Radio photons are the least energetic ones used by astronomers. Yet, their origin is often associated with highly energetic processes, coming frequently from areas of extreme conditions involving high energies, high gravitational or magnetic fields. As a result, this window of the electromagnetic spectrum is a doorway to an effective laboratory for fundamental physics. This talk will concentrate on experiments that are possible using pulsars and neutron stars, but will also cover ongoing experiments which aim to study the properties of black holes, or touch on results where LIGO and pulsar results provide beautiful complementary information.
