Merged Relativity+ / Farsight

[edd]

Straumann's first numbered equation includes the ∇p that (as predicted) Farsight failed to recognize as a pressure field.

I think that's the problem with arguing from a document like that in this case. It's like Farsight is insisting that the only variety of apple is the Granny Smith, but when you show a picture of a Golden Delicious from an article but the article text only refers to it as fruit, he just insists that's not an apple and something that merely happens to have some things in common with the thing he thinks is an apple. Even when it's clear to anyone else with a passing familiarity with fruit that a Golden Delicious is also an apple.

 

[steenkh]

There's still no mention of "pressure field" Clinger.

So you lost that argument also, and try to cover it up?

 

[Kwalish Kid]

Since everything after one of Farsight's posts has been moved, let me just write one thing.

Farsight demanded to be tested in order to show his expertise, and I offer a test: that he produce a serious description of a galaxy that uses his inhomogeneous space ideas that we can then compare to actual galaxies that we can observe and measure.

 

[Farsight]

<SNIP>

I referred earlier to space and vacuum energy, saying this energy has a mass equivalence, and that space is dark. I also spoke of the cosmological constant which is "the energy density of the vacuum of space", and the raisin-cake analogy. Space expands between the galaxies but not within. And conservation of energy means the energy-density doesn't remain constant. Instead this non-uniform expansion means the energy-density of space becomes inhomogeneous. And that's what a gravitational field is. Every galaxy has this halo or shell of inhomogeneous space, and space has its vacuum energy which has a mass-equivalence and a gravitational effect. So assessing just the visible matter to work out how stars should move around the galaxy just isn't enough. And proposing WIMPs is something that only a particle physicist would do. A particle physicist who doesn't understand the first thing about general relativity. Which is that curved spacetime is a mathematical abstraction, and the reality that underlies it is inhomogeneous space.

<SNIP>

If you want to discuss Forum Management, do so in FMF, not in-thread here.

Replying to this modbox in thread will be off topic  Posted By: LashL

 

[Kwalish Kid]

That's a fine word-salad, Farsight, but it certainly fails the test.

Can you turn that collection of words into a description that we can use to actually compare to measurements that astronomers make? If not, then you are not doing physics.

 

[Farsight]

Au contraire, it passes with flying colours. You know Einstein referred to a gravitational field as inhomogeneous space. You know about spatial energy and how the expansion of the universe is not uniform. And about conservation of energy. So you must know it leads to inhomogeneous space. Which is what Einstein said a gravitational field is. So you know why nobody has found any WIMPs. Yes?

What's not to like?

 

[ben m]

I referred earlier to space and vacuum energy, saying this energy has a mass equivalence, and that space is dark. I also spoke of the cosmological constant which is "the energy density of the vacuum of space", and the raisin-cake analogy. Space expands between the galaxies but not within. And conservation of energy means the energy-density doesn't remain constant. Instead this non-uniform expansion means the energy-density of space becomes inhomogeneous. And that's what a gravitational field is. Every galaxy has this halo or shell of inhomogeneous space, and space has its vacuum energy which has a mass-equivalence and a gravitational effect. So assessing just the visible matter to work out how stars should move around the galaxy just isn't enough. And proposing WIMPs is something that only a particle physicist would do. A particle physicist who doesn't understand the first thing about general relativity. Which is that curved spacetime is a mathematical abstraction, and the reality that underlies it is inhomogeneous space.

Nope, Kwalish is right. That's not physics, that's armchair philosophy. You have a mental picture of what you think is going on, and you're looking at the mental picture and describing it to us. Describing a picture is not doing physics; it's just as easy to describe a false picture as a true one.

Does "Every galaxy has this halo or shell of inhomogeneous space" predict the positions and amplitudes of the CMB acoustic peaks? Does "Every galaxy has this halo or shell of inhomogeneous space" correctly predict the x-ray temperatures of intracluster gas? What form does "Every galaxy has this halo or shell of inhomogeneous space" predict for the variation in rotation curves between small vs. large galaxies? If you haven't done any such comparisons how are we to know whether "Every galaxy has this halo or shell of inhomogeneous space" is a true statement or a false one?

