Why is that a conundrum? GR clearly says that on small scales, we should see contraction, not expansion (because there are inhomogenities there).


Multiple independent lines of evidence all point to the same conclusion. Yes, all of them come from "line of sight" observations, not from lab tests, but so what? As long as there is no other theory which could explain the observations as well, I think we are fully justified to accept the BBT.


Obviously, no test is ever "final".


The second has nothing to do with cosmology, the first could perhaps be explained by dark energy (sorry, I don't have the reference to the relevant paper where I read this handy right now), and the third is nicely consistent with what we expect of dark matter. So where exactly is the problem?

Did you discuss all the pieces of evidence I mentioned in my last post? I'll bet that you never even heard of all of them before.


Sorry, I didn't understand what you meant here. Could you please rephrase this?

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This is only an 'if' scenario: if Newton's G was higher (than here on Earth) isotropically through most of intergalactic space, it might explain why clouds of hydgrogen gas collapse into fusion combusting stars (G too weak otherwise), or why neutron stars have incredibly high spin, or why distant cosmic light gravitationally-redshifts naturally through very high G between the very vast spaces between visible galaxies, or why 'dark' galaxies give weak gravitational lensing... and so on. It's just a hypothetical possibility, that there is something going on 'out there' that we cannot fathom from 'our here' observations via line of sight. Can't dwell on this too much, or I will get thrown out! Thanks for asking, though.

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We are here in the ATM forum. I don't see why you should get thrown out of this forum for talking about speculative questions. The only reasons I'm aware of for throwing someone out is if someone uses insults etc. or consistently refuses to answer direct questions.

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The universe is big. Really big. It may seem like a long way to the corner chemist, but compared to the universe, that's peanuts. (Douglas Adams, Hitchhiker's Guide to the Galaxy)

Wow!

This thread has generated so many thoughful responses, I cannot respond to them all in the instant. But it was started as a sort-of "New Year's resolution" for 2007...so we still have 11+ months to resolve the proposition

Your point is well-taken, and I admit some confusion on this. I do not see how they can do these simulations without taking duality into considerating. But duality is completely absent from the popular accounts. How can duality be present-and-accounted-for by "real" cosmologists, but utterly AWOL from the popular accounts?

We could go 'round and 'round on this (PI).

Try this though-experiment: Put some dark matter in orbit around a BH. Because it does not interact with radiant matter, and it cannot radiate, it is just going to orbit the BH, not spiral in. The difference between the radiant matter spiralling in and the dark matter holding steady in its orbit is radiation. Ergo, radiation is "the cause" of the spiralling, not the other way 'round.

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PW -- Plant Whisperer

The units used is a good point of discussion.

It has been pointed out here that expansion is not a given--redshift is a given; expansion is an interpretation of redshift--but if we take expansion as a given, there are 3 basic scenarios possible: the expansion is slowing, like a canon-ball shot straight-up; the expansion is steady, like an up-elevator; and the expansion is accelerating, like a rocket just launced. In the first case, the canon-ball loses kinetic energy but gains gravitational potential energy (GPE), such that the total, kinetic-plus-potential, is constant. In the second, the elevator gains GPE at a constant rate. In the last, the rocket gains both kinetic and potential energy.

But in all 3 cases, we can give an instantaneous rate at which the object of interest is gaining GPE, i.e. so-many joules per second. Since they all weigh different amounts, it is convenient to express the GPE gain on a per-unit-mass basis, or so-many j/kg/s. No matter whether an object is accelerating, decelerating or moving at a constant rate, if it is going "up" in a gravitational field, it is gaining GPE, and the instantaneous rate can be expressed as so-many j/kg/s.

According to wiki, however, DE has units of kg/m^3 (SI):The energy required to expand a gravitaional system--any system--is expressed in j/kg; it takes energy, and the amount required depends on the mass. If you want to express it in terms of a rate, then you have to express in j/kg per unit time, or j/kg/s.

