The Shapiro time delay
The Shapiro time delay is the so-called "fourth test of general relativity". It has been tested successfully in the Solar System and in binary star systems that contain at least one neutron star. The basic formula for the time delay can be derived from the equivalence principle, although the result – similar to simplified derivations of the gravitational deflection of light – will be too small by a factor 2. The details can be found in this article:
- M. Pössel, "The Shapiro Time Delay and the Equivalence Principle" (2020). arXiv:2001.00229
Reconstructed data from the 1970/1971 measurement by I.I. Shapiro and colleagues of the Shapiro delay for radar signals reflected by Venus, published in I.I. Shapiro et al. 1971, "Fourth test of general relativity: New radar results" in Phys. Rev. Lett. 26, 1132, which is used in the above eprint, and also the script used to generate the comparison figures from the data, can be found here: