Particle physics experiments

Ultra-precise atomic clock experiments confirm Einstein’s predictions about time

Using one of the most accurate atomic clocks in the world, physicists have shown that time is a bit slower if you change your height above the Earth’s surface by a tiny 0.008 inches (0.2 millimeter), or about twice the width of a sheet of paper. The discovery is yet another confirmation of the Albert Einstein theory of relativitywhich predicts that massive objects, like our planet, distort the passage of time and slow it down.

“We’re talking about measuring a change in the functioning of a clock at a level a little larger than a human hair,” said Tobias Bothwell, a graduate student in physics at JILA, which is led by the National Institute of Standards and Technology (NIST) and the University of Colorado.

In 1915, Einstein showed that anything with mass deforms the tissue of space-time — an effect we experience as the force of gravity. You can think of gravity as a brake on the flow of time. This mind-bending idea means that clocks closest to Earth run slow compared to those farther away – a phenomenon called time dilation.

Related: 8 Ways to See Einstein’s Theory of Relativity in Real Life

Researchers have already shown that ultra-precise atomic clocks on board aircraft run noticeably slower than those on the ground, according to the manual.”Experimental tests of the nature of time(Fullerton College, 2020). In 2010, scientists set a new record by measuring the passage of time with two aluminum-atomic clocks based on atomic clocks separated in height by about 1 foot (33 centimeters), finding that the taller one ran slightly faster, Bothwell said.

The latter measurement is about a factor of 1,000 better, he added. “We really blew the doors off how much we can measure frequency,” Bothwell said.

The experiment used a collection of approximately 100,000 atoms of the isotope strontium-87, often used in atomic clocks, cooled to a fraction of a degree above absolute zero and placed in a structure called an optical lattice. An optical grating uses intersecting beams of laser light to create a landscape of peaks and valleys resembling an egg box, where each atom is cradled in one of the valleys, according to NIST.

Each strontium the atom oscillates back and forth, ticking itself inside its valley 500 trillion times per second, like the pendulum of a microscopic grandfather clock, allowing the team to measure fractions of a second to an incredible 19 decimal places, according to a 2018 article in the journal Proceedings of the National Academy of Sciences.

The strontium atoms in the optical lattice were arranged in multiple layers, much like a stack of pancakes, Bothwell said. By shining a laser on the layers, he and his colleagues were able to measure the rate at which the atoms in each layer ticked off.

“Going from top to bottom, you see each layer dancing a little differently thanks to gravity“, he said. The results were published on February 16 in the journal Nature.

“These kind of clock experiments can shed light on the nature of time itself,” said Mukund Vengalattore, an independent atomic physicist who was not involved in the work.

This is because strontium atoms are capable of being placed in what is called a superposition of states, meaning two states at once, he added. According to Quantum mechanicsparticles can exist in two places (or states) at once, so future experiments could put a strontium atom in a superposition where it’s in two different “pancakes” at the same time, Vengalattore said.

With the particle in both places at once, the team could then measure the passage of time at different points along the overlapping strontium atom, which would change thanks to the different gravitational pull it feels. This should show that “at one end of the particle, time flows at a speed,” Vengalattore said. “And at the other end, it’s spinning at a different speed.”

This incredibly bizarre possibility is at the heart of the difference between the quantum and classical worlds, he added. Classic objects, like tennis balls and people, cannot exist in overlays where they are located in two places at once. But where the switch between quantum and classical occurs is unclear. By increasing the distance between the pancakes, the researchers could essentially make the particle grow larger and potentially see when it stops behaving like a quantum particle and more like a classical particle.

Such experiments could bring physicists one step closer to a long-sought dream – a theory of everything this would unify Einstein’s theory of relativity, which describes the very large, with quantum mechanics, which describes the very small.

Meanwhile, the current experiment has helped the team envision ways to produce even more accurate atomic clocks, Bothwell said. Future instruments could be used to measure tiny differences in the mass of the Earth beneath them, potentially making the clocks useful for detecting the flow of magma inside volcanoes, changes in meltwater inside glaciers or the movement of our planet’s crustal plates, he added.

Originally posted on Live Science.