Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 14/02/2018 23:11:30

Title: Does a field require a source?
Post by: jeffreyH on 14/02/2018 23:11:30
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?
Title: Re: Does a field require a source?
Post by: Bill S on 14/02/2018 23:37:22
This assumes that the electron and positron are the source of the field.  Could you not reason that they were simply disturbances in a pre-existing field?

This has a ring of familiarity about it.  On the subject of the source of a field, I think I recall your saying that the field could just exist - that's the way it is. 
Title: Re: Does a field require a source?
Post by: Bill S on 15/02/2018 00:17:42
Jeffrey; I found the quote, and thought I should include it here, in case I had misrepresented it.

Re: Is it possible to build a gravity shield?
« Reply #32 on: 06/02/2018 20:54:06 »
You could ask where does the energy of the source come from? It is there in the form of mass, some of which derives from the Higgs field and the rest from binding energy. This is neglecting electrons. The point is it persists with no apparent source apart from itself. Why should the field be any different? The field has a potential value which only becomes energy when it interacts with particles. It also persists and has no apparent source other than itself. That is just the way it is.
Title: Re: Does a field require a source?
Post by: wolfekeeper on 15/02/2018 00:36:16
Photons. Classical electromagnetism is what you get in the largescale limit when you have charged particles that emit QM photons that travel at the speed of light.

Whether photons have independent existence when they can't hit anything because there's nothing to hit, I will demur on, unless anyone can find me a universe with no charged particles in it. But the standard answer is that the energy is carried away in the form of photons.
Title: Re: Does a field require a source?
Post by: jeffreyH on 15/02/2018 06:08:26
@Bill S I ask the question to get opinions. Fields are not straightforward when you start thinking about them in any depth.
Title: Re: Does a field require a source?
Post by: opportunity on 15/02/2018 07:15:15
It's a really good question.

If we consider the big bang, no, nothing existed before the field.

Yet if we don't consider the big bang and rely on a potential steady state model, then electron shell jumping, and so on, is responsible, thus an atom. Here now we're talking about the chicken and the egg.
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 10:01:00
This assumes that the electron and positron are the source of the field.  Could you not reason that they were simply disturbances in a pre-existing field?
We need to separate the effect of a field from cause.
Simple examples:
A wind field gives the wind vectors - direction and intensity - at any point in spacetime, but it doesn’t give information about cause eg earth heating, air movements, depressions, cyclones etc.
A temperature field can be mapped for a room, lets say it is an even 20C. So if we carry a candle through that room we could describe it as a disturbance of the temperature field, without describing the cause.
However, eg a wind field shows air movements and can lead us to draw conclusions about how the weather works and what the causes might be, particularly if we combine it with pressure field, temperature field, rain field etc.
Title: Re: Does a field require a source?
Post by: opportunity on 15/02/2018 10:33:18
Separating the field from the cause is grand scale....it proposes new time-events distinct from what we understand of relativity. Like, something can just happen in time despite spatial relativistic conditions.

Either the field is separate from the cause or the cause is something we can't properly link with the field.
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 10:43:00
Separating the field from the cause is grand scale....it proposes new time-events distinct from what we understand of relativity. Like, something can just happen in time despite spatial relativistic conditions.
No
Title: Re: Does a field require a source?
Post by: opportunity on 15/02/2018 10:45:39
692e7f2bbaf93d7db0dd84304f3df3c2.gifso why is not quantum entanglement explained in the big bang idea?

I'm thinking we're not there yet?
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 10:58:38
What’s that got to do with the question?
Big bang is a top level description of a series of events and processes, it doesn’t have to cover everything. Similarly, so-called theories of everything never describe everything, eg why did i put on white socks this morning, all work within a defined limited framework.

A field is just a description of effects, it doesnt have to describe the causes. We can get confused because of our familiarity with some fields where causes seem more obvious to us.
Title: Re: Does a field require a source?
Post by: geordief on 15/02/2018 11:03:28
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?
How is the source "gone" ? By definition the source  is located "at the source"  and only needs to exist/have existed  at that point (in spacetime )

It would be a different question if you  tried to create a field without a source.
Title: Re: Does a field require a source?
Post by: opportunity on 15/02/2018 11:56:57
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?
How is the source "gone" ? By definition the source  is located "at the source"  and only needs to exist/have existed  at that point (in spacetime )

It would be a different question if you  tried to create a field without a source.


Has a field ever been created without a source?

Has a source ever been proven without a field?

These are basic events that point to what grand scale?

If we can focus on something that doesn't add up, maybe propose something.....
Title: Re: Does a field require a source?
Post by: jeffreyH on 15/02/2018 12:26:39
OK. Let's think about a road that is stationary with respect to us. This is our field. Cars that move along the road can only move at one set constant speed. We can have the road moving with respect to us. However from our point of view the cars still move at the same speed. The cars of course represent photons. This means that if the field moves its motion has no effect on the velocity of the cars. However, if the field is static this issue never arises. The problem with this is it is like an aether solution.
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 12:39:48
Has a field ever been created without a source?
How would we ever know?

Has a source ever been proven without a field?
For anything that creates an effect you can define a field. So logically, no.

These are basic events that point to what grand scale?
What do you mean by grand scale and why should a particular field point to it?

If we can focus on something that doesn't add up, maybe propose something.....
It would be useful first to focus on that which does add up, so we can understand it.

Let’s look at another example of a commonly understood field, a contour map.
This shows lines of equal height and the spacing between lines gives us a gradient. This is useful as it has a parallel with a gravitational field where gradient of equipotential gives us value of g.
If we look at the contour map of UK Lake District we would notice certain U shaped features and lakes blocked by ridges. The map tells us nothing about the source or cause of those features, but by studying the underlying geology and comparing it to other areas we can develop a theory of glaciation as the cause. However, those causes are not embedded in the field, nor are they any feature of it.
Similarly with a gravitational field. Newton was able to describe gravitation in his laws just using the properties of the field and without resorting to a root cause.
Fields are tools to help us describe various measurements, let’s not endow them with some sort of magic, but use them to aid our understanding.

EDIT: just noticed @jeffreyH posted while i was typing.

