[Bill S]

There’s some fascinating stuff in this thread.  Obviously, there is a wide range of field types, and lots of examples of their relationship with their sources, so let’s consider an electron field.   

I’m still not clear as to what an electron field involves.

Is the field something that exists in its own right, irrespective of whether or not any electron is “active” within it?

Is an electron just a disturbance in a pre-existing field?

Is an electron the source of the electron field?

If an electron is the source of the field, it must precede the field, so how could an electron exist without the field?

Is there no straightforward answer to any of these questions?

[jeffreyH (OP)]

@Bill S Certainly a very interesting subject. Raising interesting questions. I am still thinking about it. I am going to delve a bit deeper into QM. May have more questions to pose.

[jeffreyH (OP)]

There is an interesting discussion elsewhere on the subject.
https://www.quora.com/What-is-the-electron-field-as-distinct-from-the-electromagnetic-field

[chiralSPO]

As I understand it, a field needs no source. A field just is. It's a sort of accounting or mapping tool that we can use to describe the universe. Every field exists everywhere, even if it has zero amplitude at specific places, or even everywhere.

We base our understanding on experience, so we tend to think in terms of things and actions, but "things" or "actions" can be equally well (or better) described as perturbations in the field.

Let us consider electrons. It is very comforting to think of electrons as point-like particles. But even though this works well sometimes, it becomes apparent that this is an oversimplification, because under certain circumstances, they clearly behave as waves (enter the wave-particle duality). But even this is an oversimplification. Electrons are electrons. And it turns out that (as far as we can tell) every electron is identical to every other electron. And because of the wavy aspect of their nature, it doesn't really make any sense to say there is an electron right here. We just know roughly where they are. But since they are all the same, we can just say there is a universal field of electron. The amplitude is higher here and lower there, and is changing like so. This field is related to other fields we can imagine (electric field, magnetic field, gravitational field, proton field etc.).

[chiralSPO]

As I understand it, a field needs no source. A field just is. It's a sort of accounting or mapping tool that we can use to describe the universe. Every field exists everywhere, even if it has zero amplitude at specific places, or even everywhere.

We base our understanding on experience, so we tend to think in terms of things and actions, but "things" or "actions" can be equally well (or better) described as perturbations in the field.

To continue this thought slightly differently: The gravitational field is all around us, whether or not the is a planet nearby. Whether a planet moves here or even just randomly appears here, there will be a change in the local amplitudes of the gravitational field, but the field itself has not gone from "nonexistance" to "existence."

Put yet another way: we get lazy and talk about the forcefield of an object as if it were the universal field, when in fact it is just a part of the universal field. When I turn on an electromagnet, I haven't created any new field, just changed how the electromagnetic field is.

[geordief]

Anything to say  about what causes the perturbations in the field?

Is there any connection to the famous description whereby mass- energy tells spacetime how to curve and spacetime tells  objects how to move ? (if I haven't garbled that)

[Colin2B]

The gravitational field is all around us, whether or not the is a planet nearby. Whether a planet moves here or even just randomly appears here, there will be a change in the local amplitudes of the gravitational field, but the field itself has not gone from "nonexistance" to "existence."

Put yet another way: we get lazy and talk about the forcefield of an object as if it were the universal field, when in fact it is just a part of the universal field. When I turn on an electromagnet, I haven't created any new field, just changed how the electromagnetic field is.

@Bill S - this is also the answer to your question about the electron. If we measure an area of space and find no electrons we would say the field value is 0, but if an electron moves through that area we would see a change in the field value to = electron, the electron is a disturbance in that field.
As @chiralSPO says its like an accounting or mapping tool. But like other accounting systems people read too much magic into it, a bit like the belief in pure energy.

[lightarrow]

Say we have a universe that contains only one electron and one positron. They collide and annihilate producing two gamma rays. Since the sources of the fields are gone how are the gamma rays propagating? Does the electromagnetic field, or any other field, require a source?

