Light from galaxy clusters confirms theory of relativity

Light from galaxy clusters confirm theory of relativity
Researchers have analyzed measurements of the light from galaxies in approximately 8,000 galaxy clusters. Galaxy clusters are accumulations of thousands of galaxies (every light in the image is a galaxy), which are held together by their own gravity. This gravity affects the light that is sent out into space from the galaxies. Credit: Hubble Space Telescope

All observations in astronomy are based on light emitted from stars and galaxies and, according to the general theory of relativity, the light will be affected by gravity. At the same time all interpretations in astronomy are based on the correctness of the theory of relatively, but it has never before been possible to test Einstein's theory of gravity on scales larger than the solar system. Now astrophysicists at the Dark Cosmology Centre at the Niels Bohr Institute have managed to measure how the light is affected by gravity on its way out of galaxy clusters. The observations confirm the theoretical predictions. The results have been published in the journal Nature.

Observations of large distances in the are based on measurements of the redshift, which is a phenomenon where the wavelength of the light from distant galaxies is shifted more and more towards the red with greater distance. The redshift indicates how much the universe has expanded from when the light left until it was measured on Earth. Furthermore, according to Einstein's , the light and thus the redshift is also affected by the gravity from large masses like galaxy clusters and causes a gravitational redshift of the light. But the gravitational influence of light has never before been measured on a cosmological scale.

"It is really wonderful. We live in an era with the technological ability to actually measure such phenomena as cosmological gravitational redshift", says astrophysicist Radek Wojtak, Dark Centre under the Niels Bohr Institute at the University of Copenhagen.

Galaxy clusters in the searchlight

Radek Wojtak, together with colleagues Steen Hansen and Jens Hjorth, has analysed measurements of light from galaxies in approximately 8,000 galaxy clusters. Galaxy clusters are accumulations of thousands of galaxies, held together by their own gravity. This gravity affects the light being sent out into space from the galaxies.

The researchers have studied the galaxies lying in the middle of the galaxy clusters and those lying on the periphery and measured the wavelengths of the light.

"We could measure small differences in the redshift of the galaxies and see that the light from galaxies in the middle of a cluster had to 'crawl' out through the gravitational field, while it was easier for the light from the outlying galaxies to emerge", explains Radek Wojtak.

Light from galaxy clusters confirm theory of relativity
Until now, the gravitational redshift has only been tested with experiments and observations in relation to distances her on Earth and in relation to the solar system. With the new research the theory has been tested on a cosmological scale for the first time by analyzing galaxies in galaxy clusters in the distant universe. It is a grotesquely large scale, which is a factor 1,022 times greater (ten thousand billion billion times larger than the laboratory test). The observed data confirms Einstein’s general theory of relativity. Credit: Dark Cosmology Centre, Niels Bohr Institute

Then he measured the entire galaxy cluster's total mass and with that got the gravitational potential. By using the general he could now calculate the gravitational redshift for the different locations of the galaxies.

"It turned out that the theoretical calculations of the gravitational redshift based on the general theory of relativity was in complete agreement with the astronomical observations. Our analysis of observations of show that the redshift of the light is proportionally offset in relation to the from the galaxy cluster's gravity. In that way our observations confirm the theory of relativity", explains Radek Wojtak.

New light on the dark universe

The discovery has significance for the phenomena in the universe that researchers are working to unravel. It is the mysterious dark universe – and .

In addition to the visible celestial bodies like stars, planets and galaxies, the universe consists of a large amount of matter, which researchers can work out that it must be there, but which cannot be observed as it neither emits nor reflects . It is invisible and is therefore called dark matter. No one knows what dark matter is, but they know what the mass and thus the gravity must be. The new results for gravitational redshift do not change the researchers' modelling for the presence of dark matter.

Another of the main components of the universe is dark energy, which according to the theoretical models acts like a kind of vacuum that causes the expansion of the universe to accelerate. According to the calculations, which are based on Einstein's theory of relativity, dark energy constitutes 72 percent of the structure of the universe. Many alternative theories try to explain the accelerating expansion without the presence of dark energy.

Theory tested on a large scale

"Now the general theory of relativity has been tested on a cosmological scale and this confirms that the general theory of relativity works and that means that there is a strong indication for the presence of dark energy", explains Radek Wojtak.

The new gravitation results thus contribute a new piece of insight to the understanding of the hidden, dark universe and provide a greater understanding of the nature of the visible universe.

Explore further

Astronomers Gravitate Toward Einstein's Telescope

More information: Citation: Nature: 2011-05-06822B
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Sep 28, 2011
I beleive if there is evidence to suggest the existence of dark matter then it indeed exist. Think of black holes, if they exist then how are they classified??