Yes Jeff, take a contour map. What it represents is a field of heights, because it is locked to a particular location it moves with the earth, so relative to us it is stationary.
Yes, em and photon field are interesting in terms of their relativity effects.
Title: Re: Does a field require a source?
Post by: geordief on 15/02/2018 12:49:27
OK. Let's think about a road that is stationary with respect to us. This is our field. Cars that move along the road can only move at one set constant speed. We can have the road moving with respect to us. However from our point of view the cars still move at the same speed. The cars of course represent photons. This means that if the field moves ** its motion has no effect on the velocity of the cars. However, if the field is static this issue never arises. The problem with this is it is like an aether solution.

Do fields "move" ? If there are only multiple  measurements of different organized  locations wrt an  observer then I don't see how  they (the field) moves  except  in a  specific mathematical way (fields are not rigid either ,are they?).

I was wondering  elsewhere  if it was ever possible to take measurements of a system  as a system and not as  an aggregation of  multiple measurements within the system (and I  couldn't find a way to do it even though I felt intuitively that any system could /should be able to be measured as a whole)

So I decided that all systems "bleed into "other systems .....

** I bolded your quote
Title: Re: Does a field require a source?
Post by: opportunity on 15/02/2018 12:53:33
That's the problem with thinking there was, is, a point time of our ability to rationalise.

We can theorise, but can we replicate that?

Can we prove what we theorise?
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 14:46:33
We can theorise, but can we replicate that?

Can we prove what we theorise?
As you know, the essence of a scientific theory is that it both observable and replicable. It can make falsifiable - testable - predictions. We tend to call anything else a hypothesis.
So, no, it’s not provable.
Title: Re: Does a field require a source?
Post by: opportunity on 15/02/2018 14:51:54
We can theorise, but can we replicate that?

Can we prove what we theorise?
As you know, the essence of a scientific theory is that it both observable and replicable. It can make falsifiable - testable - predictions. We tend to call anything else a hypothesis.
So, no, it’s not provable.


We know why we need to know than not. Otherwise we're just giving up.
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 17:22:39
We know why we need to know than not. Otherwise we're just giving up.
You can never know it, that’s just a fact of logic and scientific method.
You can disprove a theory, but you can’t prove it. You will never know whether it is the only explanation. You might have enough evidence to say that you are pretty certain, but knowing? No.
That’s why most scientists view theories as the best we have at the moment and are happy to modify if enough evidence comes forward, problem is many people think their flimsy ideas are enough to turn over well researched and validated theories.
Title: Re: Does a field require a source?
Post by: Bill S on 15/02/2018 19:48:36
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?
Title: Re: Does a field require a source?
Post by: jeffreyH on 15/02/2018 20:46:40
@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.
Title: Re: Does a field require a source?
Post by: jeffreyH on 15/02/2018 20:52:52
There is an interesting discussion elsewhere on the subject.
https://www.quora.com/What-is-the-electron-field-as-distinct-from-the-electromagnetic-field
Title: Re: Does a field require a source?
Post by: chiralSPO on 15/02/2018 20:56:53
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.).
Title: Re: Does a field require a source?
Post by: chiralSPO on 15/02/2018 20:58:26
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.
Title: Re: Does a field require a source?
Post by: geordief on 15/02/2018 22:15:32
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)
Title: Re: Does a field require a source?
Post by: Colin2B on 15/02/2018 23:04:47
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.
Title: Re: Does a field require a source?
Post by: lightarrow on 16/02/2018 08:31:13
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.

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lightarrow
Title: Re: Does a field require a source?
Post by: opportunity on 16/02/2018 09:21:44
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?
Title: Re: Does a field require a source?
Post by: geordief on 16/02/2018 11:23:32
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 ?
Title: Re: Does a field require a source?
Post by: opportunity on 16/02/2018 12:03:35
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


Title: Re: Does a field require a source?
Post by: opportunity on 16/02/2018 12:09:07
(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?
Title: Re: Does a field require a source?
Post by: lightarrow on 16/02/2018 17:09:43
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.
Quote

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.
Quote
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".
Quote
  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
Title: Re: Does a field require a source?
Post by: geordief on 16/02/2018 22:29:19
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".
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  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 :-(
Title: Re: Does a field require a source?
Post by: Colin2B on 17/02/2018 09:17:34
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.
Title: Re: Does a field require a source?
Post by: geordief on 17/02/2018 11:03:58
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?)
Title: Re: Does a field require a source?
Post by: opportunity on 17/02/2018 11:08:45
With energy annihilation, as for instance to resolve Dirac's postulate, does field annihilation propose a source?
Title: Re: Does a field require a source?
Post by: jeffreyH on 17/02/2018 13:44:30
@lightarrow hadn't noticed you around for a while. Welcome back.
Title: Re: Does a field require a source?
Post by: lightarrow on 17/02/2018 15:27:04
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.
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in view to make it more understandable?
The fact I used simple initial conditions is certainly in view of that.   
Quote
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
Title: Re: Does a field require a source?
Post by: lightarrow on 17/02/2018 15:35:59
@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
Title: Re: Does a field require a source?
Post by: lightarrow on 17/02/2018 18:34:15
Secondly I should have described my potential sensors as "conductive" rather than "charged".
Then that's not a problem too: a piece of dielectric material which has a charge separation (let's say a plastic or glass stick with a charge + at one end and a charge - at the other) or a simple molecular dipole (e.g. a water molecule) will rotate in an electric field which is not parallel to its axis.
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Apologies :-(
No problems at all...  :)

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lightarrow
Title: Re: Does a field require a source?
Post by: lightarrow on 17/02/2018 18:40:30
With energy annihilation, as for instance to resolve Dirac's postulate,
What do you mean with "Dirac's postulate"?
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  does field annihilation propose a source?
Sorry I can't understand what you mean here too.

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lightarrow
Title: Re: Does a field require a source?
Post by: Colin2B on 17/02/2018 22:27:10
as for instance to resolve Dirac's postulate,
Which postulate and what do you mean by resolve?
Title: Re: Does a field require a source?
Post by: Bill S on 18/02/2018 19:39:29
Quote from: Chiral
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.

You are saying, quite specifically, that a field (e.g. the electron field?) is the pre-existing entity – it needs no source.