The mainstream expresses Dark Energy as mass-per-unit-volume, and I have expressed it in "layman's terms," joules-per-kilogram-per-second. What we have here is a conceptual collision; I have no idea what DE expressed in terms of mass-per-unit-volume means.

I do not know what the answer is, but I feel a lot of the misunderstanding revolves around this differing picture. No matter how I slice it or dice it, the energy required to expand a given gravitational system at a given rate is expressed in j/kg/s.

What are they talking about, this kg/m^3?

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PW -- Plant Whisperer

Newton’s theory of gravity predicted a precession of Mercury’s orbit of something like 523 arc-seconds per century, while Einstein’s GR predicts something like 570 arc-seconds per century. The numbers are different, but the units are the same: arc-seconds per century.

If you say to me with a straight face, Newtonian gravity predicts 523 arc-seconds of precession per century, but according to GR, the figure is 0.036 m^2, I will tell you: You are straight wrong. The “problem” is in arc-seconds per century; so must the “solution.”

The same applies to any other aspect of gravitation: the difference between the prediction of Newtonian/Euclidean gravity/geometry and the prediction of GR is numerical, not dimensional. Whatever dimensions the parameter has in Newtonian gravity, it has the same dimensions in GR.

In the three 2-body examples I gave above (canon ball-earth; elevator-earth; rocket ship-earth), the rate-of-change in gravitational potential energy, for a given rate of expansion, is always joules per kilogram per second. This dimensional aspect to the problem is always the same.

Source

Now, along comes GR, and the expansion energy, instead of being expressed in j/kg/s, is given in kg/m^3, i.e. the same units as density

As Bjoern politely conceded (paraphrasing), the units I choose for contraction energy—j/kg/s—are natural and intuitively self-evident. Observationally, astronomers can measure energy output of the stars—in watts—and they can infer how much mass is there ("The mass is out there"). Divide wattage by the mass, and you are done: j/kg/s. Since expansion is the opposite of contraction, expansion energy, too, has dimensions of j/kg/s. QED.

Nonetheless, the expansion shows up observationally as redshift (z), not energy input, and z is a dimensionless number. The mainstream, through a many-runged inferential ladder, has converted the dimensionless redshift into an expansion rate, having dimensions of inverse-time.

In the DEILE thread, I present my own conversion, which extends the mainstream’s conversion to j/kg/s. I combine the observed expansion rate with the observed density, make a few assumptions, and calculate a result. Regarding my conversion, Bjoern has written (paraphrasing again), I see how you arrived at your conversion, but I am not sure it is right. And I concede the numerical value may be off by some factor, perhaps a large factor, but at least it is in the expected units (j/kg/s)!!!

Let us review this dimensional-tangle for a moment

· The first observation is redshift, a pure number having no dimensions
·· The mainstream—making certain assumptions—has converted redshift to expansion rate, having dimensions of 1/t, arriving at a numerical value of about 2.3E-17 per second.
··· Peter Wilson—making certain assumptions—has converted expansion-rate to energy-input, “to-be-explained,” having dimensions of j/kg/s, and a numerical value about 6E-9 j/kg/s.
····Cosmologists, using the field equations of GR, have inferred an energy source in the cosmos, which has dimensions of density, kg/m^, and having a numerical magnitude of about 1E-28 kg/m^3.

We are expressing 1 phenomenon in 4 different ways:
1. Pure numbers
2. A rate
3. A rate of energy per unit mass
4. A density

No one in the mainstream will concede my numbers are right (evidently), because my numbers are in j/kg/s, and their’s are in kg/m^3.

If somebody can explain, in a rational scientific manner, how you convert kg/m^3 to j/kg/s, then we can compare the two numbers and decided if contraction energy is indeed the source of expansion energy.

Or would the defenders of the mainstream prefer to simply tell stories about how important math is?

For my part, I have tried my best to convert the mainstream’s “Dark Energy,” which they give as so-many kg/m^3, into j/kg/s, the units used in Newtonian gravity. It would be nice to compare my apples to the mainstream’s orange. Yet no matter how I slice it or dice it, I cannot turn lead into gold nor kg/m^3 into j/kg/s. But as anyone who has followed my thread at all knows, I’m not very good at math.

