Study validates general relativity on cosmic scale, existence of dark matter

Mar 10, 2010 By Robert Sanders
A partial map of the distribution of galaxies in the Sloan Digital Sky Survey, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, Sloan Digital Sky Survey)

(PhysOrg.com) -- An analysis of more than 70,000 galaxies by University of California, Berkeley, University of Zurich and Princeton University physicists demonstrates that the universe - at least up to a distance of 3.5 billion light years from Earth - plays by the rules set out 95 years ago by Albert Einstein in his General Theory of Relativity.

By calculating the clustering of these galaxies, which stretch nearly one-third of the way to the edge of the universe, and analyzing their velocities and distortion from intervening material, the researchers have shown that Einstein's theory explains the nearby universe better than alternative theories of gravity.

One major implication of the new study is that the existence of is the most likely explanation for the observation that galaxies and galaxy clusters move as if under the influence of some unseen mass, in addition to the stars astronomers observe.

"The nice thing about going to the cosmological scale is that we can test any full, alternative , because it should predict the things we observe," said co-author Uros Seljak, a professor of physics and of astronomy at UC Berkeley, a faculty scientist at Lawrence Berkeley National Laboratory, and a professor of physics at the Institute of Theoretical Physics at the University of Zurich. "Those alternative theories that do not require dark matter fail these tests."

In particular, the tensor-vector-scalar gravity (TeVeS) theory, which tweaks general relativity to avoid resorting to the existence of dark matter, fails the test.

The result conflicts with a report late last year that the very , between 8 and 11 billion years ago, did deviate from the general relativistic description of gravity.

Seljak and his current and former students, including first authors Reinabelle Reyes, a Princeton University graduate student, and Rachel Mandelbaum, a recent Princeton Ph.D. recipient, report their findings in the March 11 issue of the journal Nature. The other co-authors are Tobias Baldauf, Lucas Lombriser and Robert E. Smith of the University of Zurich, and James E. Gunn, professor of physics at Princeton and father of the Sloan Digital Sky Survey.

Einstein's General holds that gravity warps space and time, which means that light bends as it passes near a massive object, such as the core of a galaxy. The theory has been validated numerous times on the scale of the solar system, but tests on a galactic or cosmic scale have been inconclusive.

"There are some crude and imprecise tests of general relativity at galaxy scales, but we don't have good predictions for those tests from competing theories," Seljak said.

Such tests have become important in recent decades because the idea that some unseen mass permeates the universe disturbs some theorists and has spurred them to tweak general relativity to get rid of dark matter. TeVeS, for example, says that acceleration caused by the gravitational force from a body depends not only on the mass of that body, but also on the value of the acceleration caused by gravity.

The discovery of dark energy, an enigmatic force that is causing the expansion of the universe to accelerate, has led to other theories, such as one dubbed f(R), to explain the expansion without resorting to dark energy.

Tests to distinguish between competing theories are not easy, Seljak said. A theoretical cosmologist, he noted that cosmological experiments, such as detections of the cosmic microwave background, typically involve measurements of fluctuations in space, while gravity theories predict relationships between density and velocity, or between density and gravitational potential.

A collection of galaxies from the Sloan Digital Sky Survey. Red galaxies composed of older stars are more luminous; the recent study used a sample of 70,000 red luminous galaxies to combine galaxy clustering, weak gravitational lensing, and redshifts to compare and test competing theories of gravity. Image by Michael Blanton for SDSS

"The problem is that the size of the fluctuation, by itself, is not telling us anything about underlying cosmological theories. It is essentially a nuisance we would like to get rid of," Seljak said. "The novelty of this technique is that it looks at a particular combination of observations that does not depend on the magnitude of the fluctuations. The quantity is a smoking gun for deviations from general relativity."

Three years ago, a team of astrophysicists led by Pengjie Zhang of Shanghai Observatory suggested using a quantity dubbed EG to test cosmological models. EG reflects the amount of clustering in observed galaxies and the amount of distortion of galaxies caused by light bending as it passes through intervening matter, a process known as weak lensing. Weak lensing can make a round galaxy look elliptical, for example.