The couple of charges, let's assume for simplicity they can be considered initially stationary in an inertial frame (difficult to define in a universe where only those charges exists, however  ) generate an electrostatic field in all space, which have its precise energy. The two charges are sources of this field.

After the charges have annihilated,  that field disappears too (not immediately of course, the information travels at c).  Its energy will be conserved in the form of em radiation which adds to the 2 gammas (infact it could be included in the gammas itself).

So the actual field generated by the charges disappears with them.

Not immediately, however. Maybe the question should be referred to this field which disappears at speed c from the charges centre.

--
lightarrow

[opportunity]

Anything to say  about what causes the perturbations in the field?

Is there any connection to the famous description whereby mass- energy tells spacetime how to curve and spacetime tells  objects how to move ? (if I haven't garbled that)

Why not put it to quantum-entanglement, something we haven't properly explained? With quantum-entanglement, where is the source?

[geordief]

The couple of charges, let's assume for simplicity they can be considered initially stationary in an inertial frame (difficult to define in a universe where only those charges exists, however  ) generate an electrostatic field in all space, which have its precise energy. The two charges are sources of this field.

After the charges have annihilated,  that field disappears too (not immediately of course, the information travels at c).  Its energy will be conserved in the form of em radiation which adds to the 2 gammas (infact it could be included in the gammas itself).

So the actual field generated by the charges disappears with them.

Not immediately, however. Maybe the question should be referred to this field which disappears at speed c from the charges centre.

--
lightarrow

Any mechanism whereby the field could be measured ?  Is there such a  (theoretical) thing
 as a measurement that is not made at the macro level?

Might it help if there were more than two charges (not practically but theoretically)  and  can an electron field be detected or measured by  sensors that are not themselves electrically charged ?

[opportunity]

The couple of charges, let's assume for simplicity they can be considered initially stationary in an inertial frame (difficult to define in a universe where only those charges exists, however  ) generate an electrostatic field in all space, which have its precise energy. The two charges are sources of this field.

After the charges have annihilated,  that field disappears too (not immediately of course, the information travels at c).  Its energy will be conserved in the form of em radiation which adds to the 2 gammas (infact it could be included in the gammas itself).

So the actual field generated by the charges disappears with them.

Not immediately, however. Maybe the question should be referred to this field which disappears at speed c from the charges centre.

--
lightarrow

[opportunity]

(had an issue with posting.....this is the response to the above quote):


Would that theoretical construction you're proposing aim to alter the reference in view to make it more understandable? Sounds wonky but is theory here taking over fact?

[lightarrow]

The couple of charges, let's assume for simplicity they can be considered initially stationary in an inertial frame (difficult to define in a universe where only those charges exists, however  ) generate an electrostatic field in all space, which have its precise energy. The two charges are sources of this field.

After the charges have annihilated,  that field disappears too (not immediately of course, the information travels at c).  Its energy will be conserved in the form of em radiation which adds to the 2 gammas (infact it could be included in the gammas itself).

So the actual field generated by the charges disappears with them.

Not immediately, however. Maybe the question should be referred to this field which disappears at speed c from the charges centre.

--
lightarrow

Any mechanism whereby the field could be measured ? 

With another charge 
When you study in a (good)  physics text what is an electrostatic field, you find a phrase like: "... the force on a test charge q per unit of that charge, providing q is so small not to perturb the charge distribution which is source of that force". 

But if the (initial) charge distribution is made only of a couple e⁺ e^- and the test charge is close to them, the measurement's error will be high. Anyway it shouldn't be a big problem, if we only want to reveal detect this field.

Is there such a  (theoretical) thing as a measurement that is not made at the macro level?

I don't think so, at least at the current state of knowledge/technology; but again it doesn't seem to me a big problem: a measurement's apparatus can amplify a microscopic system like a single particle.

Might it help if there were more than two charges (not practically but theoretically)  and  can an electron field

What do you mean with "electron field"? I ask because it exists in QFT, but I'm not sure you are talking about this here, maybe you mean "electric field generated by the charges".

  be detected or measured by  sensors that are not themselves electrically charged ?

