Fig. 2
Fig. 2. A typical search for microstructure in the light curves of a GRB can be used for placing bounds on (or detecting) the non-trivial refractive index and light-cone fluctuation effects of some models of stochastic quantum gravity. In Liouville-string models, higher-energy channels are delayed more, due to a subluminal refractive index effect of quantum gravity, and the width of the GRB pulse is wider, due to stochastic fluctuations, compared with lower-energy channels. The linear-regression plot shows the correlation of the difference in arrival times of the peaks of the GRB between two energy channels Δtp with the redshift z, which is a characteristic feature of such effects. At present, the number of GRBs whose distances are known is statistically insignificant, but it is hoped that new GRB dedicated searches will be able to provide statistically significant populations of GRB with known redshifts. This would allow more stringent bounds, or detection, of stochastic quantum-gravity effects.