US scientists have measured Albert Einstein’s theory of relativity, which holds that gravity slows down time, on the smallest scale ever seen, showing that clocks run at different speeds when separated by fractions of a millimeter.
Jun Ye, a researcher at the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, told AFP that the clock used was “by far the most accurate ever built and could pave the way for new discoveries in quantum mechanics.” .
Ye and his colleagues published their findings in the prestigious journal Nature, describing the engineering advances that allowed them to build a device 50 times more accurate than their previous best watch, made in 2010.
More than a century ago, in 1915, Einstein presented his theory of general relativity, which held that the gravitational field of a giant object distorts spacetime. This makes time pass more slowly as we get closer to the object.
But it was only with the invention of atomic clocks, which keep track of time by detecting the transition between two energy states within an atom exposed to a certain frequency, that scientists were able to test the theory.
Early experiments included 1976’s Gravity Probe A, which involved a spacecraft 10,000 km above the Earth’s surface and showed that an onboard clock was faster than its Earth equivalent by one second every 73 years.
Since then, clocks have become increasingly accurate and therefore better able to detect the effects of relativity.
A decade ago, Ye’s team set a record by watching time move at different speeds when her ultra-precise watch moved 33 centimeters higher.
Theory of the Whole
Ye’s main breakthrough was working with lattices of light, known as optical lattices, to trap atoms in ordered arrays. With this, it prevents atoms from falling by gravity, or moving in any way, which could result in a loss of precision.
Inside Ye’s new watch are 100,000 strontium atoms, stacked on top of each other like a stack of pancakes totaling about a millimeter in height.
The clock is so accurate that when scientists split the battery in two, they were able to detect time differences between the top and bottom halves.
At this level of accuracy, watches basically act as sensors.
“Space and time are connected,” Ye said. “And with such an accurate time measurement, you can see how space is changing in real time: Earth is a living, animated body.”
These clocks spread across a volcanically active region can tell geologists the difference between solid rock and lava, helping to predict eruptions.
Or, for example, studying how global warming is causing glaciers to melt and oceans to rise.
What Ye is most excited about, however, is that future clocks could mark a new beginning for the realm of physics.
Current clock can detect time differences within 200 microns. If that were reduced to 20 microns, it could start measuring the quantum world, helping to close gaps in the theory.
While relativity beautifully explains how large objects like planets and galaxies behave, it is notoriously incompatible with quantum mechanics, which deals with the very small and holds that everything can behave like a particle and a wave.
The intersection of the two fields would bring physics one step closer to a unifying “theory of everything” that explains all physical phenomena in the cosmos.
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