"Put simply, EG is proportional to the mean density of the universe and inversely proportional to the rate of growth of structure in the universe," he said. "This particular combination gets rid of the amplitude fluctuations and therefore focuses directly on the particular combination that is sensitive to modifications of general relativity."

Using data on more than 70,000 bright, and therefore distant, red galaxies from the Sloan Digital Sky Survey, Seljak and his colleagues calculated EG and compared it to the predictions of TeVeS, f(R) and the cold dark matter model of general relativity enhanced with a cosmological constant to account for dark energy.

The predictions of TeVeS were outside the observational error limits, while fit nicely within the experimental error. The EG predicted by f(R) was somewhat lower than that observed, but within the margin of error.

In an effort to reduce the error and thus test theories that obviate dark energy, Seljak hopes to expand his analysis to perhaps a million galaxies when SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS), led by a team at LBNL and UC Berkeley, is completed in about five years. To reduce the error even further, by perhaps as much as a factor of 10, requires an even more ambitious survey called BigBOSS, which has been proposed by physicists at LBNL and UC Berkeley, among other places.

Future space missions, such as NASA's Joint Dark Energy Mission (JDEM) and the European Space Agency's Euclid mission, will also provide data for a better analysis, though perhaps 10-15 years from now.

Seljak noted that these tests do not tell astronomers the actual identity of dark matter or dark energy. That can only be determined by other types of observations, such as direct detection experiments.

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tflahive
2.8 / 5 (4) Mar 10, 2010
Since the Universe has been calculated to be about 46 billion light years across, the statement: "galaxies, which stretch nearly one-third of the way to the edge of the universe" would be incorrect. It would be more correct to say: "galaxies, which stretch nearly one-third of the way to the edge of the 'visable' universe".
Crackpot
2 / 5 (4) Mar 10, 2010
Quote: "The nice thing about going to the cosmological scale is that we can test any full, alternative theory of gravity, because it should predict the things we observe,"

I hope they will test "planar gravitation" some day: http://classicala...ace.html

An explanation why the "dark matter" is confined to a spherical halo outside the visible matter would also be welcome...
Parsec
1.8 / 5 (4) Mar 11, 2010
The visible universe is, for all practical purposes, the edge of the universe. Latest measurements for the radius of then universe is about 13.73 billion light years, which does NOT lead to 46 billion light years across by any arithmetic I know of.

No theories that I know of says that dark matter is always confined to a spherical halo. However, since dark matter is sensitive to the forces of gravitation, it would tend to collect into a spherical shape just by its own mutual attraction.
frajo
2 / 5 (1) Mar 11, 2010
However, since dark matter is sensitive to the forces of gravitation, it would tend to collect into a spherical shape just by its own mutual attraction.
Obviously non-dark matter doesn't tend generally to collect into a spherical shape. Why should "dark matter" do so?
Crackpot
5 / 5 (1) Mar 11, 2010
No theories that I know of says that dark matter is always confined to a spherical halo. However, since dark matter is sensitive to the forces of gravitation, it would tend to collect into a spherical shape just by its own mutual attraction.
I meant in connection with spiral galaxies, were the "dark matter" is supposed to be concentrated in an extended halo. Sorry for not making that clear!
daywalk3r
3 / 5 (10) Mar 11, 2010
"Those alternative theories that do not require dark matter fail these tests."
And how could a theory possibly ever fail while using the dark matter "fix"? When some prediction doesn't fit with observational evidence, then lets just fill the gap with any required amount of dark matter, calculate the distribution, and violla.. EVERYTHING FITS NOW!

Heck, the whole Universe could be explained just by the basic Newton's Laws when using that kind of an approach..