If this is so, what meaning does it have to talk of the electron as the source of the field? 
Is that just sloppy terminology; or is the term "field" used in more than one sense; like "vacuum" or "nothing"?
Title: Re: Does a field require a source?
Post by: geordief on 18/02/2018 22:01:00
I think I understand a field to just be a mathematical object whereas the electron is physical in the sense it can be measured

You can't detect or measure a mathematical object ( an idea)

Does that make sense? Is it right?
Title: Re: Does a field require a source?
Post by: jeffreyH on 18/02/2018 22:32:55
The energy of a field exists. Otherwise we wouldn't have any forces. It isn't tangible. That does not mean that it is simply an abstract concept.
Title: Re: Does a field require a source?
Post by: petelamana on 18/02/2018 22:42:47
I confess that I have not read, or scanned all 40+ replies to this topic, so I am not sure if what I am about to proffer has already been so.  At any rate...

What about the force field on an electron caused by two nearby protons?  I believe the field strength is the vector sum of the two individual protons.  If so, then there wouldn't be any single source to the field.

I may be wrong, and if so, please tell me.  I strive to learn.
Title: Re: Does a field require a source?
Post by: lightarrow on 18/02/2018 22:50:23
Quote from: Chiral
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.
You are saying, quite specifically, that a field (e.g. the electron field?)
"electron field" is something else, let's call it with a better name: electric (or electromagnetic) field generated by the electron.
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 is the pre-existing entity – it needs no source.
The fact it needs a source doesn't mean it can't exists after being generated by it. You switch on a laser device: it generates a light beam; you switch off the device: the light beam keeps going towards its target.
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If this is so, what meaning does it have to talk of the electron as the source of the field?
The ancient romans created the Adrian wall; the wall is still there, but the ancient romans don't exists anymore   :)

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lightarrow
Title: Re: Does a field require a source?
Post by: geordief on 18/02/2018 23:40:43
The energy of a field exists. Otherwise we wouldn't have any forces. It isn't tangible. That does not mean that it is simply an abstract concept.
the field is not just model and  fit for scrap if superseded?

Title: Re: Does a field require a source?
Post by: lightarrow on 19/02/2018 16:05:55
The energy of a field exists. Otherwise we wouldn't have any forces. It isn't tangible. That does not mean that it is simply an abstract concept.
the field is not just model and  fit for scrap if superseded?
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?

--
lightarrow
Title: Re: Does a field require a source?
Post by: geordief on 19/02/2018 17:34:39
i
The energy of a field exists. Otherwise we wouldn't have any forces. It isn't tangible. That does not mean that it is simply an abstract concept.
the field is not just model and  fit for scrap if superseded?
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?

--
lightarrow
Can I rationalize that by saying (correctly I hope) that the source  of this effect (the source =the charges)  is not local but spread out in a wave form?

That might be word salad  as..... (well you can probably guess :-[  )
Title: Re: Does a field require a source?
Post by: Bill S on 20/02/2018 20:19:45
Quote from: lightarrow
The fact it needs a source doesn't mean it can't exists after being generated by it. You switch on a laser device: it generates a light beam; you switch off the device: the light beam keeps going towards its target.

Sorry, this makes no sense to me. 

“You switch on a laser device: it generates a light beam”.  The device is the source of the beam.
“you switch off the device: the light beam keeps going..”.  Of course, but the device is still the source of the beam!

Quote
The ancient romans created the Adrian wall; the wall is still there, but the ancient romans don't exists anymore.

Surely, the ancient Romans remain the “source” of Hadrian’s Wall; even if they are no longer with us.   

Title: Re: Does a field require a source?
Post by: Bill S on 20/02/2018 20:36:48
Quote from: Bill
Is the field something that exists in its own right, irrespective of whether or not any electron is “active” within it?

I’m going to attempt an answer to my own question.

The term “electron field” is used in two different ways:

1) A field which exists, and has probably existed since the BB, or very soon after.  The electron is not the source of this field; it is a quantum of the field.

2) An electron is a disturbance in the field described.  This disturbance “influences” the field.  That influence is what we identify as a field, of which the electron is the source. 

Does that make any sense?


Title: Re: Does a field require a source?
Post by: jeffreyH on 20/02/2018 21:04:28
Quote from: Bill
Is the field something that exists in its own right, irrespective of whether or not any electron is “active” within it?

I’m going to attempt an answer to my own question.

The term “electron field” is used in two different ways:

1) A field which exists, and has probably existed since the BB, or very soon after.  The electron is not the source of this field; it is a quantum of the field.

2) An electron is a disturbance in the field described.  This disturbance “influences” the field.  That influence is what we identify as a field, of which the electron is the source. 

Does that make any sense?




It makes sense to me.
Title: Re: Does a field require a source?
Post by: Colin2B on 20/02/2018 23:08:11
The term “electron field” is used in two different ways:

1) A field which exists, and has probably existed since the BB, or very soon after.  The electron is not the source of this field; it is a quantum of the field.

2) An electron is a disturbance in the field described.  This disturbance “influences” the field.  That influence is what we identify as a field, of which the electron is the source. 

Does that make any sense?
I wouldn’t make that distinction. I would say there is an electron field, the electron is a quantum of that field and a disturbance of the field. It isn’t so much that the disturbance influences the field, as that disturbance is what we detect and call an electron. There are other fields which the electron influences such as the electromagnetic field.
Does that make sense?
Title: Re: Does a field require a source?
Post by: geordief on 20/02/2018 23:19:08

I wouldn’t make that distinction. I would say there is an electron field, the electron is a quantum of that field and a disturbance of the field. It isn’t so much that the disturbance influences the field, as that disturbance is what we detect and call an electron. There are other fields which the electron influences such as the electromagnetic field.
Does that make sense?

What causes disturbances in the electron field that you say we call electrons when detected ?

Does one disturbance cause another?
Title: Re: Does a field require a source?
Post by: Colin2B on 20/02/2018 23:54:07
What causes disturbances in the electron field that you say we call electrons when detected ?

Does one disturbance cause another?
QFM is a descriptive and predictive tool, it doesn’t assign causes, in the same way that Newton’s law of gravity describes the interaction of 2 masses but says nothing about the cause.

