For more than a century, Albert Einstein’s theory of general relativity has been a fundamental pillar in the understanding of cosmic phenomena, from the explanation of black holes to its application in technologies such as GPS. However, more recent observations of the cosmos have begun to show discrepancies that theory cannot fully explain.
Specifically, according to this theory, gravity is the result of the curvature of space-time. However, when looking at much larger scales, such as huge galaxy clusters, Einstein’s predictions do not seem to agree with the most recent observations.
Now, a group of researchers has discovered a possible “cosmic glitch” in the universe’s gravity, which could help explain the strange behavior of the universe on a cosmic scale.
Robin Wen, leader of the study, published in the Journal of Cosmology and Astroparticle Physics, and recent graduate in Mathematical Physics from the University of Waterloo, explains it clearly: “This model of gravity has been essential for everything from theorizing the Big Bang to photographing black holes.”
However, in cosmic dimensions, the theory shows cracks: “When we try to understand gravity on a cosmic scale, on the scale of galaxy clusters and beyond, we find apparent inconsistencies with the predictions of general relativity. It is almost like “if gravity itself stopped perfectly matching Einstein’s theory. We call this inconsistency ‘cosmic glitch’: gravity weakens by around one percent when it comes to distances of billions of light years.”
Although general relativity will continue to be the reference theory for understanding gravity on more manageable scales, Wen clarifies that this is not a complete questioning of the model. “It’s not like we’re breaking how your GPS works, or a black hole. We were just trying to see if there is any deviation at the largest possible scales,” Wen explained to Business Insider.
Modify Einstein’s theory to resolve these inconsistencies
In response to these challenges, the team has proposed a new model that adjusts Einstein’s equations to address these inconsistencies without altering the cases in which the theory has been successful.
“Think of it as a footnote to Einstein’s theory,” Wen said. “Once you reach a cosmic scale, terms and conditions apply,” she added.
Although a 1% change may seem minimal, it is enough to suggest that general relativity may need to be rethought. “If this flaw really exists, it could help cosmologists explain some of the biggest mysteries of the universe,” says Wen.
The Hubble Tension
One of these mysteries is the Hubble Stress, which refers to discrepancies in measurements of the expansion speed of the universe. Observations suggest that the nearby universe is expanding faster than more distant regions, a problem that has baffled astronomers for years. According to Niayesh Afshordi, co-author of the study, 1% weaker gravity could reduce this stress, better aligning measurements of the universe’s expansion.
“Almost a century ago, astronomers discovered that our universe is expanding,” says Afshordi. “The further away the galaxies are, the faster they move, to the point that they seem to move almost at the speed of light, the maximum allowed by Einstein’s theory.”
“Our finding suggests that, at those same scales, Einstein’s theory may also be insufficient,” added Afshordi, who believes that the patch they suggest for a “cosmic failure” is just the beginning.
“This new model could be the first clue to a cosmic puzzle that we are beginning to solve across space and time,” Afshordi said.
Study the effects of dark energy on the expansion of the universe
The next step for researchers will be to examine data from the Dark Energy Spectroscopic Instrument (DESI), which measures the effects of dark energy on the expansion of the universe and has created the largest three-dimensional map of the cosmos to date. Wen and his team hope to determine whether the glitches in gravity and dark energy are related, which would further reinforce the need to fine-tune general relativity.
Despite what the new study may mean, there is still some way to go to confirm this finding. “With future data in the next 10 years, we should see if this is a real detection or just a fluctuation due to statistical power,” Wen says.
“If you asked me to bet, I would still bet on general relativity,” adds Wen. “It works so well in many ways that it’s hard to know whether alternative models will be better. But we have to be open to these strange ideas and keep investigating.”
Felipe Espinosa Wang with information from the University of Waterloo, Business Insider and the Journal of Cosmology and Astroparticle Physics.
