Photon structure

[Jacques]

Hi

I have a simple question:

How does the QM and other mainstream physic theories describe the structure (topology...) of a photon ?

Thanks

[insane_alien]

doesn't really have a structure. other than that, it is point like except when it's a wave.

[Jacques]

That's what I was expecting for answer. But if all particles are point like, how can they interact ?

[Klaynos]

That's what I was expecting for answer. But if all particles are point like, how can they interact ?

 

Using exchange particles of the 4 forces. You must also remember that whilst they are pointlike they are also wavelike...

[BenTheMan]

But if all particles are point like, how can they interact ?

 

Good question!

 

The particles don't INTERRACT the way that you're thinking---they never all meet at a point an then go their merry way.

 

The picture to have is a RANGE. When the particles get close enough, they interract. Usually ``close enough'' means something like within a compton wavelength, or something.

[Norman Albers]

I assumed a Gaussian structure in the paper you may read at the cache in my signature. What is not at all usual in my approach is allowing the vacuum to be a responsive source of charge and current density. This works beautifully if you allow a diffuse superconducting response such as I found expressed in the mathematics.

[Severian]

Photons most definitely do have structure:

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=find+t+photon+structure&FORMAT=WWW&SEQUENCE=

[Jacques]

Thanks for your answers, the image I start to view is that of a fuzzy patch of energy travelling at c. The more energetic photon are smaller than the less energetic one... Am I on the good track ?

Norman I find your paper very impressive, but I don't realy understand it. Can you describe it in more layman term ?

Thanks Severian for the links but I don't have access to these papers. Can you give us some glimpse on the contents ?

Thanks

[swansont]

I think the treatment of photons as point particles is mostly restricted to high-energy interactions where the wavelength would be small, so perhaps the treatment as such is an approximation. Or possibly a bookkeeping requirement of how the problems are treated. Certainly at the atomic scale there are many instances where it is acknowledged that photons have a spatial extent.

[Norman Albers]

Jacques, usually when we write Maxwells equations we insist on a complete vacuum except for specified unit point charges, in the small. As a plasma physicist I got used to dealing with regions of charge density, in a plasma involving populations of usually different species, electrons and ions. My study here is "simply" solving what is implied by having a wave packet. When you solve Maxwell's eqs. for waves you produce plane-wave solutions with no transverse falloff. Consider a microwave waveguide or even optic fiber. If we call propagation direction x, there are electric and magnetic fields in y,z. Where this energy impinges on the conducting wall, the wall mirrors the electric field and thus reflects it back in. Since we thus supply a "sheath", we have created a field where in a region (inside) there exists electric field in say, the y-direction, but beyond the wall, in the y-direction, there is no field, right? A mirror is a charge-current responsive availability at the frequencies you're dealing with; this is the nature of a conductor........So, I start with a disarmingly simple statement, "suppose there exists this wave packet which moves along at c in the x-direction, and that its intensity in all three dimensions, looked at in its centered frame of reference, falls off as a Gaussian exponent with a characteristic length of 'many cycles'." I proceed through the two or three steps to solve for the implied charge and current fields. The existence of such a packet requires a "diffuse mirror" to be supplied by the vacuum. This is the charge density field describing a double-double helix characterizing the thinning envelope. Grouping terms and looking at this for quite some time, I finally came to the expression for current whose first term is just what you get solving response from a superconductor: [math] j=(-\lambda^2 + \rho/U)A [/math]. Mathematically, charge density is described as "divergence of the electric field", [math]\nabla \cdot E[/math]. I offer these extensions to Maxwell's equations, namely right-hand-side source terms cooked up by the time-dependent vacuum polarizability in the small.

 

The inference of a characteristic length of "many cycles" implies a pure number, and I needed a few thousand, so why not the square of the fine structure constant?There are not many pure numbers floating around in this circumstance.

[Jacques]

Norman what do you think of Farsight soliton ? All what I readed about soliton, need some medium to work. Is vacuum some kind of medium ?