 

[Kwalish Kid]

Au contraire, it passes with flying colours. You know Einstein referred to a gravitational field as inhomogeneous space. You know about spatial energy and how the expansion of the universe is not uniform. And about conservation of energy. So you must know it leads to inhomogeneous space. Which is what Einstein said a gravitational field is. So you know why nobody has found any WIMPs. Yes?

What's not to like?

I would say that what is not to like is you pretending that you are doing physics while insulting those who do. Such behaviour really is repulsive.

You clearly avoided providing anything that we could compare to measurements. You clearly come up woefully short compared to practicing scientists that work hard to establish where dark matter can be found and how much of it there might be.

What you do is not armchair philosophy. At best, it is coming up with a first hypothesis and accepting it dogmatically. At worst, it is self-promotion through insult.

 

[Reality Check]

That Minkowski worked out the physics for a contemporary physical theory does not mean that he endorsed the theory.
...

I wondered what post you were relying to Kwalish Kid and it turned out to be one moved to AAH.
That citation is
The Fundamental Equations for Electromagnetic Processes in Moving Bodies (1908), by Hermann Minkowski. He is not presenting his theory. He is presenting other people's theories specifically Lorentz (where the "Æther" term seems to come from) and Einstein. Many of the usages of Æther in the text actually have quotes around them, e.g. in the introduction there is only "Æther".

 

[Reality Check]

...space is dark

Wrong, Farsight: Space is does not have the properties of emitting of not emitting light.
Farsight: (29 July 2014) What is the scientific definition of space?

P.S. Farsight: (29 July 2014) What is the scientific definition of a field in physics? And the follow-on: How does this make What a field in physics really is by W.D.Clinger wrong?

You got a Wikipedia quote right: cosmological constant

In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) is the value of the energy density of the vacuum of space

And there is such a thing as the raisin-cake analogy.

But then half of the truth:

Space expands between the galaxies but not within.

The other half is "because galaxies are gravitationally bound".

But then you go off into a bit of nonsense. But your mistakes seem to be

• Energy need not be conserved in GR: In special cases, yes. In general — it depends on what you mean by "energy", and what you mean by "conserved".
• The need for dark matter in galaxies is Newtonian, not GR.
• When you run out of visible matter in a galaxy (or galaxy cluster) to account for orbits then of course you have to propose dark matter to make up the difference!
• Every atom, rock, planet, star, galaxy, galaxy group, etc. has a "halo or shell of inhomogeneous space" - that is what mass curving space-time means!
• Proposing WIMPS is what anyone who knows about dark matter would propose. They are dark thus "weakly interacting". They have mass thus "massive". There are no chunks of dark matter that we have detected thus "particles".

 

[Farsight]

...Does "Every galaxy has this halo or shell of inhomogeneous space" predict the positions and amplitudes of the CMB acoustic peaks?

No. It tells you not to presume that dark matter is comprised of WIMPs. It saves you spending twenty fruitless years down a mine.

Does "Every galaxy has this halo or shell of inhomogeneous space" correctly predict the x-ray temperatures of intracluster gas?

No, and there's no reason why it should.

What form does "Every galaxy has this halo or shell of inhomogeneous space" predict for the variation in rotation curves between small vs. large galaxies?

The bigger the galaxy the more "dark matter" there appears to be, and the older the galaxy the more "dark matter" there appears to be.

If you haven't done any such comparisons how are we to know whether "Every galaxy has this halo or shell of inhomogeneous space" is a true statement or a false one?

Because you know the universe is expanding and you know about gravitational binding and vacuum energy and conservation of energy. And you know that curved spacetime relates to inhomogeneous space.

He is not presenting his theory

But he is talking about aether, I've given you the reference you asked for, and if you'd done your own research you could have found it yourself. Do note that space really is dark, that Clinger's field definition contradicts Einstein, that energy is conserved full stop, that "dark matter" need not consist of particles because spatial energy causes gravity and has a mass-equivelence, and that the "halo or shell of inhomogeneous space" is caused by the non-uniform expansion of the universe.

