Field Question

[geordief]

3 minutes ago, swansont said:

 

It already exists as philosophy. If it were science, you would need a way to test to see if it were true. How do you do that?

Is philosophy about more than truth or is it perhaps only about truth? ("to thyself be true" and "courage is the greatest virtue*")

 

Interestingly there never seems to be a final point to philosophical discourse but the same can perhaps  be said about scientific discovery .

 

Is this where we can  let ourselves down ,we imagine that we can ever reach a "final point"when all that we ever reach is staging posts(in both philosophy and scientific interpretation)?

*W.Churchill

[Mordred]

Either way a field depends on arbitrary choices, such as the choice of coordinate system or the gauge symmetry groups used. Hence the term field Treatment example conformal or canonical

 So does an arbitrary choice make a field real? of course not, the arbitrary choices we choose only describes the dynamics in question. Fields is directly involved with the mathematics and arbitrary choice of how to apply mathematics to describe the dynamics of a system. 

Edited May 7, 2018 by Mordred

[Strange]

20 minutes ago, geordief said:

Is philosophy about more than truth or is it perhaps only about truth?

It is about understanding what we can know (and what “know” means) etc. But there is a thread about this...

[MikeAL]

48 minutes ago, swansont said:

How do you tell if it correct? It's correct when it works. And then, it only tells you about behavior, not fundamental truth or reality.

So what you're saying is that a theory is a philosophy about how things work, and so long as it the ball still comes out chute B then alls good, it doesn't really matter how it got there. I take your point it seems reasonable, but I also disagree strongly with it. We find for example that while the philosophy can predict the outcome for one event, it may be completely wrong for another. The theory is thus incorrect, but may still be convenient. It seems at any rate that philosophy is inextricably linked to science.  

The good thing about science though, compared to philosophy is that we aren't trying to ponder the conscious self, because we have a real, live playground out there that we can throw rocks into.

We know, for example that masses are attracted to each other. We say gravity resides in the gap between them. Best theories tell us it's a universal gravitational field that the masses are bending around themselves. Some masses are able to bend the gravitational masses better than others - the fact that the field can be bent to different degrees or bent at all tell us therefore that the field has properties that interact with physical forms. 

We know, according to best theories, that new space is mushrooming out into our universe causing it to expand. I was wondering the effect such new space would have on the properties of the fields - why don't they diminish? It seems that this new space has the same properties as old space- and that the properties - including the fields of old space are not diminished. Strange has pointed out that The permittivity of space is unchanged. We know that vacuum space has a quantum energy value. 

"According to present-day understanding of what is called the vacuum state or the quantum vacuum, it is "by no means a simple empty space".^[1][2] According to quantum mechanics, the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.  In fact, the energy of a cubic centimeter of empty space has been calculated figuratively to be one trillionth of an erg (or 0.6 eV).^{[8]  ]https://en.wikipedia.org/wiki/Vacuum_state}

The first law of thermodynamics states: The first law of thermodynamics is a version of the law of conservation of energy, adapted forthermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed. https://en.wikipedia.org/wiki/First_law_of_thermodynamics 

So I guess the question at the heart of my question, is why doesn't an expanding universe contradict the first law of thermodynamics?

Sorry about making it so hard for you guys.

 

[StringJunky]

2 hours ago, MikeAL said:

I disagree. A theory is correct when it is correct. Any other time, a theory is simply a convenience.

As history is our witness, a theory is only correct under the prevailing accepted paradigm. That's why they are called 'theories' and not 'laws'.

[MikeAL]

On 5/6/2018 at 9:50 PM, studiot said:

Do you consider space to be finite or infinite?

I can't find the quote I'm after with this, but you said that space could still be infinite if we consider it as starting at the BB? Do you mean infinite expansive potential or infinite at the time of the BB?

