I read this article -- http://www.newscientist.com/article/...-theories.html -- on dark matter a few weeks ago and have since then been reading all the dark matter related topics on this forum, as well as looking for info in other places. I guess we can all agree that Dark Matter continues to be one of the great unsolved mysteries, and there's probably a spit-shined and gold-plated Nobel statue specially reserved for the scientist(s) who can finally figure it out.

The problem with Dark Matter, as indicated in this short article, is that based on an analysis of "28 galaxies of all shapes and sizes", it seems there is "always five times more dark matter than normal matter where the dark matter density has dropped to one-quarter of its central value".

The article suggests that as a result of these findings, paraphrasing here, there might be an as yet "undiscovered force of nature working between the dark matter and the normal matter...".

My question is, doesn't this finding seem to suggest that Dark Matter might not actually be "matter" (i.e., particles) at all, but maybe something else? Like, maybe what we observe as Dark Matter might be the effect of large clusters of massive objects (stars) pressing into the "the fabric" of spacetime -- something like that?

Thanks for helping me to understand this better.

Anomalies like the Bullet cluster, and various galaxies with significantly higher or lower dark-matter ratios undermine your hypothesis I think. If your idea was correct, these variations wouldn't occur.

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Forming opinions as we speak

Thanks antoniseb. One of the best things about this forum is that my speculative ideas on how the universe works die quick here. I'll just keep reading and hope that somebody figures it out, someday!

The study, published in Nature, did not deal with clusters of galaxies but with individual galaxies that may have had different merger histories but maintined a correlation between luminous surface density and Dark Matter surface density that remained the same over one Halo distance. This presents a serious coincidence problem to the Dark Matter Particle theories where the correlation is not to be expected. To retain these theories a new force between baryons and Dark Matter Particles needs to be invoked to maintain the observed correlations.

Don't feel bad Lindon, truth is, there are no theories that fully explain anything really. Even Einstein's relativity theory breaks down at the quantum level.

Dark Matter and Dark Energy are not really understood at all but instead are just big "?" marks for what we don't know yet.

There will undoubtedly be better theories to come a long. Never stop asking questions or pondering on it, who knows, you may be the one that figures it all out You don't have to be a physicist to answer the questions, if it makes sense it makes sense. The math will naturally follow.

I'm surprised they don't see the problem in that hypothesis-- the whole justification for invoking dark matter is that we think we understand the forces, if not the matter. If we cannot claim to understand either, there's really no point in calling it "matter" at all, it is completely unconstrained and could be anything our imaginations can conjure.

I suspect that darkmatter is just some previously undiscovered effect of ordinary(baryonic) matter......my idea that massive bodies(or any bodies) appear magnified, I thought might explain Dark Matter...if a galaxy is magnified for the distant observer....or it may be some effect like that.


Here's a thread where I asked about gravitational magnification
Gravitational lensing(or light path bending) and the apparent size of objects.

it seems that the Sun is magnified to look 2kms wider, and higher(I think it was 4 parts per million magnification), to the distant observer, due to the gravity.

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The authors did implicitly mention that some of the Modified Gravity theories are consistent with the observation and cited the threshold theory of Milgrom, known as MOND, in their references. Milgrom has since written a paper on the topic regarding an earlier similar Donato paper.

From the arXiv version of the Nature paper:

“This precise balance must be the result of some unknown fine-tuned process in galaxy formation, because it is a priori difficult to envisage how such relations between dark and baryonic galaxy parameters can be achieved across galaxies that have experienced significantly different evolutionary histories, including numbers of mergers, baryon cooling or feedback from supernova-driven winds.”

It seems another way at looking at the result is that when the baryon surface density exceeds a value within a core radius, Newton takes over and the Dark Matter Effect is rubbed out regardless of prior history and mergers of previous Dark Matter Halos.