Clearly an electron can ‘cause’ an electrostatic field by its presence, but what causes the charge that causes the field? What is the root cause?
I’m not offering answers, i’m just trying to explain how the term field is used. As @chiralSPO said “It's a sort of accounting or mapping tool that we can use to describe the universe”.
Title: Re: Does a field require a source?
Post by: geordief on 21/02/2018 02:03:47
As @chiralSPO said “It's a sort of accounting or mapping tool that we can use to describe the universe”.
Yes ,I have accepted that definition (have come across it elsewhere) but I must have/seem to have  taken my eye off the ball and regressed into attributing a physicality to the field.

If I think of an electron as being extensive  rather than local  does that mean that its associated field (as we would measure ** it ) is correspondingly  extensive although still centred at the same point? (perhaps in practice we wouldn't notice the difference and the field would have the same form as if the electron was actually a localized object)


**the field is the measurements, I keep trying to tell myself ;)


Title: Re: Does a field require a source?
Post by: opportunity on 21/02/2018 08:10:03
as for instance to resolve Dirac's postulate,
Which postulate and what do you mean by resolve?

Apologies for not responding sooner (and I think this also addresses light arrow's question).

Dirac knew that with an electron, as it speeds up under the influence of a field that the speed itself represents a feature that puts the normal relativistic energy of the system in focus above  the normal energy of the field and that relativistic energy environment in play, and thus his postulate was that there must be a sea of negative energy to keep the idea of energy creation at bay. It was then suggested that associated with elementary particles were anti-particles to accommodate for this, and thus the idea of particle annihilation. Whether that addresses negative energy is another story, yet "here" "purposefully" and as a proven idea anti-particles can annihilate standard elementary particles and thus aim to resolve the Dirac "sea" issue. Of what is being suggested in the context of this topic is that a particle, something substantiative, is directly responsible for the idea of energy and thus a field, whether creation or destruction.
Title: Re: Does a field require a source?
Post by: Colin2B on 21/02/2018 08:43:40
his postulate was that there must be a sea of negative energy to keep the idea of energy creation at bay. ......yet "here" "purposefully" and as a proven idea anti-particles can annihilate standard elementary particles and thus aim to resolve the Dirac "sea" issue. Of what is being suggested in the context of this topic is that a particle, something substantiative, is directly responsible for the idea of energy and thus a field, whether creation or destruction.
OK, I understand, it’s just that he has 10 other postulates.
The Dirac Sea idea was that there is a sea of particles over all space and antiparticles are holes in this sea. He originally thought the hole was a proton, but the discovery of the positron gave a candidate.
This thread won’t resolve that as the concept has been overtaken in particle physics by the current use of fields, where a particle, or wave quanta, is substantive but is not held responsible ‘for the idea of energy’.
Certainly the quanta, and thus the field, do transfer energy.
Title: Re: Does a field require a source?
Post by: opportunity on 21/02/2018 08:52:09
I see your point.

Quanta though as the concept of packaged light released from electron jumping can be thought of as a wave/field and a particle. It's only the notion of the Plank scale that gives it "particle" notoriety. I completely respect that, I can't not. Which.....beckons my bias (another post somewhere), but I won't let that interfere here.
Title: Re: Does a field require a source?
Post by: Colin2B on 21/02/2018 08:55:39
It's only the notion of the Plank scale that gives it "particle" notoriety.
Well, more the fact that the quanta carries momentum. Which can be quantfied with the Planck constant, but that’s more of a conversion factor.
Title: Re: Does a field require a source
Post by: opportunity on 21/02/2018 09:01:10
Yes. I have an idea (theory) though about sub-elementary particle space that "provides" quanta with momentum, hence my bias, yet it re-proposes the whole idea of the Plank scale....which proposes a long discussion, yet I would be a fool if I didn't first consider how everything is thought to work.
Title: Re: Does a field require a source?
Post by: lightarrow on 21/02/2018 15:42:22
i
The energy of a field exists. Otherwise we wouldn't have any forces. It isn't tangible. That does not mean that it is simply an abstract concept.
the field is not just model and  fit for scrap if superseded?
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?

--
lightarrow
Can I rationalize that by saying (correctly I hope) that the source  of this effect (the source =the charges)  is not local but spread out in a wave form?

That might be word salad  as..... (well you can probably guess :-[  )
No, the fact sources are spread out or not doesn't change the properties of the electrostatic/electromagnetic field outside of them; in case it changes the electrostatic's field energy inside the charge. This is an old problem, studied by Abraham - Lorentz, Dirac, Feynman and others and partially solved by Quantun Electrodynamics; look for electron's electromagnetic mass and the 4/3 problem, e. g.  https://en.m.wikipedia.org/wiki/Electromagnetic_mass
--
lightarrow
Title: Re: Does a field require a source?
Post by: Graccer on 21/02/2018 15:43:31
It is cool!
Title: Re: Does a field require a source?
Post by: lightarrow on 21/02/2018 15:57:28
Quote from: lightarrow
The fact it needs a source doesn't mean it can't exists after being generated by it. You switch on a laser device: it generates a light beam; you switch off the device: the light beam keeps going towards its target.
Sorry, this makes no sense to me. 

“You switch on a laser device: it generates a light beam”.  The device is the source of the beam.
“you switch off the device: the light beam keeps going..”.  Of course, but the device is still the source of the beam!
But the device is switched off. If the electric current or other source of energy is not there any longer, you can destroy the device, vaporize it, and nothing changes: no field is generated.

The actual source of the field are the electric current's charges in the specific potential inside the light emitting diode (if it's a laser device of this kind). When you switches it off it's just as a piece of inert stone, for what concerns the laser beam, that is, the field.
Quote
Quote
The ancient romans created the Adrian wall; the wall is still there, but the ancient romans don't exists anymore.
Surely, the ancient Romans remain the “source” of Hadrian’s Wall; even if they are no longer with us.   
In this case the ancient romans are the electric's current charges: once switched off, the laser beam remains (if you shooted it in the void, travelling in outer space) but the electric current which generated the field is gone.

--
lightarrow
Title: Re: Does a field require a source?
Post by: Bill S on 21/02/2018 17:50:17
Lightarrow. We seem to be in complete agreement on many points of our reasoning, but, somehow, we end up in different places. 