[swansont]

36 minutes ago, MikeAL said:

So what you're saying is that a theory is a philosophy about how things work, and so long as it the ball still comes out chute B then alls good, it doesn't really matter how it got there. I take your point it seems reasonable, but I also disagree strongly with it. We find for example that while the philosophy can predict the outcome for one event, it may be completely wrong for another. The theory is thus incorrect, but may still be convenient. It seems at any rate that philosophy is inextricably linked to science.  

Science is an offshoot of philosophy, but IMO it would be wrong to say that it is philosophy.

If we can tell how the ball got there, great, but sometimes that's impossible. If there's no way to test it, it's not science.

Quote

The good thing about science though, compared to philosophy is that we aren't trying to ponder the conscious self, because we have a real, live playground out there that we can throw rocks into.

We know, for example that masses are attracted to each other. We say gravity resides in the gap between them. Best theories tell us it's a universal gravitational field that the masses are bending around themselves. Some masses are able to bend the gravitational masses better than others - the fact that the field can be bent to different degrees or bent at all tell us therefore that the field has properties that interact with physical forms. 

But we still have no idea of why masses attract (or charges if E&M), and that fundamental question is one that science can't currently address. If there is no way to test ideas and compare them to experiment, even in principle, it can't be considered science. 

Quote

We know, according to best theories, that new space is mushrooming out into our universe causing it to expand. I was wondering the effect such new space would have on the properties of the fields - why don't they diminish? It seems that this new space has the same properties as old space- and that the properties - including the fields of old space are not diminished. Strange has pointed out that The permittivity of space is unchanged. We know that vacuum space has a quantum energy value. 

I will reiterate the question I have put forth several times now: why should they? Is there some testable model that predicts that they would? If there is then let's compare it with the models we have that say they shouldn't and see which one agrees better with what we observe.

But you don't appear to have a model. Just hand-waving

Quote

"According to present-day understanding of what is called the vacuum state or the quantum vacuum, it is "by no means a simple empty space".^[1][2] According to quantum mechanics, the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.  In fact, the energy of a cubic centimeter of empty space has been calculated figuratively to be one trillionth of an erg (or 0.6 eV).^{[8]  ]https://en.wikipedia.org/wiki/Vacuum_state}

The first law of thermodynamics states: The first law of thermodynamics is a version of the law of conservation of energy, adapted forthermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed. https://en.wikipedia.org/wiki/First_law_of_thermodynamics 

So I guess the question at the heart of my question, is why doesn't an expanding universe contradict the first law of thermodynamics?

 

Is the vacuum energy a constant?

Is an expanding universe an isolated system, and can you apply that classical law to a relativistic system (because while energy is conserved it is not invariant)? 

 

34 minutes ago, StringJunky said:

As history is our witness, a theory is only correct under the prevailing accepted paradigm. That's why they are called 'theories' and not 'laws'.

We use "law" to refer to mathematical relationships that hold true in certain applications.  

Theories are correct as long as they are consistent with what we observe. If we see inconsistencies, we either restrict the range of applicability of a theory, we modify it, or we junk it. (same with laws, which are sometimes subsets of theories)

[StringJunky]

14 minutes ago, swansont said:

We use "law" to refer to mathematical relationships that hold true in certain applications.  

Theories are correct as long as they are consistent with what we observe. If we see inconsistencies, we either restrict the range of applicability of a theory, we modify it, or we junk it. (same with laws, which are sometimes subsets of theories)

OK. Cheers.

[Strange]

3 hours ago, MikeAL said:

I can't find the quote I'm after with this, but you said that space could still be infinite if we consider it as starting at the BB? Do you mean infinite expansive potential or infinite at the time of the BB?

That was probably me. The Big Bang model describes the expansion of space; it makes no difference if that space has a finite or infinite volume.

[studiot]

7 hours ago, MikeAL said:

I can't find the quote I'm after with this, but you said that space could still be infinite if we consider it as starting at the BB? Do you mean infinite expansive potential or infinite at the time of the BB?

 

I wonder if you are referring to where I offered a case in Mathematics of something which has a beginning, but no end?