So where do all the now missing Dark Matter Particles go after a merger? If they are annihilated, then why do we not see energy evidence from other ongoing mergers monitored currently? If they are pushed aside to outside the Halo core why do not we see an increased lensing wave traveling like a shock wave from the core to the perimeter? If there are Dark Matter Particles, why do they never congregate to produce gravitational accelerations in excess of 10^-9 m/sec^2, a feat easy for baryons? Do they repel each other at a threshold acceleration of attraction? Otherwise, what causes their excess gravity to disappear after accruing a threshold accumulation? If Dark Matter Particles are to self-annihilate at the scale of galactic cores, then why do they not annihilate at the cores of galactic clusters? Would not all the tidal Dark Matter Particle stripping of halos of cluster galaxies contribute to a cluster core density that itself should then have a cuspy halo hole along with an even more prodigious WMAP haze that should be typical of all Dark Matter Particle dominated clusters and not just x-ray clusters? I do not recall any reports of a large cuspy halo core at the center of a cluster of galaxies, x-ray or otherwise. These only represent a subset of problems that beset the LCDM paradigm. In spite of this, it has had much success at describing phenomena at the cluster to cosmological scales.

On the other hand, any Modified Gravity theories that carry any “baggage” requiring a violation of Lorentz invariance are pretty much ruled out by the recent FERMI results. MOND suffers from a missing mass problem and has to invoke extra baryonic mass to account for additional lensing; it has already modified gravity once and can not bootstrap to modify it further without violating the first modification. It has “painted itself into a corner” so to speak by the “a priori” premise by claiming “gravity modification” of Newton’s laws and so can not logically escape from the trap imposed by the premise. Four of the major problems that seem to beset MOND are pointed out by Primack on page 10 of his paper “ Dark Matter and Galaxy Formation”. So here again is a theory that has its successes and problems.

Now there is also the Rachel Bean apparent discovery, pending further observations of larger datasets, that gravity may have affected time differently in the past, more recent than the Dark Energy S-curve inflection, than at present and the offset problem is again, perhaps undeservedly, laid at the feet of General Relativity.

Even though these diverse theories seem to have fatal flaws, the occasion of their remarkable successes should not be overlooked. They seem to be guideposts toward a better understanding.

My guess is that rather than pondering the superficial differences between them, it is rather to look for a theoretical systematic that may plague the “a priori” assumptions common and fundamental to all these theories that include LCDM as well as MOND and other theories that seek to modify the gravity of General Relativity.

References:

Universality of galactic surface densities within one dark
halo scale-length
http://arxiv.org/ftp/arxiv/papers/0909/0909.5203.pdf

The central surface density of “dark halos” predicted by MOND
http://arxiv.org/PS_cache/arxiv/pdf/...909.5184v1.pdf

Dark Matter and Galaxy Formation
http://arxiv.org/abs/0909.2021

A weak lensing detection of a deviation from General Relativity on cosmic scales
http://arxiv.org/abs/0909.3853

It's a puzzle, because although these are valid challenges to the dark matter hypothesis, antoniseb already mentioned some challenges to the "additional force" kind of approach. All I'm saying is, we should only resort to postulating both additional matter and additional forces as an absolute last resort. It would represent something of a disaster for our overall understanding of the cosmos. Then again, if we need it, we need it.

I can't say much without the details, but on the surface it would seem plausible that since gravity in the central region is only sensitive to the matter in the central region, this might just be saying that there's a tendency for dark matter to be less important when the baryonic density is centrally concentrated.
Presumably, they stay well to the outside of the action, though again specifics would be needed.
Dark matter doesn't couple to light, and this affects not only our ability to see it, but also its dynamics-- it doesn't contract to form galaxies, so it never produces large gravitational accelerations. But who knows, maybe there is something special about that acceleration scale, in regard to whatever is missing.
Yes, it seems we are in a fascinating period of trying to figure out what course to take to unify all the various observational discrepancies into a single explanation. If you have 10 discrepancies to resolve, anyone can invent a theory with 10 adjustable parameters to resolve them. The question is, can we do it with 1? Or do we need 2, 3, 4? We've been very lucky in physics and astronomy so far, we keep finding wonderfully unifying theories with very few parameters (like G, c, h and so on). What guarantee is there that this will always be true? Well, we have no choice but to look for them, and hope.
Yes, more of that same question.
It is certainly interesting to speculate on an "uber-theory" that will not simply unify GR and QM, but will have totally original elements that will only reduce to these other theories in various limits-- where cosmology is not one of those limits.