If with "not electrically charged" you mean that the system is overall neutral but it can have charges spatially separated (as in a capacitor or an electret or a simple dipole) then the answer is yes: the field can be detected and measured: your dipole will feel a torque if immersed in an external field which is not parallel to its axis.

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lightarrow

[geordief]

What do you mean with "electron field"? I ask because it exists in QFT, but I'm not sure you are talking about this here, maybe you mean "electric field generated by the charges".

  be detected or measured by  sensors that are not themselves electrically charged ?

If with "not electrically charged" you mean that the system is overall neutral but it can have charges spatially separated (as in a capacitor or an electret or a simple dipole) then the answer is yes: the field can be detected and measured: your dipole will feel a torque if immersed in an external field which is not parallel to its axis.

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lightarrow

I was wrong on two counts.

One, the term "electron field" is very new to me and I applied it (perhaps fortuitously correctly) to a field produced by a single electron that I thought was appropriate here.

Secondly I should have described my potential sensors as "conductive" rather than "charged".

Apologies :-(

[Colin2B]

I was wrong on two counts.

One, the term "electron field" is very new to me and I applied it (perhaps fortuitously correctly) to a field produced by a single electron that I thought was appropriate here.

The term electron field is a valid one, as explained by lightarrow, but it depends how you are using it.
In QFT it describes the field indicating the presence and motion of an electron. The electron is described as a wave or quanta in this field - what’s called a Class 1 wave which does not move at a fixed speed.
However, are you really talking about the field due to the charge of the electron?
You don’t seem to have said which in your reply, but i assume it is the latter.
Both are valid.

[geordief]

I was wrong on two counts.

One, the term "electron field" is very new to me and I applied it (perhaps fortuitously correctly) to a field produced by a single electron that I thought was appropriate here.

The term electron field is a valid one, as explained by lightarrow, but it depends how you are using it.
In QFT it describes the field indicating the presence and motion of an electron. The electron is described as a wave or quanta in this field - what’s called a Class 1 wave which does not move at a fixed speed.
However, are you really talking about the field due to the charge of the electron?
You don’t seem to have said which in your reply, but i assume it is the latter.

Yes ,I was thinking of  a field associated (correct term?) with a single electron.

As I cannot see how the setup in the OP  can even be  a valid (does it need to be valid?) thought experiment, can  that objection be circumvented by  taking  the universal field   (I understand this exists)
and subtracting its elements  bit  by bit until one ends up with  just the 2 components in the OP?

 A mathematical result which I cannot say  would describe any actual  reality   but perhaps it might if it applied as an approximation to  the behaviour of a positron -- electron system viewed in extreme isolation.

Btw I have no idea how  other subatomic particles  might come into the picture. Are both the electron and the positron  completely elementary or does their interaction produce  other particles when the distance between them  is small enough? (before they actually self annihilate? Could  the annihilation be process perhaps rather than a single event?)

[opportunity]

With energy annihilation, as for instance to resolve Dirac's postulate, does field annihilation propose a source?

[jeffreyH (OP)]

@lightarrow hadn't noticed you around for a while. Welcome back.

[lightarrow]

Would that theoretical construction you're proposing aim to alter the reference

It's not an "alteration": I have just specified (simple) initial conditions; the OP didn't specify them.

in view to make it more understandable?

The fact I used simple initial conditions is certainly in view of that.   

Sounds wonky but is theory here taking over fact?

Well, if we are still talking of a universe with ONLY two charges and nothing else, it's not simply theory, it's plain phylosophy   

But if we want to talk about something with some physical meaning and admit the existence of a little more than two charges only, i.e. at least a detector and a physicist  then the above simplification is acceptable.

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lightarrow

[lightarrow]

@lightarrow hadn't noticed you around for a while. Welcome back.

Thank you.
Yes, I have been away for a couple of years, too busy.

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lightarrow