Physics Help Forum fields and photons?

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 Sep 13th 2019, 03:36 AM #11 Member   Join Date: Sep 2019 Location: Azores Posts: 32 I think I understand what you are driving at. All things are quantum fields of one form or another the properties of the field decide what it is, ie an electron has properties of mass/inertia, -ve electric field and magnetic field, all these constituent parts go to make up the electron field, as a hole. A photon field has no electromagnetic properties but it does have inertia. Ethan covers it better than me https://medium.com/starts-with-a-ban...l-b670cc8462d0
 Sep 13th 2019, 04:18 AM #12 Senior Member   Join Date: Oct 2017 Location: Glasgow Posts: 474 Nice one. That seems like a good link too. There's *a lot* of physics behind everything he's summarising there and he's done a decent job of summarising it without going too crazy. I think most people will come back from studies into QM with even more questions than answers, but that's physics for you! interested likes this.
 Sep 13th 2019, 05:31 AM #13 Member   Join Date: Sep 2019 Location: Azores Posts: 32 Thanks for all the pointers.
 Sep 15th 2019, 03:58 AM #14 Member   Join Date: Sep 2019 Location: Azores Posts: 32 Sorry for coming back to this but if a particle and its properties belong its quantum field ?? Quoting the link above "That’s because, in quantum field theory (QFT), quantum fields aren’t generated by matter. Instead, what we interpret as “matter” is itself a quantum field. And these quantum fields, themselves, are made up of particles. The electromagnetic field? Made of particles called photons." Since photons are particles in their own right, with their own quantum field with no electromagnetic properties. How can an electromagnetic field from a electron/positron/proton etc be transmitted by a photon when the electromagnetic field from these particles is part of the particles own field. I keep coming back to Magnetic fields are curved, photons travel in straight lines and are not affected by electromagnetism. Is there more than one definition of a photon. Are there real photons with magnetic properties?? or are we talking about virtual photons which can have more properties than a real photon??? Should the link have said The electromagnetic field? Made of virtual photons.
 Sep 15th 2019, 04:17 AM #15 Senior Member     Join Date: Jun 2016 Location: England Posts: 1,060 Do the particles create the fields, or do the fields create the particles? My interpretation might be that particles (photons, electrons, etc.) are nodes within their fields. Perhaps a bit like where a resonance will cause patterns in sand (Note that I' am a "hobby" physicist, I'm not sure if the "proper" physicists will agree with this interpretation) donglebox likes this. __________________ ~\o/~ Last edited by Woody; Sep 15th 2019 at 05:31 AM.
 Sep 15th 2019, 01:28 PM #16 Forum Admin     Join Date: Apr 2008 Location: On the dance floor, baby! Posts: 2,857 The way my instructors (and Weinberg's books) describe it the following way: The Univese is filled with different quantum fields. So, for example, the Universe has an electron field and electrons are the quanta of that field, just as photons are the quanta of the EM field. Note: this has nothing to do with the particle/wave duality thing. -Dan Addendum: The electron field is not made of electrons any more than the EM field is made of photons. Else we would be drowning in electrons! __________________ Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup. See the forum rules here.
Sep 16th 2019, 04:06 AM   #17
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 Originally Posted by topsquark The way my instructors (and Weinberg's books) describe it the following way: The Univese is filled with different quantum fields. So, for example, the Universe has an electron field and electrons are the quanta of that field, just as photons are the quanta of the EM field. Note: this has nothing to do with the particle/wave duality thing. -Dan Addendum: The electron field is not made of electrons any more than the EM field is made of photons. Else we would be drowning in electrons!
#1

This is what I am finding difficult to believe. A photon is a particle in its own right, it is not affected by electromagnetism in any way. A photon does not weaken in strength as an electromagnetic field does as it travels through space. A photon travels in straight lines, an electromagnetic wave LF can follow the curvature of the earth without having to be bounced of the ionosphere HF. Magnetic fields associated with magnets and their atoms are curved, photons dont travel in tight circles like a magnetic field.

Goto #1

I am stuck in a loop

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Each particle itself is its own quantum field, an electron is the generic name for a field that has electron characteristics which includes its magnetic effects. A photon is the generic name for a photon field which is not affected in any way by electomagnetism.

A BARE photon can be regarded in QED as a particle and anti particle ripped from the vacuum of space. ie a pair of eigen vectors. Its a mathematical model.

Maybe Loop break ????

The particle charge properties and magnetic properties of a BARE photon cancel out.

In Radio waves the photons ripped from the vacuum of space could be regarded as polarised pairs travelling through space aligned so that their properties dont cancel out.

ie can a photon be defined in more ways than one. Polarised and none polarised.
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Should photons be regarded as being made up of virtual particle pairs?

and maybe all fields could be regarded as being made up of virtual particles. > big bang baryogenesis > Hawking radiation > Dynamic Casimir effect etc ???