 

[Kwalish Kid]

Because you know the universe is expanding and you know about gravitational binding and vacuum energy and conservation of energy. And you know that curved spacetime relates to inhomogeneous space.

You seem to know these things. As you claim that, "Evidence consists of experimental results and observations," please give us the experimental results and observations we can use for a specific galaxy to discover the inhomogeneous space that you talk about. This will require a specific way of discussing the parameters of inhomogeneous space and will thus require mathematics.

Since you know these things, you will have the means to do this at your disposal.

 

[edd]

The bigger the galaxy the more "dark matter" there appears to be, and the older the galaxy the more "dark matter" there appears to be.

What exactly do you mean by the age of a galaxy here? I mean, if I take a galaxy that's got a single stellar population of 10 billion years old and x₁ amount of apparent dark matter, and merge it with a galaxy with a single stellar population that is 8 billion years old and x₂ apparent dark matter, is the new galaxy 0 billion years old, 10 billion years old, or some weighted average based on the total stellar mass, or some weighted average based on total apparent mass, or some other weighted average, or what? And what is the resulting apparent dark matter content?

edit to add: you shouldn't particularly expect a galaxy to be made up of a single stellar population, but it makes life easier. Also I'd like to know how this works for other galaxy-like objects. Does it work for dwarf galaxies? Does it work for globular clusters?

 

[Farsight]

What exactly do you mean by the age of a galaxy here? I mean, if I take a galaxy that's got a single stellar population of 10 billion years old and x₁ amount of apparent dark matter, and merge it with a galaxy with a single stellar population that is 8 billion years old and x₂ apparent dark matter, is the new galaxy 0 billion years old, 10 billion years old, or some weighted average

Weighted average.

edit to add: you shouldn't particularly expect a galaxy to be made up of a single stellar population, but it makes life easier.

OK. IMHO the important thing is how long has the universe has been expanding whilst this galaxy has been gravitationally bound. Imagine a 2x2x2 cube, a 4x4x4 cube, and an 8x8x8 cube to represent the expanding universe at different epochs. Let's say these are 12 billion years ago, 6 billion years ago, and now. If the galaxy formed 12 billion years ago the space within it has 64 times the energy density of intergalactic space now. If the galaxy formed 6 billion years ago the space within it has 8 times the energy density of intergalactic space now. So the older galaxy looks like it's got 8 (?) times as much dark matter. As for how much, I don't know, and the vacuum catastrophe and the negative-pressure reducing strength of space cause issues anyway.

Also I'd like to know how this works for other galaxy-like objects. Does it work for dwarf galaxies? Does it work for globular clusters?

I imagine so. Turn the usual rubber-sheet picture upside down. The rubber sheet starts as a high flat plateau, and as space expands the intergalactic regions drop. The in-galactic regions are like flat-topped mesas, height being related to galactic age. But if the galaxy is small it's more like a peaked mountain. Imagine you're viewing this from the top. Draw two concentric circles, and vary the size of the inner circle. The region between your two circles is the inhomogeneous space, the dark matter halo. The smaller galaxy appears to have a bigger halo, and the cuspy halo problem maybe doesn't sound so intractable.

 

[W.D.Clinger]

what the word "field" means in physics

Do note that space really is dark, that Clinger's field definition contradicts Einstein,

Do note that

1. "Clinger's field definition" is the definition used by physicists,
2. including Einstein.

Regarding that first point, here's the definition given by Frederick W Byron Jr and Robert W Fuller in Mathematics of Classical and Quantum Physics, Dover edition, 1992, at the beginning of Chapter 1, Section 7:

I.7 DIFFERENTIAL OPERATIONS ON SCALAR AND VECTOR FIELDS

If to each point x_i (i = 1, 2, 3) in some region of space there corresponds a scalar, φ(x_i), or a vector, V(x_i), we have a scalar or a vector field. Typical scalar fields are the temperature or density distribution in an object, or the electrostatic potential. Typical vector fields are the gravitational force, the velocity at each point in a moving fluid (e.g. a hurricane), or the magnetic-field intensity. Fields are functions defined at points of physical space, and may be time-dependent or time-independent.

