SpaceX Launches Atomic Clocks With Lasers To Test Einstein Theory
Artist's impression showing the European space laboratory Columbus that is part of the International ... More Space Station with the Atomic Clock Ensemble in Space containing the PHARAO and Space H-Maser atomic clocks.
The Atomic Clock Ensemble in Space will 'redefine how we measure time,' according to the European Space Agency, which developed it. It will transmit the most accurate time signal ever from space and create an 'internet of clocks,' comparing them to measure the flow of time. That will help scientists study Earth's gravity.
According to ESA, an atomic clock measures time by observing an atom's transition from an excited state to a ground state with a fixed frequency. The ACES clocks — PHARAO and SHM — will be used to test fundamental physics from orbit, including Albert Einstein's theory of general relativity and the search for dark matter, said ESA. It will do that by defining how time and space are related.
Built by the French space agency CNES and Safran Timing Technologies in Switzerland, the ACES clocks are so precise that they would lose just one second in 300 million years. However, they will not stay in orbit for long. With the ISS due to be deorbited in the late 2020s, they are destined to burn up in Earth's atmosphere alongside the rest of the station.
The ACES clocks have a time transfer system built by German company TimeTech that will use microwave and laser links to synchronize time between space and Earth. The mission will also test how to synchronize clocks worldwide using GPS satellites.
'We are placing the most precise timepiece ever sent to orbit aboard the International Space Station — opening new frontiers in fundamental physics, time transfer, and global synchronization,' said Daniel Neuenschwander, Director of Human & Robotic Exploration at ESA. He called it a 'major milestone for European science and international cooperation in space.'
The ACES clocks launched atop a SpaceX Falcon 9 rocket from NASA's Kennedy Space Center in Florida at 4:15 a.m. EDT on Monday, April 21. It was part of NASA's SpaceX 32nd Commercial Resupply Services mission to fly scientific experiments and 6,700 pounds of supplies to the International Space Station in a Dragon space capsule. It will dock at the ISS around 8:20 a.m. Tuesday, April 22.
The ACES clocks are scheduled to be installed outside ESA's Columbus module on Friday, April 25, facing Earth, where they will begin at least 10 measurement sessions, each lasting 25 days.
The 'bowling ball on a sheet' analogy is a popular way to visualize gravity in general relativity.
Albert Einstein's general theory of relativity describes how the cosmos works. The universe is 4D — it has three dimensions in space and one in time. Relativity is about what happens when you introduce mass into the 4D universe. The theory is encapsulated by the bowling ball (mass) on the trampoline (space-time), with the former stretching the latter. Mass curves space-time. Space-time controls how mass moves. If space-time is curved, everything with mass moves in a curved line. Gravity is a symptom of curved space-time; the sun changes the geometry of space-time around it, and light beams curve as they pass through curved space-time.
According to NASA, ACES will measure Einstein's 'gravitational redshift,' an effect of Einstein's theory whereby light shifts to redder colors because of gravity. Gravitational redshifts impact the accuracy of GPS positioning.
This theory was first published by Einstein in 1915, during the First World War, but remained unproven until photographs were taken during a total solar eclipse on May 19, 1919, that demonstrated light deflection.
The images showed that the presence of the sun's mass in a dark sky shifted where stars appeared to be because the sun curved space-time. The light from stars around it traveled in a curve through it and appeared in a slightly different place than where they normally would.
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