From: lip@s1.gov (Loren I. Petrich)
Subject: Re: Duality of wave/particle, human/divine [Was:... or chavinism?]
Organization: LLNL
Date: Tue, 10 Nov 1992 02:31:47 GMT

In article <lftfnvINNhgj@exodus.Eng.Sun.COM> emarsh@hernes-sun.Eng.Sun.COM (Eric Marsh) writes:
>>nyikos@math.scarolina.edu (Peter Nyikos) writes:

>>As far as the EXPLANATION about the particle/wave nature of matter, that would
>>involve a lot more time and effort to describe than the fact that it *has* been
>>explained.  If you haven't seen the explanation and are really interested in
>>knowing about it, get a Quantum Mechanics textbook and/or take a course.

>How about giving us a brief layperson's explanation?

	Although I am not Peter Nyikos, I will happily do so.

	Entities on bigger-than atomic scales tend to have two
possible sets of properties: particle-like, with well-defined mass and
location, and wave-like, with just the opposite. Familiar material
objects, in whatever their physical state, are particle-like, while
electrical/magnetic and gravitational fields are wave-like.

	It would at first seem that entities must be one or the other,
and that seems self-evident for most observed entities, BUT...

	In the first few decades of this century, a host of paradoxes
became apparent that forced a rejection of this either/or view for
small-scale entities. Examples:

	The "Ultraviolet Catastrophe": Inside a box, electromagnetic
waves (radio waves -- microwaves -- infrared -- visible -- ultraviolet
-- X rays -- gamma rays) will interact with its walls and eventually
reach thermal equilibrium. Each wave mode will get the same amount of
energy, and since there are an infinite number of these, the energy
should be infinite, as determined by summing over higher and higher
energies, and hence the name. BUT, in 1900, Max Planck proposed that
electromagnetic-wave energies can come only in discrete units, or
quanta:

	(energy) = h * (frequency)

	where h is Planck's constant, which is _very_ small in
familiar units. At higher frequencies, it would be unlikely for a mode
to have a quantum of energy, which keeps this great catastrophe from
happening, and the theoretical intensity precisely matches what is
observed.

	This paradoxical proposal, that light acts like a particle,
was shown to account for properties of the Photoelectric Effect, in
which light can make electrons evaporate from a metal. The electrons'
energy is precisely the the energy of the light quanta minus the
threshold energy, as it turns out, and is independent of the intensity
of the light. It was his demonstration of this, and not the Special
Theory of Relativity, that won Einstein his Nobel Prize.

	Needless to say, in high-energy particle-collision
experiments, gamma-ray quanta, or photons, look just like particles
from the way they interact.

	But if a wavelike entity like light can act like particles,
can elementary "particles" like electrons act like waves?

	When atoms were discovered to have positively charged nuclei
surrounded by electrons, the question arose of why the electrons
didn't spiral in. What Niels Bohr and Joseph De Broglie proposed can
be summed up rather crudely in the following fashion: If energy and
frequency can be related in the fashion given earlier, then momentum
(mass*velocity) and wavenumber (1/wavelength) of an associated wave
might be related in a similar fashion:

	(momentum) = h * (wavenumber)

	In Bohr's approximation, imagine an electron going in a
circle. The electron-wave must go through an integer number of cycles
as one goes around the nucleus. Since its momentum must be enough for
it to stay in orbit, one obtains some predictions of what the
electron's allowable energies are. And for the simplest system,
hydrogen, one gets essentially the right numbers. True, one _does_
have to work out this standing-wave picture in more detail
(Schro"dinger's equation and whatnot), and one has to add some other
principles, such as the Pauli Exclusion Principle, but one does come
up with the reason why atoms don't collapse upon themselves.

	But if electrons have wave properties, can these properties be
directly observed? First off, the waves for electrons of any readily
available speed will be _very_ short. But by using crystalline
materials, one can show that atom-sized entities have wave properties.
This is done routinely with X-rays, for instance. If one looks in the
right direction, the X-rays from each plane of atoms in the crystal
will not interfere with each other by being out of phase, but will add
up, creating bright spots on a detector. Interpreting these spots has
been a standard crystallographic technique for some time. Doing this
experiment with an electron beam aimed at a thin film reveals that
electrons have wavelike properties, just like X-rays.


	The result:

	Particle-wave duality is an abundantly observed phenomenon.

	One consequence is the Uncertainty Principle, in which two
closely related quantities cannot be measured simultaneously. One can
measure a position or a momentum, but their product can not be
measured to an accuracy greater than h. The same for time and energy.
But this cosmic fuzziness is, rather fortunately for us, on a _very_
small scale.


	Not surprisingly, quantum mechanics has given rise to a host
of paradoxes, which have given rise to lots of arguments among
philosophers of science. One of them might be called the
"wavefunction-collapse" paradox. Consider two thin slits and a light
beam shined on both of them. They outcoming light will spread out and
interfere, producing light and dark bands on a screen. This is clearly
a wave property. But it also happens no matter how low the intensity
of the light is, even when one can be sure that there is only one
photon at a time going through. Apparently, the photon is very spread
out as it travels, yet it shrinks to a point on the screen, where it
will make a dot of exposure on a photographic film. The resulting
pattern of dots has an intensity pattern precisely equal to the
wave-interference pattern expected.

	One proposed resolution of the Incredible Shrinking Photon and
similar paradoxes is to ascribe them to "the observer effect"; that
the act of observation does the shrinking. This may well be a
reasonable solution, in some form or other, but there are some who
draw conclusions that border on the unreasonable. It is claimed by
some that it is the presence of the observer that fixes phenomena, in
the fashion of a photographic film fixing photon positions. The
"unreasonable" part is the implication that somehow there is some
effect of consciousness on physical systems with the implication that
"wishing will make it so", which seems to be the "conclusion" that a
lot of naive amateur philosophers derive from Quantum Mechanics.


	Anything more on this subject?


Newsgroups: talk.abortion