The magical creation of the photon.

[CraigD]

I’ll take a shot at the question. I’m not capable of the formal math of it, but think I can outline photon-atom interaction without it.

Let me begin by filling in some of what I think are key details needed for understanding in Little Bang’s original description

Originally Posted by Little Bang

I have two hydrogen atoms on a collision course at some low velocity. When the fields of each atom …

Here, we need to consider what we mean by “the fields of each atom”.

In particle physics, force fields (except for gravity) are the result of exchanges of particles in the boson family by particles in the fermion family. In this example, the bosons are photons of magnetic force, exchanged mostly between the two electrons of the hydrogen atoms, but also, to a smaller net effect, between the two protons. Protons, or more properly, their constituent quarks, are also exchanging photons of magnetic force with electrons. Because we can’t measure these photons any way but by their effect on the protons and electrons, they’re called virtual. Precisely how many and when they’re exchanged is a matter of probability, not certainty – “quantum weirdness”, but very physically real.

The major thing all this virtual photon exchanging accomplishes is changing the momentum of the most massive parts of the atoms, their protons – or more properly, their most massive constituents, which are not their quarks, but the boson exchanged by the quarks, gluons.

… get to some point in their approach each electron jumps to a higher energy level …

In the process of this, the electrons will be placed in a “higher”, which is to say, less statistically likely, ”orbit”. These orbits are due to the exchange of magnetic force photons with the quarks of their protons, and are further constrained by the quantum wave functions of the electrons. These wave functions essentially require that the circumference of the electrons’ orbits be an even multiple of their de Broglie wavelength, causing these orbits to be discrete, or “quantatized”. The electrons then return to their lower, “ground” orbits. In so doing, they emit real photons of radiation. A hydrogen atom, or a system of two hydrogen atoms, can emit only photons of various discrete frequencies. Since this example states that the atoms were colliding at a low speed, we can assume that the electrons will have been raised to orbits not much greater than their ground states, and all these photons will be fairly low energy, in the infrared range.

… and then as they began to separate each electron falls back to the lower energy level …

There’s no requirement that the hydrogen atoms separate. They can remain close together, with nearly all of the kinetic energy of their former relative motion converted to photons of infrared radiation. This is the process by which a warm hydrogen gas, and eventually, a liquid and solid, cools, and can continue until the atoms near absolute zero temperature, and their relative motion is too low to raise many electrons above their ground orbits.

… and creates a complete infrared waveform with a crest and trough. …

The electrons just emit discrete photons of an energy exactly equal to the difference in potential energy between their higher, “excited” orbit, and their ground orbit. The wave nature of this photon is inherent in it, requiring no special timing on the part of the electron or the other particles interacting with it.

If you research the details of the above, the degree of my simplification of my explanation will become apperant. In particular, you’ll see I fudged considerably with the idea of the ground state orbit of an electron, because hydrogen emits infrared photons only for transitions to it’s second-from lowest orbital and above (for example, for Paschen series transitions to its 3rd orbital).

As Qfwfq notes, actually working out the details of what I’ve outlined would be a very complicated calculation. You’d have to statistically account for a literally infinite number of discrete exchanges of virtual photons, and many other difficult details. As many physics wags have noted over since Dirac and others first described this stuff, the only simulator really adequate for these sorts of calculations is the universe itself I hope, though, I’ve left Little Bang with a different opinion than

Originally Posted by Little Bang

We do not have an understanding of the steps that produce a photon. The equations work beautifully but they do not paint (the picture is worth a thousand words). In my opinion we are missing an important piece of information about the relationship between the electron and proton. What that might be I don't know. I hope that someone somewhere will answer that question before I die.

The understand he seeks exists, I think, even if the exact mathematical mechanics of it are complex beyond practical calculation, and even approachable only by a small number of superbly educated and practiced physicists.

[Little Bang]

Craig, your post was excellent. It was well written and showed good knowledge of the standard model. Is it guaranteed that all forces are carried by a particle or is there some small possibility that we are totally wrong and that they might in fact be magnetic in nature? I realize that 99% of the community thinks the standard model is the only way to go so it is very hard to get anyone to entertain anything outside of it. We all know that SM has many gaps or gray areas that need improvement. I suspect this to be one.

[Qfwfq]

First, the Standard Model isn't necessary, what Craig was talking about was quantum field theory. I wasn't talking about that, even. I said one could, at least conceptually, integrate the differential equation starting from initial state. It would only be a matter of gross number crunching and not nearly as complicated as working it out in terms of virtual particles, which however would have to (if there be justice) give the same result as using a potential; actually this would be, strictly, neglecting effects which are very slight in the case you are discussing.

