A radio wave is an electromagnetic field. On my first day of fields
class, I asked the professor what an electromagnetic field was. His
reply: "An electromagnetic field is a mathematical model that enables us
to explain certain phenomena which we can measure." The professor was
Carl T. A. Johnk. I have in front of me his text, _Engineering
Electromagnetic Fields and Waves_. On page 1, it says, "A field is taken
to mean a mathematical function of space and time."

"Stuff" isn't transferred from one place to another by electromagnetic
fields, but energy most definitely is. Force can be applied through
space from one place to another by means of an electromagnetic field,
and energy can be transferred by means of a field. Since the energy
contained in a field can be calculated, I'll go out on a limb and say
that a radio wave can be regarded as a form of energy, like heat or
falling water. Perhaps a purist or physicist can find grounds to argue
with that statement, it's certainly a valid concept for engineering
purposes.

As far as photons and waves go, be really, really careful in extending
your everyday experience to quantum mechanical objects. Feynman very
nicely illustrates in "Quantum Behavior" in his book _Six Easy Pieces_
that neither particles nor waves is adequate to describe such things:

"Things on a very small scale behave like nothing that you have any
direct experience about. They do not behave like waves, they do not
behave like particles, they do not behave like clouds, or billiard
balls, or weights on springs, or like anything that you have ever seen.
.. . Historically, the electron, for example, was thought to behave like
a particle, and then it was found that in many resepects it behaved like
a wave. So it really behaves like neither. Now we have given up. We say:
'It is like *neither*'"

I highly recommend this book, and other of his writings, if you're
interested in understanding these phenomena on a more basic level.

Roy Lewallen, W7EL

jj wrote:
This may at first sound like a stupid question. But after some years
as a radio enthusiast, I don't know what a radio wave is - what it
really is. Supposedly, modern physics does not believe there is such
a thing as "action at a distance". In other words, if you launch a
radio wave and I intercept it, there must be a transfer of "stuff"
between you and me. You can't just say that if I wiggle an electron
at point A, I can cause a wiggle at the same wiggle rate at point B.
I mean you can say it, but it doesn't explain anything.

OK, so the latest science says that electromagnetic energy is really
particle-waves. I guess this means that when I transmit, my antenna
is firing particles in the form of low-energy photons (energy
packets), and that these photons do not really exist anywhere but
exist only as probability waves - until, of course, someone intercepts
the wave. Then, magically, the photons appear at the receiving
antenna, in which they manage to produce oscillating electrons.

So, the best I can ascertain is that radio waves are really
probability waves. I'm not sure that really helps with an intuitive
understanding. Does anyone have a good description for what a radio
wave really is?

- JJ