Today, scientists are using atoms to measure the curvature of space-time.

In 1797, British scientist Henry Cavendish measured the strength of gravity with a torsion scale made of shot put, wooden stick and wire. In the 21st century, scientists are using more complex tools-atoms-to do very similar things.

The experiment belongs to atomic interferometry, which takes advantage of the principles of quantum mechanics: just as light can be described by particles, a particle, such as an atom, can also be represented as a "wave packet". Just as broadcasts can overlap and interfere, so can matter wave packets.

In particular, if the wave packet of an atom is divided into two, the two go through different processes, and then recombine the two, it will be found that the two wave packets are not aligned. In other words, the phase of the two has changed.

"people are trying to extract useful information from phase shifts," Albert Roura, a physicist at the Ulm Institute of Quantum Technology in Germany, said in an interview. On the study, he also published an "opinion" article on the website of Science.

The principle of gravitational wave detector is similar. By studying particles in this way, scientists can pinpoint the key numbers that dominate the universe behind appearances, such as how electrons work, how strong gravity is, and their subtle changes over short distances.

This is the last effect measured by Chris Overstreet of Stanford University and his colleagues in the new study. To do this, they created an "atomic fountain" consisting of a 10-meter-high vacuum tube with a ring at the top.

Researchers control atomic fountains by emitting laser pulses. They use a laser pulse to emit two atoms up from the bottom. The two atoms reached different heights before being shot down by a second laser. When they fall to the bottom, a third pulse captures both, overlapping their wave packets.

The researchers found that the phases of the two wave packets were not consistent, suggesting that the gravitational field in the atomic fountain was not exactly the same.

"this. In general relativity, it can actually be understood as the influence of the curvature of space-time. " Roura said in an interview. General relativity is one of Einstein's most famous theories.

Because the higher atom is closer to the ring, it bears more gravitational acceleration because of the ring's gravity. In a perfectly uniform gravitational field, the two atoms should have the same degree of change. In the atomic fountain, due to the influence of different gravitation, the time expansion of the two atoms is not synchronous, and the phase of their wave packets is also out of sync.

This leads to only a slight change, but atomic interferometry is sensitive enough to detect it. Scientists can control the position and quality of the ring, Roura said. "they can measure and study these effects."

"this. In general relativity, it can actually be understood as the influence of the curvature of space-time. " Roura said in an interview. General relativity is one of Einstein's most famous theories.

Because the higher atom is closer to the ring, it bears more gravitational acceleration because of the ring's gravity. In a perfectly uniform gravitational field, the two atoms should have the same degree of change. In the atomic fountain, due to the influence of different gravitation, the time expansion of the two atoms is not synchronous, and the phase of their wave packets is also out of sync.

The researchers say that while the atomic interferometry that contributed to all this may seem mysterious, it could one day be used to detect gravitational waves and achieve navigation systems with higher precision than GPS.