From a layman's point of view -- at least from my point of view -- it sometimes seems that modern physics is (over-?) prone to "invent" a particle to explain an observed phenomena that can't otherwise be explained. For gravity, we have the graviton. For empty space, we have the self-anihilating (sp?) virtual pairs "borrowed" from somewhere else. For dark matter we have the as yet undiscovered dark matter particles and we have yet another theoretical particle for dark energy. I realize that all of these theoretical particles are very useful in explaining what we CAN observe, and that for the most part they hold up under intense mathmatical tests. But intuition tells me that we're missing something really, really big here that ties dark matter, dark energy and gravity together in a way that when finally realized is going to blow open the doors to our understanding of the universe, and our ability to manipulate it. Or, as Ken so eloquently puts it, "unify all the various observational discrepancies into a single explanation". Until that time comes, you can count on me to keep asking the "dumb" questions and proposing speculative answers. I believe there is an answer to all this, and it's probably hiding right under our noses. We (you -- the scientists) just haven't recognized it, yet. Count me as one of your most ardent cheerleaders. BTW, I still like the "idea" I had that first brought me to this forum and that I mistakenly posted in the "Against The Mainstream" area -- big mistake. What's wrong with the idea that the universe is under "pressure", and that pressure (which is not the type of pressure we're most familiar with) is responsible for gravity and for the rapid expansion (stretching) of the universe?

It is certainly prone to do that, it's hard to say if it is "overly" so. After all, it is how we got the electron, proton, neutrino, etc. All of these particles are vastly successful at helping us organize and make sense of the phenomena we observe. Using a sports analogy, if you are having an undefeated basketball season by putting up three point shots because your team is great at shooting them, are you going to try to win your next game by forcing the ball inside?

That is certainly possible, we need to realize that if we come up against a team that commits to stopping the three-point shot, we might need that inside game!

Certainly, question and speculate away. We have a real mystery here, to make Sherlock Holmes proud, so no avenue should be left unpursued.

Hindsight is 20-20, but my guess is, if we need to think "outside the box" to solve this, the answer is going to seem really shocking and alien at first, at least as much so as relativity and quantum mechanics did. It might even be outside the range of our intellect, but hopefully not.
I'd say the problem is, the suggestion moves us in the wrong direction-- we want to go in the direction of something that is unknown and strange being brought into the realm of things we do understand (that's what introducing new particles do, or new equations, since we know how to manipulate those entities). You have not told us how to manipulate your "pressure" idea, so it does not replace something we do not understand with something we do.

Ken, I really appreciate the feedback. Yeah, I didn't have any hope for the "pressure on the universe" idea, not sure why it's sticking with me. And I have also considered the possibility that "the big answer" is outside the range of our intellect. If that ends up being true, how will we know? Maybe humanity is going to have to go through the next stage of evolution before understanding is possible. Like you, I hope not. I've got my fingers crossed.

Yeah, and then there's the issue of what we'll see in our own lifetimes, which has somewhat less chance than the future of all of humanity.

Lindon,

That it is not actually matter but of a presently unknown character which is the cause of gravity itself or enhances it, is probably one of the possibilities you ran across in your research.

Here is a couple of links that seem to be along similar lines of possibilities to what you are discussing, I think.
http://www.eurekalert.org/pub_releas...-ert082306.php
http://news.nationalgeographic.com/n...-matter_2.html

To illustrate what I mean...

Here we have the light path from part of a galaxy, as the solid green line.
The position of the origin of that light would appear along the dotted green line, and would show the galaxy as pictured, as it would be seen by the distant observer.
But as the real source of that light would be a star closer to the galactic center, then it's speed/rotation-around-the-galaxy rate would appear higher than it should, based upon a model without magnification.
That might account for the flat rotation curve of galaxies, or it might not....I don't know if the effect of magnification would be enough....but it illustrates, I suppose, one way in which present understanding could be extrapolated to account for dark matter.

