Electromagnetic radiation and photons

[Saado]

Hey all, my first post here. I'm 17 years old and am taking physics at A level. (Just finished my end of year exam today)

So the understanding I have of light is that it is the oscillation of an electric field and of a magnetic field perpendicular to each other. I've come to the conclusion that light can not be a wave because of it's particle nature. I understand how phasor arrows give a better explanation than the wave explanation.

I know light as an oscillation of those 2 fields but I think of it as discrete packets of energy. I think of the photon as energy and once the energy is transferred the photon is gone. How can light be a photon (discrete packets of energy) and the oscillation of those 2 fields at the same time?

My understanding of the electric and magnetic field tell me that these fields are only present where there is electrons. So should light not then be electrons? I know that sounds stupid but I think I am missing a fundamental point here.

 

[Bill_K]

I think of the photon as energy and once the energy is transferred the photon is gone.

Saado, Even though the photon carries energy, it is not just a packet of energy. It's one type of elementary particle, having many other properties besides. It just happens to have zero mass. Thanks to the electroweak theory it is shown to be closely related to other particles such as the W and Z boson that do have mass.

 

[DrChinese]

... I've come to the conclusion that light can not be a wave because of it's particle nature. ...

Welcome to PhysicsForums, Saado!

Light can be demonstrated to have a particle nature. It can ALSO be demonstrated to have a wave nature at times. The double slit experiment is usually cited as an example of the wave nature when interference effects are demonstrated.

 

[Saado]

Thanks for the replies! While I understand Young's experiment, I don't understand how light can be the oscillations of an electric and magnetic field and at the same time be photon with different properties. Is the photon a product of the electromagnetic field? I guess I'm looking for a unification of the two. I'm okay with the fact that particles can show wave behavior and waves can show particle behavior.

 

[vanhees71]

Welcome to the club of people puzzled by quantum theory! The answer is to forget what you read about photons in popular science books. The problem with them is that they try to explain a very complicated issue in an inappropriate language, namely plain English with some very bad meant-to-be-intuitive pictures.

The only appropriate language is relativistic quantum field theory, and this is difficult, if not impossible, to express in an intuitive way. First of all you should not think about elementary particles as miniature every-day bodies like billard balls. For massive particles this works under certain circumstances sometimes quite well, but for photons it's totally wrong. Photons, e.g., do not have a position observable at all. The right picture is a very mathematical abstract one and is described by a quantum field. The quantum field describes, as far as we know today, the properties of photons correctly, and this includes both phenomena what we call in classical analogies "wavelike" (classical em. wave fields) and "particle-like" (classical bodies with negligible extension) in a consistent way.

Light in everyday life is unlikely to be a photon or more precisely a single-photon state. It's more likely a superposition of states with an arbitrary photon number, known as a "coherent state", and this behaves pretty much like a classical electromagnetic wave. In almost any typical circumstances in everyday experience with em. fields (light, radio waves, etc.) you thus are better off with the field (wave) picture than with the particle picture.

 

[Saado]

Thank you for that reply :) That helped a lot. In the physics class my teacher did say that the wave explanation works for most things but the truth was light was always a photon.

Well, that's one mystery solved for me. Time to look at something else :D