The gravitational wave signal proves that Einstein was right about relativity

The loudest collision ever recorded between two black holes allowed scientists to test Einstein’s theory of general relativity in unprecedented detail, showing that the physicist’s predictions were right again.

In 2025, an international collaboration of gravitational wave detectors, consisting of ultra-sensitive laser fields, detected strong ripples in the structure of space-time, designated GW250114, likely created by the merger of two black holes.

The detectors, which include the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US and the Virgo detector in Italy, are much more sensitive than when LIGO made its first detection in 2016. This meant that GW250114 had the cleanest and noisiest data of any gravitational wave to date, making it a unique prediction from otherwise tested physics tests.

Last year, scientists used data from GW250114 to test Stephen Hawking’s theorem, proposed more than 50 years ago, that the event horizon of a merging black hole, the region where light can no longer escape, will not be smaller than the sum of its parent black holes. The results showed with almost 100% certainty that Hawking was right.

Now, Keefe Mitman at Cornell University in New York and his colleagues went a step further and tested whether merging black holes conformed to Albert Einstein’s general relativity.

Einstein’s original equations describe how any material object moves through space-time. When these equations are adjusted for the merger of two black holes and then solved, a clear picture emerges. The black holes first spiral around each other with increasing speed, then collapse together and release a colossal burst of energy before vibrating at different frequencies, much like the ringing of a bell after being struck.

These frequencies, called circular modes, were too weak to be seen in previous gravitational wave events, but GW250114 was loud enough for the modes predicted by Einstein’s equations to be properly tested. Mitman and his colleagues simulated Einstein’s equations and made predictions about how loud and at what frequencies these black hole vibrations should be. When they compared them to the measured frequencies, they matched closely.

“The amplitudes we measure in the data agree incredibly well with the predictions from numerical relativity,” says Mitman. “Einstein’s equations are really hard to solve, but when we solve them and observe the predictions of general relativity in our detectors, they both agree.”

“The bottom line is that Einstein is still right,” he says Laura Nuttall at the University of Portsmouth in Great Britain. “Everything looks like what Einstein says about gravity.

Despite GW250114’s loudness, the frequencies were still so faint that Mitman and his team could not rule out that they could differ from Einstein’s predictions by less than 10 percent. This is mainly a consequence of limitations in the sensitivity of our detectors, says Mitman, and should decrease as we improve the sensitivity of gravitational wave detectors. However, if Einstein’s theory is wrong in some way, then this difference will remain.

“As we observe more and more events or see louder individual events, it could be that these error bars could shrink to around zero or could shrink to zero,” says Mitman. “If it boils down to zero, it’s a lot more interesting.”

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