AstroGrav pizza lunch - Dimitrios Emmanoulopoulos Seminar

Discussion group meeting

Einstein postulated that "Light always propagates through a vacuum at a definite velocity, c, which is independent of the state of motion of the emitting body". This is the framework of classical special relativity, having no fundamental length-scale associated with it (Lorentz invariance). However, quantum effects at the Planck scale, where gravity becomes a strong force, are expected (although not yet proven) to strongly affect the nature of space-time, causing violations of this invariance. It is believed that such violations can be tested by measuring time-lags between very high energy (VHE: > few GeV) photons, emitted simultaneously from distant astrophysical sources, expressing possible variations of photon speed as a function of energy. Since blazars (i.e. VHE emitting AGN) are in relatively cosmological distances and emit variable emission in VHE they are considered ideal candidates to test such deviations. I will describe the current astrophysical detection techniques, involving ground based and space-borne detectors, and then I will present the latest results.