Thanks Schmelzer. I'm ok with the GR math but have forgotten much of the terminology. Most of the confusion you point out is due to that. As I learn more I'll make another attempt at it. I'm aiming to produce a high-level intro (not much math) for people unfamiliar with ether theory.

Schmelzer: The interesting point of Volovik's \(^3He\) research is that it gives some qualitative insights. It is very good and useful research, but I have not used it. So there is nothing in the evolution of the cosmos "modelled on \(^3He\)".

- Sorry, my mistake. But the properties of ether, in your view, are similar to superfluids, aren't they?

Schmelzer: In the ether interpretation, the ether has a stress tensor or pressure tensor, instead of simply some scalar pressure. This is what one has to use in condensed matter theory to define solids.

- Yes. Tensors first were used to describe stress / strain in solids. BTW we also use words like pressure, tension (the word tensor comes from this), shear, etc for these qualities. The words are not important, the tensor math gives the exact physical results. Anyway, three orthogonal planes are defined at a point. Each has 3 numbers, one for pressure through the plane (normal stress), and two within the plane (shear). The interesting physical fact - the reason this works - is that these 9 numbers are sufficient to give the stress in any direction: it behaves linearly (at least, this first linear approximation is good enough for most work). This is the same stress tensor you mean, right? In my post I referred simply to "stresses and strains". If this causes the misunderstanding that I mean only a scalar, I'd better throw in the word "tensor".

Schmelzer: About dark matter: There appear some fields in the ether which may play the role of dark matter. For every electroweak pair of fermions there has to be a massive scalar field with much greater mass and similar color. Those corresponding to leptons would not have any interaction at all, thus, would be good candidates. But the ether as a whole differs from dark matter - it is everywhere. There can be places without dark matter, but not without the ether.

- Yes, I see. Ether as such can't do what DM does, since it's evenly distributed. The reason I mentioned it: DM is the only example of non-baryonic matter most people have heard of, and it seems to me ether must be non-baryonic. Maybe that's wrong? I didn't know there was a lepton field with "no interaction at all" (except gravity I presume); that sounds like a possibility for DM. Don't forget, what actually needs explaining is the observed galactodynamics. DM is the mainstream candidate but also modified gravity is possible. Anyway, probably not a good idea to bring in DM at all, causes confusion.

Schmelzer: The metric is not a hidden variable.

Right, poor choice of words on my part. I meant the underlying coordinates of the 3-d frame, which would be known only to "God" or whoever. We arbitrarily assign our own coordinate system to it. The word "metric" should only be used only to refer to \(g_{\mu\nu}(x,t)\). Perhaps the point is unimportant anyway.

Schmelzer: What is hidden is what makes the coordinates I use preferred coordinates. But they are valid coordinates and the can be used in standard cosmology. No GR theoretician has anything to object if I use these coordinates - except that he can ask the question "why these? why not others?"

- Aren't they just the standard co-moving observer coordinates?

Schmelzer: And the spatial part of the metric - as visible as all other parts of the metric \(g_{\mu\nu}(x,t)\) - is not a 3-vector, but a 3-metric, a symmetric tensor, with two indices \(g_{ij}(x)\) instead of one \(a^i(x)\) of a vector field.

- More incorrect language! I should refer to the FLRW ansatz - or something - not "metric evolution". a(t), of course, is just the normal FLRW scaling factor.

Schmelzer: With a small enough parameter \(\Upsilon>0\) the solution gets as close to the Big Bang solution as one wants.

- Right, but there are other constraints on \(\Upsilon\) aren't there? You have to get quite close (a few minutes) to BB to use their model to generate the light elements. Will such a small \(\Upsilon\) causes problems elsewhere?

Schmelzer: The interesting point of Volovik's \(^3He\) research is that it gives some qualitative insights. It is very good and useful research, but I have not used it. So there is nothing in the evolution of the cosmos "modelled on \(^3He\)".

- Sorry, my mistake. But the properties of ether, in your view, are similar to superfluids, aren't they?

Schmelzer: In the ether interpretation, the ether has a stress tensor or pressure tensor, instead of simply some scalar pressure. This is what one has to use in condensed matter theory to define solids.

- Yes. Tensors first were used to describe stress / strain in solids. BTW we also use words like pressure, tension (the word tensor comes from this), shear, etc for these qualities. The words are not important, the tensor math gives the exact physical results. Anyway, three orthogonal planes are defined at a point. Each has 3 numbers, one for pressure through the plane (normal stress), and two within the plane (shear). The interesting physical fact - the reason this works - is that these 9 numbers are sufficient to give the stress in any direction: it behaves linearly (at least, this first linear approximation is good enough for most work). This is the same stress tensor you mean, right? In my post I referred simply to "stresses and strains". If this causes the misunderstanding that I mean only a scalar, I'd better throw in the word "tensor".

Schmelzer: About dark matter: There appear some fields in the ether which may play the role of dark matter. For every electroweak pair of fermions there has to be a massive scalar field with much greater mass and similar color. Those corresponding to leptons would not have any interaction at all, thus, would be good candidates. But the ether as a whole differs from dark matter - it is everywhere. There can be places without dark matter, but not without the ether.

- Yes, I see. Ether as such can't do what DM does, since it's evenly distributed. The reason I mentioned it: DM is the only example of non-baryonic matter most people have heard of, and it seems to me ether must be non-baryonic. Maybe that's wrong? I didn't know there was a lepton field with "no interaction at all" (except gravity I presume); that sounds like a possibility for DM. Don't forget, what actually needs explaining is the observed galactodynamics. DM is the mainstream candidate but also modified gravity is possible. Anyway, probably not a good idea to bring in DM at all, causes confusion.

Schmelzer: The metric is not a hidden variable.

Right, poor choice of words on my part. I meant the underlying coordinates of the 3-d frame, which would be known only to "God" or whoever. We arbitrarily assign our own coordinate system to it. The word "metric" should only be used only to refer to \(g_{\mu\nu}(x,t)\). Perhaps the point is unimportant anyway.

Schmelzer: What is hidden is what makes the coordinates I use preferred coordinates. But they are valid coordinates and the can be used in standard cosmology. No GR theoretician has anything to object if I use these coordinates - except that he can ask the question "why these? why not others?"

- Aren't they just the standard co-moving observer coordinates?

Schmelzer: And the spatial part of the metric - as visible as all other parts of the metric \(g_{\mu\nu}(x,t)\) - is not a 3-vector, but a 3-metric, a symmetric tensor, with two indices \(g_{ij}(x)\) instead of one \(a^i(x)\) of a vector field.

- More incorrect language! I should refer to the FLRW ansatz - or something - not "metric evolution". a(t), of course, is just the normal FLRW scaling factor.

Schmelzer: With a small enough parameter \(\Upsilon>0\) the solution gets as close to the Big Bang solution as one wants.

- Right, but there are other constraints on \(\Upsilon\) aren't there? You have to get quite close (a few minutes) to BB to use their model to generate the light elements. Will such a small \(\Upsilon\) causes problems elsewhere?