- For more than a century, Einstein’s general theory of relativity has played a key role in understanding gravity.
- But new research suggests that this theory “fails” in the far reaches of space.
- This does not mean that we throw Einstein’s theory out the window. But this may require a slight modification.
Over the past 100 years, countless studies have proven that Albert Einstein’s greatest theory – his theory of general relativity – is virtually foolproof, capable of everything from predicting black holes to guiding your GPS technology.
However, as scientists equip themselves with more powerful and sophisticated technology capable of observing the cosmos in unprecedented detail, they are discovering phenomena that they cannot explain with Einstein’s theory.
Einstein’s theory of general relativity states that the curvature of space-time causes gravity. But by zooming in on enormous scales, like clusters of galaxies spanning billions of light years, the laws of Einstein’s theory of gravity appear to change.
“It’s almost as if gravity itself no longer fits Einstein’s theory perfectly,” Robin Wen, a recent University of Waterloo graduate, said in a university news release.
Wen is part of a collaboration between the University of Waterloo and the University of British Columbia seeking to solve the mystery, calling this discrepancy in Einstein’s theory a “cosmic problem.”
Their new study, published in the Journal of Cosmology and Astroparticle Physics, suggests that gravity becomes about 1% weaker on very large scales. If gravity behaved according to Einstein’s theory, then this 1% difference should not exist.
Cosmologists aren’t going to give up on general relativity anytime soon. This is still a surprisingly accurate framework for understanding gravity at smaller scales.
“It’s not like we’re breaking your GPS, or a black hole. We’re just trying to see if there’s a gap on the largest possible scale,” Wen told Business Insider.
If this problem actually exists, it could help cosmologists explain some of the biggest mysteries of the universe.
Ease cosmological tensions
The research team was looking through cosmic microwave background data when they discovered this apparent problem.
The cosmic microwave background is a vast expanse of persistent radiation left behind by the Big Bang. Scientists use it to understand the early stages of the universe, such as the formation of the first galaxies and what happened immediately after the Big Bang.
Wen and his colleagues used a model — based on fundamental physical laws like Einstein’s theory of general relativity — and compared their model’s prediction of what CMB data should look like with observational CMB data.
Their scientific model did not match observations – what we actually see in the distant universe.
However, when they modified Einstein’s theory to account for a 1% gravitational deficit, their model aligned more closely with observational data, Wen told BI by email.
A 1% adjustment may not seem like a big deal, but it’s enough to suggest that Einstein’s theory might need a rethink. And what’s more, this problem could help us better understand some puzzling behavior in the universe.
The cosmos, as we understand it, is filled with tensions. Sometimes different measurements of the same phenomenon do not agree. One example is Hubble voltage, a problem that has perplexed astronomers for years.
Hubble tension refers to conflicting measurements of the universe’s expansion rate. According to our standard physics model, the expansion rate of the universe should be the same everywhere. However, observations from the near universe suggest that the expansion rate is faster than that of regions in the distant universe. Astronomers have proposed several possible explanations, but have not yet settled on one.
Now, with this cosmic problem, a new explanation is on the table.
1% weaker gravity on large scales could reduce the Hubble strain by bringing the universe’s expansion rate closer to local observational measurements, said Niayesh Afshordi, study co-author and professor of astrophysics. at the University of Waterloo, in a recent YouTube interview.
Go off the beaten track
The fact that this cosmic problem could potentially help astronomers resolve the Hubble tension is a good sign that it might actually exist. But this study does not offer definitive evidence for a 1% gravity deficit on a large scale, Wen said.
At this time, it is still possible that this problem is the result of a statistical error. “With future data in the next 10 years, we should expect to see whether this is actually a real detection, or just a fluctuation due to your statistical power,” Wen said.
Valerio Faraoni, professor of physics and interim dean of science at Bishop’s University, told BI it was reasonable to think the problem might exist because general relativity has not been tested in the distant universe .
So, “it’s entirely 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 study of cosmic problems does.
“We probably need something outrageous,” he said. “It looks exotic, it looks strange. But I think we absolutely have to be open to all these strange ideas.”
Next, Wen and his colleagues will take a close look at new data from the Dark Energy Spectroscopic Instrument (DESI). DESI measures the effects of dark energy on the expansion rate of the universe and has created the largest 3D map of the cosmos to date.
Additionally, DESI discovered that, like gravity, dark energy does not behave as astronomers expect on large cosmological scales. Wen wants to find out if these two “problems” are related in any way, which would provide even more evidence for the need to refine general relativity.
But even he remains skeptical about the limits of general relativity. “If you ask me to bet on something, I might still bet on GR. GR works so well, doesn’t it? For alternative models, it’s hard to say at this point,” a- he declared.