According to Einstein’s theory of gravity, general relativity, clocks tick faster the farther they are from Earth or another massive object. In theory, this should also apply to very small differences in watch sizes.
Now an incredibly sensitive atomic clock has pinpointed that acceleration on a sample of atomsi of millimeter dimensions, revealing the effect on a smaller height difference than ever. Time moved slightly faster at the top of that sample than at the bottom, the researchers report on Sept. 24 arXiv.org.
“Is fantastic”says theoretical physicist Marianna Safronova of the University of Delaware in Newark, who was not involved in the research. “I thought it would take a lot longer to get to this point”. The extreme accuracy of the atomic clock measurement suggests the possibility of using sensitive clocks to test other fundamental concepts of physics.
An inherent property of atoms allows scientists to use them as clocks. Atoms exist at different energy levels and a specific frequency of light causes them to jump from one level to another. That frequency, the speed of oscillation of light waves, serves the same purpose as the second hand which ticks regularly.
For atoms farther from the ground, time passes faster, so a higher frequency of light will be needed to blow up the energy. Previously, scientists had measured this shift in frequency, known as gravitational redshift, on a height difference of 33 centimeters.
In the new study, physicist Jun Ye of JILA in Boulder, Colorado, and colleagues used a clock made up of about 100,000 ultracold strontium atoms. Those atoms were arranged in a lattice, which means that the atoms sat at a range of different heights as if they were on the rungs of a ladder. Mapping how the frequency changed over those pitches revealed a shift.
After correcting for non-gravitational effects that could shift frequency, the clock’s frequency changed by about one hundredth of a quadrillionth of a percent over a millimeter, just the amount predicted by general relativity.
Furthermore, after collecting data for about 90 hours, comparing the ticking of the upper and lower sections of the clock, the scientists determined that their technique could measure the relative ticking rates with an accuracy of 0.76 millionths of a trillionth of a percent. . This makes it a record for the most accurate frequency comparison ever performed.
In a related study, also presented on September 24 at arXiv.org, another team of researchers loaded strontium atoms into specific portions of a lattice to create six clocks in one. “What they did is also very exciting”says Safronova.
Shimon Kolkowitz of the University of Wisconsin-Madison and colleagues measured the relative ticks of two of the watches, separated by about six millimeters, with an accuracy of 8.9 millionths of a trillionth of a percent, which in turn would have been a new record. if he hadn’t been beaten by Ye’s group. With that sensitivity, scientists could detect a difference between two clocks ticking at such a slightly different speed that they disagree only a second later. about 300 billion years.
Ye’s clock could detect an even smaller discrepancy between the two halves of the clock by one second accumulated over about 4 trillion years. Although Kolkowitz’s team has not yet measured the gravitational redshift, the configuration could be used for this in the future. The authors of both studies declined to comment, as the papers have not yet undergone the peer review process.
Clocks as Future Dark Matter Radars
The accuracy of the measurements suggests future possibilities, says theoretical physicist Victor Flambaum of the University of New South Wales in Sydney. Eg, “Atomic clocks are now so precise that they can be used to search for dark matter”, He says. This stealthy, unidentified substance it hides invisibly in the cosmos; some hypothesized types of dark matter could alter the ticking of clocks.
Scientists could also compare atomic clocks made of different isotopes, atoms with varying numbers of neutrons in their nuclei, which could suggest new, unknown particles. And atomic clocks can help to study whether the fundamental constants of nature may vary.
The ability to accurately compare different watches is also important for an important timekeeping goal: update the definition by one second. The one-second length is currently defined using an older generation of atomic clocks that are not as accurate as the newer ones like those used in the two new studies.
“There is a very bright future for watches,” says Safronova.