I’m going to try to clarify my position:-

A = cause.  B = effect.

A causes B, which is a continuing effect through time.

A is destroyed; giving rise to two lines of reasoning:

One might say that B no longer has a cause. 

The other might say that, although A no longer exists (at least, not in its original form), it remains the cause of B, and will always remain so.

I accept that each of these lines of reasoning is accurate, within its particular context; but each is the answer to a different question.

The second line of reasoning is the one I was following.
Title: Re: Does a field require a source?
Post by: Bill S on 21/02/2018 19:30:11
Could be its silly to ask another question before the previous one has been addressed, but I'm slipping this one in before I forget about it.  Fixation amnesia, whatever that is.  :)

Quote from: Lightarrow
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?

My understanding is that the electrostatic field must carry energy, therefore, according to E=mc2 it must have “mass”.  However, would this equate to rest mass, or would it be better described in terms of inertia?
Title: Re: Does a field require a source?
Post by: lightarrow on 21/02/2018 23:12:04
Could be its silly to ask another question before the previous one has been addressed, but I'm slipping this one in before I forget about it.  Fixation amnesia, whatever that is.  :)
  :)
Quote

Quote from: Lightarrow
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?
My understanding is that the electrostatic field must carry energy, therefore, according to E=mc2 it must have “mass”.  However, would this equate to rest mass, or would it be better described in terms of inertia?
Good question.
The first you wrote.
As you know, the more general equation is not E=mc2 but is:
E2 = (mc2)2 + (cp)2
where p is the system's total momentum (vector).
If the electric field is stationary, and only in this case, its momentum is zero, so the equation reduces to the much known you wrote.

However I don't like to call m "rest" mass because nowadays it's simply called "mass" (the so called "relativistic mass" is an  obsolete term and concept).

--
lightarrow   
Title: Re: Does a field require a source?
Post by: Colin2B on 21/02/2018 23:47:12

As you know, the more general equation is not E=mc2 but is:
E2 = (mc2)2 + (cp)2
@Bill S - as @lightarrow points out it’s important to bear in mind the full formula. Another example is the photon, having 0 mass so the first term in the equation is 0, leaving only the momentum contribution.
Title: Re: Does a field require a source?
Post by: Bill S on 22/02/2018 02:09:48
Quote from: Lightarrow
However I don't like to call m "rest" mass because nowadays it's simply called "mass" (the so called "relativistic mass" is an  obsolete term and concept).

How far off the mark would I be if I interpreted this as saying: "rest" mass = total mass; "relativistic mass" = inertia? 

Title: Re: Does a field require a source?
Post by: Bill S on 22/02/2018 02:18:30
Quote from: Lightarrow
If the electric field is stationary, and only in this case, its momentum is zero,

Quote
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?

Isn't the electrostatic field always stationary?
Title: Re: Does a field require a source?
Post by: lightarrow on 22/02/2018 18:49:35
Quote from: Lightarrow
However I don't like to call m "rest" mass because nowadays it's simply called "mass" (the so called "relativistic mass" is an  obsolete term and concept).
How far off the mark would I be if I interpreted this as saying: "rest" mass = total mass;
Ok, unless you give particular interpretations to "total" mass. Better to say "system" mass.
Quote
  "relativistic mass" = inertia? 
Do you like a concept of inertia which is different along different directions? Along the direction of the body's velocity you have a value of inertia, that is: γ3m, where γ is the gamma Lorentz factor:
γ = 1/sqrt[1-(v/c)2];
in the ortogonal direction you have a different value, that is: γm.
Conclusion: better not to talk about relativistic mass at all.
IMHO.

--
lightarrow
Title: Re: Does a field require a source?
Post by: Bill S on 23/02/2018 21:58:03
Quote
Conclusion: better not to talk about relativistic mass at all.

I expressed my intended meaning badly.  By "relativistic mass" = inertia, I meant something like: If you meet the term relativistic mass, it is better to think of it as inertia.

Would that be better?
Title: Re: Does a field require a source?
Post by: alancalverd on 24/02/2018 00:22:47
Sorry to pick this one up so late.

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?
What field? An electromagnetic wave is selfpropagating. Nothing to do with an external field.
Title: Re: Does a field require a source?
Post by: opportunity on 24/02/2018 02:22:22
This subject is moot. It is counterproductive to a theory of everything. A theory of everything would require everything to require everything.

Of course if reality just comes and goes, anything and everything requires nothing and vice versa.
Title: Re: Does a field require a source?
Post by: lightarrow on 24/02/2018 13:25:26
Quote
Conclusion: better not to talk about relativistic mass at all.
I expressed my intended meaning badly.  By "relativistic mass" = inertia, I meant something like: If you meet the term relativistic mass, it is better to think of it as inertia.
Would that be better?
IMHO it would be better "energy" (in the sense "total energy") since relativistic mass is just energy/c2.
Concerning "inertia", not, for what I wrote: you should remember that you have *two* different inertias simultaneously in the same body:
1) tangential inertia = γ3m
2) transversal inertia = γm
where m is the body's (rest/proper/invariant) mass.

If you are sure to remember that, ok, but when you talk of "inertia" you always have to specify *which of the two*

--
lightarrow
Title: Re: Does a field require a source?
Post by: geordief on 24/02/2018 13:54:15
Sorry to pick this one up so late.

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?
What field? An electromagnetic wave is selfpropagating. Nothing to do with an external field.
Yes ,can we talk about fields without specifying?

Any detail by the way on the way em  fields "self propagate"?

Is any energy involved ?

