Message-Id: <v01540b02af5dd0cfb66d@[153.90.236.25]>
Date: Tue, 25 Mar 1997 12:44:50 -0700
To: pinhole@exploratorium.edu
From: eiger@montana.edu (Steven Eiger)
Subject: polarizing filters
I am hesitant to say anything here as it has been years since I have taught
physics but the conversation intrigues me so shall have a go at it.
First, I think it is informative to talk about how the filters
work. The molecules are laid down in such a fashion that electrons are
constrained to mostly move in a single direction. Thus the light waves
coming in can only massage them along a certain axis, and the reemission of
light is therefore also constrained.
There are two good explanations of how light gets through when the
45 degree filter is placed between the perpendicular filters . One is as a
wave phenomenon; and here light getting through the first filter and being
polarized in a single direction is thought to be a vector. Then we do some
magic. Since a vector can be broken down into other vectors we can break
our single light vector into two vectors, one of which will pass thru the
45 filter. We repeat the process through the third filter. Thus some
light gets thru all three filters. It will not get through just two
perpendicular filters as the perpendicular component of a starting vector
is zero (this is stated poorly, sorry). This assumes things like we can
use just two component vectors and that neither of the component vectors
can be larger than the original vector. I mentioned the nature of the
filters because one might like to muse about why this might be so, given
the nature of light.
The second good explanation, at least to some people is a quantum
one. And that relies on the statistical likelihood of a photon passing
through each filter. It may make sense to some people, but I like
Feynman's discussion of these matters, which goes something like "It is not
intuitive, may make no sense, but accurately describes the situation, thus
is useful". This is not a quote, just my vague recollection. He does say
"nobody understands quantum mechanics". So, if one looks at the numbers,
the likelhood of a photon passing through the 45 oriented filter is
non-zero and we can just multiply these probabilites to find our result.
The probability through a 90 filter must be zero. I believe he discusses
these sorts of things in his little book QED.
I like neither explanation, but am awaiting someone like David Bohm
to explain the quantum results in a deterministic light, and preferably in
a language I can understand. I recently read a book review (Science, vol
263, p. 254, 14 Jan 94) on a book by Peter Holland which is a step in this
direction (explaining Bohm's work); I need a few more steps, some giant
ones.
Yours in Science,
Steven Eiger, (406) 994-5672
eiger@montana.edu
Biology Department
Montana State University
Bozeman, MT 59717-0346