For instance the natural counting numbers.

 

I was going to observe that there is another process in Mathematics whereby something is generated indefinitely, constantly expanding the something.

 

For instance between every pair of real numbers there is another real number.

The same is true of the rational numbers, but in that case there are also other non rational numbers between every pair.

 

I thought you had given up responding to me, and as everyone else seems only to want to take the piss I had given up on the thread.

 

 

[beecee]

11 hours ago, MikeAL said:

I think you guys are the philosophers. I am not pondering the meaning of the word 'real' and having existential epiphanies as I chant mantras under a waterfall. I am referring to the sharp distinction between mathematics and physics. In physics, mathematics is an overlay, that attempts to explain what is in our universe. It is not the other way around. The universe is not an abstract imaginary form used as an overlay for mathematics. 

Early on in my foray into this forum, I obviously upset a couple of philosophers by quoting Bertrand Russell: "Science is what we know: Philosophy is what we don't know"...and with an even more telling quote from Feynman: "Philosophy is for the birds"

I would also add that a better definition of mathematics, is that it is the language of physics...a language sadly that I never properly delved into. I have read with interest the point you have been putting in this thread, and that point aligns with what I also accepted, ie the reality of fields etc. But I also now am thinking very deeply on that opinion due to the argument being put by others as to that reality, or in their opinion, lack of reality. They make some good points. Like I said earlier, I have watched discussions on this subject over many years on at least three forums, and the point is still rather debatable with no firm outcome...philosophical if you will.  

Quote

There is a difference between something being right or wrong, knowing and not knowing, existing or not existing. 

 

10 hours ago, MikeAL said:

I disagree. A theory is correct when it is correct. Any other time, a theory is simply a convenience.

If any theory is wrong, according to observational and experimental data, then it is modified and/or discarded and a new theory formulated that better describes the universe around us. We know gravity exists...we have two models that describe those effects to varying degrees of precision, and the knowledge has taken us to the Moon, sent probes to all the planets, and enabled us to understand the universe reasonably well. 

Quote

We know something we call gravity is causing objects with mass to be attracted toward each other. Our current best theories tell us this is because of a gravitational field. If you tell me the field is not real, then what you are in effect saying is that the theory is incorrect.

I don't accept that summation. Our theories of gravity  as I have said above, has enabled us to understand the universe, despite not really knowing what gravity/spacetime is, why it exhibits itself when mass curves that spacetime, or even the question being discussed, as to whether it is real or not. Did you see my oft repeated Feynman video re magnets? Our theories and their successes are what makes science such a powerful discipline. 

10 hours ago, Strange said:

Although some philosophers might argue about whether the universe is real or to, I won't. But I would say physics describes, rather than explains, the universe. It tells us how it behaves, not what it is ultimately made of.

A wise and profound statement. At this time and after listening to wiser heads, I won't either. 

Edited May 7, 2018 by beecee

[studiot]

8 hours ago, MikeAL said:

So I guess the question at the heart of my question, is why doesn't an expanding universe contradict the first law of thermodynamics?

I have already answered this more than once.

The First Law does not apply to infinite systems, though relying on Wiki is dicy at best.

Furthermore it is not known if the Universe is an isolated system.

7 hours ago, swansont said:

If we can tell how the ball got there, great, but sometimes that's impossible. If there's no way to test it, it's not science.

I find this too restrictive a condition on the definition of Science.

 

For instance in many cases you have no way to test the actual happening of a historical event, but Science can investigate and provide probabilities of possible facts.

 

A simple example would be the so called coffin ships.

Edited May 7, 2018 by studiot

[MikeAL]

21 minutes ago, studiot said:

The First Law does not apply to infinite systems, though relying on Wiki is dicy at best.

I'm rushing a bit as I'm already late for work, but how do you know we are in an infinite system? Multiverses, an singular infinitely spread universe, what is your basis for saying this?