Can anyone here on the board explain how one converts the kg/m^3 of dark-energy in GR to the more familiar j/kg/s of gravitational potential energy in Newtonian gravity? Can anyone express the mainstream’s mysterious kg/m^3 in layman’s terms?

Think about how elusive the problem of Dark Energy has been. Indeed, we may never find the mysterious 1E-28 kg/m^3, if what we are looking for is a certain number of j/kg/s !!!

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PW -- Plant Whisperer

There are others. One of them is to push your own ATM ideas outside your own thread or in another's thread. Nutant abandoned his defense of his idea of a variable G and now just mentions it in other threads.

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Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Neptune- The original Dark Matter.

The author feels that this technique of deliberately lying will actually make it easier for you to learn the ideas. - Donald Knuth

Peter, part of the problem is you are assuming that what the mainstream is looking for is energy. It's possible that energy is what they are looking for and j/kg/s could possibly be correct. Then again, it may not be as it could be an observational effect. DE may be an unfortunate name for it. It gives the layman some sort of idea that energy is what is being looked for. DE is simply the name given to the effect that is apparently increasing the speed of expansion. What the cause actually is, is unknown. The name was originally given becase the cause of the effect was unseen (hence dark) and the term (cosmological constant) that can account for it, appears on the energy side in the GR field equations.

One of the reasons the mainstream uses kg/m³ is that the expansion can be thought of as a decrease in the density (the same amount of mass in a larger area) and in some of the calculations, it's easier to work in density.

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Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Neptune- The original Dark Matter.

The author feels that this technique of deliberately lying will actually make it easier for you to learn the ideas. - Donald Knuth

Thanks Tensor, for explanation. I "can't go there" without reviving my argurments for variable G, other than an occasional 'honorable' mention if relevant to topic discussed. And even then I am always on thin ice, until such time there is independent confirmation of such a possibility, empirically, so can't revive that old, not yet. Cheers.

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Ok, let me see if I understand this correctly:

Dark Energy was a "missing energy" problem, until 903512 pointed out an obvious, overlooked energy-source.

Since a probable source of Dark Energy has been identified, are you saying the Dark Energy problem is "possibly" not an an energy problem, after all?

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PW -- Plant Whisperer

Yep, it's possible, but unlikely. Since the cosmological constant is part of the energy term in GR, it is assumed that some sort of energy is involved. Read the history of the term "Dark Energy". It is, in reality, the name given to the cause of the apparent acceleration of the expansion of the universe. That cause is, at this time, unknown. It could be the result of errors in observations (although this is now quite unlikely), it could be some kind of force, or it could be something we have no idea about. We simply don't know and the term is simply a placeholder for the cause, until and if, we figure out what is causing the acceleration.

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Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Neptune- The original Dark Matter.

The author feels that this technique of deliberately lying will actually make it easier for you to learn the ideas. - Donald Knuth

Not exactly.
What we see is an exclusive 2 aspects of something we call light. The REAL light remains unknown to us.

Consider a dead red fish in an aquarium. We have only one camera, that we can point to 2 directions only and exclusively. What we see : 2 different images that cannot be seen at the same time, kuz we only have one camera. These are 2 aspects of the same thing: a very complicated organism.

So, what is really light ?? nobody knows.
Light for us, is merey the wave-function-collapsed of the REAL light.

That sounds a bit like MOND. Are you familiar with that?

And: can your idea also explain these observations?

* F. Prada et al., Observing the dark matter density profile of isolated galaxies, Astrophys. J. 598 (2003) 260 (astro-ph/0301360)

* http://cosmicvariance.com/2006/08/21...matter-exists/

If you think this is off topic for this thread, please open a new one.

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Then look up the actual papers, and see for yourself.

Essentially, what they are doing is perturbation theory (do you know what that is?) for the BBT. They study what influences small deviations of the large-scale homogenity have, and how these develop with time.

As I said: it's complicated stuff. Few people even grasp a homogeneous universe - inhomogenities are much more difficult!

