Does light have a definite shape?

[Eric McClean]

Light does not have a shape.

 

[RoughRoad]

Wavefront do have shapes. So doesn't light has a shape?

 

[lightarrow]

...
Once again I will defer to referencing two of Art Hobson's papers. These are two sort papers about teaching students the electron matter wave in hopes of clarifying the electron interference pattern. Despite focusing on electrons, the quantum field model for electron wave and light waves are the same.

http://physics.uark.edu/hobson/pubs/07.02.TPT.pdf

An interesting statement is done in that document:

"Thus, a photon is not really a particle. It is simply a way of talking about the energy increments hf of a spread-out, continuous EM field.

 

[LukeD]

All interactions with photons in QED are at single points, so we can say that as far as QED is concerned, photons are single points. (Though I believe there are theories in which it is larger than a single point and indeed has a shape)

The wave of a photon really isn't the same thing as the photon. We can think of the wave as corresponding to the probabilistic effects of a single photon. However, everything has a wave, even molecules, and the wave of an object can encompass much more space and have a different shape than the object itself.

 

[lightarrow]

All interactions with photons in QED are at single points, so we can say that as far as QED is concerned, photons are single points.

Ok. Now the question is: where is that single point? In the space between source and detector or at detector location?

 

[emc2cracker]

Light particles are massless correct? If they are massless I don't think they can have a real shape. Light waves radiate and if you charted their path on paper or in a 3-d model that would have a shape... but I don't really know how one would answer that lol.

 

[Born2bwire]

Ok. Now the question is: where is that single point? In the space between source and detector or at detector location?

At the detector. I usually like to say point-like just to be correct. For all intents and purposes particles are treated as point objects though it sometimes gets a bit murky when we talking about just how much of a point a particle truly is (like with the electron). But as Art Hobson is trying to point out, and Zee does this too in his text though others may not do so as explicitly, is that the QED light, or any quantum field, is not really made up of particles called photons. Instead, photons described the energy/momentum quanta that quantize the fields and occur in an interaction. What it comes down to is that quantum field theory treats all matter as fields. The classical particles that we are used to observing and measuring are simply the interaction of the fields with measurement. So in our macroscopic world, and our clumsy attempts at connecting with the quantum world, the observable effects of these quantum fields resembles how we think of a classical particle.

 

[lightarrow]

At the detector. I usually like to say point-like just to be correct. For all intents and purposes particles are treated as point objects though it sometimes gets a bit murky when we talking about just how much of a point a particle truly is (like with the electron). But as Art Hobson is trying to point out, and Zee does this too in his text though others may not do so as explicitly, is that the QED light, or any quantum field, is not really made up of particles called photons. Instead, photons described the energy/momentum quanta that quantize the fields and occur in an interaction. What it comes down to is that quantum field theory treats all matter as fields. The classical particles that we are used to observing and measuring are simply the interaction of the fields with measurement. So in our macroscopic world, and our clumsy attempts at connecting with the quantum world, the observable effects of these quantum fields resembles how we think of a classical particle.

Thanks.