The aim of this fundamental physics experiment is to test Albert Einstein’s theory of general relativity. PHARAO is part of ESA’s Atomic Clock Ensemble in Space (ACES) mission.
It’s an unprecedented experiment in fundamental physics! Today’s ground-based atomic clocks are so accurate that they only drift by one second every 50 million years. The PHARAO clock, on the other hand, would only drift by one second every 300 million years. Such precision is made possible by weightlessness, where cold atoms are in free fall, facilitating the measurement of time. This makes it possible to test general relativity to an unprecedented degree of precision, validate new space technologies and contribute to the improvement of global time scales.
The role of the Laboratoire Temps-Espace and the Laboratoire National de Métrologie et d’Essais in the mission}
The Laboratoire Temps Espace (LTE) at Observatoire de Paris-PSL has been involved in the PHARAO project from the outset, as part of the ACES mission, and has participated in every stage of its development. After designing and testing the prototype clock in microgravity on board the CNES 0g aircraft, LTE teams played a key role in the environmental and performance tests carried out. The laboratory is also responsible for the operation of the ground clocks and their synchronization with the microwave terminals located on the Observatory buildings. On the scientific front, LTE is responsible for data analysis, from raw microwave data to final scientific products.
The Laboratoire National de Métrologie et d’Essais (LNE-OP), part of the Laboratoire Temps Espace (LTE), plays an essential role in this mission. Specializing in time and frequency metrology, it is a key player in the design of atomic fountains, cold cesium atom clocks and new-generation optical clocks, which define the unit of the second with extreme precision.
A source of collective pride for Observatoire de Paris - PSL
“We are delighted with this launch, which marks the culmination of several years’ collective effort,” says Fabienne Casoli, President of Observatoire de Paris - PSL. "PHARAO represents a major breakthrough for fundamental physics and high-precision metrology. The Laboratoire Temps Espace is continuing its commitment to pushing back the limits of current theories, by developing instruments to explore space-time with unprecedented precision."