But this is not "utterly" absent from popular accounts. There are some accounts which discuss this. I have a paper somewhere from the popular press which talks about that, IIRC, but I have to dig it up first...


In the meantime, this goes a bit into this direction...
http://www.newscientist.com/article.ns?id=dn6871

This webpage is also on a more popular level, but doesn't really tell much of the underlying physics:
http://www.virgo.dur.ac.uk/new/index.php


I'd argue that the crucial difference here is that dark matter does not even interact with itself, whereas normal matter does. I. e. for normal matter, there is friction, which leads to spiralling in, which leads to heating up, which leads to radiation. For dark matter, there is no friction, etc.

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The universe is big. Really big. It may seem like a long way to the corner chemist, but compared to the universe, that's peanuts. (Douglas Adams, Hitchhiker's Guide to the Galaxy)

I've also mentioned already several times that beside redshift, there are also other pieces of evidence for expansion (e. g. time dilation in SN brightness curves, Tolman tests, changing temperature of the CMBR, ...)


Agreed.


So, what you call the "rate of expansion" would actually be the "rate of energy gain per mass". I could live with that.


Actually, that's the unit of the density of DE (multiplied by c^2).


The two are not the same. The first is the momentaneous density of DE, the second is the rate of change of the amount of DE, per mass.

You could as well say that a position and a velocity are the same!

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Yes, I know Milgrom's MOND hypothesis for 'flat rotation curves' in outer portions of galaxies. It is not OT if kept within the MOND aspects of why Hubble expansion may be due to higher G readings on outer galaxy's fringes. In your referenced article on "Dark Matter" it says: I suspect what MOND shows, though we have no proof at this point, is that outer galaxy fringes act 'as if' gravity (for normal baryonic matter) were greater out there. If so, then it would also means (per Equivalence Principle) that normal baryonic matter our there has higher 'inertial mass' than closer inside the galaxy. My take on this, as yet unconfirmed from any other sources, is that this 'higher inertial mass' phenomenon is more common in the vast spaces of inter-galactic space, but not easily identifiable within intra-galactic space. One possible indication of this is the very weak acceleration towards the Sun by both Pioneer 10 & 11, where they might be (totally specualtive here) gaining inertial mass as they exit our solar system. Again, if so, there may be an uncomfirmed, and as yet not theorized, inverse relationship between 'inertial mass G' and solar radiant energy. This would fit, if true, into a pattern of greater inertial mass with distance from 'hot' galaxies; it would also explain why 'cold' dark galaxies exhibit weak gravitational lensing. So no exotic 'dark matter' is needed is it is all chalked up to merely higher G cum inertial mass in the colder regions of space.

That said, without taking you into the math by which these ideas were developed, this idea's hypothesis of a variable (and higher) G far from hot solar sources can be tested falsifiably. But as of yet, we have not dedicated any such tests for the outer solar system, where such small variations to G would first be registered (ala Pioneer Anomaly). Perhaps the Pluto probe, now at near Jupiter, can be adapted to test for this hypothesis, but not written up anywhere I know of. What about CMBR, "Bullet Cluster" observations, 'dark energy' space expansion, non-baryonic exotic matter? They would have to be refigured, if G is found variable, and the Hubble constant's match to redshifted distant cosmic light would of necessity be not from the 'Doppler effect' of expanding space, but from gravitational redshift instead. This is what is at stake here, and why it may be potentially contentious, even for ATMers. Of course, if gravitational redshift is cause, meaning 'expansion' is illusional, then GR comes into question as well. Today, that is still largely unacceptable by mainstream cosmology, and even unacceptable for ATM; that is, it is unacceptable until we find some independent confirmation that G is higher farther away from hot energy source. "Duality" would then become the interaction of 'hot' energy with 'gravitational' potential energy, in effect, inversely proportional to each other (no math here). Essentially, that's where it rests for now.

I rate all this, personally, as "puzzling" and "qualitative" only, until such time that we have "quantitative" confirmation... or am I on the wrong thread?