Sep 16th 2019, 04:31 AM   #18
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 an electromagnetic wave LF can follow the curvature of the earth without having to be bounced of the ionosphere HF
Not strictly true.
All elecro-magnetic waves travel in straight lines, in a vacuum.
However the transparency of rock and water etc. will change with different wavelengths,
Also Low Frequency waves may diffract around the curvature of the Earth.
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Sep 16th 2019, 05:22 AM   #19
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Many of your questions, interested, are based on composition and propagation via some kind of mechanism:

 How can an electromagnetic field from a electron/positron/proton etc be transmitted by a photon?
 The electromagnetic field? Made of virtual photons
 Should photons be regarded as being made up of virtual particle pairs?
However, you have to be aware that there is a difference between what something *is* and *how* something works and that some of the names given to concepts really address the *how* rather than the *is*.

Let's use a elastic scattering between two charged particles (such as electrons) as an example.

In terms of what things *are*, all we can absolutely be 100% sure of is that there are two charged particles. That's it. They have charges, q1 and q2, and masses, m1 and m2. We also care about their initial velocities, v1 and v2 (and hence we can derive their initial kinetic energies and momenta).

Those two charges are going to interact and their velocities will change. Consequently, each particle will change their trajectory, kinetic energy and momentum. Those variables are the main ones of interest to physicists. Our question becomes this: given two known charges, masses and any other fundamental properties, how do we expect the two charged particles to behave according to the EM interaction?

As physicists or engineers, we can now try and model that interaction in various ways:

Method 1: classical electromagnetism: Every charged particle can be associated with an electric field. Other charged particles lying within this electric field will be subject to a force.
Method 2: particle physics EM interaction. Every charged particle emits virtual photons to every other charged particle, which exchange energy and momentum according to conservation laws.
Method 3: QED: every charged particle is a quantum particle. Quantum particles interact with each other based on a theory of quantum systems, which are described using a combination of wave functions and operators and whose results are (typically) eigenvalues describing the possible set of outcomes for a given observation
Method 4: QFT: every charged particle is a quantum field. Quantum fields interact with each other according to QFT (using functionals and other unique QFT concepts).

These methods are not necessarily distinct (can re-use terminology and theory) and some are clearly easier to model than others, but some of the more detailed models are probably more reliable for more complex situations.

So... you can debate until the cows come home whether an electric field is a real, material entity or not, or try and guess what it is composed of, but when different concepts can be applied to describe the same thing, we have to be aware that the way we describe the world is exactly that; a description. Descriptions are open to debate.

And, before anyone asks... I'm not trying to delegitimise debates into how things truly are... I'm just trying to make the point that it's very often not fruitful at all to take the view that there is only one valid way to see the universe and there's only one possible way to see how everything *is*. There are many perspectives and descriptions which are useful for different situations and the truthfulness of reality is revealed to us using all sorts of weird and abstract concepts, some of which are so bonkers you might do yourself a favour in taking everything with a pinch of salt... you'll tear your hair out trying to make everything fit into a single picture. Many people already have; and do!.

P.S. I have very little hair now!

P. P. S. As a materialist realist, I take great insight towards a quote made by the Greek philosopher, Democritus, who said "There are atoms, and there is void. Everything else is opinion." although his statement is rather out of date, considering there was no knowledge of subatomic particles at the time.

Last edited by benit13; Sep 16th 2019 at 05:32 AM.

Sep 16th 2019, 07:33 AM   #20

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 Originally Posted by interested This is what I am finding difficult to believe. A photon is a particle in its own right, it is not affected by electromagnetism in any way. A photon does not weaken in strength as an electromagnetic field does as it travels through space. A photon travels in straight lines, an electromagnetic wave LF can follow the curvature of the earth without having to be bounced of the ionosphere HF.
Yes, the photon is a particle in its own right. I am not saying that it isn't. In QED a photon is the mediator of the EM field. This means that it "carries" the momentum between two distinct particles. (See diagram 1.)

 Originally Posted by interested A BARE photon can be regarded in QED as a particle and anti particle ripped from the vacuum of space. ie a pair of eigen vectors. Its a mathematical model.
I don't know what you are trying to say here. There is no such thing as a photon that is not a bare photon. (I think I mentioned this in this thread...
There is an interaction between photons but the effect is very minor and not really what a dressed photon would be.)

About particles/anti-particles: A photon is a photon. It does not need an anti-particle pair to exist. Also, the anti-particle to a photon is a photon so there is no distinction to mention at this level.

And, yes, I'm well aware of eigenvalues and their properties.

 Originally Posted by interested Magnetic fields associated with magnets and their atoms are curved, photons dont travel in tight circles like a magnetic field.
I wanted to take this one out for a special comment. Magnetic fields are created by electric currents. Magnetic fields can change over time but they don't "travel" at all, much less in tight circles. Perhaps you are thinking of the trajectory of charged particles in a magnetic field, such as in a bubble chamber?

-Dan
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