Re: Why is a partice sometimes described as a particle and sometimes as a wave?

Date: Mon Apr 13 15:09:37 1998
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Physics
ID: 892075519.Ph

Message:

Why is a particle sometimes described as a particle and sometimes as a wave?

Because that's the way we are able to measure it. Very small objects have both "wave-like" and "particle-like" properties, and which we concern ourselves with will often depend on what we want to do with the particle, or more specifically what measurement we are performing at the time. For example, light can be diffracted (a wave property) but will also knock electrons loose from metals (a particle property). Electrons are, of course, particles, except that they can also be diffracted -- that's how an electron microscope works!

This view of the world is decidedly counter-intuitive, but has the advantage of being true. I can pull some recommendations for further reading off the top of my head:

The Quantum World, by John Polkinghorne: This is an exposition of quantum effects by someone who has some standing in the field, as Polkinghorne is a (now retired) theoretical particle physicist who studied under Dirac and taught at Cambridge. The book is written for lay people.
The Meaning of Quantum Theory, by Jim Baggott: This book is a bit more challenging because it presents the mathematics involved -- though it's designed for undergraduate chemistry majors, and so isn't as tough as something written for, say, a graduate-school physics student. This is probably the best single book on the subject, because it is a nice compromise between qualitative understanding and quantitative mathematical treatment (which often is difficult or impossible to put into words).

There are, of course, lots of other books out there which treat the same sorts of things -- though I counsel you to keep away from some of the more New-Agey treatments like Fritjof Capra's The Tao of Physics or Gary Zukav's The Dancing Wu Li Masters. Not that you won't achieve some understanding from them, but to my mind they draw unwarranted conclusions from the information.

A few websites:

David Sherrill's Brief Review of Elementary Quantum Chemistry, which presents most of the basic concepts without metaphysical speculation. However, it is mostly oriented toward chemical applications.
UCSD has a simpler site on quantum mechanics, again for chemistry students, but download times are prohibitive.
Kansas State University's Visual Quantum Mechanics Project, which is centered around a Modern Physics course
Eastern Illinois University has some basic information in the Quantum Mechanics section of its Principles of Physics course pages.

	Dan Berger
	Bluffton College
	http://cs.bluffton.edu/~berger

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