If light is a wave, what is waving?

DaleSpam

Quote by harrylin

Where did I get what from? That "field" referred to some kind of state of a medium that exercises a force? As far as I know that concept originated with Maxwell and contemporaries.

ADDENDUM: That turns out to be incorrect (imprecise), and interestingly, already Maxwell spoke of "the electromagnetic field" (in singular).
That's in a paper* of 1864, and it sounds as if there he actually invented the term "field" for something that "has to do with the space in the neighbourhood of the electric or magnetic bodies [...] The electromagnetic field is that part of space which contains and surrounds bodies in electric or magnetic conditions". And he argued that this indicated the existence of a medium: "actions which go on in the surrounding medium as well as in the excited bodies".
*A Dynamical Theory of the Electromagnetic Field, 1864

Synonyms for "electromagnetic field" would thus be "electromagnetic area" or ""electromagnetic region".
So, thanks for asking!

OK, so that is an historically correct "when did you stop beating your wife" question.

PhilDSP

It seems that the field concept originated with Faraday and Maxwell resisted making it a structural component of his theory in some ways. At least, if Maxwell could identify a non-field component as something else: force, polarization or positional displacement for example, he would prefer that to a field value. That makes sense to me as it seems Maxwell tried to make his theory as physical as possible. (His mentor William Thompson AKA Lord Kelvin didn't really fully approve of Maxwell dabbling with the metaphysics of fields)

Drakkith

I feel any answer other than "the electric and magnetic fields" is more philosophical than scientific currently.

*Studiot*

Talking of metaphysics the difficulty is this:

If we require a medium (field, aether, whatever) for the wave to travel in it implies that the medium was present before the wave started travelling and the wave spreads through the undisturbed medium at the wave velocity.

So if this medium is an electric or magnetic or electromagnetic field for a light source, how did the medium get there before the first emission of the light?

Alternatively we can suggest that the wave somehow takes its medium along with it or creates its own medium as it goes along.

harrylin

Quote by DaleSpam

OK, so that is an historically correct "when did you stop beating your wife" question.

Yes indeed - I didn't mention or elaborate on that as I didn't want to step on someone's toes.

harrylin

Quote by Studiot

[..] So if this medium is an electric or magnetic or electromagnetic field for a light source, how did the medium get there before the first emission of the light?

A similar "difficulty" would be raised by the question "if the light source is an atom that will emit the light, how did the atom get there before the first emission of the light?".

Alternatively we can suggest that the wave somehow takes its medium along with it or creates its own medium as it goes along.

That's a very different model - can you illustrate that with a water or sound wave? Or do you know an article describing that model?

*Studiot*

That's a very different model - can you illustrate that with a water or sound wave? Or do you know an article describing that model?

Well for an ordinary common or garden type Hawaiian surfing wave the water is there beforehand for the wave to propagate in(to). The wave can be seen to develop, travel and finally disappear.

On the other hand, when a tidal bore or surge occurs there is little or no water present beforehand. Certainly not enough to accomodate the oscillation amplitude. The bore front takes sufficient water along with it.

PhilDSP

I feel any answer other than "the electric and magnetic fields" is more philosophical than scientific currently.

Isn't it worth considering fields to be transformational devices that manipulate and transform other qualities such as force, energy, potentials, momentum, polarization potentials, etc., in a consistent and physically meaningful way? In a sense, fields collect what we know about how those other qualities are coupled together. In analogy to house construction, they provide the blueprint, but not the physical realization of the framing, plumbing, electrical system and so forth.

Swetasuria

Quote by FredericGos

First of all the field doesnt travel. It's just there, everywhere, including the vacuum. In reality the field is made up of quantized harmonic oscilators.

Fields can have directions, right? If they are "just there, everywhere", then how come fields are vector qantities?

harrylin

Quote by Swetasuria

Fields can have directions, right? If they are "just there, everywhere", then how come fields are vector qantities?

Forces have directions, and as you can see in post #68, it seems that originally (and technically), fields were just the neighbourhoods where those forces were felt. However, later the term field strength (and sometimes simply "field") was used as a measure for the strength of forces that can be felt in the field - which includes directionality.

PS I'm amazed by this accurate intro in Wikipedia (although it is messed up by the there following "qualitative description"):
"In physics, an electric field is the region of space surrounding electrically charged particles and time-varying magnetic fields."
-http://en.wikipedia.org/wiki/Electric_field

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Drakkith Recognitions: Gold Member	I feel any answer other than "the electric and magnetic fields" is more philosophical than scientific currently.