What does polarization really mean?

[lugita15]

I'm trying to understand the meaning of polarization. I know the actual definition, which concerns the directions in which a transverse wave oscillates, as opposed to the direction of propagation. For instance a standing wave on a string is linearly polarized in the vertical direction, meaning that each element wil go up or down. And electromagnetic waves are often circularly polarized, meaning that the electric field vector will trace out a circle perpendicular to the direction of the wave vector.

But I don't really have an intuitive grasp of what polarization is all about. What is the physical significance in asking how a wave is polarized? I don't mean what the practical applications are, which are certainly numerous, but what feature of the physical world does polarization fundamentally refer to?

Maxwell's discovery that light is an electromagnetic phenomenon came relatively late in the development of optics, so how was the polarization of light understood before it was even connected to the electric field? For that matter, Maxwell himself was under the impression that the electric field was some kind deformation of the "aether", so did he think of polarization in terms of some mechanical model? On a related note, are there examples of circularly or elliptically polarized waves in purely mechanical systems like strings and membranes? Finally, why do photons have polarization, and what does it even mean in a quantum context?

Sorry if I'm asking too many questions in a single post, but I just finished taking a course on waves and I'm embarrassed to have never really grasped such an important idea.

Any help would be greatly appreciated.
Thank You in Advance.

 

[jtbell]

On a related note, are there examples of circularly or elliptically polarized waves in purely mechanical systems like strings and membranes?

Fasten one end of a stretched string to a wall, and hold the other end in your hand. When you shake your hand up and down, you get a vertically polarized wave. When you shake your hand left and right, you get a horizontally polarized wave. When you move your hand round and round in a circle (with the plane of the circle perpendicular to the string) you get a circularly polarized wave.

 

[lugita15]

Fasten one end of a stretched string to a wall, and hold the other end in your hand. When you shake your hand up and down, you get a vertically polarized wave. When you shake your hand left and right, you get a horizontally polarized wave. When you move your hand round and round in a circle (with the plane of the circle perpendicular to the string) you get a circularly polarized wave.

Wow. I can't believe such a simple example never even occurred to me. OK, one question down...