Ps: Here's an interesting article by NewScientistSpace: http://space.newscientist.com/article.ns?id=dn8631 on "Gravity theory dispenses with dark matter". It says: But I think the reasoning here is false, because when I figured MOND for Pioneer Anomaly, I got this, where (delta) -a = 8.417E-7 m s^-2, which is close to what it should be: ~a = -8E-8 cm/s^2, but not close enough.

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It also made predictions that do not agree with observation: that the universe would not be flat; that the horizon everywhere would look different; and that the expansion would be slowing down.

As mentioned in DEILE thread, the BBT now rests on two (2) unknown-to-science energy fields, that is, unknown outside cosmology where they hold up the theory: Inflation & Dark Energy.

Give me two arbitrary, made-to-order energy fields to work with, and I can make any theory fit any set of observations.

The point is, duality offers an explanation of the observed expansion, the flatness, the horizon, and the acceleration, without any ad-hoc conjectures!

There is no Dark Energy problem when duality is taken into account. "Dark Energy" is a problem within the current model that has been accepted as "truth," inspite of striking out on most of its predictions.

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PW -- Plant Whisperer

And the way to get the attention of the astronomers is to show the data with your predicted curve overplotted. If it fits as well, or better, than the current cosmological theory, then you will definitely attract attention.

I think until you can do that, you won't get much attention, sorry to say...

There are also other proposed explanations for the flatness etc. beside inflation, so make this one, not two.

(1) Please do.
(2) Please do then additionally the following: take these two energy fields which you made up based on observations and use them to predict what new observations will show. Then make these new observations and compare. (hint: that was done for both inflation and dark energy)

As long as you mean "qualitative story" when you say "explanation"... Please show how your idea of "duality" quantitatively explains at least some of the observations. E. g. show a plot with the SN data and the prediction of duality.

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You wrote lots of interesting stuff (thanks to the link to the New Scientist article - I had not heard of that before), but as far as I can see, you did not address the evidence in the two articles I cited. Please do so.

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I'm unable to open (astro-ph/0301360), so can't comment on it. On the second: http://cosmicvariance.com/2006/08/21...matter-exists/ , I did open, but not sure what part of this article you are asking me to address. Can you restate your question, regarding what you would like me to address? Are your referring to this? My point is that without empirical evidence to show gravity may have a different G from what we know on Earth, there is not much we can do at this point. I too agree 'large scale' departure from GR would be unexpected, which is what MOND does, so we should keep an open mind that perhaps we have it wrong by assuming Newton's G is a 'universal constant'.

Or if I misunderstood, please specify which part you wanted me to address. Thanks.

[Ps: If I may add, Dark Matter is a gravity problem, while Dark Energy is an 'anti-gravity' problem, so both end up being gravity problems. If we got gravity wrong, especially if cosmic light redshift is gravity-related (deep space gravitational redshift) rather than 'expanding space' related, then in principle, a better understanding of gravity could resolve this 'duality' conundrum, IMO. This would be resolved with nearness not being expansionary, while farness is, at least from our observations.]

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Sorry. Corrected link:
http://www.arxiv.org/abs/astro-ph?papernum=0301360
You can download a pdf file there.

The actual observations: that after the galaxy collision, the cluster gas remains close to the collision point, whereas most of the matter of the galaxies simply moves along with them (i. e. is collisionless and therefore not gas).


The CMBR is thought to be redshifted light (you probably now that), and in the CMBR, one can find evidence for gravitational redshift. It's a tiny effect compared to the total redshift, but it can be seen. Look here for more about that and some references:
http://www.talkorigins.org/faqs/astr...gbang.html#isw

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Thanks for reference, Bjoern, especially how ‘gravitational redshift’ affect CMBR, where it says:

” As CMBR photons pass through the foreground large scale structure, they pass through many such gravitational wells. If the depth of the well is static (or rather if the depth of the well is increasing at the same rate as the expansion of the universe), then the net energy change is zero. All of the energy they gained falling in is lost climbing out. However, if the universe contains dark energy (or has an open geometry), then the universe expands faster than the gravitational wells around massive objects can grow. As a result, the CMBR photons do not lose all of the energy they gained falling into the potentials. This makes the CMBR look very slightly hotter in the direction of these potentials, which also contain the highest concentrations of galaxies.
Following the release of the WMAP data, studies done by Scranton (2003), Afshordi (2004), Boughn (2004), and Nolta (2004) measured this effect using galaxies selected in a number of different ways. The signal-to-noise in any one of the measurements was not very large. However, taken together (and combined with the WMAP observation that the geometry of the universe was best fit by a flat universe), they provide significant evidence that this effect is real and is best explained by the standard Lambda CMD model of BBT.”

This may be a case of ‘finding what we’re looking for’ with postulated BBT, but in this case the gravitational potentials are wells caused by visible galaxies, not invisible ‘dark matter’ so don’t know if they really discounted the gravitational redshift for cosmic light in its entirety, especially after they are adjusted for expected space expansion. If space is full of higher-G defined ordinary baryonic matter, dark because it does not emit light, and where G is orders of magnitude greater than our Earth’s 1G, the gravitational related redshift might account for most of what is observed, with no expansion (factored in) necessary. I treat this all as speculative for now, however, until there is collaborative evidence for a variable, in space higher, Newton’s G, which per Equivalence would make deep space matter act ‘as if’ it were more massive (than the same matter would be on Earth). To be studied further.
I don’t know enough of what is happening here to answer yours. It says: ”The gravitational field, as reconstructed from lensing observations, is not pointing towards the ordinary matter.” However, I would not expect it otherwise, since ‘ordinary matter’ is what is visible to observation, whereas ‘dark matter’ is not, so must be ‘reconstructed’. If dark matter is merely non-luminous (higher G) matter, then it would act as the images present: things get pulled gravitationally towards what is not luminously visible, but dark and 'heavy' gravitationally. However, I’m no expert on these images. Maybe someone else has a better explanation?
I’ll copy this, and when have read it will get back to you. Just glancing at the abstract, it says: ” After a careful, model-independent removal of interlopers, we find that the line-of-sight velocity dispersion of satellites declines with distance to the primary. For an L* galaxy the r.m.s. line-of-sight velocity changes from ~120 km/s at 20 kpc to ~60 km/s at 350 kpc. This decline agrees remarkably well with theoretical expectations, as all modern cosmological models predict that the density of dark matter in the peripheral parts of galaxies declines as rho_DM propto r^{-3}. Thus, for the first time we find direct observational evidence of the density decline predicted by cosmological models; we also note that this result contradicts alternative theories of gravity such as MOND.” This is ‘line-of-sight’ observed, as it only can be, and it fits modeled ‘density decline predicted by cosmological models’ so it all looks right. Will need to read in full before can comment more. For now, Dark Matter is what is modeled, with which I have no disagreement; my definition of this dark matter is that it is not some exotic stuff, but merely unlit baryonic matter exhibitting higher G related mass, so gravitationally it acts ‘as if’ it were some gravitationally denser exotic matter. The higher density halos around galaxies could be no more than that, higher-G cum higher inertial-mass baryonic non-luminous matter. Will read the paper, thanks.

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Ok... I think he's talking about the "Bullet Cluster". This is the jist of it:

There are two galaxy clusters that have collided. In between the two galaxy clusters is a large amount of x-ray luminous gas. This is believed to be the remnant of the collision. The galaxies themselves will have passed through each other, but the gas in each of the clusters will have collided and heated up in the process.

Based on the X-ray data, you can estimate a mass of material in the gas. When compared to the luminous matter in the galaxies, this gas should represent the bulk of the matter in this system. However, based on weak lensing observations (i.e. looking at how the mass of the clusters affects the shapes of the images of background galaxies) the bulk of the mass is in the clusters.

This means that there must be a source of mass that is associated with the clusters, is collisionless (otherwise it would be where the X-ray gas is), and completely unseen.

Voila! Dark matter....

At this point, I just want to know if it is right or wrong.