[Strange]

9 hours ago, MikeAL said:

So I guess the question at the heart of my question, is why doesn't an expanding universe contradict the first law of thermodynamics?

Because that only applies to a single frame of reference (and a closed system, etc).

So, the energy of a photon that has undergone cosmological red shift is less than the original photon. That energy hasn't gone anywhere, we are just measuring it in a different frame of reference. The concept of energy, and therefore the conservation law, is not easily defined in GR:

Is Energy Conserved in General Relativity?

Energy is Not Conserved

 

[studiot]

31 minutes ago, MikeAL said:

I'm rushing a bit as I'm already late for work, but how do you know we are in an infinite system? Multiverses, an singular infinitely spread universe, what is your basis for saying this?

I don't, it is one of the questions no one knows the answer to, although many have considered it over the millennia.

But then, exactly the same can be said of a finite system.

But I will wait for you to have time to respond properly to my last two posts instead of misreading them in haste.

 

 

 

[MikeAL]

19 hours ago, swansont said:

But we still have no idea of why masses attract (or charges if E&M), and that fundamental question is one that science can't currently address. If there is no way to test ideas and compare them to experiment, even in principle, it can't be considered science. 

Why do you say we have no idea? Einstein gave us an explanation. Have we reached the point of abandonment of his theory in our own thinking? Einstein did prove his theory with countless experiments with time, lensing and gravitational calculations. He said gravity was a field. As scientists do we not accept this and try and work forward from there to determine the implications as they apply to other universal phenomenon- even if it leads us to a point of ultimate contradiction (thus disproving the theory)?

 

10 hours ago, Strange said:

The concept of energy, and therefore the conservation law, is not easily defined in GR:

This is an intriguing reference, Strange (http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/). I'm going to let it sink in a bit - well actually I'm going to try and write it out here to see if I can get it right.

Point 1: Because space is changing, the energy of the particle is transferred to it, thus the energy of the particle (of the photon) is not truly lost, thus there is no violation of conservation rules.

Quote: ''Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved."

Then it uses this example to say:

Quote:"In the case of dark energy, that evolution is pretty simple: the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space (comoving along with galaxies and other particles) grows as the universe expands. So the total energy, density times volume, goes up."

OK, I agree and that's what this thread's been banging on about as being a bit weird... but then:

Quote: "This bothers some people, but it’s nothing newfangled that has been pushed in our face by the idea of dark energy. It’s just as true for “radiation” — particles like photons that move at or near the speed of light. The thing about photons is that they redshift, losing energy as space expands. If we keep track of a certain fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy decreases. A decrease in energy is just as much a “violation of energy conservation” as an increase in energy, but it doesn’t seem to bother people as much. At the end of the day it doesn’t matter how bothersome it is, of course — it’s a crystal-clear prediction of general relativity."

This crescendo of the argument seems to me to fall to pieces because it seems to be saying in the first instance that there was no violation, only a reshuffling between space and particles due to the dynamic nature of both. However new space, with new energy - the increase in energy - they speak of, is not energy flowing from existing space into particles, but from new space into particles.

Quote: "In particular, a lot of folks would want to say 'energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.' Which seems pretty sensible at face value." "And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down."

Here it seems to be suggesting that some people believe the gravitational field energy is weakening (I assume) to compensate. - which was the thread question.

Quote: "There’s nothing incorrect about that way of thinking about it; it’s a choice that one can make or not, as long as you’re clear on what your definitions are. I personally think it’s better to forget about the so-called “energy of the gravitational field” and just admit that energy is not conserved."

I think this above part is the debate that we have been having here.

However, after this discussion you guys, I now have a problem with saying the field is weakening, because of the permittivity of space remaining unchanged. It seems like the new space that enters our universe comes prefabricated with field conductivity and even field energy (potential- the gravitational field can be bent to different degrees and will regain form). - Yes I am aware I am referring to the field as being real.

 

11 hours ago, studiot said:

Furthermore it is not known if the Universe is an isolated system.

