What’s SaToR-G?

Einstein’s general theory of relativity (GR) represents the best description we have for the description of the gravitational interaction, both at the high and low energy scales, and it is the pillar of modern cosmology to understand the universe that we observe through a number of different techniques. Indeed, after more than 100 years, GR has passed a wide number of experimental verifications and it is currently considered the “Standard Model” for gravitational physics.

Starting in 2020, SaToR-G (Satellite Tests of Relativistic Gravity) will expand the activities carried on by the LAser RAnged Satellites Experiment (LARASE, 2013-2019), investigating possible experimental signatures of deviation from GR. Similarly to LARASE, SaToR-G is dedicated to measurements of the gravitational interaction in the weak-field and slow-motion (WFSM) limit of GR by means of laser tracking to geodetic passive satellites orbiting around the Earth. SaToR-G exploits the improvement of the dynamical model of the LAGEOS, LAGEOS II and LARES satellites achieved by LARASE. These satellites represent the proof-masses of the experiment. While for LARASE the main scientific target was a reliable and robust measurement of the Lense-Thirring effect, SaToR-G focuses on verifying the gravitational interaction beyond the predictions of GR, looking for possible effects connected with new physics, and foreseen by different alternative theories of gravitation.

SaToR-G is part of a world-wide, ongoing effort  that aims to discriminate among metric theories of gravitation, like  GR, scalar-tensor and vector-tensor theories.
Our experimental contribution to this effort focuses on two directions:

1. Detecting possible deviations from the inverse square law of gravity at distance the between the Earth and the satellites (about 10^7 m), and
2. Precise and accurate measurements of some parameters of the so-called PPN (Parametrized Post-Newtonian) formalism.

These are in fact two powerful tools for testing the predictions of different theories beyond GR itself.

Precisely measuring the effects on the orbits of artificial satellites allows to test GR vs other metric theories in their most profound aspects: related to the curvature of spacetime, to motion on geodesic and to the field equations. Metric theories of gravitation share Einstein's Equivalence Principle (EEP), the Lorentzian structure of spacetime and the equations of motion. In other words, in all metric theories of gravitation the structure of spacetime is the same, as is the way in which the geometry of spacetime determines the way mass-energy moves in it. What instead profoundly distinguishes GR from the other metric theories of gravitation are the equations of the gravitational field, that is, how the mass-energy of the field orders the geometry of spacetime to curve.