New research puts Einstein to the test

Professor Alex Nielsen and doctoral fellow Vegard Undheim have just published a new set of gravitational wave observations. In these observations, we find the strongest gravitational wave signal ever seen.

The new signal, called GW230814, is so strong that it allows scientists to perform some of the most rigorous tests of Einstein's theory of gravity ever. Nielsen says Einstein's theory still passes the test, but this time with a small "maybe."

Was Einstein wrong?

"Einstein's theory of gravity is a cornerstone of modern science, but as scientists we want to find out where it fails. Our observations come from the collision of black holes. These are the most violent events in the known universe. If Einstein's theory is going to fail, I hope it fails for these black holes," says Professor Alex Nielsen at the University of Stavanger.

In 1915, Einstein completed his theory of gravity, the general theory of relativity. This is a theory not only of gravity, but also of time and space. According to the theory, what we usually perceive as the motion of a body under the influence of gravity is the straightest possible motion of a free body in a curved, four-dimensional spacetime.

Einstein's theory predicted gravitational waves that transport energy from black hole collisions into the universe. It took 100 years for scientists to find these waves. Now scientists find signals from gravitational waves all the time, it happens routinely. But some signals are stronger than others.

"When I saw the signal from GW230814, my first reaction was “wow!” This was a signal so strong that we just had to check if it really matched what Einstein predicted," says Nielsen.

Two years of control work

It has taken two years to verify the observations. Along the way, the researchers came across some unexpected aspects of the signal that they had to smooth out. Another challenge was that the signal was only found in one of LIGO's detectors, as the other detectors were disconnected at the time.

The gravitational wave observations were made in collaboration with colleagues from LIGO (Laser Interferometer Gravitational-Wave Observatory), Virgo interferometer and KAGRA (Kamioka Gravitational Wave Detector). Scientists from all three observatories have now reviewed the observations and used their expertise to analyze the signal.

"Our final conclusion is that the signal is consistent with Einstein's predictions – probably. We have now actually come so far in our research that new mathematics must be invented just to keep up with the observations. It's exciting," says Nielsen.

The article is published here. You can also read a popular science summary of the article at LIGO's web pages.