Do the 2 constituent waves interact with each other continuously?  (I have only a very sketchy understanding of what might be going on)

Unless I am digressing a lot.....
Title: Re: Does a field require a source?
Post by: Colin2B on 24/02/2018 18:21:25
Yes ,can we talk about fields without specifying?
We can but only in general terms.
Any detail by the way on the way em  fields "self propagate"?
@alancalverd  didn’t say the em field propagates, he said the em wave propagates. The field does not propagate, as we’ve said before a field is a set of measurements over time and space, a description. Try not to make it more than it is.
Is any energy involved ?
Yes, the wave transfers energy
Do the 2 constituent waves interact with each other continuously?  (I have only a very sketchy understanding of what might be going on)
You have to be much more specific about which waves and what circumstances.
Title: Re: Does a field require a source?
Post by: geordief on 25/02/2018 02:27:32
Any detail by the way on the way em  fields "self propagate"?
@alancalverd  didn’t say the em field propagates, he said the em wave propagates. The field does not propagate, as we’ve said before a field is a set of measurements over time and space, a description. Try not to make it more than it is.
Is any energy involved ?
Yes, the wave transfers energy
Do the 2 constituent waves interact with each other continuously?  (I have only a very sketchy understanding of what might be going on)
You have to be much more specific about which waves and what circumstances.


Yes I apologize (again  :-[  )for saying the em field propagates.I have a mental block with the words "wave" and "field" and keep confusing them (and you)

Still interested to learn in a little more detail possibly  , how this "self propagating" mechanism  of the em wave works .

Same question : is any energy involved(between the two component waves)

? The electrical wave seems to "feed" the magnetic wave ???

Any detail on that ?
Title: Re: Does a field require a source?
Post by: Bill S on 25/02/2018 14:19:30
Quote from: Colin #78
…a field is a set of measurements over time and space, a description. Try not to make it more than it is.


I’m trying not to make it more than it is, but I'm struggling a bit.

Quote from: Chiral
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.

Is a field a physical thing?
If it is just a set of measurements, what does it measure?
Title: Re: Does a field require a source?
Post by: geordief on 25/02/2018 14:39:57


Is a field a physical thing?
If it is just a set of measurements, what does it measure?

I am trying to work through his too.

It measures potential events?Models them ...

I keep telling myself it is not a thing.

I have tried to rationalize this by saying the "origin" of the field" is extensive**but this interpretation (elsewhere I think) was not accepted I think.

** again I think I was confusing "wave" and "field" (cannot yet get to "ground zero" with my terms...)
Title: Re: Does a field require a source?
Post by: Bill S on 25/02/2018 14:47:16
Could be, Evan_au adds to this discussion with this extract from  Does dark matter and the graviton exist?

Quote from: Evan #3
I would express is as: gravity is created by the presence of mass.

A disturbance in the gravitational field is carried by gravitons. Such a disturbance would be caused by acceleration of large masses, like two black holes merging.

Could this be interpreted as saying that gravity is a force “created" by the presence of mass in spacetime, and that the gravitational field is just the totality of the possible measurements that could be applied to that force?

I know that will raise other questions, but one step at a time.
Title: Re: Does a field require a source?
Post by: geordief on 25/02/2018 15:22:48
Could be, Evan_au adds to this discussion with this extract from  Does dark matter and the graviton exist?

Quote from: Evan #3
I would express is as: gravity is created by the presence of mass.

A disturbance in the gravitational field is carried by gravitons. Such a disturbance would be caused by acceleration of large masses, like two black holes merging.

Could this be interpreted as saying that gravity is a force “created" by the presence of mass in spacetime, and that the gravitational field is just the totality of the possible measurements that could be applied to that force?

I know that will raise other questions, but one step at a time.


If mass tells spacetime how to curve can that be described as "forcing" the field?

I don't think that is force as f=ma , but  it seems to be responsible for a change in the direction of movement of a test object in  the field (all the test objects presumably are identical in some way-same velocity perhaps**)

**if light was slowed to the speed of a feather it would fall at the same rate in the Earth's gravity field,wouldn't it ?
Title: Re: Does a field require a source?
Post by: Colin2B on 25/02/2018 16:37:33
If it is just a set of measurements, what does it measure?
Depends. A temperature field measures temperature at different points in spacetime, a wind field the wind vectors at different points in spacetime. Both temperature and wind are physical things. Fields are considered to be objects, but remember we talk about objects in programming languages.

the gravitational field is just the totality of the possible measurements that could be applied to that force?
As you know to measure a gravitational field you use a small test mass and measure the force on it, if there are more than one big mass nearby then yes the resultant field at that point is the vector sum of the individual forces, etc.
Title: Re: Does a field require a source?
Post by: Bill S on 25/02/2018 17:12:53
Quote from: Colin
Depends. A temperature field measures temperature at different points in spacetime, a wind field the wind vectors at different points in spacetime. Both temperature and wind are physical things. Fields are considered to be objects, but remember we talk about objects in programming languages.

Let’s start with the temperature field.

Temperature is a measure of heat.
Heat is the physical manifestation of the kinetic energy of atoms/molecules in a system.
Thus, temperature is a measure of the average kinetic energy of the particles in a system.

This seems to suggest that particles, energy and motion are prerequisites for the definition, or even the existence, of a field.   

I’m trying to equate this with the idea that a particle is a disturbance in a (pre-existing) field.   
Title: Re: Does a field require a source?
Post by: Bill S on 25/02/2018 17:19:50
Quote from: Geordief
if light was slowed to the speed of a feather it would fall at the same rate in the Earth's gravity field,wouldn't it

Are you confusing the speed of light with the deflection of a beam of light by gravity?
Title: Re: Does a field require a source?
Post by: alancalverd on 25/02/2018 18:08:34
In physics, a field is something that is defined (by a number or a vector) at every point in space. Nothing more, nothing less.

As we like effects to have causes, we expect to find a source for any field.
Title: Re: Does a field require a source?
Post by: geordief on 25/02/2018 20:15:18

Are you confusing the speed of light with the deflection of a beam of light by gravity?
Don't think so.I was just trying to show that light fell into a gravity well in the same way as any other object.

It only seems different because its speed is so great.
Title: Re: Does a field require a source?
Post by: lightarrow on 25/02/2018 21:13:38
In physics, a field is something that is defined (by a number or a vector) at every point in space. Nothing more, nothing less.
You are talking of the mathematical definition only, here. But in physics a field has a physical meaning too.
Did you read my post where I write that even a static field has energy and a mass too?
Also, I don't get why you say that a field don't propagate.
It's true I haven't attended the forum for a couple of years, but it sounds strange to me that physics has changed so much meanwhile  :)

--
lightarrow
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 06:33:50
Sorry to pick this one up so late.

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?
What field? An electromagnetic wave is selfpropagating. Nothing to do with an external field.


