Gamma-ray bursts appear to be related to the deaths of massive stars. Amelino-Camelia and colleagues claim that if the difference in the arrival times of photons with different energies can be measured, they will be able to test various theories of quantum gravity. This is because some of the theories treat the vacuum as a region in which particles with different energies travel at different velocities.

In these theories the vacuum is treated as an 'energy foam' in which microscopic quantum energy fluctuations occur on approximately the Planck length (10-33 cm) and time (10-19 GeV). As photons pass through the vacuum, they deform and excite these fluctuations and this, in turn, reduces the photon's velocity. The higher the energy of the photon, the greater the effect. Therefore, because of the vast distances travelled by the photons from gamma-ray bursts, the difference in arrival times could be on the scale of milliseconds, which is well inside the capabilities of present gamma-ray observatories.