Einstein’s theory ‘improved’?

Monday 13 February 2006

Research from the University of St Andrews has revealed that a `simple’ fine-tuning in Einstein’s theory of gravity could solve a dark mystery in galaxies that has baffled astrophysicists for three- quarters of a century.

By refining the law of gravity, Chinese astronomer Dr HongSheng Zhao and his Belgian collaborator Dr Benoit Famaey of the Free University of Brussels (ULB), aim to improve Einstein’s theory and prove whether the mysterious Dark Matter actually exists in galaxies.

Theories of the physics of gravity were first developed by Isaac Newton in 1687 and refined by Albert Einstein’s general theory of relativity in 1905 so that the speed of gravity is equal to the speed of light. While it is the earliest-known force, gravity is still very much a mystery with theories still unconfirmed by astronomical observations in space.

The ‘problem’ with the golden laws of Newton and Einstein is that they do not explain the accelerations of stars in galaxies where there is more gravity observed than predicted.

Legend has it that Newton began thinking about gravity when an apple fell on his head, but according to Dr Zhao: ‘It is not obvious how an apple would fall in a galaxy. Mr Newton’s theory would be off by a large margin; his apple would fly out of the galaxy.’

Astronomers believe that these stars move so fast they would fly apart if they were not being held together by the gravitational attraction of a huge amount of unseen material, first noted by Fritz Zwicky in 1933 and now commonly referred to as Dark Matter (or DM).

Though astronomers cannot detect Dark Matter directly because it emits no light or radiation, it is thought to account for up to 90% of the Universe. Not all scientists believe in the DM theory however, with some preferring to believe the theory proposed by Moti Milgrom in 1983 (and backed up by Jacob Bekenstein in 2004) that a boost in the gravity of ordinary matter is the cause of this acceleration.

Dr Zhao, a lecturer at the School of Physics and Astronomy at St Andrews and member of the Scottish Universities Physics Alliance (SUPA), continued:

‘Efforts to restore the apple on a nice orbit around the galaxy has over the years led to two schools of thoughts: Dark Matter versus non-Newtonian gravity. There has always been a fair chance that astronomers might rewrite the law of gravity. We have tested a new formula for gravity, which allows gravity to be boosted gradually from the Einstein/Newtonian prediction further away from the solar system.

‘Our ‘simple formula’, which is actually a refinement of Bekenstein’s, is consistent with galaxy data so far, and if further verified for solar system and cosmology, it could solve the Dark Matter mystery. We may be able to answer common questions such as whether Einstein’s theory of gravity is right and whether the so-called Dark Matter actually exists in galaxies.’

‘A non-Newtonian gravity formula is now fully specified on all scales by a smooth continuous function; it is ready for fellow scientists to falsify. It is time to keep an open mind while we continue our search for Dark Matter.’

The new formula will be presented to an international audience of experts at Edinburgh’s Royal Observatory in April, which will be given the opportunity to test and debate the reworked theory. Drs Zhao and Famaey will demonstrate their new formula to an audience of Dark Matter and gravity experts from ten different countries.

Dr Famaey commented: ‘It is possible that neither the modified gravity theory, nor the DM theory, as they are formulated today, will solve all the problems of galactic dynamics or cosmology.

‘The truth could in principle lie in between, but it is very plausible that we are missing something fundamental about gravity, and that a radically new theoretical approach will be needed to solve all these problems.

‘Nevertheless, our formula is so attractively simple that it is tempting to see it as part of a yet unknown fundamental theory. All galaxy data seem to be explained effortlessly’.

The results are published in the US-based Astrophysical Journal Letters.




UK – HongSheng Zhao, University of St Andrews – 01334 463135 or email [email protected]

Belgium – Benoit Famaey , Université Libre de Bruxelles (ULB), +32-2-6502833, mobile +32- 475383982 , email [email protected]


Dr Zhao is a PPARC (Particle Physics and Astronomy Research Council) Advanced Fellow. For further info contact Julia Maddock, Tel 01793 442094 or email: [email protected]

Dr. Zhao also holds a NSF Overseas Outstanding Young Scholarship from National Astronomical Observatory of China (contact Dr. B. Qin at Beijing Observatory, [email protected])

The paper is available on line at: http://adsabs.harvard.edu/cgi- bin/nph-bib_query? bibcode=2006ApJ…638L…9Z



Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook, Press Officer on 01334 467227 / 462529, mobile 07900 050 103, or email [email protected] Ref:Gravity 130206.doc View the latest University press releases at http://www.st- andrews.ac.uk

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