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Re: a question from an AP Chem student...





On Tue, 6 Oct 1998, Jerome Epstein wrote:

It is perhaps a little better to think of the photon as interacting with
the atom, rather than the elctron. The "how does the electron know"
question implies the view of an electgron as a point particle that
begins travelling to a higher orbit (like a planet getting kicked), and
how does it know the end point of the trip. But that view is just not
tenable.

The atom is in an energy state, it has other possible states. If the
right amouint of energy is available, a transition can take place. If
the energy of the photon does not correspond to an energy transition of
the atom, and is insufficient to remove an electron from the atom, the
electron will either scatter off the atom or simply pass through
unaffected.
Jerry Epstein


Correct, of course. But it begs the question asked. How does either
particle receive information that the interaction is a "go"? If the
energies aren't matched, the interaction doesn't happen. Presumably the
interaction is a substantial "event". What mechanism of interaction
between the approaching particles sets the stage for the even to happen.
An event can't happen until the participating entities "know" (receive
physical stimuli/information) from each other.

What is wanted (by the student with the inquiring mind) is the detailed
mechanism of the interaction from the first stage to the last. To say "it
happens or it doesn't depending on the energies" is a cop-out. At least
we'd like to know where the explanation must lie, and if that involves
physics or math beyond the introductory level, we should simply say so and
defer the question till later, when one takes quantum mechanics.

-- Donald