Although this is marked as "best answer", I'd like to do a post-mortem on the great reply.

An electromagentic field propogates of it's own accord in the absence of a source. That's a frame of reference though. We know electromagnetic fields are central to electrons jumping through electron shells, together with atomic decay......lets just say "atomic dynamics". The idea of an external field is not a consideration.
Title: Re: Does a field require a source?
Post by: Colin2B on 26/02/2018 08:52:41
An electromagentic field propogates of it's own accord in the absence of a source.
Could you please explain, with example, why you think this is the case.
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 09:03:32
An electromagentic field propogates of it's own accord in the absence of a source.
Could you please explain, with example, why you think this is the case.

Of course, as a frame of reference as I put?

It's like witnessing an event without cause or effect, you just take photos.
Title: Re: Does a field require a source?
Post by: Colin2B on 26/02/2018 10:21:43
An electromagentic field propogates of it's own accord in the absence of a source.
Could you please explain, with example, why you think this is the case.
Of course, as a frame of reference as I put?
This really isn't an answer to my question.
You said "An electromagentic field propogates of it's own accord in the absence of a source"
Physics says it's the electromagentic wave which propagates.

Could you explain why you think the field propagates.
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 10:25:34
An electromagentic field propogates of it's own accord in the absence of a source.
Could you please explain, with example, why you think this is the case.
Of course, as a frame of reference as I put?
This really isn't an answer to my question.
You said "An electromagentic field propogates of it's own accord in the absence of a source"
Physics says it's the electromagentic wave which propagates.

Could you explain why you think the field propagates.

The field propagates from a source in search of something, right? Why does a field propagate from an atom? Because it can? This is where "time" becomes bespoke to events in space.
Title: Re: Does a field require a source?
Post by: geordief on 26/02/2018 10:43:13
Are  waves the source of a Field ?

Is there a primordial field( set of potential events if we treat "field" as a mathematical term) ,created  as far back as we can know which successive wave events  alter and so appear  create new fields?
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 10:55:55
Are  waves the source of a Field ?

Is there a primordial field( set of potential events if we treat "field" as a mathematical term) ,created  as far back as we can know which successive wave events  alter and so appear  create new fields?

Waves are themselves not the source of a field. We ask the question, yet we can often question also if waves create gravitational events?......

Why not ask what creates an earthquake? Plate movement, right? Fire below "appears" to create that.......what causes that? Heat and pressure? Why not say gravity is a result of heat and pressure?
Title: Re: Does a field require a source?
Post by: geordief on 26/02/2018 11:31:22
Is it pointless trying to ask the source of a macro event? (so many inputs)

My "wave creates field"suggestion was that a quantum event such as the detection of a wave causes a change in the existing field.

"The field" exists as far back as we look but ongoing changes  occur all the time.

I am not sure if my pre-existing field idea would apply to all kinds of fields-I mainly have the gravity field in mind (and now the electro field)
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 11:45:12
Why not say gravity is the failure of every other field force?
Title: Re: Does a field require a source?
Post by: Colin2B on 26/02/2018 12:03:52
The field propagates from a source in search of something, right?
Wrong, a field is not searching for anything
Why not say gravity is the failure of every other field force?
Why say it. There is no reason to do so.


Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 12:06:12
The field propagates from a source in search of something, right?
Wrong, a field is not searching for anything
Why not say gravity is the failure of every other field force?
Why say it. There is no reason to do so.


So as opposed to a failure there's an "effect"?

Trying not to be esoteric, but, if we're failing to define the source, we have no clue for the outcome......?
Title: Re: Does a field require a source?
Post by: jeffreyH on 26/02/2018 12:42:42
Another question to keep things fresh. What is the source of the Higgs field?
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 12:59:53
It's created in theory.....as a (disputed) source one can only consider why. They made it, right?

The point you're making is moot.

Why not ask, "can we see the end of time"? That would be easier than suggesting a field is independent to the cause of it's phenomena. Does a field exist outside of time?
Title: Re: Does a field require a source?
Post by: geordief on 26/02/2018 13:45:58
Can we say that there is a comprehensive gravity field for the galaxy we are in?

In theory can we model this field in time?

If so can we model it backwards in time?

Can this process be applied to groups of galaxies as they reverse approach the Big Bang as it is theorized?

So is there an uninterrupted dynamic model from that period to "now"?

Is that when fields were first modelable and is  there a  "source"  to be found at that time period?
Title: Re: Does a field require a source?
Post by: Colin2B on 26/02/2018 15:15:30
Trying not to be esoteric, but, if we're failing to define the source, we have no clue for the outcome......?
Is that true?
Consider Newton, he did not find a source for gravity, other than ascribing it to an attraction of masses, but he very accurately described a series of outcomes. Science is the method of observing and then making predictions based on those observations, we don’t necessarily know the root cause.

Let’s go back to my original question to you:
You said "An electromagentic field propogates of it's own accord in the absence of a source"
Physics says it's the electromagentic wave which propagates.

Could you explain why you think the field propagates.
Your answer doesn't address this question:

The field propagates from a source in search of something, right? Why does a field propagate from an atom? Because it can? This is where "time" becomes bespoke to events in space.
Let me explain why I have a problem with your response.
Take the example of fields which we are very familiar with. Sound waves in air, waves on water. We do not talk about the air pressure, or the water amplitude propagating, nor do we talk about the air or water propagating, we talk about the wave propagating.
OK, these are examples of non-relativistic fields which require a medium, but we apply the same terminology to relativistic fields eg EM field where we have not detected a medium.
So we say that the light wave (quantum = photon) propagates through the em field. That field is a set of measurements of electric and magnetic field strengths.

So a field does not propagate from a source in search of anything.
“Why does a field propagate from an atom? Because it can?” - no, the wave propagates from an atom because an electron changed state and energy was released as an oscillation that we detect as a wave.
“This is where "time" becomes bespoke to events in space.” - haven’t a clue what that means, sounds like pseudoscience or word salad.

