China Space Station Laser Time Transfer Improves Gravitational Redshift Testing

This paper presents a significant advancement in the testing of gravitational redshift, a fundamental aspect of General Relativity, through the use of laser time transfer between the China Space Station (CSS) and a ground station. By developing a comprehensive observation equation based on a c^{-3} order relativistic model for space-ground clock comparison, the researchers have achieved a gravitational redshift verification precision of (1.8 ± 47)*10^{-7}, representing an order of magnitude improvement over previous experiments. The use of a laser-based approach avoids the ionospheric effects and first-order Doppler shifts that plague microwave-based methods, contributing to the enhanced precision. The achieved precision enables gravitational potential difference measurements with 0.1 m^2/s^2 precision, opening up new possibilities for both fundamental physics investigations and geodetic applications, including intercontinental height transfer. However, the researchers identify tropospheric delay variations and atmospheric turbulence as the primary remaining uncertainty contributors, highlighting the need for further research to mitigate these effects and further improve the precision of the measurements. This work establishes a new benchmark for high-precision tests of relativistic physics and demonstrates the transformative potential of space-based optical time transfer.

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