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Wow that sounds completely unscientific to me!? I thought science was all about constructing "models" that embrace all the empirical/observational facts at our disposal? Occam's razor? If a model sounds berzerk & bizarre and yet acknowledges all our observations and measurements, surely we must pay attention...?

I know this is an amateur's "skeptics" forum, but surely you folk are advocates of "science"??? Even if the "science" flies in the face of our "common sense"??

Good idea, but the effect of gravitational lensing is orders of magnitude too weak to explain the observed rotation curves.

Indeed, Occam's Razor was my whole point. One always tries to come up with a theory with the least number of free parameters, so invoking both a new kind of matter and a new kind of force is not likely to satisfy it, and should be viewed as a kind of last resort.

It's quite easy to come up with a model that acknowledges all the observations, what's hard is for the model to unify those observations into something that can also predict other things. If the model is too "retro fit" to the observations, it won't do that, which is why, when we have observations we don't understand, we look for unifying principles instead of just more bells and whistles. A new kind of matter might come with a new kind of force, but it would be nice if we had at least some way to unify it with the physics we already have.
It can certainly go against the intuition we have built up about our immediate environment, but the "common sense" that it cannot fly in the face of is the common sense of what is good science (i.e., the common sense of Occam's Razor).

Dark Matter “Uber” Theories or Investigation of Fundamentals?

There already have been some synthetic ideas already suggested. Here is a list, not exhaustive, of some ideas over the past year or so:

Is dark matter an extra-dimensional effect?
http://arxiv.org/abs/0809.1915

MOND and the dark baryons
http://arxiv.org/abs/0901.4935

Dark Halo or Bigravity?
http://arxiv.org/abs/0902.0072

Modified gravity or modified matter ?
http://arxiv.org/abs/0902.1712 Abstract in English but PDF in French

Mirror dark matter (2007)
http://arxiv.org/abs/0706.2694

Tully-Fisher relation, key to dark matter companion of baryonic matter
http://arxiv.org/abs/0906.0668

From this months Science 11-6-09 book review section
Einstein’s Theory of Gravity and the Problem of Missing Mass
http://www.sciencemag.org/cgi/conten...t/326/5954/812

Reconciling MOND and dark matter?
http://arxiv.org/abs/0811.3143

This last one invokes a synthesis of the good parts and buries the bad parts of both CDM and MOND by suggesting CDM takes on MOND behavior at the galactic and lower scale. This is something of the flip side of invoking CDM or Dark Baryons to complement the pure MOND inability to account for additional weak lensing mass monitored at cluster scales with extra regard to X-ray clusters.

In any event, there are a lot if inventive ideas that try to resolve some of the difficulties each theory meets with.

The idea of looking for a theoretical systematic is usually to look at the fundamental assumptions and question their validity when observations no longer support a theory.
More often than not, the fundamental error is topological.

I give three examples:

This year Joy Christian, a topologist, wrote a paper questioning a fundamental assumption made by Bell regarding his famous inequalities. From her paper, it seems Bell made a naïve assumption regarding how two points were related. He assumed they could only be on a straight line between them. But there are up to seven ways to relate them. You may have heard of Flatlander in descriptions of GR. Well, there is also Linelander and Spherelander. There is a way to associate the points in such a way as to preserve EPR, albeit only in its strictest sense. Entanglement then becomes an illusion at best and nonsense at worst from this topological perspective.

Disproofs of Bell, GHZ, and Hardy Type Theorems and the Illusion of Entanglement
http://arxiv.org/abs/0904.4259

Similar topological considerations will also be needed to discuss the distinctions between symmetrical quantum time and the thermodynamic arrow of time. One needs to consider what topology to ascribe to time before considering its “arrow”.

Also before molding a theory of everything that melds the quantum physics with General relativity, one needs to keep topological considerations at hand as well.

