Testing General Relativity with Atomic Clocks

We discuss perspectives for new tests of general relativity which are based on recent technological developments as well as new ideas. We focus our attention on tests performed with atomic clocks and do not repeat arguments present in the other contributions to the present volume. In particular, we present the scientific motivations of the space projects ACES and SAGAS.Comment: Contribution for "The Nature of Gravity" (eds. F. Everitt et al

Quantum Physics Exploring Gravity in the Outer Solar System: The Sagas Project

We summarise the scientific and technological aspects of the SAGAS (Search for Anomalous Gravitation using Atomic Sensors) project, submitted to ESA in June 2007 in response to the Cosmic Vision 2015-2025 call for proposals. The proposed mission aims at flying highly sensitive atomic sensors (optical clock, cold atom accelerometer, optical link) on a Solar System escape trajectory in the 2020 to 2030 time-frame. SAGAS has numerous science objectives in fundamental physics and Solar System science, for example numerous tests of general relativity and the exploration of the Kuiper belt. The combination of highly sensitive atomic sensors and of the laser link well adapted for large distances will allow measurements with unprecedented accuracy and on scales never reached before. We present the proposed mission in some detail, with particular emphasis on the science goals and associated measurements.Comment: 39 pages. Submitted in abridged version to Experimental Astronom

Advancing Fundamental Physics with the Laser Astrometric Test of Relativity

The Laser Astrometric Test of Relativity (LATOR) is an experiment designed to test the metric nature of gravitation - a fundamental postulate of the Einstein´s general theory of relativity. The key element of LATOR is a geometric redundancy provided by the long-baseline optical interferometry and interplanetary laser ranging. By using a combination of independent time-series of gravitational defelction of light in the immediate proximity of the Sun, along with measurements of the Shapiro time delay on interplanetary scales (to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will significantly improve our knowledge of relativistic gravity and cosmology. The primary mission objective is i) to measure the key post-Newtonian Eddington parameter gamma with accuracy of a part in 10^9, 1/2(1 - gamma) is adirect measure for presence of a new interaction in gravitational theory, and, its search, LATOR goes a factor 30,000 beyond the present best result, Cassini´s 2003 test. Other mission objectives include: ii) first measurement of gravity´s non-linear effects on light to ~ 0.01 % accuracy; including both the traditional Eddington beta parameter and also the spatial metric´s 2nd order potential contribution (never measured before); iii) direcht measurement of the solar quadrupole moment J2 (currently unavailable) to accuracy of a part in 200 of its expected size of ~ 10^-7; iv) direct measurement of the "frame dragging" effect on light due to Sun´s rotational gravitomagentic field, to 0.1 % accuracy. LATOR´s primary measurement pushes to unprecedented accuracy the search for cosmologically relevant scalar-tensor theories of gravity by looking for a remnant scalar field in today´s solar system. We discuss the science objectives of the mission, its technology, mission and optical designs, as well as expected performance of this experiment. LATOR will lead to very robust advances in the tests of fundamental physics: this mission could discover a violation or extension of general relativity and/or reveal the presence of an additional long range interaction in the physical law. There are no analogs to LATOR; it is unique and is a natrual culmination of solar system gravity experiments