Is time enough in order to know where you are?
  This talk discusses various aspects of the structure of space-time presenting mechanisms leading to the explanation of the "rigidity" of the manifold and to the emergence of time, i.e. of the Lorentzian signature. The proposed ingredient is the analog, in four dimensions, of the deformation energy associated with the common threedimensional elasticity theory. The inclusion of this additional term in the Lagrangian of empty space-time accounts for gravity as an emergent feature from the microscopic structure of space-time. Once time has legitimately been introduced, a global positioning method based on local measurements of proper times between the arrivals of electromagnetic pulses from independent distant sources is presented. The method considers both pulsars as well as artificial emitters located on celestial bodies of the solar system as pulsating beacons to be used for navigation and positioning. 
Angelo Tartaglia
gr-qc astro-ph.CO