[Bill S]

…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.

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?

[geordief]

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...)

[Bill S]

Could be, Evan_au adds to this discussion with this extract from  Does dark matter and the graviton exist?

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.

[geordief]

Could be, Evan_au adds to this discussion with this extract from  Does dark matter and the graviton exist?

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 ?

[Colin2B]

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.

[Bill S]

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.   

[Bill S]

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?

[alancalverd]

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.

[geordief]

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.

[lightarrow]

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

[opportunity]

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.

[Colin2B]

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.

[opportunity]

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.

[Colin2B]

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.

[opportunity]

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.

[geordief]

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?

[opportunity]

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?

[geordief]

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)

[opportunity]

Why not say gravity is the failure of every other field force?

[Colin2B]

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.