-------
Seljak: "Rachel, how far off are we, compared to the observational data?"
Rachel: "43%, Mr. professor."
Seljak: "OK. Lets add some dark matter here, a bit here, and a tiny bit there. What's the status now?"
Rachel: "17%, Mr. professor."
Seljak: "Good job Rachel! You see, this dark matter theory is really awesome! Others just fail so much.. Let's keep it up, we are getting there!"
-------

Am I missing something or is the pot of logic and rational thinking slowly cracking at Berkeley and Princeton?
broglia
not rated yet Mar 11, 2010
TeVeS theory claims to replace dark matter effect by aditional curvature of space-time - but matter itself is nothing, but curved space-time. From this point both theories are dealing with the same stuff.

The point, in which TeVeS differs from reality is the fact, the space-time deformed in TeVeS contains additional amount of material particles, trapped in it. In this way, the space-time deformed by dark matter is always curved more, then the TeVeS theory could predict, because this theory accounts only to omnidirectional expansion of space-time, but not to the observable matter distribution.

The question is, whether relativity could differ from observation at all, if it's using the amount of matter observed for estimation of space-time curvature. In this way relativity cannot violate observations in the same way, like epicycles model, which fitted model to observed data. But TeVeS model actually predicts dark matter!
Bloodoflamb
4.5 / 5 (6) Mar 11, 2010
The visible universe is, for all practical purposes, the edge of the universe. Latest measurements for the radius of then universe is about 13.73 billion light years, which does NOT lead to 46 billion light years across by any arithmetic I know of.

You've quoted the age of the universe multiplied by the speed of light as the radius of the universe. Such a simplified calculation will not give you the radius of the universe given the inflation that is likely to have occurred after the Big Bang.
Bloodoflamb
4.7 / 5 (3) Mar 11, 2010
And how could a theory possibly ever fail while using the dark matter "fix"? When some prediction doesn't fit with observational evidence, then lets just fill the gap with any required amount of dark matter, calculate the distribution, and violla.

That's... Not how it works... =\

You take a theory, for example, General Relativity, and make predictions about the universe. Then we ask: "Where does it fail? Why does it fail where it does?" Then we look for answers to those questions. The fact that the prediction of dark matter accounts for not only the disagreement of GR with the observed rotational velocities of galaxies, but the anisotropy of the the CMB gives strong evidence that it's a possibly valid explanation. It's also testable, otherwise I would also be labeling it a bunch of phooey.
pbfred
1.3 / 5 (4) Mar 11, 2010
Convincing observational support for Aristotelian astronomy years was due to an artifact that gave the impression that the Heavens rotated around the earth in a 24 hour period. This artifact was the the earth rotating on its axis every 24 hours. Is it possible that scientists have been been misled by another artifact as regards gravitational phenomena? Astronomers know that there is a high correlation between the mass of a star and it luminosity and they know that the amount of luminosity leaving mass varies as 1/r^2. Could it be that it is the earth's heat and not its mass that attracts the moon? We could not have let ourselves repeat the mistake as the Aristotelians and allow ourselves be misled by an artifact that only gives the impression that mass attracts other mass or warps space? For 5 experiments showing a weight change ranging from 2% to 16% for a test mass that has been sandwiched between a hot source and cold source go to http://vixra.org/...07.0018. Peter Fred
daywalk3r
2.2 / 5 (9) Mar 11, 2010
That's... Not how it works... =\
But that's how it is done.. Sadly.

You take a theory, for example, General Relativity, and make predictions about the universe. Then we ask: "Where does it fail? Why does it fail where it does?" Then we look for answers to those questions.
And when there are no clear answers, we fill the error margin with some dark stuff..

And by the way, I'm well aware of the whole preceding process, but the only thing that matters are the final conclusions.

