Over the past 100 years, countless studies have proven that Albert Einstein’s greatest theory – his general theory of relativity – is virtually bulletproof, capable of everything from predicting black holes to controlling your GPS technology.
But as scientists arm themselves with more powerful and sophisticated technology capable of peering into the cosmos in unprecedented detail, they are discovering phenomena that they cannot explain using Einstein’s theory.
Einstein’s general theory of relativity states that the curvature of spacetime causes gravity. However, when you zoom out to enormous scales, such as galaxy clusters billions of light years across, the laws of Einstein’s theory of gravity appear to change.
“It’s almost as if gravity itself no longer corresponds perfectly with Einstein’s theory,” said Robin Wen, a recent graduate of the University of Waterloo, in a university news release.
Einstein’s general theory of relativity provides an astonishingly accurate account of the interactions of gravity with the space-time structure of the nearby universe. vchal/Getty Images
Wen, part of a collaboration between the University of Waterloo and the University of British Columbia seeking to solve the mystery, calls this discrepancy in Einstein’s theory a “cosmic error.”
Their new study, published in the peer-reviewed Journal of Cosmology and Astroparticle Physics, suggests that gravity is weakening by about 1% on very large scales. If gravity behaves according to Einstein’s theory, this 1% difference should not exist.
Cosmologists won’t give up on general relativity anytime soon. It is still an amazingly precise concept for understanding gravity at smaller scales.
“It’s not like we’re breaking the way your GPS works or a black hole. We were just trying to figure out if there were deviations on the largest possible scale,” Wen told Business Insider.
If this error actually exists, it could help cosmologists explain some of the universe’s greatest mysteries.
Relieving cosmological tensions
The Planck telescope and a map of the cosmic microwave background. Wen and his colleagues found clues to their cosmic error in CMB data. ESA and Planck
The research team was combing through data from the cosmic microwave background when they discovered this apparent error.
The cosmic microwave background is a huge area of residual radiation left behind by the Big Bang. Scientists use it to understand the earliest stages of the universe, such as how the first galaxies formed and what happened immediately after the Big Bang.
Wen and his colleagues used a model – based on fundamental physical laws such as Einstein’s general theory of relativity – and compared their model’s prediction of what the CMB data should look like to observational CMB data.
Their scientific model didn’t match observations – what we actually see in the distant universe.
However, when they optimized Einstein’s theory to account for a 1% gravity deficit, their model matched the observational data better, Wen told BI by email.
A 1% adjustment may not sound like a big deal, but it’s enough to suggest that Einstein’s theory may need to be reconsidered. And what’s more, this bug could help us better understand some confusing behaviors in the universe.
A diagram of the expansion of the universe since the Big Bang. Observational data from our local cosmic region suggests that the nearby universe is expanding faster than the distant universe, which according to the usual laws of physics should not be the case. NASA
The cosmos, as we understand it, is full of tensions. Sometimes different measurements of the same phenomenon do not agree with each other. An example of this is the Hubble voltage – a problem that has puzzled astronomers for years.
The Hubble tension refers to conflicting measurements of the universe’s expansion rate. According to our standard model of physics, the expansion rate of the universe should be the same everywhere. However, observations of the nearby universe suggest that the expansion rate is faster than in regions of the distant universe. Astronomers have suggested several possible explanations but have not yet agreed on one.
With this cosmic error, a new explanation is now on the table.
A 1% weaker gravity on a large scale could reduce Hubble tension by bringing the universe’s expansion rate closer to measurements from local observations, Niayesh Afshordi, study co-author and professor of astrophysics at the University of Waterloo, said recently in a YouTube interview.
think in other directions
Galaxy cluster IDCS J1426. Resolving the tensions between our observable local universe and distant, far-reaching galaxy clusters like this one requires “weird” solutions. NASA/CXC/Univ of Missouri/M. Brodwin et al; NASA/STScI; JPL/CalTech
The fact that this cosmic error could potentially help astronomers resolve the Hubble tension is a good sign that it actually exists. But this study does not provide definitive evidence of a 1% gravity deficit on a large scale, Wen said.
At this point, there is still a chance that this error is due to a statistical error. “Using future data over the next 10 years, we should expect to see whether this is indeed a real discovery or whether it is just fluctuations due to your statistical power,” Wen said.
Valerio Faraoni, professor of physics and interim dean of natural sciences at Bishop’s University, told BI it was reasonable to assume the error could exist because general relativity has not been tested in the distant universe.
“So it’s quite possible, at least in principle, that we don’t understand gravity on a larger scale,” said Faraoni, who was not involved in the study.
He believes that to resolve conflicts between predictions and observations of our universe, we need to think outside the box. And that’s exactly what this cosmic glitch study does.
“We probably need something outrageous,” he said. “It actually looks exotic, it actually looks weird. But I think we have to be absolutely open to all these weird ideas.”
The Dark Energy Spectroscopic Instrument (DESI) has created the largest 3D map of our universe yet. This sliver of the cosmos shows its high and low density regions. Collaboration between Claire Lamman and DESI; Custom color chart pack from cmastro
Next, Wen and his colleagues will examine new data from the Dark Energy Spectroscopic Instrument (DESI). DESI measures the effects of dark energy on the universe’s expansion rate and has created the largest 3D map of the cosmos to date.
In addition, DESI has found that dark energy, like gravity, does not behave as astronomers expect on large cosmological scales. Wen wants to find out if these two “perturbations” are somehow connected, which would provide even more evidence for the need to tweak general relativity.
But even he is skeptical about the limits of general relativity. “If you asked me to bet on something, I might still bet on GR. GR works so well, right? With the alternative models, it’s hard to say at this point,” he said.