When Testing Einstein’s Theory of General Relativity, Small Modeling Errors Can Add Up Fast

 

Small modeling errors may gather faster than previously predicted when scientists combine multiple gravitational wave events (such as colliding black holes) to check Albert Einstein’s theory of general relativity, suggest physicists at the University of Birmingham in the United Kingdom.

 

The study, published in the journal iScience, propose that catalogs with as few as 10 to 30 events with a signal-to-background noise ratio of 20 (which is typical for events used in this type of test) could offer misleading deviations from general relativity, mistakenly pointing to new physics where nothing exists. Because this is close to the size of existing catalogs used to evaluate Einstein’s theory, the authors conclude that researchers should progress with caution when executing such experiments.

 

“Analyzing general relativity with catalogs of gravitational wave events is a very innovative area of study,” says Christopher J. Moore, a professor at the School of Physics and Astronomy & Institute for Gravitational Wave Astronomy at the University of Birmingham in the United Kingdom and the chief author of the study. “This is one of the first research to look in detail at the significance of theoretical model errors in this very new type of test. While it is well acknowledged that errors in theoretical models need to be handled cautiously when you are trying to assess a theory, we were amazed by how rapidly small model errors can gather when you start merging events together in catalogs.”

 

Einstein published his theory of general relativity, in 1916, which describes how massive celestial objects bend the interconnected fabric of space and time, causing gravity. The theory predicts that intense outer space events such as black hole collisions upset space-time so severely that they generate ripples called gravitational waves, which travel through space at the speed of light. Devices such as LIGO and Virgo have now identified gravitational wave signals from loads of merging black holes, which scientists have been using to put Einstein’s theory to the test. So far, it has every time passed. To push the theory even advance, researchers are now testing it on catalogs of multiple assembled gravitational wave events.

 

“When I got attracted to gravitational wave study, one of the main interest was the opportunity to do new and more severe tests of general relativity,” says Riccardo Buscicchio, a PhD student at the School of Physics and Astronomy & Institute for Gravitational Wave Astronomy and a co-author of the study. “The theory is amazing and has already passed an enormously remarkable array of other tests. But we identify from other areas of physics that it can’t be entirely correct. Trying to find precisely where it fails is one of the most significant questions in physics.”

 

Though, larger gravitational wave catalogs could bring researchers closer to the answer in the nearby future, they also strengthen the possibility for errors. Since waveform models certainly involve some calculations, simplifications, and modeling errors, models with a high extent of precision for individual events could prove distorted when used for large catalogs.

 

To define how waveform errors rise as catalog size increases, Moore and his team used basic, linearized mock catalogs to undergo large numbers of test calculations, which involved drawing signal-to-noise ratios, divergence, and model error alignment angles for every gravitational wave affair. The physicists found that the rate at which modeling errors gather depends on whether or not modeling errors tend to average out through many different catalog measures, whether deviances have the similar value for each event, and the distribution of waveform modeling errors across procedures.

 

 

References:

 “Testing general relativity with gravitational-wave catalogs: the insidious nature of waveform systematics” by Christopher J. Moore, Eliot Finch, Riccardo Buscicchio and Davide Gerosa, iScience.

https://doi.org/10.1016/j.isci.2021.102577