Sep 28, 2011
My assumptions:
1) I am understanding this correctly,
2) Gravitational red shift is related to spacetime curvature.

Given those assumptions, it seems to me what they have proven is that GR accurately predicts spacetime curvature given a specified amount of gravity. The specified amount of gravity is based on what would be required to match the observations of the visible matter. Those observations result in an equivalent GR mass to produce that gravity. Given that equivalent GR mass, GR predicts spacetime curvature that agrees with observations of gravitational red shift.

Given that the GR mass explanation results in GR predictions that agree with observations, it seems to me that if something other than GR mass was responsible for the observed amount of gravity, then any such theory could be tested to see how accurately it predicts the same gravitational redshifts.

Why not put the other theories to the test and see how they fare?

Sep 28, 2011
First, it was jarring to read an article saying that these are the first measurements of gravitational redshifts (GRs) outside the laboratory (or outside the solar system) on with a chart that shows the data from Sirius B. GRs have also been measured for neutron stars and supermassive black holes. No dark matter there, or at least, if there is, it is inside the black hole. Or technically, the local galaxy cluster is immersed in dark matter, so most local measurements don't need to be corrected for dark matter.

As for those who question dark matter, don't be so 20th century. ;-) There was a time when dark matter was a questionable hypothesis. Then astronomers discovered cases involving galactic collisions where the GRs showed that the dark matter became separated from one of the galaxies. Other galaxies were discovered which had less normal matter than expected, but from GRs enough dark matter to hold the galaxy together.

As to what dark matter is, we all have our theories. ;-)

Sep 29, 2011
eachus: not sure what your first sentence is saying. To clarify my understanding of the article. These observations are the first at this scale to confirm gravity's affect on light. The blue items on the chart show observations confirming GR to date. The red are this one. 10 to the 22 further away than previously. The gravity of the clusters, billions of light years away is causing the shift, instead of Sol.

those who question dark matter ... collisions ... less normal matter than expected, but from GRs enough dark matter to hold the galaxy together.
Yeah, guess how they determined how much dark matter is there? They added enough to explain the observation. So guess what? The amount of dark matter they determined explains the observation. Rather circular, don't you think?
Again, dark matter is one idea. So far the best and most thoroughly researched. It still might be bunk. Front runner doesn't equal right. Ask the planet Vulcan.

Sep 29, 2011
>Rather circular, don't you think?
Yep, we already discussed here (and I was downvoted for it heavily).

But in this case I'm not sure, it's the circular reasoning of the same category and the physicists are just refusing the dark matter models with using of dark matter models. The method they used is actually independent to any models of dark matter - it's the simply measurement of gravitational red shift inside of galactic clusters. If the dark matter would be "heavy", it would contribute to the red shift inside of them with increasing of gravitational potential there. Well, it should - but it doesn't.

Which means, the dark matter is lensing the light, but it floats around the observable matter without exerting any gravitational pressure to it. Such result is pretty fundamental instead. It actually violates the relativity heavily and it supports models, which are assuming the antigravity of dark matter.

Sep 29, 2011
Before some time I started to think, what would happen, if we would observe the gravitational lensing of some pile of antimatter. The antimatter should excert antigravity to itself, but because it lives inside of reverse time arrow, the arrow of antigravity will be reversed too. So that from outside perspective the antimatter wouldn't exert gravity to the normal matter, but its lensing would appear exactly the same, like the lensing of finely dispersed matter. But because the antimatter is repulsive mutually, it wouldn't increase the gravitational potential inside of (cluster of) normal matter, which is surrounding. Got it?

The remaining question is, if the antimatter is repulsive, why it simply doesn't float away from cluster of matter, which it surrounds? Well, the things are more complex here. The antimatter is attracted to the negative gradient of space-time, which surrounds every massive object.

Sep 29, 2011
The general relativity theory considers, the space-time curvature about every massive object increases toward center of this object in monotonous way. It enables the black hole to crush itself into hypothetical singularity. But real stationary objects don't behave so. They exert the gravity field, but the volume area of highest gravity force (i.e. the curvature of space-time) is just at the surface of every massive object. Therefore the space-time curvature is not monotonous function of distance and it has rather bell shape profile similar to Gauss curve. And the antimatter is attracted just at the negatively curved areas of space-time here.

IMO this effect is of quantum field nature and it could be explained with using of general relativity postulates under assumption of mass-energy equivalence in higher dimensions, then just four. Some theories (TeVeS, STVG) are already attempting to do so.