The fact that the prediction of dark matter accounts for not only the disagreement of GR with the observed rotational velocities of galaxies, but the anisotropy of the the CMB gives strong evidence that it's a possibly valid explanation.
Of course it is possibly valid, but it is far from being possibly the most valid. And using CMB anisotrophy as proof is a rather weak argument aswell.
Yes
3.8 / 5 (6) Mar 11, 2010
@pbfred.
Why is nothing attracted to the flame of a candle?
Newton used heavy balls to study gravity. According to what you say, a flame of a candle should interfere with this experiment. I don't think so.
broglia
1 / 5 (2) Mar 11, 2010
..You take a theory, for example, General Relativity, and make predictions about the universe. Then we ask: "Where does it fail? Why does it fail where it does?" Then we look for answers to those questions. ..
The whole joke is in the point, the article is saying, TeVeS theory which predicts dark matter badly is worse, then the relativity, which cannot predict dark matter at all...
Bloodoflamb
5 / 5 (3) Mar 11, 2010
..You take a theory, for example, General Relativity, and make predictions about the universe. Then we ask: "Where does it fail? Why does it fail where it does?" Then we look for answers to those questions. ..
The whole joke is in the point, the article is saying, TeVeS theory which predicts dark matter badly is worse, then the relativity, which cannot predict dark matter at all...

TeVeS, as a theory of gravitation, cannot predict dark matter. Since it intrinsically does not deal with the theory of electromagnetism, there is no means by which to predict matter that does not couple (or at least does not do so very strongly) to photons. General relativity does not predict the existence of matter. It describes the behavior of spacetime in the presence of mass-energy.
solrey
3 / 5 (4) Mar 11, 2010
"Dark matter was postulated by Fritz Zwicky in 1934, to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters"

Dark Matter has been a fudge factor from the very beginning. It was not predicted a priori, it was postulated a posteriori to salvage a failed theory. It's a mathematical variable, among several others, that's required for the theory of GR to match observations.

Plasma Cosmology does not require fudge factor variables to match theory with observation. PC simulations provide an accurate match of observed rotation curves, radiation signatures, relative percentages of galaxy types, and the general structure of the cosmos. It's just a simple matter of including electromagnetic forces along with gravity, which makes sense given the universe is 99% plasma.

http://plasmascie...esII.pdf

http://plasmascie...S-II.pdf

Dark matter/energy are just substitutes for EM forces ignored by GR.
seneca
1 / 5 (2) Mar 11, 2010
TeVeS, as a theory of gravitation, cannot predict dark matter.
But TeVeS predicts most of dark matter phenomena, like rotational curves of stars inside of galaxies and orbital velocities of galaxies in clusters, which general relativity cannot explain at all by itself.
Skeptic_Heretic
5 / 5 (2) Mar 11, 2010
Obviously non-dark matter doesn't tend generally to collect into a spherical shape. Why should "dark matter" do so?

Want to rephrase that? I think you made a misstep in your statement.

In the article above I have some rather serious disagreements. In order for this methodology to be plausably eliminative in it's testing of gravitational theory it must first address how gravity does work and what it is composed of.

For all we know gravity could be the stable sum of two universes seperated by a division of a planck length. After all, we never did find out where all that antimatter went....
Bloodoflamb
5 / 5 (2) Mar 11, 2010
"Dark matter was postulated by Fritz Zwicky in 1934, to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters"

Dark Matter has been a fudge factor from the very beginning. It was not predicted a priori, it was postulated a posteriori to salvage a failed theory. It's a mathematical variable, among several others, that's required for the theory of GR to match observations.

Plasma Cosmology does not require fudge factor variables to match theory with observation. PC simulations provide an accurate match of observed rotation curves, radiation signatures, relative percentages of galaxy types, and the general structure of the cosmos. It's just a simple matter of including electromagnetic forces along with gravity, which makes sense given the universe is 99% plasma.

http://plasmascie...esII.pdf

Dark matter/energy are just substitutes for EM forces ignored by GR.

All theory is a posteriori. By definition.
frajo
4 / 5 (4) Mar 11, 2010
All theory is a posteriori. By definition.
Theories must be able to explain observations - this is their a-posteriori duty.
But theories must also be able to generate (observable) predictions - this is their a-priori duty.
DM was never a prediction as there was and is no theory postulating DM. Especially no particle physics prediction.
kasen
4.5 / 5 (2) Mar 11, 2010
Isn't that which we are trying to measure tied too strongly with that which we use to measure? The EM radiation picked up by telescopes is used to infer curvature, but curvature is supposed to affect the path of said radiation. Each one is defined completely by the other, especially at these scales, am I right? So, no tertiary means of verification.

