PARIS: Einstein's theory of relativity, which states that gravity affects the flow of time, just got 10,000 times more accurate.
How quickly time passes depends on where you are, a lesson learnt the hard way by that first-time reviewer of Wagner who observed: "After two hours, I looked at my watch and found that 20 minutes had gone by."
For physicists rather than opera-lovers, relativity was famously expressed in 1915 by Albert Einstein who suggested, among other things, that the flow of time was affected by the force of gravity.
Clocks will run faster the farther they are from a large gravitational source and run slower they closer they are to it, goes the theory.
Various experiments have been carried out to explore Einstein's insight.
They include a 1976 exploit in which an atomic clock was taken on a 115-minute rocket ride to a point some 10,000 km above Earth, and was found to measure more time compared to a counterpart on Earth.
Now physicists in the United States have gone a step further.
They have proved Einstein's theory with an accuracy 10,000 times greater than before, according to a paper published in the British journal Nature.
A team that included Nobel winner Steven Chu - now U.S. energy secretary - used a trap that involved three lasers that zapped waves of caesium atoms, making them move up and down like a fountain.
The waves were used as super-fast clocks, oscillating at nearly a million billion billion times per second.
The team's technique invoked a strange-but-true phenomenon of quantum mechanics: that an atom can be excited into two states at the same time.
In one of the states, the atom was "pushed" by laser pulse one tenth of a millimeter (0.004 of an inch), giving it a minute boost away from Earth's gravitational field. In the other, it remained unmoved.
A split-second later, a second laser flash sent the high-flying atoms downwards, and the stationary ones upward. The two states were then reconstituted in a single atom by a third laser pulse.
The task was then to measure the difference in energy oscillation in the waves during these states.
During the 0.3 seconds they spent in freefall, the waves oscillated about a million extra times - in other words, a wee bit more time elapsed as a result of the brief reduction in gravitational pull.
The numbers should be put in perspective, said Holger Mueller, an assistant professor of physics at the University of California at Berkeley.
"If the time of freefall was extended to the age of the universe, 14 billion years, the time difference between the upper and lower routes would be a mere one hundredth of a second, and the accuracy of the measurement would be 60 picoseconds, the time it talks for light to travel about half an inch (1.27 cm)."
The results add further gloss to Einstein's renown, he said. "This experiment demonstrates that gravity changes the flow of time, a concept fundamental to the theory of general relativity," Mueller said.
Practical benefits also stem from it.
Global Positioning Satellites (GPS) work by sending out precisely timed signals, calibrated by atomic clocks, which are then triangulated to provide a position on the surface of the Earth.
If the best available clocks were used in GPS satellites, satnav users could find their position to the millimetre - but this accuracy could be wrecked if the satellite were moved by just a metre (yard) in altitude, said Mueller.
How quickly time passes depends on where you are, a lesson learnt the hard way by that first-time reviewer of Wagner who observed: "After two hours, I looked at my watch and found that 20 minutes had gone by."
For physicists rather than opera-lovers, relativity was famously expressed in 1915 by Albert Einstein who suggested, among other things, that the flow of time was affected by the force of gravity.
Flow of time gets tested
Clocks will run faster the farther they are from a large gravitational source and run slower they closer they are to it, goes the theory.
Various experiments have been carried out to explore Einstein's insight.
They include a 1976 exploit in which an atomic clock was taken on a 115-minute rocket ride to a point some 10,000 km above Earth, and was found to measure more time compared to a counterpart on Earth.
Now 10,000 times more accurate
Now physicists in the United States have gone a step further.
They have proved Einstein's theory with an accuracy 10,000 times greater than before, according to a paper published in the British journal Nature.A team that included Nobel winner Steven Chu - now U.S. energy secretary - used a trap that involved three lasers that zapped waves of caesium atoms, making them move up and down like a fountain.
The waves were used as super-fast clocks, oscillating at nearly a million billion billion times per second.
The team's technique invoked a strange-but-true phenomenon of quantum mechanics: that an atom can be excited into two states at the same time.
In one of the states, the atom was "pushed" by laser pulse one tenth of a millimeter (0.004 of an inch), giving it a minute boost away from Earth's gravitational field. In the other, it remained unmoved.
A split-second later, a second laser flash sent the high-flying atoms downwards, and the stationary ones upward. The two states were then reconstituted in a single atom by a third laser pulse.
The task was then to measure the difference in energy oscillation in the waves during these states.
Just how accurate?
During the 0.3 seconds they spent in freefall, the waves oscillated about a million extra times - in other words, a wee bit more time elapsed as a result of the brief reduction in gravitational pull.The numbers should be put in perspective, said Holger Mueller, an assistant professor of physics at the University of California at Berkeley.
"If the time of freefall was extended to the age of the universe, 14 billion years, the time difference between the upper and lower routes would be a mere one hundredth of a second, and the accuracy of the measurement would be 60 picoseconds, the time it talks for light to travel about half an inch (1.27 cm)."
Practical benefits
The results add further gloss to Einstein's renown, he said. "This experiment demonstrates that gravity changes the flow of time, a concept fundamental to the theory of general relativity," Mueller said.
Practical benefits also stem from it.
Global Positioning Satellites (GPS) work by sending out precisely timed signals, calibrated by atomic clocks, which are then triangulated to provide a position on the surface of the Earth.
If the best available clocks were used in GPS satellites, satnav users could find their position to the millimetre - but this accuracy could be wrecked if the satellite were moved by just a metre (yard) in altitude, said Mueller.
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