Sep 29, 2011
There is no point in claiming that is the problem when sating that both Graviataional redshift and the expansion of the Universe are compatable with General Relativity, when astrophycisist's report the results that confirm thier theories, simply reports on what they state they have found. Fringe theories, oops I should say alternative explanations, have many more issues then a simple postulate that all energy whetehr it be electro-magnetic dark matter or dark energy causes effects in the Universe which are testable by Einstein's theory. When the results of measurements and calculations agree to any uncanny degree with that theory it seems to be pretty good confirmation to me. Quit beating the dead horse that the messenger of tidings you wish were not true, is the issue, when the astronomer or physicist doing the observing is the one reporting the results.

Sep 29, 2011
Another point is that we are all good at claiming that untested extensions to General Relativity in order to marry it to quantum theory such as strings MOG, and others, are better than or explain things better than GR itself. One thing to remember about most of these "extensions" is that they propose refinements to GR not to replace it completely. GR is one of the most tested and verified theories in science today, and while it can't be the final theory of everything it is necessary to explain the Universe as a whole. MOG, and other untested refinements simply hope to extend the success of GR into the realm of the sub-microscopic high energy domain, while maintaining it's unqualified success on the large scale. They had better GR may be 96 years old but it is still batting 1000.

Sep 29, 2011
The added redshift here attributed to dark matter could just as easily result from
... anti-gravity matter


Sep 29, 2011
This stuff appears complex, but it could be imagined quite easily in context of quite common social situation. Lets say, I'll bring some new idea which will attract interest of many people, i.e. this idea is behaving like some gravitating body. Every such a significant idea attracts the people from opponent camp too, which are thinking in the opposite way in an effort to dishonest this idea and make it less significant. These people aren't attracted to the idea as such, but to its weakest part with negative curvature of space-time (every idea has such part, because the scope of theories is limited in aether model).

But just the interest of opponents makes the whole story more significant in the eyes of the rest of detached people in the spirit of slogan: "negative advertisement is an advertisement too". Therefore these negativists actually don't influence the impact of this idea, they're just making it more controversial.


Sep 29, 2011
One thing to remember about most of these "extensions" is that they propose refinements to GR not to replace it completely.
Actually, if we extent the GR into more dimensions in an effort to make it more general, it will start to violate (the postulates of) the existing version of low-dimensional theory. It's actually the problem of string theory, because their hyper-dimensional extensions are violating Lorentz symmetry or equivalence principle on which this theory is based too.

For example it's rather easy to explain superluminal speed of neutrinos with brane model of string theory - but this explanation violates the Lorentz symmetry, on which this explanation is itself based. The result is fuzzy landscape of many solutions, which no one can handle reliably.

The same applies to various extensions of general relativity, which are violating the equivalence principle, on which general relativity is based. Which is why these extensions are accepted with caution so far.

Sep 29, 2011
Until such time as dark energy and dark matter are proven they remain nothing more than a fantasy.
Please let us dispense with those two names because they encourage many to regard them as proven and to quote the theories as of their existance as if they were fact. Call them property L and property M or something equally vague until, if ever, they prove them, then is the time to name whatever they find

Sep 29, 2011
IMO the dark energy and dark matter are quite properly chosen names. Even more important is, these effects weren't ad-hoced with some mystic or lattice M/L-theories: they were revealed experimentally by accident, so to say. And experiment always goes first in physics.

Dark matter manifests with curvature of space-time, and every (particle of) matter is just composed of space-time curvatures. Why not to call the dark matter the matter, after then? The only question is, whether its space-time curvature is composed of large scale curvatures, or rather small scale particles.

IMO we wouldn't make any mistake, if we would consider the both. The large space-time fluctuations ("cold dark matter") attract/trap the small scale fluctuations ("warm dark matter") of the similar nature into itself - so they usually occur in tandem. The very lightweight particles (like the neutrinos) together with these heavier ones (positrons, atom nuclei).

Sep 29, 2011
Dark matter is gonna be mini black holes that are part of the fabric that makes space.

Heard it hear first don't forget. Will be waiting for my Nobel prize :p

Sep 29, 2011
With regards to a unit of Dark energy; has a scientist ever seen a unit of ordinary energy?
Sir Isaac Newton said that he made no conjecture regarding the precursor of gravity.
Professor Albert Einstein provided a kinematical account of gravity, and concluded that gravity is an illusion resulting from the warping of the space-time continuum.
The illusionary gravity appears to exhibit quite substantial physical abilities, and are those abilities illusions also.
Dark matter first gained postulated existence due to an inability to explain the Pioneer spacecraft anomalies, and now are being endowed with abilities opposite too or similar too ordinary matter, whichever way suits best.
Multi-universes, umpteen dimensions, spooky abilities, worm holes in the space-time continuum, black holes, dark energy and dark matter; the more we learn concerning this incredible universe, the more imaginative we become in our attempts to arrive at a description that fits that observed.

