29 September 2003

For immediate release

Attention: Science Editors/Producers

 

New research challenges the laws of gravity

 

Two Swinburne University of Technology astronomers have challenged Einstein’s and Newton’s fundamental laws of gravity by presenting the first simulations that depict what the universe would look like using Modified Newtonian Dynamics (MOND) –– an alternative theory of gravity. Dr Alexander Knebe’s and Professor Brad Gibson’s simulations paint a picture of a universe that looks remarkably similar to that observed by large ground- and space-based telescopes, despite emanating from a model that breaks tradition with the theories of gravity cherished throughout the 20th century.

 

These traditional models demand that 90 percent of the universe be composed of “dark matter”, the composition of which remains a mystery to scientists, despite decades of intensive scrutiny.  In contrast, instead of resorting to dark matter as an explanation for the motions of galaxies and the stars within them, MOND proponents suggest that “what you see is what you get in the universe” and that it is the laws of gravity which need revision.  Under MOND, any object whose acceleration drops below some small threshold value receives an extra accelerative “kick” – this kick is tiny, a 1 part in 10 billion effect.  An undetectable modification on Earth today, but its effect on the scale of galaxies is profound, potentially eliminating the need to invoke dark matter.

 

Knebe, from Swinburne’s Centre for Astrophysics & Supercomputing, explained that MOND did not make the traditional laws of gravity redundant.  “Our traditional laws are very well-tested on planetary scales, but they have not been confirmed on the larger scales of galaxies or the universe as a whole.  MOND can be thought of as a subtle extension to the traditional laws, becoming relevant only in cases where the traditional laws may not hold,” Knebe said.

 

MOND has been used successfully in explaining the internal motions of stars within galaxies, and has even been suggested as having an influence on the acceleration of the Pioneer 10 and 11 satellites as they drift away from our solar system.  Despite these clues, MOND had never been tested in a high-powered simulation of structure formation throughout the entire universe.  Dr Knebe and Prof Gibson have successfully rendered the first such model.

 

Prof Gibson says the results aren’t dissimilar from Newton’s original theory, concluding  “Our simulations revealed, much to our surprise, that a MONDian

universe does not look all that different from a dark matter dominated one. It would appear that we may not yet be able to rule out this alternative theory!”

 

Accepted for publication in the Monthly Notices of the Royal Astronomical Society

High-resolution images available here.

 

Download media release here.

 

Media Contacts: Dr Alexander Knebe, Tel: (03) 9214 4318;
                             Prof Brad Gibson, Tel: (03) 9214 8036 or 0438 358 709