The BAUT community has been trying to pick it apart for about a year now, and no one has succeded. Naturally, I cannot see any error in it...but no one else can show an error, either.

Disparaging remarks, naturally, do not count as finding an error.

And changing the goal-posts does not count, either. By that I am referring to the dark-energy-is-not-really-energy comments.

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PW -- Plant Whisperer

There is a simple reason for that: so far, you have not attempted to actually address the real data. If you didn't know: that always the only sensible test of a new idea. That is the way for finding out if an idea is "right or wrong".

So, why don't you do that?

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But as far as we know (e. g. from gravitational lensing, rotation curves of galaxies etc.), every visible galaxy is surrounded by even more dark matter. Hence these wells are caused primarily by dark matter, not by the visible stuff.


I wanted to point out that we know what "gravitational redshift" looks like, that we can separate it in the data from other sources of redshift. That we can do that rules out a gravitational cause for the usual redshift, I'd say...


If you already admit that non-luminous, collisionless matter may exist, then why do even need to postulate a higher G for that stuff? Its existence alone, with the usual G, is enough to explain the observations. (if it is collisionless)


But "unlit baryonic matter" is not collisionless. Hence in the bullet cluster galaxy collision, "unlit baryonic matter" had to remain between the galaxies in the collision (as seen for the hot gas - which is, BTW, also "unlit baryonic matter", essentially). But the observations of gravitational lensing show that most of the matter still remains with the galaxies - i. e. most matter is collisionless. And hence this can't be simply "unlit baryonic matter".

Further, for "unlit baryonic matter", you can't get a decline of the density proportional to 1/r^3. Again, this only works for collisionless matter. So again, the invisible stuff around galaxies can't simply be "unlit baryonic matter".

Do you understand now why these two observations provide evidence that dark matter is not baryonic, but something more exotic?

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The universe is big. Really big. It may seem like a long way to the corner chemist, but compared to the universe, that's peanuts. (Douglas Adams, Hitchhiker's Guide to the Galaxy)

It's not about right or wrong, it's about matching the observations. It's good physics if it works.

I must admit I do not see the difference between 'exotic' non-baryonic (dark) matter, and ordinary (dark) baryonic matter exhibitting higher G (gravity) when cold and dark. The hypothesis, if it is more than mere speculation, is that ordinary matter, i.e., hydrogen (HI) gas, in space when far from hot energy sources (stars and galaxies) acts 'as if' if were gravitationally exotic, in that it displays higher gravitational attraction (not 1G, but much higher G) to give both flat galactic rotation curves and weak gravitational lensing. There is an intermediate 'warm dark matter' which should, by this reasoning, show similar characteristics (as observed) but of lesser intensity ("warmer" is still potentially higher G than 1G). But that said, I don't really understand what they mean by "collisionless dark matter" so am stumped here... though Amber Robot explained it above. If colliding 'dark matter' gases get heated up, they are now 'warm dark matter' remnants of collision, then I don't understand how they are "collisionless" but colliding, for example. This 'dark matter' does interact with light, if gravitational lensing is considered, though it does not appear to interact with ordinary matter, if I understand correctly. Then again, I must admit I am slow here (still reading the paper).