Another example deals the biological idea of a “Tree of Life”. Since Carl Woese developed the idea of lateral gene transfer, this literally poked holes into the surface where the concept of tree has any meaning. Trees work on surfaces whose Euler number is 0. A doughnut with one hole has Euler Number1 and a doughnut with two holes has Euler number two and so on. Lateral gene transfer increases the Euler number. But there is more. It has been monitored that entire genome transfers or parts of genomes have occurred. This is beginning to look more the set of subsets is involved which begets the question of the cardinality of the Euler number. It could be transfinite or Aleph-null. So far from the Euler number 0 which accommodates the tree idea, a better model may be eventually based upon a higher or even transfinite Euler number.

A third example has to do with music theory. Back in 1720, before Euler invented topology, Rameau developed a theory to analyze chord progressions of the new, at the time, tonality. While the flat, two dimensional, Euler number 0, theory of Rameau gives some insights, it also leads astray from understanding the topology of tonality. The Rameau theory may have served a better purpose to describe the earlier 16th century tendencies than the newer 18th century tonality. By the time of the completion of the Bach Chorale Preludes, already the better surface to describe tonality therein is best matched to a directed four-holed torus. Even later, in 1739, when Euler had a go at music theory in his “Tentament” he consciously chose the inductive path rather than choosing samples from the literature to favor the deductive path. This was unfortunate as the problems he would have faced would have forced him to discover Euler numbers himself. Instead, they were discovered by a student of a student of his some hundred years later while the number is named after the original inventor of topology. From the flat two dimensional point of view of the Rameau theory, interest in tonality should have died out quickly in comparison to the richer more varied church modes that were destroyed by tonality. Yet it still persists to this day. This may be in large part due the observation that tonality investigates higher Euler numbered surfaces than the modal music. It is topology in practice and experience even though it preceded its mathematical invention a bit later by Euler.

With regard to the present Dark Matter Thread, the difference suggested rather than the synthetic theories is rather to look for a possible systematic that derives from the fundamental assumptions whether or not what is being questioned is necessarily of a topological nature. There are a number of “a priori” assumptions made from where to start a theory. Each of these may be investigated but there is no promise that anything significant will come of such a study.

One idea that was inspired from viewing one of the layman directed Feynman lectures now available is his unwillingness to ascribe a fundamental property of mass to matter. Instead, he referred to mass rather as a co-efficient of inertia rather than granting it fundamental importance. We have all heard of friction and probably that, depending on circumstances, there is more than one co-efficient of friction, static and dynamic. So the question then is whether mass can have more than one co-efficient, like friction, that expresses itself when the occasion of its existence becomes manifest.

The simplest start is to enquire if each subspace has its own co-efficient. There are four dimensions so each would have its own co-efficient. This is not to say that there are four different inertias but that each subspace has its own co-efficient.

The first is the most familiar 4 dimensional co-efficient upon which General Relativity is based. This is a 3 + 1 dimensional co-efficient. Gravity due to it is approximated by the Newtonian inverse squared law. Going down to the 2+1 subspace, you multiply by r, so you get the inverse linear gravity that appears associated with Dark Matter observations. This has already been noted by a number of others in the context of a holographic idea for Dark Matter. When you go down to a 1+1 subspace and multiply by r again, you get a co-efficient of inertia that no longer depends on distance and is constant. Originally, I hoped to search here for an alternative to Milgrom’s somewhat unaesthetic Dark Baryons, but even the simple math will not permit this localization. This problem as well as the halo truncation problem is best addressed by the sine value of the projection of the 2+1 inertia upon the 3+1 inertia as discovered in the flyby anomalies. Should the sign of this constant be the opposite of normal General Relativity gravity and Dark Matter gravity, one gets something like the cosmological constant that was discovered in 1998 and associated with Dark Energy. Since there is no r or distance, the effect of this co-efficient of inertia is cosmological.

