Why does light have a secondary oscillation?

[questionposter]

A photon carries both an electric and magnetic oscillation, but why does it have both? How does it have both? Or is it just one of those math things where there "needs" to be some two oscillations to do something like also change the vector state or something for all of the rest of the math to work out properly?

Or I guess, how does an electron jumping an energy level actually make two different oscillations?

 

Also, how do we know those oscillations are perpendicular to each other?

Edited April 15, 2012 by questionposter

[Enthalpy]

A varying electric field always means a magnetic field as well, and a varying magnetic field always means an electric field as well.

You can create pure electric or pure magnetic fields, but only static ones. Static fields don't propagate far: they're local, or "near-field".

This is just observation, or if you prefer, the way Nature works, or name it accordingly to your beliefs.

Yes, some maths could "prove" it... But actually, the result only proves that the maths chosen by Maxwell adhere to reality.

 

In fact, the incomplete equations pre-existed; Maxwell added that the current corresponding to the polarization of dielectrics and of vacuum creates a rot(B) just as a flow of charged particles does. This tells that, as a varying electric field creates a polarization current, the induction can't be uniformly zero then. With that addition, Maxwell explained EM waves. So the maths would be flexible enough to model other EM behaviours than the one observed.

 

In an atom, orbitals are immobile solutions for an electron in the sense that the electron's wave amplitude doesn't depend on time (the phase does, it rotates around the nucleus over time, which explains why an orbital can have a mechanical and a magnetic momentum). These immobile, or stationary solutions, don't radiate - for lack of movement if you wish.

 

A weighted sum of orbitals isn't a stationary solution any more. The wave amplitude does vary over time, at a frequency equal to the energy difference between the stationary orbitals, and this movement of the charged electron does absorb or radiate light at that frequency. You're right to make a very concrete mental image of this process, as long as you don't imagine a point-like electron.

 

Now, if you want to imagine as a short oscillating current this "movement" of a charged electron that still pertains both to the old and new orbitals, or if you compute the field produced by a short antenna, you can use the Biot&Savart equations. The current gives you a magnetic vector A with B=rot(A) and the pair of charges at the wire's ends gives you an electric field E. The current accumulates charges and the charges result in a current, as soon as they oscillate - and so do the resulting B and E fields.

[swansont]

A photon carries both an electric and magnetic oscillation, but why does it have both?

 

Because they obey Maxwell's equations

 

Also, how do we know those oscillations are perpendicular to each other?

 

Because they obey Maxwell's equations

 

http://farside.ph.utexas.edu/teaching/em/lectures/node48.html

[questionposter]

Those finished equations seem like they were designed after the discovery to fit what was being discovered, but it seems like light isn't just any kind of field, it seems like it is a moving version of the same field it was emitted from, but I don't see why simply oscillating allows a photon to carry consistent values while a static field itself dies out over time, unless photons are an oscillation within a static magnetic/electric field, but then I don't understand what they don't die out over time.

Edited May 10, 2012 by questionposter

[Cap'n Refsmmat]

Because they obey Maxwell's equations

 

http://farside.ph.utexas.edu/teaching/em/lectures/node48.html

I find it amusing that you cite Dr. Fitzpatrick's lecture notes here, because this is exactly the sort of answer he would give to a question like this. There is no physical motivation. There is only maths.

[swansont]

I find it amusing that you cite Dr. Fitzpatrick's lecture notes here, because this is exactly the sort of answer he would give to a question like this. There is no physical motivation. There is only maths.

 

It's more than that, I think. Maxwell's equations didn't appear out of thin air. They were the result of many years of investigation. So especially for the "how do we know" question, it's shorthand for "many people did experiments, ultimately resulting in these equations, which tell us how they behave"

 

 

For "why" question, that quickly becomes philosophy. We don't know why. Physical law isn't derived, it is discovered.

 

Those finished equations seem like they were designed after the discovery to fit what was being discovered, but it seems like light isn't just any kind of field, it seems like it is a moving version of the same field it was emitted from, but I don't see why simply oscillating allows a photon to carry consistent values while a static field itself dies out over time, unless photons are an oscillation within a static magnetic/electric field, but then I don't understand what they don't die out over time.

 

A static field does not, by definition, die out over time.

 

If a photon's oscillation died out, where would the energy go?

[qsa]

You can read about it in this classic book for free. There is also volume II up to QM discovery.

 

A history of the theories of aether and electricity : from the age of Descartes to the close of the nineteenth century

 

http://archive.org/details/historyoftheorie00whitrich

 

[John Cuthber]

"A photon carries both an electric and magnetic oscillation, but why does it have both? "

Because electricity and magnetism are both aspects of the same, electromagnetic, force.

[swansont]

"A photon carries both an electric and magnetic oscillation, but why does it have both? "

Because electricity and magnetism are both aspects of the same, electromagnetic, force.

 

That's true but I think it's a step subtler than that, because you can have a static electric or magnetic field. But if you are in motion with respect to e.g. the electric field you will also see a magnetic field because of this relationship. So it should't be too surprising that a time-varying electric field gives you a magnetic field, or vice-versa. It goes further, though, because the varying E field gives you a varying B field and a varying B field gives you a varying E field. But it has to be that way because of the question I raised before: if the oscillation died out, what happens to the energy? And all of that has to be true regardless of the frame from which you observe it, which gives you an invariant speed. It's all tied together.