The main issue of this thread, "Duality: Explanation of the Hubble expansion, or not?", is whether both expanding and non-expanding space at a distance can coexist simultaneously. However, that implies that 'dark energy' is responsible for expansion, while 'dark matter' gravitationally should somehow counteract this; so both conditions exist. My understanding is colored by a different hypothesis, one is that 'expansion' is an optical illusion from gravitational redshift, which means the universe is static, and not expanding, because gravity G is greater in intergalactic space; while at the same time, greater gravity far from hot energy sources (per my hypothesis), which translates into a higher G, is what represents 'dark matter', not exotic non-baryonic matter but merely higher-G baryonic matter. The fact that such HI gases are non-luminous, or 'warm' only at the X-ray range of observation rather than light waveband, is the puzzle still to be resolved: How can a higher G universe, what represent the 'cold' dark regions of space gases, be responsible for distant cosmic light redshifting, that which causes us to think the universe is expanding at the Hubble constant? My opinion, really just a speculation for now until such time that G is shown to be variable, is that there is no Hubble constant expansion, merely how light redshifts at the Hubble constant, because of the higher-G mechanics of what happens to light when it passes through HI gases, and other space gases, on its way to our instruments measuring spectral redshift. So I see all this as an observational artefact, not a Doppler like space expansion artefact, which leads me to think 'dark energy' is not a real phenomenon. On the other hand, I do think 'dark cold matter' does exist, but it is not what we think, as exotic matter different from normal baryonic matter, but merely higher-G matter in deep space. Nevertheless, this whole point is moot until such time that we find some evidence, any evidence, that Newton's "universal constant" G is anything but. The Dark Matter Density Profile of Galaxies is then a function of how much higher is G "out there", and not non-baryonic matter made up of some new (as yet undiscovered) elemental basic particles. Nothing exotic about that, just a natural progression of observations that may fit a new idea, one which as of yet remains untested, that Newton's G is not constant, nor space 'homogenous and isotropic' at 1 G as now assumed.

The origin of this idea is explored on this page, something called the Axiomatic Equation: http://www.humancafe.com/discus/messages/70/108.html , where using a modified deBroglie equation, E = hf, is matched against a modified Einstein equation: E = mc^2, then applied to orbital energy for each of the planets; the end result shows proton mass changing at a ratio that leads to Newton's G plotted on a straight line, where G grows at the rate of about 1G per 1 AU. This is too complicated to explain here, however, and would be OT anyway. So I leave this reference, imperfect that it is to explain, here for anyone interested in reading further on how a variable G might work as a function of distance from the Sun, or any hot energy star system. (I am posting this link only to show the math, not to push my idea, which is meaningless at this point without real evidence of variable G.)

FYI, there was a very long discussion on a now close thread, where variable G and variable mass were discussed: Hypothetical variable mass in hypo variable G?

(Luna2uno, Lunatik, NG71, and Ivan Alexander, are all the same person: http://www.bautforum.com/showthread....567#post433567 )

Bottom line, is there a "duality" between expansion and gravitational contraction of space at a distance? Yes, observationally, but no, not necessarily in reality, if G is variable. In short, there is nothing 'exotic' about dark matter, if G is variable. At this time, this is as yet unknown, and certainly unproven.

[Note: there's a lot riding on Newton's G remaining a universal constant, since any evidence of it being variable would deeply impact much of today's cosmology based on GR/BBT, which would require a major rethink. I don't expect an easy time of this, if a variable G proves true empirically.]

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[et al]

There is a general misunderstanding that I have not quantified duality. I have, but it does have a tendency to get lost.

Local Contraction energy: Since j/kg/s is not very intuitively, it may help to change it to more familiar units: inches of elevation at the surface of the earth. The conversion comes out to about 2.5 inches per year, (down). In other words, visible matter in the universe is “falling” an average of 2.5"/yr into local gravitational wells, and radiates away that much energy per year in the process. Remotely, everything is "rising" at a rate of 0.8"/yr.

The universe is "falling" (2.5 inches per year) faster than it is rising (0.8"/yr). There is more energy released via contraction than taken up by expansion, by a factor of about 3.

How is that not quantitative?

As for matching the model to the redshift-luminosity data, that was done, although admittedly rather sloppily, at the end of the original DEILE thread.

Summarizing briefly:

If contraction energy is driving the expansion, the expansion must be exponential (i.e. the Hubble constant, H, must be constant). A constant Hubble constant does not match the data very well.

Contraction is not constant, however, but is basically represented by the star-formation rate, which is known to be slowly decreasing.

In order to match exponential expansion to the observed data, H must decrease about 6% per billion years. I do not know if this is the rate a which star-formation is decreasing, but it sounds about right.

So the model is quantified, and it matches the data reasonably well. The math is there and it makes a reasonable fit to the data.

The reason for reluctance in accepting duality lies somehere deeper...

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