True. In fact the appearance of prefabricated space really suggests it's not. I had always assumed that the new space acquired the properties of the old space, thus leading me to think it would dilute it - it appears not so.

11 hours ago, beecee said:

 

21 hours ago, MikeAL said:

I disagree. A theory is correct when it is correct. Any other time, a theory is simply a convenience.

If any theory is wrong, according to observational and experimental data, then it is modified and/or discarded and a new theory formulated that better describes the universe around us. We know gravity exists...we have two models that describe those effects to varying degrees of precision, and the knowledge has taken us to the Moon, sent probes to all the planets, and enabled us to understand the universe reasonably well. 

I agree with you Beecee. I meant if disproven/superceded and it was still being used as a tool then it was a convenience, but no longer a tenable theory. I don't know if I saw you Feyman video on magnets, although I do have vague recollections of watching an interview where he talked about them to a reporter (you might have put me onto that last time). Always good to read your comments.

 

 

 

 

Edited May 8, 2018 by MikeAL

[swansont]

1 hour ago, MikeAL said:

Why do you say we have no idea? Einstein gave us an explanation. Have we reached the point of abandonment of his theory in our own thinking? Einstein did prove his theory with countless experiments with time, lensing and gravitational calculations. He said gravity was a field. As scientists do we not accept this and try and work forward from there to determine the implications as they apply to other universal phenomenon- even if it leads us to a point of ultimate contradiction (thus disproving the theory)?

That doesn't address why mass and energy do what they do. Only that they bend spacetime.

[Strange]

1 hour ago, MikeAL said:

Why do you say we have no idea? Einstein gave us an explanation.

He gave us a (quantitative, mathematical) description of how mass-energy affects space-time. He didn't explain why it does it. It just seems to be in the nature of mass-energy and space-time to behave like that.

1 hour ago, MikeAL said:

As scientists do we not accept this and try and work forward from there to determine the implications as they apply to other universal phenomenon- even if it leads us to a point of ultimate contradiction (thus disproving the theory)?

Yes, science works forward from there. Working backwards to explain "why" is philosophy, not science.

1 hour ago, MikeAL said:

This crescendo of the argument seems to me to fall to pieces because it seems to be saying in the first instance that there was no violation, only a reshuffling between space and particles due to the dynamic nature of both.

It doesn't say that at all.

It says that, on the one hand, some people object to dark energy being a property of space and hence increases with expansion. On the other hand, people don't usually object to the "disappearance" of energy in red-shifted photons. Nowhere does it equate these two things (ie. nowhere does it say that the loss of energy by photons is the source of dark energy).

1 hour ago, MikeAL said:

Quote: "In particular, a lot of folks would want to say 'energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.' Which seems pretty sensible at face value." "And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down."

Here it seems to be suggesting that some people believe the gravitational field energy is weakening (I assume) to compensate. - which was the thread question.

I have no idea how you reach that conclusion. It doesn't say anything about the gravitational field energy weakening. It is just pointing out that the potential energy of the gravitational field is negative (which is just an "accounting trick" to make the equations work).

[swansont]

12 hours ago, studiot said:

 I find this too restrictive a condition on the definition of Science.

 

For instance in many cases you have no way to test the actual happening of a historical event, but Science can investigate and provide probabilities of possible facts.

 

A simple example would be the so called coffin ships.

I think there's a distinction to be made between activities that are science, and activities that include science (i.e. can be done in a scientific way) History is not science, but one may apply science to it to draw conclusions.

[MikeAL]

1 hour ago, Strange said:

He gave us a (quantitative, mathematical) description of how mass-energy affects space-time. He didn't explain why it does it. It just seems to be in the nature of mass-energy and space-time to behave like that.

 

1 hour ago, swansont said:

That doesn't address why mass and energy do what they do. Only that they bend spacetime.

