Gravitation and time are intimately linked via the Einstein equivalence principle and the theory of general relativity. Hence, it does not come as a surprise that optical clocks with frequency resolution in parts of 1E18 are interesting tools to probe gravity – both, as a test of our theories and in applications. Comparisons of optical clocks are subject to relativistic shifts that can be interpreted to test general relativity or derive information on physical heights with centimetre resolution. This offers a new measurement capability in geodesy that can help to unify height systems and allow for better monitoring relevant processes on Earth in times of climate change. With our transportable and laboratory clocks and optical fibre links for their comparisons, we contribute to these developments.
This work is supported by DFG (EXC-2123/2, SFB 1227, FOR 5456) and EPM (2IEM01, 23FUN02, 25IEM09)