Shapiro Delay


The Shapiro Delay, discovered in 1964 by Irwin Shapiro, reveals predictable delays in radar signals sent close to planetary bodies. This phenomenon, akin to gravitational lensing, demonstrates that once energy is bent, it departs with less energy. Shapiro’s experiment sheds light on the gravitational interaction between celestial bodies and electromagnetic radiation.


The Shapiro Delay, a consequence of Einstein’s theory of general relativity, manifests as a delay in radar signals traveling near massive celestial bodies. Irwin Shapiro’s groundbreaking experiment provided empirical evidence for the gravitational bending of light and the consequent time delay in signal propagation. This delay, analogous to gravitational lensing, elucidates the intricate interplay between gravity and electromagnetic radiation.

Experiment Details

Shapiro’s experiment involved sending radar signals from Earth to spacecraft passing near distant planets. By measuring the time it took for the radar signals to travel to the spacecraft and return, Shapiro observed a systematic delay compared to the expected travel time in the absence of gravitational effects. This delay, known as the Shapiro Delay, confirmed Einstein’s prediction of the gravitational time dilation effect.

Results and Significance

The Shapiro Delay experiment demonstrated that gravitational fields of massive celestial bodies, such as planets, can influence the propagation of electromagnetic radiation. This effect, analogous to gravitational lensing, highlights the bending of light and the consequent time delay experienced by radar signals. Shapiro’s findings provided empirical support for Einstein’s theory of general relativity and contributed to our understanding of gravity’s influence on electromagnetic waves.


The Shapiro Delay experiment conducted by Irwin Shapiro in 1964 revealed the predictable delays in radar signals traveling near planetary bodies, confirming Einstein’s theory of general relativity. This experiment, alongside gravitational lensing, illustrates the bending of electromagnetic radiation by gravitational fields. Shapiro’s work significantly advanced our understanding of the interplay between gravity and electromagnetic waves, shedding light on the fundamental nature of the universe.