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A New Confirmation of General Relativity

Einstein’s Special Theory of Relativity remains much in the news after a weekend of speculation about the curious neutrino results at CERN. Exactly what is going on with the CERN measurements remains to be seen, but the buzz in the press has been intense as the specifics of the experiment are dissected. It will be a while before we have follow-up experiments that could conceivably replicate these results, but it’s interesting to see that another aspect of Einstein’s work, the General Theory of Relativity, has received a new kind of confirmation, this time on a cosmological scale.

Here we’re talking not about the speed of light but the way light is affected by gravitational fields. The work is out of the Niels Bohr Institute at the University of Copenhagen, where researchers say they have tested the General Theory at a scale 1022 times larger than any laboratory experiment. Radek Wojtak, an astrophysicist at the Institute, has worked with a team of colleagues to analyze measurements of light from galaxies in approximately 8,000 galaxy clusters. Each cluster is a collage of thousands of individual galaxies, all held together by gravity.

Image: Researchers have analysed measurements of the light from galaxies in approximately 8,000 galaxy clusters. Galaxy clusters are accumulations of thousands of galaxies (each 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: Niels Bohr Institute/ Radek Wojtak.

The Copenhagen team was looking specifically at redshift, where the wavelength of distant galaxies shifts toward the red with increasing distance. Redshift has been used to tell us much about how the universe has expanded since the light being studied left its original source. Normally we think of the redshift being the result of the changing distance between the distant light source and ourselves as we both move through space. This is the familiar Doppler shift, and it could be either a redshift or, if the objects are approaching each other, a blueshift.

But another kind of redshift can come into play when space itself is expanding. Here the distance between the distant light source and ourselves is also increasing, but because of its nature, we call this a cosmological redshift rather than a Doppler shift. Gravity can also cause a redshift, as light emitted by a massive object is affected by the gravity of the object. The loss of energy from emitted photons shows up as a redshift commonly called a gravitational redshift.

The General Theory of Relativity can be used to predict how light – and thus redshift – is affected by large masses like galaxy clusters. In the new work, we’re focusing on both cosmological and gravitational redshift, effects apparent when the light from galaxies in the middle of the galactic clusters is compared to those on the outer edges of the cluster. Wojtak puts it this way:

“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.”

Going on to measure the total mass of each galaxy cluster, the team could then use the General Theory of Relativity to calculate the gravitational redshift for the differently placed individual galaxies. What emerged from the work was that the theoretical calculations of the gravitational redshift based on the General Theory of Relativity were in agreement with the astronomical observations. Says Wotjak:

“Our analysis of observations of galaxy clusters show[s] that the redshift of the light is proportionally offset in relation to the gravitational influence from the galaxy cluster’s gravity. In that way our observations confirm the theory of relativity.”

Does the testing of the General Theory on a cosmological scale tell us anything about dark matter and its even more mysterious counterpart, dark energy? On that score, this Niels Bohr Institute news release implies more than it delivers. The new work confirms current modeling that incorporates both dark matter and dark energy into our model of the universe, but beyond that it can provide no new insights into what dark matter actually is or how dark energy, thought to comprise 72 percent of the structure of the universe, actually works. We can make inferences from our understanding of the behavior of the light, but we have a long way to go in piecing together just what these dark components are.

The paper is Wojtak et al., “Gravitational redshift of galaxies in clusters as predicted by general relativity,” Nature 477 (29 September 2011), pp. 567–569 (abstract).


Comments on this entry are closed.

  • Roger September 28, 2011, 20:39

    Could it be that the accelerating expansion of Space is what is giving us the forward arrow of Time? Space and Time are a single continuum. General Relativity explains that Mass can cause the bending of Space and Time. The accelerating expansion of Space is another type of bending. I wonder what the affect of this expansion on Time would be if calculated according to General Relativity? 74% of the Universes energy is devoted to it.

