Is the polarization of electromagnetic waves definite or in superposition?

[fanieh]

Hi,

In Classical electromagnetic wave.. does it have definite polarization when the EM wave leaves the sun for example? Or is it in superposition and the polarization only exist after measurement just like in QM?

I don't understand the Maxwell Equation. Does Superposition in Maxwell Equation means the polarization is in superposition and doesn't have definite value before measurement?

Thank you.

 

[Sturk200]

Hi,

In Classical electromagnetic wave.. does it have definite polarization when the EM wave leaves the sun for example? Or is it in superposition and the polarization only exist after measurement just like in QM?

I don't understand the Maxwell Equation. Does Superposition in Maxwell Equation means the polarization is in superposition and doesn't have definite value before measurement?

Thank you.

Natural sunlight is randomly polarized, meaning that the electric and magnetic fields do not oscillate in any preferred direction. They are indeed a superposition of orthogonal components, as you say. However this is not a superposition in the quantum mechanical sense. It is a superposition in the classical sense of of the superposition of electric and magnetic fields. The field at any given instant does have a definite value and direction, but it is generally oscillating so wildly that as far as I know our equipment cannot distinguish the changes, and so we say that the light is unpolarized or randomly polarized.

 

[fanieh]

Natural sunlight is randomly polarized, meaning that the electric and magnetic fields do not oscillate in any preferred direction. They are indeed a superposition of orthogonal components, as you say. However this is not a superposition in the quantum mechanical sense. It is a superposition in the classical sense of of the superposition of electric and magnetic fields. The field at any given instant does have a definite value and direction, but it is generally oscillating so wildly that as far as I know our equipment cannot distinguish the changes, and so we say that the light is unpolarized or randomly polarized.

But if you will use quantum field theory and the electromagnetic field becomes photons.. the superposition is actual and the field at any given instant doesn't have any definite value.. so how can changing mathematical tool makes the polarization becomes indetermined in principle?

 

[Sturk200]

But if you will use quantum field theory and the electromagnetic field becomes photons.. the superposition is actual and the field at any given instant doesn't have any definite value.. so how can changing mathematical tool makes the polarization becomes indetermined in principle?

But why would you do that if you want to talk about a classical electromagnetic wave?

 

[fanieh]

But why would you do that if you want to talk about a classical electromagnetic wave?

I mean.. when we want to talk about light coming from sun.. must we use the description of classical electromagnetic wave with random but deterministic polarization or photon with truly indeterministic polarization? What is the actual?

 

[vanhees71]

Without understanding classical mechanics and classical electrodynamics first, you haven't any chance to understand quantum mechanics and quantum field theory! So first, get a good understanding about classical physics! A good starting point are the Feynman Lectures. You find them online for free:

http://www.feynmanlectures.info/

 

[Nugatory]

But if you will use quantum field theory and the electromagnetic field becomes photons...

That's a very misleading way of thinking about what's going on here. Vanhees71's advice in #6 is good.