What does a single photon look like

[exponent137]

I've always wondered what is considered to be 1 photon. We always see things like "When two of these particle collide, they produce this and that particle, and ONE photon." The hell does that look like?!

Is it like a monochromatic plane wave but just a line.. like a frozen segment of a sine wave propagating at c in some direction..?

I think that this is the best article about photon:

http://arxiv.org/PS_cache/quant-ph/pdf/0410/0410179v2.pdf"

and 2 articles connected in triplet with this article. I hope you will find references for both of them.

 

[03myersd]

We would never be able to "see" a photon as the act of seeing things is our brain interpreting certain physical properties of photons in a certain way. These photons have bounced off of something which is what changes the properties. (wavelength in this case giving colour). We can only see objects as a difference in colours.

Now as I said the only way we can see things is by bouncing photons off of the object. To see a photon would require bouncing a photon off of another photon. But because of this the most we could get is a colour? (Which would be incorrect. A photon does not have a colour. Essentially it IS colour.)

Congratulations to anyone who manages to follow that. Its very difficult for me to explain. :D

 

[enotstrebor]

So you are replacing the well defined term photon with a fuzzy one that represents your idea of a photon. Sorry the name is taken, you may call your photon the enotstrebor-photon, and define it any way you like.

I am not replacing anything! Your just being supersilious.

So let's start again.

It is a description of a state of the em field.

Answer one question: Can you say conclusively that the Maxwell equation photon solution(EM wave description) or QFT version; 1) represents the photon or 2) represents the interaction (inter-particle) effect of the photon.

Study the history of physics. These are (historically and experimentally) purely models of the inter-particle behavioral effects (and not from an set of underlying elements of a particle theory and the resultant mathematical model designed to produce the resultant behavioral effects), i.e the observables.

Thus you can not say that Maxwell's equations and QFT represent the particle when all that is known is that they represent (reproduce) the inter-particle behavior!

It is a description of a state of the em field.

As to the question of conservation of energy at any instant in time, just look at (EM wave description) http://en.wikipedia.org/wiki/Image:Onde_electromagnetique.svg (from http://en.wikipedia.org/wiki/Electromagnetic_radiation)

As both the E field and B field can both be given by an in-phase sine wave (or both by in-phase cosine) then at some instant of time say t=0 the normalized E,B field energy is zero (i.e. sin(0)) and at a later instant in time the normalized E,B field energy is one (i.e. sin(90).

This is why the original version of the photon had the E and B fields 90 degrees out of phase (field energy = cos^2 +sin^2=constant) until it was shown experimentally that the E and B fields were in phase (field energy=sin^2+sin^2).

 

[0xDEADBEEF]

I am not replacing anything! Your just being supersilious.

Yeah. Physics is more fun that way. To paraphrase Asimov: Those who think they know everything, are a great annoyance to those of us who do.

[...]
Answer one question: Can you say conclusively that the Maxwell equation photon solution(EM wave description) or QFT version; 1) represents the photon or 2) represents the interaction (inter-particle) effect of the photon.

I don't understand your question, and by virtue of my haughtiness I blame you for posing a bad question. Does the kinetic gas theory describe a kinetic gas or the interaction of the kinetic gas with the world? What's the difference? Ontology? Then this thread needs to move to philosophy now.

Study the history of physics. These are (historically and experimentally)

... but not theoretically and modernly...

purely models of the inter-particle behavioral effects (and not from an set of underlying elements of a particle theory and the resultant mathematical model designed to produce the resultant behavioral effects), i.e the observables.

Again I don't understand. Are you saying Maxwell doesn't follow from a subset of QFT? First course in QFT we derived Maxwell from the Lagrangian. What's your point?

Thus you can not say that Maxwell's equations and QFT represent the particle when all that is known is that they represent (reproduce) the inter-particle behavior!

Inter charge behavior, inter electron behavior but no inter photon behavior.

[something about no energy with zero poynting vector]

So if your point is that we don't know if there are further details to photons stemming from some underlying theory, I'd agree. And then you might say we don't know what a photon really is, but than we don't need an argument about how e/m theory was discussed 100 years ago, but one about QFT.

But in the end it doesn't matter. We can make beautiful theories that describe things well without any underlying theory. We don't need to know about atoms for the description of rigid bodies.

 

[enotstrebor]

So if your point is that we don't know if there are further details to photons stemming from some underlying theory, I'd agree.

This is the essence of what I am saying.

Remember the original question I was addressing was, "What does a single photon look like?"

If a behavior involves only the particle itself then one can say the behavior is fundamental to the nature of the particle. If the behavior is the result of one particle (massed or massless) with another particle then the behavior is an inter-particle behavior.

The mathematical modelling of the behavior may attribute an aspect to the particle (in this case the photon) which is actually the resultant effect on the second particle (e.g. the electron). For example (hypothetical example), as an inter-particle effect, the photon could have a single field which produces two effects on the other particle (e.g. an electron). Noting the similarity between the signs of the F_uv matrix elements and the four dimensional torsion matrix of a gyroscope is suggestive that given particle spin, the E is potentially an in-plane (spin) gyroscopic action and the B effect a plane-normal gyroscopic reaction. Thus hypothetically the E,B effects are not two fields but two resultants of a single field.

Which brings us back to the question, "Can you say conclusively that the Maxwell equation photon solution (EM wave description) or QFT version; 1) represents the photon or 2) represents the interaction (inter-particle) effect of the photon."

But if the mathematical model (QFT or Maxwell's) is not a model of the photon but of its effects on the particle this goes to the heart of the question "What does a single photon look like?"

The answer is we don't and can't know from the present models.

but than we don't need an argument about how e/m theory was discussed 100 years ago, but one about QFT..

Does QFT tell us anything more about the photon than we knew 100 years ago? QFT can't tell use anything fundamentally true about the nature of the photon as it can not answer the question, does the photon in QFT ; 1) represents the photon or 2) represents the interaction (inter-particle) effect of the photon.

That is to say that in 100 years of effort we still cann't answer the question "What does a single photon look like?"

What's the difference? ...But in the end it doesn't matter..

If it doesn't matter, then why does the question still arise?

Why when the question is asked, do not those who are knowledgeable just simply explain/admit that the present mathematical models can not tell us what the photon looks like.

"What does a single photon look like?",

The answer is, after 100 years of theoretical developement, we haven't got a clue.

But we have a great model of its inter-particle behavioral effects.