  • Joy September 29, 2011, 5:04

    GR is not a TOE, as it doesn’t address physics at very small scales. But, it is not only extraordinarily Elegant, but has many times over shown robust Predictive Value.

    Nothing else in physics compares. The SM is only pseudo-predictive, it works fine as long as you input numerous arbitrary values, but has no explanation for the values themselves. Not elegant at all. It is a mathematic construct lacking any deep understanding of what it is modeling. The trees have been studied in detail, but the forest has not yet been glimpsed.

    And ST … well, no predictive value at all, more abstract mathematical art or theology than a theory.

    After 103 years, Einstein still rules the cosmos. Still waiting for the next one, assuming that humans are capable of understanding more physics than we do now …

  • Martin J Sallberg September 29, 2011, 6:06

    General relativity is not the same as special relativity. Einstein himself realized that general relativity takes precedence over special relativity. Maybe general relativity is right while special relativity is at least part wrong. Maybe it was a general relativity effect that enabled the neutrinos at CERN to travel faster than light.

  • ljk November 14, 2011, 18:18

    Sunday, November 13, 2011

    Einstein’s challengers

    On Einstein’s Opponents, and Other Crackpots

    “This world is a strange madhouse. Currently, every coachman and every waiter is debating whether relativity theory is correct. Belief in this matter depends on political party affiliation.”1

    Thus begins a letter by Albert Einstein to his one time close collaborator, mathematician Marcel Grossmann. It was written on 12 September 1920, just some three weeks after Berlin’s Philharmonic Hall had hosted a rambunctious rally at which Einstein had been denounced as a fraud and scientific philistine.

    The event, together with the public debate between Einstein and nobelist Philippe Lenard of a month later, constitutes the first apogee of, what has become known as, the anti-relativity movement. Sentiment against relativity had been brewing for some time, in various quarters; one of the speakers at the Berlin event, Ernst Gehrcke, spectroscopist and extra-ordinary professor of physics, had for instance started publishing against the theory already in 1911.

    However, since the very public announcement of the eclipse results of 1919, opposition against relativity had gained great momentum. These results had confirmed Einstein’s predictions of light bending in the gravitational field of the Sun, and the ensuing publicity had propelled him into the international limelight; clearly, the enormous interest in relativity is manifest in the above letter to Grossmann.

    Read more…

    “Essay review of “Einsteins Gegner. Die öffentliche Kontroverse um die Relativitätstheorie in den 1920er Jahren” by Milena Wazeck” by Jeroen van Dongen



    Friday, November 11, 2011

    Bad hairday for Einstein?


    Two important and unpleasant events occurred in Albert Einstein’s life in 1920: That August an antirelativity rally was held in the large auditorium of the Berlin Philharmonic, and a few weeks later Einstein was drawn into a tense and highly publicized debate with Philipp Lenard on the merits of relativity at a meeting in Bad Nauheim, Germany.

    I review these events and discuss how they affected Einstein in light of new documentary evidence that has become available through the publication of Volume 10 of the Collected Papers of Albert Einstein.

    “Reactionaries and Einstein’s Fame: German Scientists for the Preservation of Pure Science, Relativity, and the Bad Nauheim Meeting” by Jeroen van Dongen


  • ljk December 28, 2011, 20:18

    The Einstein Theory of Relativity: a 1923 Silent Animated Film

    by Socrates on December 28, 2011

    The Einstein Theory of Relativity is a 20 minute silent black and white animated film. It was produced in 1923 by the Fleischer Studios, best known for their Betty Boop cartoons.

    The film aims to explain Albert Einstein’s Theory of Relativity to anyone willing to invest 20 minutes in watching the movie. Though it is almost a hundred years old, its simple but ingenious animation is very effective in demystifying Einstein’s theory without the need of advanced physics or mathematics.

    The movie starts by examining the meaning behind the term relativity and how it relates to the general theory. It then proceeds to demonstrate how things such as motion, direction, size, speed and time are all relative to the observer’s point of view or the general frame of reference.