We get a very small amount of light from far away objects, yet those objects, and their mass, are very large, so there's a big proportionality constant somewhere(bear with my lack of expertise). Then, wouldn't even small observation errors translate into serious prediction errors?

Maths and physics start breaking down, and getting interesting, as we approach 0 or infinity. Trying to get close to 0, we got quantum phenomena. Maybe something similar will occur near infinity. Bit further from us than 0, though.
seneca
Mar 11, 2010
This comment has been removed by a moderator.
seneca
1 / 5 (1) Mar 11, 2010
See for example "The Foundation of the General Theory of Relativity" at http://www.albert...-200.pdf . On page 185 Einstein says "the energy of the gravitational field shall act gravitationally in the same way as any other kind of energy". But such relationship was never inserted into Einstein's field equations because of complexity of resulting solution. It was only partially considered in work of Cartan, Yilmaz, Heim, Moffat and others.

The fact, Einstein's was aware of this consequence of relativity we can demonstrate further by famous Einstein’s 1920 Leyden lecture (see http://www.zionis...vity.htm ), where he talks about the stress-energy of space itself, and says its inhomogeneous:

".. the recognition of the fact that "empty space" in its physical relation is neither homogeneous nor isotropic.."
broglia
not rated yet Mar 12, 2010
Einstein did not include the energy density of the gravitational field into the stress-energy tensor used in general relativistic field equations, which we all use. A reason was that the source term (stress-energy tensor) on the RHS of the field equations would then have functions of metric quantities via gravitational field energy, making the equations highly nonlinear and not amenable to straightforward solutions.
pbfred
1 / 5 (2) Mar 12, 2010
@pbfred.
Why is nothing attracted to the flame of a candle?
Newton used heavy balls to study gravity. According to what you say, a flame of a candle should interfere with this experiment. I don't think so.

If you look at my site where my experiments are posted, you will see that in four of the experiments, the masses were heated by a 1000 W heat element for 4-5 minutes. This is more energy compared to what a candle can put out. Also I used a cold source to make heat tend to flow in one direction. As as I have said, I observed a 2% to 16% change in the weight of the test mass. It is this experimental set-up and not some candle and heavy ball situation, that must be looked at and properly interpreted by scientists who have believed for 300 years that some mysterious, yet-to-be-specified property of mass can either attract other mass or warp space. Who incidentally have spent close to a billion dollars looking for years for the dark matter which so far has not been found.
pbfred
1 / 5 (2) Mar 12, 2010
q]@pbfred.
Why is nothing attracted to the flame of a candle?
Newton used heavy balls to study gravity. According to what you say, a flame of a candle should interfere with this experiment. I don't think so.
If you look at my site where my experiments are posted, you will see that in four of the experiments, the masses were heated by a 1000 W heat element for 4-5 minutes. This is more energy compared to what a candle can put out. Also I used a cold source to make heat tend to flow in one direction. As as I have said, I observed a 2% to 16% change in the weight of the test mass. It is this experimental set-up and not some candle and heavy ball situation, that must be looked at and properly interpreted by scientists who have believed for 300 years that some mysterious, yet-to-be-specified property of mass can either attract other mass or warp space. Who incidentally have spent close to a billion dollars looking for years for the dark matter which so far has not been found.
kasen
4.8 / 5 (5) Mar 12, 2010
Could it be that it is the earth's heat and not its mass that attracts the moon?


Someone tell that to the climatologists, so they can update their models. Global warming leads to variations in the Moon's orbit, thus affecting tides and creating yet another feedback loop!

pbfred, did you perform your experiments in a vacuum, by chance? You do know how a hot-air balloon works, right? Furthermore, did you take into account dilation and contraction? Different shapes have different centres of mass. Last, but not least, try to perform your experiment with just the heat source and the force sensor you keep in a wooden box. See what happens to the sensor.

Oh, and it was actually Cavendish who used balls and a sensitive torsion pendulum to study gravity.
shockr
1 / 5 (1) Mar 12, 2010
pbfred, your link is inaccessible. Could you post another link to your experiments?
frajo
not rated yet Mar 12, 2010
pbfred, your link is inaccessible. Could you post another link to your experiments?
As in most of these cases, it was forgotten to put a separating blank between the link and the period.
pbfred
1 / 5 (2) Mar 13, 2010
"pbfred, You do know how a hot-air balloon works, right? Furthermore, did you take into account dilation and contraction? Different shapes have different centres of mass. Last, but not least, try to perform your experiment with just the heat source and the force sensor you keep in a wooden box. See what happens to the sensor."

The percentage change of weight of the test mass which was placed between a hot source and a cold source was for each of the 5 experiments was 1.9%, -4.9%, 8.9%, 9.6% and 16%. This is a considerable amount of weight change. In one experiment the cold source was placed above the test mass which resulted in a decrease of weight of 4.9%. In my paper you will see that I made precautions that I thought appropriate to insure that the results were not spurious. I have made enough I think for some one else to see if they can be replicated. My site:
http://vixra.org/...18v4.pdf
kasen
5 / 5 (3) Mar 13, 2010
You're deriving mass from a force sensor. First off, was the initial weighing made with the same sensor at the same height, with the same formula?

Secondly, depending on how the sensor is oriented(object weight vector vs. sensor surface normal), an increase in mass could actually mean a decrease in force and vice versa. You're not really showing that wooden box anywhere. Also, you still haven't addressed the dilation of the spheres. Oh, and, I assume that after you heated the sensor to see how that would affect it, you used another one, not the one you just fried, right?

Most importantly, however, considering your experimental setup, a 10% error range is quite acceptable. I'm not going over the theory, but I doubt it's anywhere near as exhaustive as it should be for such an assertion.
Lorentz
1 / 5 (1) Mar 14, 2010
Is dark matter inertial mass caused by the universe accelerating?
NeilFarbstein
2 / 5 (1) Mar 14, 2010
What is the distribution of neutrinos in the universe? Their gravitation might be-affecting things.
Tissa_Perera
1 / 5 (1) Mar 14, 2010
I challenge the group to calculate the EG based on my theory of dark matter.
My hypothesis has no real DM but emulates DM effectively giving a mass equivalent of DM. Check the publication on 5th tab at cosmicdarkmatter dot com.
broglia
5 / 5 (1) Mar 16, 2010
What is the distribution of neutrinos in the universe? Their gravitation might be-affecting things.
Neutrinos are too sparse and lightweight to do that. For example, if we can measure neutrino flux from sun and compare it with theory of neutrino oscillations, it means, we are detecting most of neutrinos existing inside of solar system. Currently only up to five percent of dark matter could be attributed to photons and neutrinos, accordingly.
broglia
not rated yet Mar 16, 2010
What is the distribution of neutrinos in the universe? Their gravitation might be-affecting things.
Neutrinos are too sparse and lightweight to do that. For example, if we can measure neutrino flux from sun and compare it with theory of neutrino oscillations, it means, we are detecting most of neutrinos existing inside of solar system. By current theories only up to five percent of dark matter could be attributed to photons and neutrinos, accordingly. There are another theories, considering existence of so-called sterile neutrinos without charge - but I don't know, how to distinguish such thingies from another particles, like axions, after then..

http://www.physor...032.html
taka
1 / 5 (2) Mar 16, 2010
In contrary to heading, until this dark matter is not caught it looks more like invalidation of GR.
seneca
1 / 5 (1) Mar 16, 2010
In contrary to heading, until this dark matter is not caught it looks more like invalidation of GR.
Of course - this was my point, too. Whereas TeVeS is ad-hoced theory, but it can predict at least something new about dark matter.
Yes
1 / 5 (3) Mar 16, 2010
Maybe the radius of an electron is Maybe the radius of an electron is 6.8*10 minus 58 meter.
The radius of a dark matter particle can reach from the order of 1 cm to 10000 light years depending on where it is.
I am serious..
seneca
Mar 17, 2010
This comment has been removed by a moderator.