Also,I readed a recent paper about the measurement or computation of the probality function of the photon and what was surprising is that in the middle of the photon the probability was negative... I tried to find that paper without success. Maybe someone here knows about it...

[Norman Albers]

Jacques, good statement: yes, the vacuum is a medium. I corresponded a good deal with H. Puthoff and he certainly agreed that it is being seen as such. (We exchanged quite a bit on the topic of gravitation, but disappointingly he has offered nothing on this photon study.) I have allowed it to be so and derived the "superconducting" response I wrote. In a superconducting material, there is an electron population giving a finite, massive, but resistanceless response to impinging magnetic fields, and until overwhelmed by intensity, a skin current forms keeping out the B-field. Here, and in my electron study, I express "massless" dipole field availability; this seems to fit well with the QM concept of zero-point fluctuations of the virtual electron-positron field.

[BenTheMan]

Is vacuum some kind of medium ?

 

I think this idea was called the luminiferous aether, and was shown to be wrong in the nineteenth century.

[Norman Albers]

It seems to me nowadays we call it the virtual field.

[Jacques]

Does photons interacts? I mean something else than interference. For example if I have a photon coming from the right and an other comming from the left will they just pass through each other? Is the result of photon collision depend on the energy ? Like if I have two .6Mev photon will they produce an electron positron pair when they collide ? Stupid question but it bugging me

[Klaynos]

They do interact but it is VERY small.. I'm not familiar with the mechanics of it other than that though. I think I've seen Severian go into greater detail in the past though.

[Norman Albers]

You ask good questions. Up to the energy level you describe photons don't interact, though I have heard knowledgeable people say they repel somewhat; a Stonybrook prof. put it: "they oppose 'til they superpose, I suppose." At high energies interaction becomes possible; I've heard it described as nonlinear process. Also S.Doniach at Stanford described dueling x-ray lasers, from the e-p storage rings at SLAC, where a region of very high intensity could be expected to "boil the vacuum" and show pair production. Look up "Schwinger pair ...".

 

Talking with Puthoff: (NA): I think we can both say the vacuum gets thicker in terms of dipole manifestation, but how do we connect this with permeability?

(HP): I think (loosely) of the vacuum as a virtual electron-positron plasma. The permeability would be associate with the spins. There has been recent measurement of birefringence induced in the vacuum by a magnetic field, which supports this idea. They definitely conclude that the vacuum is a medium. Published in Phys Rev I think. Hal ...................There is an electromagnetic background, the CMB of blackbody sprectrum. This is not the same as the virtual fluctuation field. Google on 'virtual fluctuations' and you'll read why I am doing what I am. A blackbody equilibrium spectrum described by the Planck distribution does not Lorentz-transform into itself. The QM vacuum spectrum is described with an [math]\omega^3[/math] dependence which does L-t into itself. I went on to argue against his saying we need spins intrinsically to do E&M business.

[swansont]

There's an interaction that scales with the square of the vector potential (A dot A), so it only becomes important at higher energies. But yes, you can scatter photons off of each other.

 

http://www.madsci.org/posts/archives/feb99/919892082.Ph.r.html

http://2physics.blogspot.com/2006/03/photon-photon-scattering.html

[Norman Albers]

Excellent, Swansont, exciting references. Severian, can you help us understand the f2([math]\gamma[/math]) function in your ref?

[elas]

Point-like particles

 

In the term zero point the ‘zero’ refers to dimensions, not to force. In a collapsed vacuum field the zero point contains the total field force. When the force is extracted the vacuum field expands on a ratio of one unit of force to one unit of distance until the total force is extracted. This will be referred to as the nuclear field.

Any further expansion is only possible by transferring force from the nucleus to a ‘shell’ field the strength of this field is determined by the area the transferred force is spread over. It is for that reason that the force strength is determined by the inverse square law.

 

The strong and weak forces are nuclear forces and therefore the strength increases with distance until the zero point force is zero.