(The definition I gave is more general. Their definition doesn't mention tensor fields because tensors will be introduced in the following section 8. The domain is restricted to three-dimensional Euclidean space because the purpose of section 7 is to review freshman- and sophomore-level vector calculus, which is limited to three-dimensional Euclidean space.)

As noted previously, Einstein's doctoral dissertation involved pressure fields and velocity fields. Farsight's denial of that fact serves only to remind us that Farsight does not understand freshman-level vector calculus.

Because Farsight does not understand Einstein's mathematics, he can only search for the word "field" and guess at what Einstein means by it, but Farsight's arguments fail even at that primitive level of textual exegesis.

In The Meaning of Relativity, Einstein refers to the g_μν-field, the Coriolis field, to electric and magnetic vector fields that "draw their separate existence from the relativity of motion", to the electromagnetic tensor field that combines those two separate fields into a single coordinate-independent field, to the Newtonian gravitational field, and to "a radial centrifugal field" distinct from the Coriolis field.

Farsight denies the separate existence of the electric and magnetic fields that Einstein explicitly affirmed. Farsight also rejects the meaning of "field" that Einstein relied upon in his mathematics, saying it is inconsistent with the "state of space" Einstein used in his Leiden address to offer his nontechnical audience some intuition for the g_μν-field (spacetime). (To show respect for Lorentz, his host, Einstein referred to that g_μν-field as "the relativistic ether".)

Farsight is wrong when he says the "state of space" intuition is inconsistent with the mainstream identification of Einstein's "relativistic ether" with spacetime (or, less precisely, with the gravitational field—see below) because the tensor field g_μν really does describe the observer-invariant local geometry of spacetime (not space).

On the other hand, it may appear that Farsight's "state of space" intuition is inconsistent with several other fields mentioned by Einstein, including not only the electric, magnetic, Coriolis, and centrifugal fields but also the field that Einstein describes as the gravitational field. From page 66 of The Meaning of Relativity:

In the immediate neighbourhood of an observer, falling freely in a gravitational field, there exists no gravitational field. We can therefore always regard an infinitesimally small region of the space-time continuum as Galilean.

To a mathematician, that isn't quite correct. As becomes clear from what Einstein wrote following the words I quoted, what Einstein actually means here is that any free-falling observer is free to select a coordinate system for spacetime in which, at every point on the observer's spacetime world line, the ten coordinate-dependent components of the pseudo-metric tensor g_μν coincide with those of the Minkowski metric in the standard basis. That means the free-falling observer can always imagine himself to be free from the influence of gravity, attributing the rapidly accelerating approach of the earth (for example) to acceleration of the earth rather than acceleration of the observer.

But that means Einstein's notion of the gravitational field cannot be identified with a state of spacetime, because a state of spacetime would be the same for all observers. Einstein's "state of space" imagery is rescued by relativity: Yes, Einstein's notion of the gravitational field depends upon the observer's arbitrary choice of coordinate system, but so does the observer's notion of space. The same choice of coordinate systems that lets the free-falling observer imagine himself to be free from gravitational influence also determines that observer's decomposition of spacetime into space and time. By choosing a coordinate system that eliminates gravity everywhere along the observer's world line, the observer has also chosen a notion of space that makes (Einstein's notion of) the gravitational field disappear at every point of space through which the observer travels. Note well, however, that the gravitational field may disappear at those points only for the instant the observer travels through them.

Most of those same considerations apply to the electric, magnetic, Coriolis, and centrifugal fields. Those fields can also be regarded as states of space—provided we understand the "space" in question is observer-dependent.

So Farsight is wrong across the board: When speaking of gravitational, Coriolis, centrifugal, electromagnetic, electric, or magnetic fields, Einstein's metaphorical "state of space" provides an intuition consistent with physicists' technical definition of a field, which is of course the definition used in Einstein's own mathematics.

 

[Kwalish Kid]

Weighted average.