Sep 29, 2011
In response to all the single one votes, which I can only figure is someone who just generally disagrees with everybody, I have given every comment thus far a 3 rating.

Sep 29, 2011
@Richochet: you can check the voting trolls at the account activity status page easily, for example here: http://www.physor...activity
In this thread it's a Deesky account, for example.

Sep 29, 2011
@Richochet: you can check the voting trolls at the account activity status page easily, for example here: http://www.physor...activity
In this thread it's a Deesky account, for example.

I know, but I didn't feel like it...

Sep 29, 2011
Any theory, including mine, that explains gravity, will indicate that light is affected by it. This only proves Einstein tried to explain gravity. It doesn't mean he's right.

Sep 29, 2011
In aether theory the speed of light is wavelength dependent and the space-time is formed with tiny density fluctuations, which have character of fractal foam. We are just at the middle of the dimensional scale of that foam, which manifests with CMBR noise of 2 cm wavelength. The visible light of shorter wavelength is focused towards density gradients of this foam, whereas the microwaves are essentially ignoring the space-time curvature, so they can escape from black holes like the Hawking radiation.

There is interesting question, in which direction the radiowaves should deflect around gravitational lens. IMO they should be deflected from them, but because they're tachyons, they will deflect in similar way, like the visible light - but their speed will be accelerated during this and we would observe blue shift.

In general, the Universe expansion should be valid only for visible light, in microwaves it should appear stationary and in radiowaves contracting instead of expanding.

Sep 29, 2011
In aether theory the speed of light is wavelength dependent
In general, the Universe expansion should be valid only for visible light, in microwaves it should appear stationary and in radiowaves contracting instead of expanding.

Wow. You do realize this directly contradicts observation don't you? Don't you want to make something up that matches observations instead? Stop cluttering up the comment board.

To clarify the point in my earlier comment that several people apparently had a problem with. This research shows light from galaxies at roughly the same distance from us displaying varying redshift depending on the depth within the gravity well of the cluster that the light is coming from. This is a new confirmation of GR (at least as explained by the article).

Sep 29, 2011
You do realize this directly contradicts observation don't you?
Not quite. For example, in microwaves we cannot observe the red-shift, because of lack of reliable reference sources at long distances, but many effects typical for red shift just disappear in CMBR (the Integrated Sachs-Wolfe effect, for example).


In light of wavelengths larger then CMB wavelength the blue shift and positive violation of inverse square law should be observed. Last July, US astronomers announced surprising results from a high-altitude balloon experiment called ARCADE-2, which had made careful measurements of the sky at radio wavelengths. The background radio emission, which is the component smoothly distributed across the whole sky, was several times brighter than anyone was expecting.


Oct 16, 2011
Dark Matter was postulated to explain the observational data of the motion of stars in Galaxies, and the retention of Gas in galaxies that should have lost all of thier internal gas if the only gravitational attraction was from the observed visible matter. The term "Dark" was applied simply because the "matter" causing the gravitational curvature "seems" not to emit electro-magnetic radiation or light, therefor it is ipso facto "Dark" or unseen. What exactly is causing the Gravitational curvature is nice to speculate about, but this experiment again proves that taking a geometrical tensor approach to applying curved geometry to space, gives a real good approximation to how space seems to actually behave and that this does seem to be due to the amount of matter present in it, not some arbitrary "force" acting from no cause at all.

Oct 16, 2011
To clarify my comment a little GR is simply a mathematical formula that describes geometric curvature, and then goes on to explain what may be causing that curvature. Specifically this is Reimanian Geometry, If the formula is then used or applied "properly" then the theory is perfectly capable of predicting what should be observed. Therefore when you do conduct observations that agree with the calculated results of the theory it is highly likely that space is curved in accordance with the specific metric tensor used by Einstein to describe gravity, and this is why objects move within that space as observed. The theory is in such agreement with the observed motion, because the curvature dictates the behavior purely from derived mathematical principles of curved spaces.

Oct 16, 2011
In otherwords GR is a dual theory that describes the curvature caused by the presence of something causing that curvature by observing the motion of objects through the curved Geometry, which allows you to deduce how much of the something necessary to create the observed curvature is present.

Oct 16, 2011
We should realize, the same curvature of space-time appears from inside like the place, which slows down the speed of clock, while the path of light remains straight - but from outside (where speed of clock is not affected with gravity field anymore) it appears like gravity lens, curving the path of light. These two perspectives are mutually dual and albeit they're both predicted with general relativity, one of them violates the special relativity heavily. Compare the complementarity of black holes.


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