In new theories anything goes, but in this section we need to be very clear and precise in what we are saying otherwise we run the risk of creating what (in another thread) you have termed fake news.
Title: Re: Does a field require a source?
Post by: jeffreyH on 26/02/2018 17:23:53
A little light reading. The Higgs field and the big bang.
https://home.cern/topics/higgs-boson/origins-brout-englert-higgs-mechanism
Title: Re: Does a field require a source?
Post by: Bill S on 26/02/2018 19:27:21
Quote from: Alan
In physics, a field is something that is defined (by a number or a vector) at every point in space. Nothing more, nothing less.

Alan this will probably be sorted out in your response to Lightarrow (#89}, but when you say “a field is something”, I wonder what form that “something” takes. 

Is it a physical thing in which waves/particles propagate, or is it just a measurement?
If it is a measurement, what is the “something” it measures?

There have been times when I have, justifiable, been charged with nit-picking, but such is not the case here, I’m trying to reconcile in my mind two opinions that seem to be incompatible. 

So far, I suspect that "field" may be being used in more than one sense.     
Title: Re: Does a field require a source?
Post by: opportunity on 26/02/2018 22:10:58
Trying not to be esoteric, but, if we're failing to define the source, we have no clue for the outcome......?
Is that true?
Consider Newton, he did not find a source for gravity, other than ascribing it to an attraction of masses, but he very accurately described a series of outcomes. Science is the method of observing and then making predictions based on those observations, we don’t necessarily know the root cause.

Let’s go back to my original question to you:
You said "An electromagentic field propogates of it's own accord in the absence of a source"
Physics says it's the electromagentic wave which propagates.

Could you explain why you think the field propagates.
Your answer doesn't address this question:

The field propagates from a source in search of something, right? Why does a field propagate from an atom? Because it can? This is where "time" becomes bespoke to events in space.
Let me explain why I have a problem with your response.
Take the example of fields which we are very familiar with. Sound waves in air, waves on water. We do not talk about the air pressure, or the water amplitude propagating, nor do we talk about the air or water propagating, we talk about the wave propagating.
OK, these are examples of non-relativistic fields which require a medium, but we apply the same terminology to relativistic fields eg EM field where we have not detected a medium.
So we say that the light wave (quantum = photon) propagates through the em field. That field is a set of measurements of electric and magnetic field strengths.

So a field does not propagate from a source in search of anything.
“Why does a field propagate from an atom? Because it can?” - no, the wave propagates from an atom because an electron changed state and energy was released as an oscillation that we detect as a wave.
“This is where "time" becomes bespoke to events in space.” - haven’t a clue what that means, sounds like pseudoscience or word salad.

In new theories anything goes, but in this section we need to be very clear and precise in what we are saying otherwise we run the risk of creating what (in another thread) you have termed fake news.

Colin, I agree with everything you've said according to the arrow of time, the currently accepted model for time and space. Very good.
Title: Re: Does a field require a source?
Post by: Colin2B on 27/02/2018 00:02:48
Colin, I agree with everything you've said according to the arrow of time, the currently accepted model for time and space. Very good.
If that arrow ever reverses I’m sure we will be the first to know. Or do I mean last. Or have I got that backwards?  ;)
Title: Re: Does a field require a source?
Post by: Colin2B on 27/02/2018 00:03:57
Alan .......when you say “a field is something”, I wonder what form that “something” takes. 

Is it a physical thing in which waves/particles propagate, or is it just a measurement?
If it is a measurement, what is the “something” it measures?
I know Alan gets quite busy, so I’ll put in an interim.
Clearly if you can measure something it is physical.
Take an electric field. The measurement you take (or imagine you take) is of the force (vector) on an infinitesimal test charge at a particular point. That force is real, but take away the test charge and it disappears, and it doesn’t affect a neutral test object. So there is something physical - the force - and we are measuring that force and calling the set of measurements the field. We don’t know what causes the force (other than saying that a charge causes it!) but we can model it and using that model describe how charged particles behave. Clearly, the measurement we took of the force does not cause the force, but it is often convenient to consider the field as a physical object and use shorthand/shortcut terminology like “the field causes the force” or “the field stores energy”. As Matt Strassler will tell you, such thinking shortcuts can be dangerous, we must never forget what lies behind the description.
Simple example. Replace the electric field with a spring. Extend the spring and measure the force for various distances, we have a force field.  As the spring extends it gains potential energy, so we can say the field stores energy, but does it? The spring stores the energy, but the phrase is a convenient shorthand. In the case of a spring reality is obvious, for other fields it might mislead us.

A little light reading. The Higgs field and the big bang.
https://home.cern/topics/higgs-boson/origins-brout-englert-higgs-mechanism
Note the terminology - interacting with the field.
Title: Re: Does a field require a source?
Post by: geordief on 27/02/2018 00:38:45
A little light reading. The Higgs field and the big bang.
https://home.cern/topics/higgs-boson/origins-brout-englert-higgs-mechanism

All fields I can think of have "local centres."

The gravity field,whilst everywhere is stronger near (to take an example) Black Holes and diminishes further away.

Same with an electron field...

What about this Higgs field?
Does it also wax and wane depending on the environment?

Or is it uniform as I had assumed from what I have heard?
Title: Re: Does a field require a source?
Post by: opportunity on 27/02/2018 00:44:49
Colin, I agree with everything you've said according to the arrow of time, the currently accepted model for time and space. Very good.
If that arrow ever reverses I’m sure we will be the first to know. Or do I mean last. Or have I got that backwards?  ;)

Haha, nice point, yet time doesn't necessarily have to be reversed if it's not a simple arrow, it could be a type of equation in its own right...,that's another discussion though.
Title: Re: Does a field require a source?
Post by: hamdani yusuf on 28/02/2018 11:45:51
The energy of a field exists. Otherwise we wouldn't have any forces. It isn't tangible. That does not mean that it is simply an abstract concept.
the field is not just model and  fit for scrap if superseded?
Probably I'll amaze you now, but did you know that an electrostatic field has a mass too?

--
lightarrow
Do you have any reference for that?
How do you measure it?
Title: Re: Does a field require a source?
Post by: Bill S on 28/02/2018 15:00:13
Quote from: Colin
The spring stores the energy, but the phrase is a convenient shorthand. In the case of a spring reality is obvious, for other fields it might mislead us.

The Higgs field comes to mind.  What fills the role of the “spring” in relation to the Higgs field?