OK. IMHO the important thing is how long has the universe has been expanding whilst this galaxy has been gravitationally bound. Imagine a 2x2x2 cube, a 4x4x4 cube, and an 8x8x8 cube to represent the expanding universe at different epochs. Let's say these are 12 billion years ago, 6 billion years ago, and now. If the galaxy formed 12 billion years ago the space within it has 64 times the energy density of intergalactic space now. If the galaxy formed 6 billion years ago the space within it has 8 times the energy density of intergalactic space now. So the older galaxy looks like it's got 8 (?) times as much dark matter. As for how much, I don't know, and the vacuum catastrophe and the negative-pressure reducing strength of space cause issues anyway.

I imagine so. Turn the usual rubber-sheet picture upside down. The rubber sheet starts as a high flat plateau, and as space expands the intergalactic regions drop. The in-galactic regions are like flat-topped mesas, height being related to galactic age. But if the galaxy is small it's more like a peaked mountain. Imagine you're viewing this from the top. Draw two concentric circles, and vary the size of the inner circle. The region between your two circles is the inhomogeneous space, the dark matter halo. The smaller galaxy appears to have a bigger halo, and the cuspy halo problem maybe doesn't sound so intractable.

As you wrote that, "Evidence consists of experimental results and observations," could you please translate what you have written here into something that we can compare to the observational details? Otherwise, you have no evidence according to your own criterion.

 

[edd]

Weighted average.

OK. IMHO the important thing is how long has the universe has been expanding whilst this galaxy has been gravitationally bound. Imagine a 2x2x2 cube, a 4x4x4 cube, and an 8x8x8 cube to represent the expanding universe at different epochs. Let's say these are 12 billion years ago, 6 billion years ago, and now. If the galaxy formed 12 billion years ago the space within it has 64 times the energy density of intergalactic space now. If the galaxy formed 6 billion years ago the space within it has 8 times the energy density of intergalactic space now. So the older galaxy looks like it's got 8 (?) times as much dark matter. As for how much, I don't know, and the vacuum catastrophe and the negative-pressure reducing strength of space cause issues anyway.

I imagine so. Turn the usual rubber-sheet picture upside down. The rubber sheet starts as a high flat plateau, and as space expands the intergalactic regions drop. The in-galactic regions are like flat-topped mesas, height being related to galactic age. But if the galaxy is small it's more like a peaked mountain. Imagine you're viewing this from the top. Draw two concentric circles, and vary the size of the inner circle. The region between your two circles is the inhomogeneous space, the dark matter halo. The smaller galaxy appears to have a bigger halo, and the cuspy halo problem maybe doesn't sound so intractable.

The oldest objects are globular clusters (which in times of less precise cosmology were often dated as older than the universe!). They're also very compact.

Unfortunately their dynamics also show no evidence for dark matter.

Bit of a problem I think.

 

[ben m]

No. It tells you not to presume that dark matter is comprised of WIMPs. It saves you spending twenty fruitless years down a mine.

Ha ha! This is great. In the other thread you were just telling us, very clearly, that you believed that all of the equations of General Relativity (the ones used by non-Farsight practitioners) are well-tested and give correct real-world results, and you only wanted to talk about interpreting the equations and not re-solving them. (ETA: see here) Now you're telling us that your version of GR differs from standard GR to the extend that it can explain astronomical observations without including dark matter.

There's lots of pretend going on here, Farsight. Let's face it, you're only pretending to care about equations or predictions or numbers at all. When someone comes along with a claim you don't want to argue with---"GR correctly predicts the Moon's orbit to 1mm precision"---it's convenient for you to pretend that your equations are the same as the GR equations. When someone comes along with a claim you do want to argue with---"GR doesn't explain basic galaxy structures unless dark matter is present"---it's convenient for you to pretend that your equations lead to exciting, paradigm-shifting new predictions. (I presume that if someone asks you to actually work out those new predictions, i.e. to use the equations, you'll return to pretending that your solutions are the standard ones, allowing you to pretend that you don't need to calculate anything because such standard calculations were already done somewhere.)

 

[ben m]

Imagine you're viewing this from the top. Draw two concentric circles, and vary the size of the inner circle. The region between your two circles is the inhomogeneous space, the dark matter halo. The smaller galaxy appears to have a bigger halo, and the cuspy halo problem maybe doesn't sound so intractable.

