Even a millimetre seems insignificant, and even such a small distance can drastically affect time. In Einstein’s general relativity theory of gravity, clocks tick faster as they are distanced from Earth or another massive object (SN: 10/4/15).
Even for minimal variations in clock heights, that should be true. In a millimetre-sized sample of atoms, an incredibly sensitive atomic clock has detected this speedup, showing that it extends over a more negligible height difference than ever before.
Researchers report on September 24 at arXiv.org that time moved slightly faster at the top of the sample than at the bottom.
A theoretical physicist at the University of Delaware in Newark, Marianna Safronova, says the research is fantastic.
As a result of the extreme precision of the atomic clock’s measurements, it is possible to test other fundamental concepts in physics by using these sensitive timepieces.
A THEORETICAL PHYSICIST’S OPINION
Scientists use atoms as timepieces due to their inherent property. Different atoms exist at different energy levels; a specific light frequency causes them to jump from one station.
The frequency – the rate at which light waves wiggle – serves the same purpose as a regular second hand on a clock.
A higher frequency of light would be needed at atoms farther from the ground since time moves faster to make an energy jump. Researchers have previously measured gravitational redshift across a height difference of 33 centimetres (SN: 9/23/10).
THE RESEARCHERS AT JILA
Researchers at JILA in Boulder, Colorado, have developed a clock consisting of roughly 100,000 ultracold strontium atoms.
The atoms were organized in a lattice, which means that they sat at varying heights as if climbing a ladder. We found a shift when we mapped out the frequency changes over those heights.
Considering the presence of non-gravitational effects that could affect the frequency, we found that the clock’s frequency changed by about a tenth of a quadrillionth of a percentage over a millimetre, in line with general relativity.
Researchers determined their technique’s accuracy by comparing the ticking in upper and lower clock sections over about 90 hours. The relative ticking rates are measured to 0.76 millionths of a trillionth of a percentage—quite an improvement over the previous attempt.
STUDIES BY ANOTHER TEAM
According to a separate study, which the submission provided to arXiv.org on September 24, another team of researchers created six clocks in one by positioning strontium atoms at specific points in a lattice. Safronova says she is thrilled by what they achieved as well.
Using that sensitivity, scientists could detect one second of difference between two clocks ticking at a slightly different rate after approximately 300 billion years.
A discrepancy of one second displayed by Ye’s clock over roughly four trillion years is even more minor than its predecessors. Kolkowitz’s team did not yet measure gravitational redshift with the setup but used to do so in the future.
The authors of both studies declined to comment, as the documents have not yet undergone peer review.
Physicist Victor Flambaum from the University of New South Wales in Sydney says the precision of the measurements suggests future possibilities. Using atomic clocks as an example, he thinks they may use to identify dark matter.
An unidentified substance lurks invisibly in the cosmos; it could affect the tick-tock of clocks. Additionally, scientists can compare atomic clocks with differing isotopes – nuclei of atoms with differing nuclei – which might shed light on undiscovered particles. Atomic clocks can also verify whether fundamental constants of nature change (SN: 11/2/16).
A second primary goal of timekeeping is to update the definition of a second with the ability to compare various clocks precisely (SN: 3/24/21). Current atomic clocks that measure the length of a second are not as accurate as newer ones, such as those used in the two recent studies (SN: 5/20/19).
According to Safronova, clocks have a bright future.