Well, I don't want to open up a theory on the matter, but I believe that the why only becomes a problem when we consider mass and energy and space as discreet entities. I kind of see it as all twisted together with one form dominant over another in different contexts. I don't think this is anyway unique thinking on my part, especially these days, but I think it is helpful.

1 hour ago, Strange said:

Yes, science works forward from there. Working backwards to explain "why" is philosophy, not science.

I think there are two different types of why here though. There is the why does the apple fall to the ground why, which creates the theory (which is a type of philosophy) and there is the why that is more existential and certainly philosophically based.

1 hour ago, Strange said:

Nowhere does it equate these two things (ie. nowhere does it say that the loss of energy by photons is the source of dark energy).

No, I didn't say it did. His conclusion seemed incongruent with his introductory remarks however.

1 hour ago, Strange said:

I have no idea how you reach that conclusion. It doesn't say anything about the gravitational field energy weakening. It is just pointing out that the potential energy of the gravitational field is negative (which is just an "accounting trick" to make the equations work).

No, I don't think it's an accounting trick. I think he is referring to the gravitational field being inverted in dark energy, such that the center of the field is a hill as opposed to the trough we find that matter creates - and thus repelling mass from it. It may have been invented to solve a few problems with GR, but I think it has moved on a bit from there. Do you disagree?

 

Edited May 8, 2018 by MikeAL

[Mordred]

I would like you to consider a previous unexplained statement I made. " A matter only universe will still expand".

 Now consider the distrinution of mass without changing the number of particles. Just the distribution...

 Specifically matter forming large scale structures such as galaxies etc.

 Is it accurate to suggest the gravitational field is weakening? or is it more accurate to recognize that the field is no longer evenly distributed in its mass/energy density distrubution throughout the field ?

 Also recall the strength of gravity from a mass source falls off 1/r^2.

I would also like you to consider the difference between the energy/mass density and the total energy of a field...ie the total energy stays constant but the energy density itself decreases as the volume increases.

 Then reread that article and think of how the above applies with regards to redshift etc.

Edited May 8, 2018 by Mordred

[Strange]

1 hour ago, MikeAL said:

Well, I don't want to open up a theory on the matter, but I believe that the why only becomes a problem when we consider mass and energy and space as discreet entities. I kind of see it as all twisted together with one form dominant over another in different contexts. I don't think this is anyway unique thinking on my part, especially these days, but I think it is helpful.

Unless you can develop a mathematical, quantitatively testable model of this it is philosophy not science.

 

[MikeAL]

37 minutes ago, Mordred said:

A matter only universe will still expand

Hey Mordred, the sentence is a bit ambiguous for me.

Are you referring to the release of energy from matter through entropy? Or are you saying that even if the universe only contained matter and no space, that the matter would expand? - I'm not sure which you want me to consider it.

39 minutes ago, Mordred said:

Now consider the distrinution of mass without changing the number of particles. Just the distribution...

Right, the necklace effect, or bubble wrap appearance with matter sunk into slender corridors.

40 minutes ago, Mordred said:

 Is it accurate to suggest the gravitational field is weakening? or is it more accurate to recognize that the field is no longer evenly distributed in its mass/energy density distrubution throughout the field ?

I take your point on the latter definitely. The distribution has changed. Can we say that the gravitational field has weakened? - Ah, not the field no, unless weakening is a directional measure.

43 minutes ago, Mordred said:

I would also like you to consider the difference between the energy/mass density and the total energy of a field...ie the total energy stays constant but the energy density itself decreases as the volume increases.

That is what I was alluding to with a weakening field due to expansion at the beginning of the thread. So, in a way, you agree with the idea but think it was clumsily worded? Since then though, the information we've discussed seems to say that total energy does not stay constant - that the new space brings with it everything it needs, including energy, and does not acquire the properties but instead is born with them. - the permittivity doesn't change with expansion. Is this wrong?

