Physicists are close to performing the most accurate test of Einstein’s ideas about gravity ever undertaken. Their unprecedented experiment will use his two types of cryogenic atoms on the International Space Station (ISS).
A key principle of Einstein’s theory, and one that researchers have been testing for decades, is the equivalence principle. This shows that if only gravity acts on an object, all objects will fall with the same acceleration.
One of the most sensitive tests of the principle so far relied on putting. A very cold rubidium atom falls freely At a special facility in California. Another test involved investigating the effect of gravity on a precisely measured mass of material launched into space by a satellite.
Nasser Galur Now, researchers at the Leibniz University of Hannover in Germany have constructed an experiment that combines elements of both of these previous experiments, using ultracold atoms from space.
they used Cold Atomic Laboratory (CAL) The ISS was launched in 2018 and was built to study quantum effects that are only noticeable when atoms are extremely cold and have extremely low gravity. Inside a CAL, atoms are confined within a chip and become extremely cold as they are pushed, pulled, and bombarded by magnetic forces and lasers.
At temperatures just a billionth of a degree above absolute zero, quantum effects cause these atoms to behave more like collections of overlapping “waves of matter” than individual particles. In the new experiment, the researchers cooled potassium and rubidium atoms on the same chip and manipulated them in a way that effectively turned the chip into two separate devices called interferometers.
Interferometers measure acceleration based on patterns created internally by colliding matter waves. The ISS is always in free fall, constantly accelerating due to gravity. Therefore, if the two interferometers record different acceleration values, the equivalence principle breaks down.
The researchers have now successfully created two interferometers with CAL, but the two devices need to be further optimized before they can be used to fully test the equivalence principle.
“The equivalence principle is fundamental to our understanding of gravity, but these experiments could be more than just a test of general relativity. There are new particles not included in the Standard Model that violate this principle. There is a possibility.” Timothy Kovacy at Northwestern University in Illinois. He said the accuracy of atom-based interferometers improves the longer the atoms are allowed to fall in free fall, but there are time constraints on how long such a free fall can be sustained on Earth. , it would be necessary to go to space to reach the ultimate precision.
And doing so will be a growing and competitive field, says Gharul. In 2017, he was part of a team sponsored by the German Space Agency (DLR) that achieved atomic interferometry using ultracold rubidium atoms instead of potassium atoms. on a research rocket. The DLR team plans to launch another rocket in the coming months, this time carrying both potassium and rubidium atoms.
The CAL experiment is expected to yield results hundreds of times more accurate than those obtained from satellite-based experiments and hundreds of thousands of times more accurate than those obtained from Earth-based experiments, but ultimately it will be needed. Mr. Gharul says it will be. Beyond the ISS. “The ISS is not ideal for precision experiments because of vibrations caused by astronauts cycling and other activities,” he says. “But here we confirm the technology for equivalence principle testing, which will ultimately be performed on a dedicated satellite.”