Re: Light slows down in glass?

["Donald E. Simanek" <dsimanek@eagle.lhup.edu>]

On Fri, 6 Feb 1998, William Beaty wrote:

> My own opinion is that there are various models for what light does, and
> if we insist that light is emitted and reabsorbed, then we really are
> saying that the particle model for light is correct and the wave model is
> false.  After all, it is *photons* which are absorbed and re-emitted. 
> Light wavelength is far larger than the spacing between atoms, and I
> cannot see how "absorbed/emitted" applies to the EM fields or to EM waves. 
> Instead, the transparent material acts as a non-vacuum medium, having an
> altered propagation velocity.  If we insist on "absorbed/emitted", then we
> fly in the face of wave/particle duality.

Alistair Frasier from Penn State U., who has the excellent site "Bad
Science" spoke at our university a couple of days ago. He made some
excellent points about how science badly presented to students and the
public. In his discussion of the greenhouse effect (which operates in the
atmosphere, but *not* in greenhouses) he criticized textbook
"explanations" which say that light from the earth is absorbed and
re-emitted by the atmosphere. He said "How can you 'absorb and re-emit'
light? When photons are absorbed they are *gone* and what is subsequently
emitted are *different* photons. Besides, in the atmosphere, the *light*
emitted is in its important characteristics *different* from that which is
absorbed, it has a different spectral distribution." 

I.e., in my view, part of the problem is a semantic one: the way we use
words.

In our case (refractions) the photons emitted have a phase shift relative
to those absorbed. And what about their directional distribution (many
photons) and their polarization. 

In another discussion group, on an entirely different subject, someone
wondered whether a particular subject could be taught in high school
without telling some lies. I wonder whether *any* subject, including
physics, can be taught in schools without telling lies, unless one limits
oneself to mundane facts and phenomena, and makes no attempt to "explain". 

Alistair Frasier made another comment which is worth pondering. He said
it's easy to teach new things. What's hard, nearly impossible, is to
correct something someone has leared which is wrong, but they are
convinced its right. After the age of puberty, he said, it's impossible
for someone to unlearn or correct the wrong explanations they are
convinced are right. 

Here's the URL references to a couple of pages dealing with common errors.
Anyone know of any others?

http://smart.net/~badastro/bad.html
The Bad Astronomy Page. Phil Plait's page.

http://www.ems.psu.edu/~fraser/BadScience.html
Bad Science. Alistair Frazer's page.

	-- Donald

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Dr. Donald E. Simanek                            Office: 717-893-2079
Professor of Physics                                FAX: 717-893-2048
Lock Haven University, Lock Haven, PA. 17745
dsimanek@eagle.lhup.edu                 http://www.lhup.edu/~dsimanek
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