Gamma-ray observations challenge physics
Washington: The underlying quantum ‘graininess’ of space must be at much smaller scales than previously predicted, a new study has revealed, which will dramatically affect the search for physics beyond Einstein.
Einstein``s General Theory of Relativity describes the properties of gravity and assumes that space is a smooth, continuous fabric.
Yet quantum theory suggests that space should be grainy at the smallest scales, like sand on a beach. One of the great concerns of modern physics is to marry these two concepts into a single theory of quantum gravity.
Now, the European Space Agency``s (ESA) Integral gamma-ray observatory has placed stringent new limits on the size of these quantum ‘grains’ in space, showing them to be much smaller than some quantum gravity ideas would suggest.
According to calculations, the tiny grains would affect the way that gamma rays travel through space. The grains should ‘twist’ the light rays, changing the direction in which they oscillate, a property called polarization.
High-energy gamma rays should be twisted more than the lower energy ones, and the difference in the polarization can be used to estimate the size of the grains.
Philippe Laurent of CEA Saclay and his collaborators used data from Integral’s IBIS instrument to search for the difference in polarization between high- and low-energy gamma rays emitted during one of the most powerful gamma-ray bursts (GRBs) ever seen.
“This is a very important result in fundamental physics and will rule out some string theories and quantum loop gravity theories,” said Dr. Laurent.
This new observation is much more stringent, however, because GRB 041219A was at a distance estimated to be at least 300 million light-years.
In principle, the tiny twisting effect due to the quantum grains should have accumulated over the very large distance into a detectable signal. Because nothing was seen, the grains must be even smaller than previously suspected.
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