[jeffreyH (OP)]

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?

[Bill S]

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. 

[Bill S]

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.

[wolfekeeper]

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.

[jeffreyH (OP)]

@Bill S I ask the question to get opinions. Fields are not straightforward when you start thinking about them in any depth.

[opportunity]

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.

[Colin2B]

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.

[opportunity]

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.

[Colin2B]

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

[opportunity]

so why is not quantum entanglement explained in the big bang idea?

I'm thinking we're not there yet?

[Colin2B]

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.

[geordief]

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.

[opportunity]

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.....

[jeffreyH (OP)]

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.

[Colin2B]

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.

[geordief]

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

[opportunity]

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?

[Colin2B]

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.

[opportunity]

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.

[Colin2B]

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.