If we go down one more to the 0+1 subspace, the spatial dimensions have been exhausted and we are left with a co-efficient of inertia that only depends of time. It either rots or ripens with time and its approach to limits is either asymptotic or linear. This seems to be what Rachel Bean discovered earlier this year. If one blames the first co-efficient for the fourth co-efficient inertia, then one will propose that GR is off significantly. The original proposal was to lay the 4th co-efficient at the feet of the second co-efficient, but it is then unusual that there is excess dark matter outside z=2 but not any closer. Same problem applies to laying it at the feet of the third co-efficient as Dark Energy would then not be a constant but more like a fluid that suddenly takes on unusual properties at z=2. It may be simpler to suggest there is a new discovery by Bean only 11 years after the discovery of Dark Energy of a co-efficient of inertia that arrived (decayed to) at its asymptotic value at z=2 rather than to seriously damage and contort the other three theories to try to account for it.

All this, of course, is rather simple and may be too simple. But it underscores how questioning a seemingly fundamental concept like mass may lead to a view where perhaps only one co-efficient of inertia is too arbitrary an “a priori” assumption in light of evidence to the contrary.

The earlier synthetic theories as well as the common theories all accept the idea of only one co-efficient as given. This is what both MOND and LCDM have in common. In order to explain the phenomena without Dark Matter, Milgrom is then forced to consider a modification of GR which already works perfectly fine for the 4 dimensional co-efficient of inertia. When Milgrom and a few others peruse Modified Inertia, again the “a priori” notion accepted is that there is only one co-efficient of inertia and that it is the only one that can be modified, that is, the 4 dimensional co-efficient of inertia. The various other theories, such as TeVeS, which invoke new parameters to allow GR as a limit, also proceed from the same fundamental assumption.

All I am suggesting, is that because so many theories are to some extent in disarray, it might be prudent to also investigate whether our “a priori” assumptions are valid.

That sounds like an avenue well worth exploring, in the spirit of turning over every "easy" stone first, with no regard to its bizarreness. Aversion to bizarreness has never served physics, but looking for what is simple certainly has.

Bizarreness

Bizarreness is a relative term in comparisons with our everyday classical experience. Often it fades to the background even when it is present. From a classical point of view, it is very bizarre that our TVs and computers even work at all since they can only work due to bizarre attributes of quantum mechanics. The bizarreness can be experimentally verified to be there even though most people just use the equipment without considering how it works. Bizarreness stems from being rather acclimated to the common classical experience in spite of quantum mechanical evidence to the contrary.

Likewise, the apparent bizarreness of the 4 co-efficients or intertia idea also stems from common classical experience. We usually only notice one when there is a sum of all 4 in action. We do not do experiments or generally make observations that distinguish the first co-efficient from the other 3. For example, take the multitude of Eotvos experiments performed over the last century that imply to 11 orders the constant ratio of gravitational to inertial mass. This is to be expected from the special case under which the experiments were conducted. They do not, however, represent the results for the general case and such extrapolation represents a logical fallacy. In particular, they are not done during either eccentric or hyperbolic orbit where anomalies have already been noted to occur. Say there have been over a million Eotvos experiments done on the surface of Earth, but only 6 flybys and a handful of GPS eccentric orbits to monitor as well as a 8 sigma DAMA/LIBRA signal on a larger eccentric orbital scale. But this represents a million oranges and 6 or so apples. Because the experimental conditions under which the apples are observed are potentially radically distinct from the conditions under which the oranges are observed, one can not use the large number of orange observations to invalidate the apple observations. Instead, do a million more apple observations and the bizarreness disappears. Our knowledge increases rather than being hampered by preconceptions formed by limiting experiences of special experimental conditions.

Basically, the idea is to unify the diverse discoveries of GR, Dark Matter, Dark Energy, and the new problem made more manifest in the Rachel Bean paper. The idea is to "blame" matter for all of it rather than invoking new particles or invoking new modifications to gravity.

One of the interpretations favored by the Bean result is that Dark Energy is a modification of GR rather than a constant Lambda. But if gravity is to be modified, what does this say about the LCDM paradigm? Just as MOND was compromised by the need of Dark Matter or Dark Baryons, so too then is Dark Matter compromised by the need of MOND to explain the Bean study. Until this Bean study, we had three nutshells each with their own nut: GR had its domain supported by relatively local observations; Dark Matter Particles were invoked to explain the lensing and unusual velocities of stars and galaxies; the Cosmological Constant was invoked or brought back from its 1921 grave to account for Dark Energy. But now we have a fourth nut without a nutshell to go under. By trying to imagine that it is an "illusion" that results from a misunderstnding of how the three other nutshells work could likely lead to a destabilization of the three existing nutshells to where no one can trust their predictions on account of the addition of too many new free parameters to account for the Bean discovery.

