Two atomic clocks will be flown to the International Space Station by 2016 and they will be used to study the relationship between time and space. Since the time of Einstein, physicists have been discovering how time and space are linked and how time is relative with movement through the time/space continuum. These relativistic experiences in the time/space continuum exist beyond the capabilities of our natural perceptions on Earth. The planned experiments that will employ the atomic clocks on the International Space Station will undoubtedly expand the knowledge about time and space in ways that are hard to imagine now.
One of the new atomic clocks is called Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbit, or PHARAO for short. PHARAO employs lasers that cool cesium atoms until they are at a very low temperature, in this case, 273 degrees celsius, which is close to absolute zero. When the atoms are cooled, their movement slows down. PHARAO was created by the space agency in France called CNES. It was recently delivered to the Airbus Space and Defense agency in Germany for assembly.
The other atomic clock that will be installed on the International Space Station to study time and space is called the Space H Maser (SHM) and it measures time using hydrogen atoms and microwave radiation. The two clocks working together will become a cohesive device that is highly accurate at measuring time. The accuracy will lose just one second in every 300 million years.
When the two clocks are working together it will be called the Atomic Clock Ensemble in Space (ACES). Both clocks working in unison will create a system that can measure time with a highly stable, unique time reference to space. The Cadmos User Support and Operations Centre in France will be responsible for operating and managing the ACES instruments on the International Space Station.
The European Space Agency has an 18 month mission planned for ACES. The clocks in space will be connected to atomic clocks in Europe, Australia, Japan and the United States. The ACES device will test Einstein’s general theory of relativity. Specifically, the scientists will test the idea that a clock working in a higher gravitational field will measure time passing slower than a clock measuring time in a low gravity field. For example, there is a lower gravitational field at the top of a high mountain on Earth compared to sea level, which explains why time travels faster at the mountain top than it does at sea level. This has already been demonstrated with current atomic clock technology. The ACES device will be expanding knowledge on this phenomenon by comparing time in various gravitational fields in space with high accuracy.
Very precise atomic clocks have become important in everyday earthly activities. For example, precise atomic clocks are used in GPS and banking systems. The ACES device will be much more precise than these time measuring systems and will also be used to run experiments on the time/space continuum that would be impossible if only dealing with the Earth’s environment.
By Margaret Lutze