Printer friendly version
Share
News Release
Research Provides New Glimpses of Space and Time
28 October 2009
Hertfordshire, University of
A paper which provides rare experimental evidence about the very structure of space and time, unified as space-time in Einstein’s theories, will be published in the online issue of Nature today.
Dr Jonathan Granot at the University of Hertfordshire’s School of Physics, Astronomy and Maths, who led the work on the paper, worked with an international team of researchers using the National Aeronautics and Space Administration’s (NASA) Fermi Gamma-ray Space telescope.
"Physicists would like to replace Einstein's vision of gravity -- as expressed in his relativity theories -- with something that handles all fundamental forces," said Peter Michelson, principal investigator of Fermi's Large Area Telescope (LAT) at Stanford University in Palo Alto, California. "There are many ideas, but few ways to test them."
Many approaches to new theories of gravity try to unite it with quantum theory, and picture space-time as having a shifting, frothy structure at physical scales trillions of times smaller than an electron. Some models predict that the foamy aspect of space-time will cause higher-energy gamma-rays to move slightly more slowly than photons at lower energy.
This would violate Einstein's edict that all electromagnetic radiation -- radio waves, infrared, visible light, X-rays, and gamma rays -- travels through a vacuum at the same speed.
On May 10, 2009, Fermi and other satellites detected a so-called short gamma-ray burst designated GRB 090510. Ground-based studies show that the event took place in a galaxy 7.3 billion light-years away. Its short duration, of about one second, and large distance from us make it ideal for constraining a possible dependence of the speed of light on the energy of the particles of light – photons. This is done by placing strict limits on a possible difference in the arrival time of highly energetic photons relative to less energetic photons.
“What makes our limit unique is that it requires the relevant energy (or length) scale of a linear dependence of the speed of light on the photon energy (or inverse linear dependence on its wavelength) to exceed the Planck scale, at which quantum effects on the nature of space-time are expected to become strong,” said Dr Granot.
"This measurement strongly disfavours models in which the speed of light varies linearly with photon energy," Dr Granot said. "Since it requires their energy or length scale to be significantly beyond the Planck scale, which is unnatural.”
Dr Granot concludes by saying: “I find it very impressive that more than a century after Einstein came up with his theory of special relativity, it still passes all experimental and observational tests, up to the highest available precision.”