 

Gravity and electromagnetic forces are shell forces. In order for these forces to be calculated from a central point it is necessary to modify the inverse square law by the introduction of constants in place of the nucleus. As a direct result of this the electro-magnetic force law creates the impression that particles are points surrounded by a field; as emf is used to interpret experiments; the claim is made that experimenters observe point-like particles.

 

Two forces are related to the vacuum force, the remaining two forces are related to the anti-vacuum force.

[Norman Albers]

I won't say I have wrapped my head around your offerings but your vision is intriguing, Elas. You speak on constants of the vacuum in place of a nucleus. I dial up electrons and photons as responses from the vacuum field characterized by the fine structure constant, which expresses the proportional response of the vacuum to the field and thus the envelope of the disturbance. . . . .Over in 'German claim...' I read of Gaussian wave packets. I suspect they are not the same as the ones I have dialed up in my photon paper. Doesn't quantum wave theory start with an uncertainty spread in momentum in the propagation direction? What is achieved? Is there a repeating pattern which is normalized, and is there any falloff in the transverse direction? Nobody commented on my efforts to Fourier transform my model, but if I have done it correctly there is a well-defined single momentum in the x-direction producing a delta function in [math]k_x[/math] but a spread in the transverse spectrum reflecting the exponential falloff.

[pioneer]

Photons have spin or angular momentum. How does a photon wave spin and still make a flat wave that does not appear to be spinning? This is due to its particle nature. Since a photon particle is traveling at C, do they need to spin perpendicular to motion to avoid the surface spin travelling faster than C? A visual analogy is a wheel, with the hub at C. The rim, if it spun in the forward direction, would get ahead of the hub. At least in the perpendicular direction it never gets ahead of the C-hub.

 

On the other hand, if it spun perpendicular to the motion, it may never get ahead of the hub, but it would appear to transverse more distance than the hub at C, in less time. One way to compensate for that could be a SR affect, that alters distance and time, at the rim of the spin, so that it only travels the same distance as the hub while it spins.

 

This sounds far fetched until you compare two different photons. If we have a SR rocket traveling near C, it would appear distance contracted to a certain amount. Say it appeared distance contracted to half, while we knew it was going faster and should be double than. One way to explain this, is the surface of the ship is in one SR reference and core of the ship is somehow in another. This is what happens with photons. They all travel at C. Although all should look like a point wavelength, they can display a variety of outputs, not normally associated with C reference.

 

Relative to photons to maintain the transverse distance of the rim, so it does not exceed the C speed of the hub, it needs variable SR affects, to compensate for the amount of angular momentum and adjust distance and time. This results in the photon being in two references at the same time, part in C and part less than C.

 

Again, if a rocket was traveling near C, we should see distance contraction that is directly related to this velocity, or else the surface would have to be in a different reference than the body of the rocket. One might explain this with the ship generating a stealth type layer of SR to cloak its speed parameters. Photons are able to cloak their speed output, to make diverse wavelength or diverse distance and time output parameters.

[Norman Albers]

I calculate, according to electrodynamic rules, angular momentum density of the field. The contribution from inhomogeneous sourcing in my model is: [math] J_x =\int d^3 V \rho \hat x \cdot r \times A [/math]. I use a coordinate origin riding with the center of the packet. Where there exists vector potential A and charge density [math]\rho[/math] there is linear momentum of their product. Angular momentum is the crossproduct [math] r\times \rho A [/math], and I take the component in the x-direction.

[Jacques]

Swanson:

There's an interaction that scales with the square of the vector potential (A dot A), so it only becomes important at higher energies. But yes, you can scatter photons off of each other.

At these energies, how can we make the difference between real photon scattering, and pair creation and the scattering of photons with electron or positron ? In the later case it make me think of the electron and the positron being the "force" carring particle for the photons interaction...

[Norman Albers]

Good discussion, Jacques. Isn't this what they do in QFT, figure all possible transition paths according to quantum math?