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Stability of natural constants in space and time confirmed

Annual Report 2021

Comparisons between ytterbium and caesium atomic clocks in different places (x) and at different times (t) have confirmed the stability of natural constants.

A natural constant should always have the same value, regardless of when or where it has been determined. And Einstein’s theory of relativity exploits this fundamental assumption too, which is known as local position invariance (LPI). Scientists from PTB have now confirmed the validity of LPI by means of a clearly improved experimental test. These investigations were motivated by modern string theories that predict LPI violations (e.g., temporal variations of natural constants). While trying to find experimental evidence of this new concept of physics, the scientists from PTB used the comparison of their highly accurate atomic clocks and were able to improve the results of earlier tests of LPI by up to a factor of 20.

They used atomic clocks whose reference frequencies have different dependencies on the values of selected natural constants. A combined comparison between optical clocks based on the ytterbium ion and conventional caesium clocks allows a search for changes in the fine-structure constant α and in the ratios of the masses of an electron and a proton. The agreement of the highly accurate atomic clocks over a period of several years has shown that changes in the value of α over one year may only occur from the 21st decimal place on.