Accretion disks around compact objects have been known for about 60 years however their study has been limited because they are unresolved sources in the optical/ultraviolet and X-rays, where they emit. Hanbury Brown & Twiss discovered intensity interferometry in the 1950s, and explained as a quantum effect in the early 60s. We review the capabilities of intensity interferometry in the optical which are becoming available with the advent of very large area telescopes and very fast single photon detectors and their potential to measure accretion disks parameters. Correlating the arrival times of photons detected by Telescopes with mirror areas reaching 1000m2 allows to reach resolutions of nano degree in the optical and to reconstruct images of accretion disks and jets in galactic and extragalactic sources, the potential sources of UHECR.