  In recent years several ideas for experimental searches of effects induced by
quantum properties of space-time have been discussed. Some of these ideas
concern the role in quantum spacetime of the ordinary Lorentz symmetry of
classical flat spacetime. Deviations from ordinary (classical) Lorentz symmetry
are now believed to be rather natural in non-commutative space-times, models
based on String Theory and models based on Loop Quantum Gravity. Observations
of gamma rays and ultra-high-energy cosmic rays could play a key role in the
development of this research programme.