So, for example, because the gravitation feels is distorted by matter to different degrees, that implies an 'elastic' component - an energy component. For permittivity not to change wouldn't that mean that space must bring it's own energy with it rather than diluting the existing space? - thus in a sense suggesting it is prefabricated?

51 minutes ago, Mordred said:

Then reread that article and think of how the above applies with regards to redshift etc.

The total energy of the photon remains the same but the distribution of that energy has... been converted to mass.... I don't know. 

Are you saying when it traverses a gravitational field bent by matter part of its energy is converted into mass and the loss of apparent energy as it pulls away causes it to appear redshifted?

You totally got me on this one Mordred. You're going to have to explain it to me again. What is the connection?

2 minutes ago, Strange said:

Unless you can develop a mathematical, quantitatively testable model of this it is philosophy not science.

 

Yeah, that's fine. A little bit of philosophy helps focus the ideas. I'm just saying that imagining it this way has helped me get my head around some mind bending stuff. Probably also led me astray.  

[Mordred]

Take a toy universe consisting of only matter. Matter always has space between particles. Now start a uniform distribution for simplicity start with roughly the density of a plasma cloud. Now I don't know if your familiar with Shell theory if not please ask.

 As matter collapses from this cloud to form galaxies etc. The average density will decrease away from the galaxy while at the precise same time increase in the galaxy locale.

 The volume of the universe filled with nothing other than fermionic matter will expand because the average density on the global distribution has decreased. Yet the total mass itself or total energy remains constant. (The LCDM model total particle count is roughly [latex] 10^{90} [/latex] particles since the BB till now. The number of each particle species may vary but the number in total stays roughly constant.

 Now we have an expanding toy universe that does not require radiation nor DE. This obviously is not our universe itself but we model each contributor seperately to understand how each contributes to expansion and contraction.

 The temperature, pressure and density of an expanding volume always decreases in accordance to the ideal gas laws. The FLRW metric utilizes these laws to model our universe.  Now every textbook will teach that our universe follows an adiabatic and isentropic fluid. ( no net inflow or outflow of energy/entropy). This makes sense as the universe is everything there is....So there is no possibility of an outflow of entropy or energy. This is true for both a finite or infinite universe.

 Temperature is the average kinetic energy. So if the temperature decreases the average kinetic energy of each locale will decrease but the total energy of the entire volume will remain constant.

 So yes its partly how you described field weakening.

 If you stated the average energy or mass density decreases then you would be correct for an expanding volume modelled under field treatment. However if you simply state the field weakens you would be incorrect. The first example demostrates this as certain locales will increase while other locales decrease. The total field strength defined by its total energy would however stay constant.

 Now redshift. It will help to understand that energy of a signal or the strength of a signal is related to its frequency. So photons lose energy due to redshift but the energy must go somewhere. With gravitational redshift its considered to goto the gravitational potential.

 With cosmological redshift it goes into the spacetime regions along the photon path. So the field strength total energy remains unaffected its distribution of energy merely changes. Particles being field excitations. The photon being a localized excitation will lose energy but that energy is redistributed to the field. So total energy is still unchanged. In essence you trade off tbe kinetic energy of the particle to the potential energy of the field and vice versa. However total energy of the system remains unchanged.

 In an expanding universe it is the average energy density that decreases due to larger volume not the field potential/strength of the total field.

 The field potential may be greater or lesser at some locales just as In The case of the matter field in the first example.

 

 

Edited May 9, 2018 by Mordred

[MikeAL]

9 hours ago, Mordred said:

In an expanding universe it is the average energy density that decreases due to larger volume not the field potential/strength of the total field.

Thanks for clearing that up. That makes a lot of sense. One quick question though.

9 hours ago, Mordred said:

The volume of the universe filled with nothing other than fermionic matter will expand because the average density on the global distribution has decreased.

Sure, I get the density redistribution toward the galaxy locales, and can accept the drop in average density as such a large outlier now has a dispropotionately low density, but I don't see how that would increase the volume of the universe, unless density is a constraining factor to expansion.