Mainstream problem: Numerically solving the equations-of-motion of matter, using computationally-tractable approximations to the laws of physics, yields "cuspy" galaxy halos. These cusps are not seen in the real world so there's something wrong.

Mainstream solution: Try to make the standard model computations (finer resolution, better "gastrophysics", supernova feedback) closer to what's actually happening; test similar computations with nonstandard physics (MOND, SIDM, WDM, etc.) and see whether cusps emerge or not.

Farsight solution: Draw a cartoon picture and don't put in a cusp. Look, no cusp! Problem solved.

 

[Farsight]

The oldest objects are globular clusters (which in times of less precise cosmology were often dated as older than the universe!). They're also very compact. Unfortunately their dynamics also show no evidence for dark matter. Bit of a problem I think.

I won't persue that with references. Good luck with the WIMPs.

As noted previously, Einstein's doctoral dissertation involved pressure fields and velocity fields. Farsight's denial of that fact serves only to remind us that Farsight does not understand freshman-level vector calculus.

To reiterate: your reference didn't mention pressure fields, nobody talks of pressure fields, but I have referred to the gravitational field as "a pressure gradient in space" which you said was wrong.

In The Meaning of Relativity, Einstein refers to the gμν-field, the Coriolis field, to electric and magnetic vector fields that "draw their separate existence from the relativity of motion", to the electromagnetic tensor field that combines those two separate fields into a single coordinate-independent field

Which is why I've repeatedly told you that the field that's there is the electromagnetic field.

Farsight also rejects the meaning of "field" that Einstein relied upon in his mathematics, saying it is inconsistent with the "state of space" Einstein used in his Leiden address...

The field is a state of space comes from Einstein's 1929 field theory article.

Farsight is wrong when he says the "state of space" intuition is inconsistent with the mainstream identification of Einstein's "relativistic ether" with spacetime

That's your identification, and it's wrong. Robert Laughlin said space, not spacetime.

...As becomes clear from what Einstein wrote following the words I quoted, what Einstein actually means here is that any free-falling observer is free to select a coordinate system for spacetime in which, at every point on the observer's spacetime world line, the ten coordinate-dependent components of the pseudo-metric tensor gμν coincide with those of the Minkowski metric in the standard basis. That means the free-falling observer can always imagine himself to be free from the influence of gravity, attributing the rapidly accelerating approach of the earth (for example) to acceleration of the earth rather than acceleration of the observer.

That's wrong too. Einstein was clear that you cannot transform away a special (=real) gravitational field. It's in section 20 of Relativity: the Special and General Theory, and I quote:

"We might also think that, regardless of the kind of gravitational field which may be present, we could always choose another reference-body such that no gravitational field exists with reference to it. This is by no means true for all gravitational fields, but only for those of quite special form. It is, for instance, impossible to choose a body of reference such that, as judged from it, the gravitational field of the earth (in its entirety) vanishes".

So Farsight is wrong across the board

As you can see from the above, I'm not.

Ha ha! This is great. In the other thread you were just telling us, very clearly, that you believed that all of the equations of General Relativity (the ones used by non-Farsight practitioners) are well-tested and give correct real-world results...

I didn't say that. I've said previously that there's issues with FLRW models and black hole point singularities. But I've also said GR is one of the best-tested theories we've got.

Now you're telling us that your version of GR differs from standard GR to the extend that it can explain astronomical observations without including dark matter.

Yes. Because GR doesn't start with the the assumption of homogeneity and isotropy of space, the Friedman Lemaitre Robertson Walker metric does. Even though Einstein described a gravitational field as inhomogeneous space. When you assume homogeneous space you need to add matter to explain the gravitational anomalies.

There's lots of pretend going on here, Farsight. Let's face it, you're only pretending to care about equations or predictions or numbers at all.

Not so. The above point is quite crucial. The FLRW metric starts with the assumption of homogeneity and isotropy of space. That's space with no gravitational field in it. It doesn't allow for the non-uniform expansion of space that converts homogeneous space into inhomogeneous space, which is what a gravitational field is.