you soon get to the point where almost nothing is fully transparent.

Right. But I like to talk about theoretical matters sometimes. Also in science or physics they use to talk about ideal situations which do not exists in practice, such as (in electricity) an ideal coil, an ideal capacitor, or in general, movement without friction.

Maybe it's Invisible talking, or physical philosophical nonsense. I think it's just fun.

[Muzozavr]

Fog is not nothing, it's tiny-tiny water droplets that are hard to see. If we get back, then it seems dense enough to be noticed. Up-close, it's not dense enough.
Perfect mirror -- embedded in a surface, the mirror itself is invisible. Not embedded in anything, the edges give it away.
100% white surface -- invisible, but detectable by the eye.
100% black surface -- directly undetectable to the eye but VISIBLE through non-direct means: it blocks everything that's behind it.

Polarisation -- actually I have no clue too.

[Marinus]

Yes, about the white, black and mirror surfaces, I think they are not really visible, but the edges are, when you're close enough and you have two eyes, you can see the distance. Also, since a real mirror is glass that has a visible thickness, the edges are always visible of course.

But, what you say about fog, isn't that the same thing as the air: the blue sky, or the atmosphere seen from a space shuttle? You don't see water droplets, you don't see air, but you see a white or blue haze.

[Muzozavr]

Forget it, haze is just a reduced visibility. Air is actually more "visible" than fog in that sense. At least it's blue. It has colour.

We don't "see" fog -- we see that the visibility of everything else is reduced in a particular way -- and then we ASSUME the fog. Our brain sees what our eyes do not.

... I think. Anyway this is getting weird, which is half the fun.

EDIT: And when we come closer, the reduced visibility no longer makes a big difference. Then we stop seeing the fog that's all around us.

[Marinus]

OK. Thanks.