Regardless of this being feasible or not, I agree that an understanding isn't impossible. What we don't understand is certain aspects of quantum reality itself.

[Little Bang]

Q, quantum field theory is not part of the standard model, if not then I was incorrect, but my question is still valid.

[Erasmus00]

I will give the original post a bit of an attempt, based on my understanding of field theory/standard model. HOWEVER, keep in mind there is sort of a heisenberg uncertainty between clarity and actual truth.

Anyway, we don't NEED two hydrogen atoms to make a photon. Simply punching (accelerating) an electron will create a photon. In this case, I believe that narrative description would be as follows:

The electron is sitting in space, surrounded by a cloud of virtual particles, constantly absorbing and emitting them in accordance with the uncertainty principle (). When the electron is accelerated away, it will leave behind (one or more) virtual particles, which become real, and travel away as photons. Descriptions for hydrogen atoms work similarly- only is a bit more complicated due to the fact that there are more particles involved.

Originally Posted by Little Bang

Is it guaranteed that all forces are carried by a particle or is there some small possibility that we are totally wrong and that they might in fact be magnetic in nature?

It might be possible that certain forces (well, at least gravity) might NOT be carried by a particle. It is,though, considered very unlikely. However, gravity can't be magnetic in nature as magnetic forces have no (observed) monopoles, while gravitational monopoles are everywhere. (anything with mass).

We have observed the particle that carries the electromagnetic force (photons), we have also observed W and Z bosons (carrying the weak force). We have not yet observed gluons, but have lots of circumstantial evidence. This suggests that if not all, most of the fundamental forces are carried by particles.

I realize that 99% of the community thinks the standard model is the only way to go so it is very hard to get anyone to entertain anything outside of it. We all know that SM has many gaps or gray areas that need improvement.

I don't think this is necessarily true- the problem with the standard model is that a. we know it isn't perfect, and b. there are absolutely no experimental faults in it. The problem isn't that it has many gaps or gray areas, but rather that it has too few!

I admit that the lack of a good "gut-level" interpretation of everything quantum (not just the standard model) is very unsettling. However, given that our intellects evolved to deal with a certain scale (not too fast, not too small), I don't think it should be a deal breaker that our intuition fails at the quantum level.
-Will

[Little Bang]

Excellent post Will, I could not put up any argument against anything in your response. I just have difficulty buying that all the forces are carried by particles and I still think there is a relationship between charge and gravity. One more question and I'll drop it. What particle carries the force that holds the electron to the proton?

[Erasmus00]

Originally Posted by Little Bang

What particle carries the force that holds the electron to the proton?

More photons. A proton is surrounded by virtual photons that it is emitting and absorbing (just like an electron). When we put an electron down in this cloud of virtual photons it interacts with them (and it has its own cloud of virtual photons which interact with the proton).

It is this mutual exchange of photons that holds the electron to the proton.
-Will

[CraigD]

Originally Posted by Little Bang

What particle carries the force that holds the electron to the proton?

Originally Posted by Erasmus00

More photons.

That’s my understanding, also.

What I’ve long wanted to know, and haven’t been able to find or calculate on my own, is what energies are typical of the virtual photons of magnetic force in various atoms and collections of atoms – that is, where they would fit in the spectrum – their “color” - if they were real photons of EM radiation?

[Erasmus00]

Originally Posted by CraigD

What I’ve long wanted to know, and haven’t been able to find or calculate on my own, is what energies are typical of the virtual photons of magnetic force in various atoms and collections of atoms – that is, where they would fit in the spectrum – their “color” - if they were real photons of EM radiation?

First, a caveat- virtual photons can be quite different then "real photons" because often the thing that makes them virtual is that they are "off-shell." Off shell is a funky phrase that sort of means "has the wrong mass." Which for photons means some of the virtual guys have non-zero mass.

Because some of the virtual photons have non-zero mass, some of the photons can be longitudinal (a spin z of 0, instead of +1 or -1), and so are very different then the photons we often think about.

That being said, virtual photons are exchanged across the spectrum. Often, virtual photons are inside loops in feynman diagrams which means their momentum and energy are unconstrained, which means integrating over every momentum, and every energy. However, they are weighted so that the further "off shell" (the more massive the photon) the less likely the probability of that virtual photon.
-Will

[snoopy]

Originally Posted by Erasmus00

Because some of the virtual photons have non-zero mass, some of the photons can be longitudinal (a spin z of 0, instead of +1 or -1), and so are very different then the photons we often think about.

-Will

If they are longitudinal does that mean they can exceed C ??