6 January 2010
The holy grail of physics
One of the holy grails of modern physics is to unify the theories of general relativity and quantum physics, which both work well separately but are mutually incompatible.
A unified theory is the dream of all physicists. But to reach that goal, we first need to be capable of measuring time more accurately than ever before.
This is where the agreement recently signed by CNES and ESA comes in.
The agreement paves the way to combine the performance of 2 atomic clocks: CNES’s PHARAO1 and ESA’s SHM2, which together will make up ACES (Atomic Clock Ensemble in Space).
Quite simply, ACES is the most accurate and most stable space clock every built, with a time error of about one second over 300 million years.
A large cube measuring 1 metre on a side, ACES will be launched in 2013 and attached to the outside of the European Columbus laboratory on the International Space Station (ISS).
“PHARAO is the heart of the system,” explains Sylvie Léon-Hirtz, PHARAO Project Manager at CNES. “It’s a new-generation laser-cooled caesium atomic space clock offering excellent long-term stability, combined with the short-term stability of SHM.”
Comparing time measurements
To achieve a unified theory, scientists must first test Einstein’s theory of relativity.
“In terms of compatibility between the competing theories, scientists have reached a dead end. They predict tiny effects that would violate the principles of relativity, like for example constants that would no longer be constant,” says Sylvie Léon-Hirtz.
Thanks to measurements of unprecedented accuracy, ACES will make it possible to test some of these constants, notably the fine-structure constant (denoted ?) characterizing the strength of electromagnetic interaction that governs how atoms hold together.
Sylvie Léon-Hirtz is excited about the prospects: “With ACES, we will be able to compare all existing atomic clocks across the globe in 2013, whether they use caesium, rubidium or any other types of atom.”
But before then, given the many technological firsts involved in the mission, ACES will undergo calibration and validation testing for 6 months.
1 Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbite
2 Space Hydrogen Maser