While it may, at least at first, to appear somewhat bizarre to suggest there may be more than one co-efficient of inertia which questions one of the "a priori" fundamental assumptions made by current theory, it may be an aesthetic alternative to the mess that is now looming over current theory further accentuated with the recent Bean paper.

Yes, that's very much why aversion to bizarreness has never been a reliable physical principle.

Let's just say that we need to have all our oars in the water, so that if one catches a crab, we can continue on with the others!

For the sake of balance

There are these two recent papers that can impact on discussion.

When looking through “eta-colored glasses”, four sources were viewed: CMB ISW, galactic and weak lensing, and galactic ISW cross-correlations. This is reference to the Bean paper. The looking at galactic ISW was at the higher redshift of interest. There has been a recent paper that argues that these galactic cross-correlations may not be so reliable at somewhat lower redshifts:

Cross-correlating WMAP5 with 1.5 million LRGs: a new test for the ISW effect
http://arxiv.org/abs/0911.1352

Today there is a LCDM perspective upon the Donato et al and Gentile et al papers:
New evidence for dark matter
http://arxiv.org/abs/0911.1774

A flood of neutralinos out of the LHC might help sort out whether there are independent Dark Matter Particles (Press release):
In SUSY we trust: What the LHC is really looking for
http://www.newscientist.com/article/...oking-for.html

You might be surprised to learn that the posters here are not all the same person. We are actually different people, with different views. You really shouldn't generalize from what Ken G writes to "you folk."

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As above, so below

A couple of comments.

The graviton has not been invented in order to explain gravity. It really has not been invented at all. The graviton is a name that will be given to the carrier of the gravitational force in some future quantum theory that includes gravity -- if such a theory is ever formulated. So, all that the graviton is at this point in time is a pre-selected name.

We already know that gravity exists, and we have a pretty good theory that describes it, general relativity. Unfortunately general relativity and quantum theory are not compatible, and if the ultimate resolution is a quantum theory of gravity, the graviton stands as ready terminology. If, on the other hand, it is quantum mechanics that is most changed in an eventual reconciliation, then we may not need that particular word.

It is quite possible that the universe is under pressure and that the pressure is the cause of the accelerated expansion of the universe. Quantum electrodynamics predicts the characteristics of the vacuum, and that prediction results in a negative pressure term that, when applied to the stress-energy tensor of general relativity results in a positive "cosmological constant". It is a positive cosmological constant that is currently used to model "dark energy" and accounts for accelerating expansioin. The problem is that the value predicted by QED is somewhat high -- 120 orders of magnitude too high.

This discrepancy may be due to problems with quantum field theories themselves and the ultimate resolution could be better understanding of the quantum vacuum and a value for the zero point energy that is consistent with the observed expansion of the universe. So, a negative pressure term arising from quantum considerations might indeed be the driving force for accelerated expansion.

On the other hand, itis not responsible for gravity as the sign is wrong and it is a repulsive term. This is due to the fact that the pressure term arising in this way is negative. Positive pressure terms are part of the stress-energy tensor and do contribute to curvature of space-time and hence to what we call gravity.

The problem of the over-prediction of the cosmological constant by quantum field theories is indeed a major issue. I think Wilczek characterized it as the biggest open problem in quantum field theory. A solution could well, as you note, lead to a dramatic increase in our understanding of fundamental physics. But it is a very difficult problem indeed.

There is notihng ATM about this. However, there are some distinctly ATM notions regarding potential solutions.

DrRocket, I sincerely thank you for your feedback on this topic, which I find so very interesting. Be assured that I will be reading your post over and over, and doing Google searches, to understand what you've written the best I can. Regards.