Cal physicist helps confirm Einstein theory
Published 4:00 am, Monday, February 22, 2010
A UC Berkeley physicist and a Nobel prize-winning colleague now in President Obama's Cabinet report they have confirmed one of Albert Einstein's most revolutionary theories 10,000 times more accurately than ever before.
Einstein's theory of general relativity has already been tested and confirmed to a degree as a true picture of reality by scores of experimenters, ever since he proposed it to the world nearly a century ago.
In the immediate decades after the theory's publication, legend had it that only 12 people in the world could understand it, although physicists have long revered it.
Even today, relativity remains an arcane subject for most of us, but it does have relevance to all science and even to everyday life - for meticulous timekeepers, for space explorers, for astronomers studying black holes and even for anyone driving a car with a Global Positioning System device navigating around the Bay Area's tricky freeway mazes.
One basic prediction from Einstein's theory is that the tug of gravity makes clocks slow down.
Now Holger Müller, a physicist at UC Berkeley, together with Steven Chu, former director of the Lawrence Berkeley National Laboratory and now Obama's energy secretary, as well as Achim Peters of Humboldt University in Berlin, report they have developed what is by far the best confirmation yet of Einstein's monumental achievement.
Details of their work are published in the current issue of the journal Nature.
Soon after Einstein's theory was published in 1916, British astronomers realized it implied that very massive objects should be able to bend light. To confirm that theory, Sir Arthur Eddington took advantage of a total eclipse of the sun in 1919 to measure the light from a star as it was bent almost imperceptibly by the sun's gravity.
That was the first confirmation of Einstein's theory.
In recent years scientists have used different techniques to test and confirm other aspects of the theory - among them by flying atomic clocks across the Atlantic and seeing them slow down, and by measuring the difference in time between one hydrogen maser clock resting on Earth and another clock boosted 6,200 miles high by rocket.
Now Müller and his colleagues have turned to the field of quantum mechanics for their experiment. According to the concept of quantum mechanics, everything in the universe, including light itself and all matter, has the properties of both particles and waves, properties that can't be seen at the same time.
"It goes beyond everyone's imagination," Müller said in an interview, "but atoms vibrate at such a high frequency that they usually can only be seen as particles, not as waves. And the same is true for ordinary matter."
In laboratory experiments Müller and his colleagues used the oscillation of cesium atoms vibrating as waves at a million billion billion times a second while a carefully tuned laser flashed at the vibrating wavelike atoms.
Each flash of laser light can change the direction of a wave-like cesium atom as it moves, and as one flash pushed part of the wave upward against Earth's gravity, another part remained unmoved.
In Einstein's concept of space-time, the particles pushed upward experienced time passing swiftly, while the particles that lay sunken in the Earth's gravitational well experienced time passing normally. So as waves, the Earth-bound particles oscillated more slowly than the upward ones in a movement physicists term their gravitational red shift.
"Our experiment shows once again how well Einstein's theory describes the real world," Müller said. "It demonstrates that gravity does indeed change the flow of time, a concept fundamental to the theory of general relativity."