    In fact, all measurement is relative and space is bent…

    Full article and film here:


  • ljk September 28, 2012, 0:02

    Albert Einstein’s Methodology” by Galina Weinstein‏


    This paper discusses Einstein’s methodology. The first topic is: Einstein characterized his work as a theory of principle and reasoned that beyond kinematics, the 1905 heuristic relativity principle could offer new connections between non-kinematical concepts.

    The second topic is: Einstein’s creativity and inventiveness and process of thinking; invention or discovery.

    The third topic is: Einstein considered his best friend Michele Besso as a sounding board and his class-mate from the Polytechnic Marcel Grossman – as his active partner. Yet, Einstein wrote to Arnold Sommerfeld that Grossman will never claim to be considered a co-discoverer of the Einstein-Grossmann theory. He only helped in guiding Einstein through the mathematical literature, but contributed nothing of substance to the results of the theory. Hence, Einstein neither considered Besso or Grossmann as co-discoverers of the relativity theory which he himself invented.

    “Albert Einstein’s Methodology” by Galina Weinstein


  • ljk October 10, 2012, 17:32

    Extending Einstein’s Theory Beyond Light Speed

    ScienceDaily (Oct. 10, 2012) — University of Adelaide applied mathematicians have extended Einstein’s theory of special relativity to work beyond the speed of light.

    Einstein’s theory holds that nothing could move faster than the speed of light, but Professor Jim Hill and Dr Barry Cox in the University’s School of Mathematical Sciences have developed new formulas that allow for travel beyond this limit.

    Einstein’s Theory of Special Relativity was published in 1905 and explains how motion and speed is always relative to the observer’s frame of reference. The theory connects measurements of the same physical incident viewed from these different points in a way that depends on the relative velocity of the two observers.

    “Since the introduction of special relativity there has been much speculation as to whether or not it might be possible to travel faster than the speed of light, noting that there is no substantial evidence to suggest that this is presently feasible with any existing transportation mechanisms,” said Professor Hill.

    Full article here:


  • ljk November 16, 2012, 19:00


    Wednesday, November 14, 2012

    “Mistaken Identity and Mirror Images”…quirky stories

    Albert Einstein accepted a “special” visiting professorship at the University of Leiden in the Netherlands in February 1920. Although his appointment should have been a mere formality, it took until October of that year before Einstein could occupy his special chair.

    Why the delay? The explanation involves a case of mistaken identity with Carl Einstein, Dadaist art, and a particular Dutch fear of revolutions. But what revolution was one afraid of? The story of Einstein’s Leiden chair throws new light on the reception of relativity and its creator in the Netherlands and in Germany.

    “Mistaken Identity and Mirror Images: Albert and Carl Einstein, Leiden and Berlin, Relativity and Revolution” by Jeroen van Dongen


  • ljk December 4, 2012, 12:11

    Einstein Discovered Dark Energy, Says Historian of Science

    Einstein discussed the phenomenon that physicists now call dark energy in correspondence with Schrodinger, reveals a physicist and historian of science


  • ljk January 22, 2013, 18:32

    What Einstein meant when he said “God does not play dice …”

    Authors: Vasant Natarajan

    (Submitted on 5 Jan 2013)

    Abstract: We analyze Einstein’s views on God and religion, and his views on Quantum Mechanics.

    Comments: 7 pages, no figures

    Subjects: Popular Physics (physics.pop-ph)

    Journal reference: Resonance Volume 13, Number 7, pp. 655-661 (July 2008)

    Cite as: arXiv:1301.1656 [physics.pop-ph]
    (or arXiv:1301.1656v1 [physics.pop-ph] for this version)

    Submission history

    From: Vasant Natarajan [view email]

    [v1] Sat, 5 Jan 2013 05:45:01 GMT (374kb)


    Plus this paper from 2006:


    And this one from January of 2013: