by There is no denying the awesome predictive power Albert Einstein1915 Theory of gravity, general relativity – still, the theory still has inconsistencies in its effect on calculating vast distances. And new research suggests that these discrepancies may be the result of a “cosmic glitch” in gravity itself.
In the 109 years since it was first formulated, general relativity remains the best description of gravity on a galactic scale; time and again, experiments confirmed its accuracy. This theory was also used to predict aspects of the universe that would later be confirmed observationally. This includes the Big Bang, the existence of black holes, gravitational lensing of light and tiny ripples in space-time called gravitational waves.
But, like the Newtonian theory of gravity that he surpassed, general relativity may not give us the full picture of this enigmatic force.
“This model of gravity has been essential for everything from theorizing the Big Bang to photographing black holes,” Robin Wen of the University of Waterloo’s Mathematical Physics Orogram said in a statement. “But when we try to understand gravity on a cosmic scale, on the scale of galaxy clusters and beyond, we see apparent inconsistencies with the predictions of general relativity.”
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“Gravity becomes about one percent weaker when dealing with distances in the billions of light years,” Wen said. “We’re calling this discrepancy a ‘cosmic glitch.’ It’s almost like gravity itself stops Einstein’s theory perfectly.”
The cosmic glitch described by the team would require a change in a value known as the gravitational constant. This change would occur as calculations approach the “superhorizon,” or the maximum distance light may have traveled from the origin of the universe.
This adjustment can be made, the team says, by adding a single extension to the standard cosmological model. This model is called the cold dark matter lambda model. Once completed, the amendment should clarify inconsistencies in measurements on cosmological scales without disrupting current successful uses of general relativity.
What is general relativity and could it be wrong?
The discovery of general relativity was so revolutionary that, instead of describing gravity as a mysterious force, it stated that gravity arises from a very complex curvature of space and time, united as a single entity called “space-time.” And this curvature, Einstein realized, is shaped by things with mass.
Imagine that balls of increased mass are placed on a stretched rubber sheet. A tennis ball would cause a tiny, almost imperceptible dent; a cricket ball would create more prominent teeth; and a bowling ball would spur a huge curve that pulls anything else on the sheet towards it. It’s the same concept as objects in space, although the curvature of space-time is in four dimensions, so there are some important differences. Still, moons have less mass than planets, planets less than stars, and stars less than galaxies—so, the gravitational influences of the respective celestial bodies increase.
Einstein’s theory of gravity was like a successor to Newtonian theory, although the latter still works well on terrestrial scales and is accurate enough to get rockets to the moon. However, Einstein’s theory could explain things that Newton could not, such as Mercury’s irregular orbit around the sun.
Newton was not exactly wrong about gravity — it wasn’t right on the scales of planets, stars and galaxies.
Is general relativity wrong, though?
Well, probably not. As a theory, it was too accurate in predicting aspects of the universe we didn’t know about. For example, the first image of a black hole captured by the Event Horizon Telescope was revealed to the public in April 2019. This image was somewhat disturbing because of how close the appearance of the supermassive black hole M87* was to the predictions of general relativity.
However, scientists know that there are some issues with general relativity that may eventually require revision. For example, the theory does not agree with quantum mechanics; our best description of physics at fundamental levels smaller than the atom. That’s mainly because there is currently no quantum theory to describe gravity.
Therefore, adjustments to general relativity at some point to “extend” it to the smallest scales of the universe – and according to this team, the largest scales – seem inevitable.
For decades, researchers have tried to create a mathematical model that helps general relativity overcome its inconsistencies, and University of Waterloo applied mathematicians and astrophysicists have been heavily involved in this quest.
Change general relativity? What!
If the idea of revising general relativity seems like heresy, consider that this is not the first time that the related theories have had to be adjusted.
Shortly after Einstein first introduced the theory, he and others expanded on it to develop an equation to describe the state of the universe. As a result of general relativity, this equation predicts that the universe should be changing. The issue with this was that the scientific consensus at the time said that the universe was static. And, although Einstein was no stranger to throwing the status quo into flux, he happened to agree with this cosmic picture that is not changing.
To ensure that general relativity predicts a static universe, Einstein added a “fudge factor” that he later described as his “big blunder,” This is called the cosmological constant, and is represented by the Greek letter lambda. The constant would not have been thought of when Edwin Hubble convinced Einstein that the universe is non-static. It is expanding, he insisted. And as far as we know today, Hubble was indeed right.
Lambda, however, really make a comeback. It would begin to serve a different function at the end of the 20th century, when astronomers discovered that not only was the universe expanding, but that it was doing so at an accelerating rate.
“Nearly a century ago, astronomers discovered that our Universe is expanding,” Niayesh Afsharid, a University of Waterloo professor of astrophysics and researcher at the Circumference Institute, said in the statement. “The further away galaxies are, the faster they move, to the point where they appear to be moving at almost the speed of light, the maximum allowed by Einstein’s theory. Our results suggest that Einstein’s theory, on those scales, may also be inadequate.”
The University of Waterloo team’s proposal for a “cosmic glitch” of gravity changes the length and breadth of Einstein’s mathematical formulas to deal with this without “overturning” the theory.
“Think of it as a footnote to Einstein’s theory,” Wen said. “When you reach a cosmic scale, terms and conditions apply.”
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The researchers behind this cosmic glitch theory suggest that future observations of the large-scale structure of the universe and a universal “fossil” radiation field known as the Cosmic Microwave Background (CMB) may result from an event that occurred shortly after the Big Bang shed light. on whether a cosmic glitch in gravity is responsible for current “cosmic tension.”
This may include the reason why quantum theory assigns a value to lambda that is a huge factor of 10¹²¹ (10 and 120 zeros) more than astronomical observations such as reflection (no wonder some physicists give the name “the worst theoretical prediction in the history of physics!”).
“This new model may be the first clue in a cosmic puzzle we are beginning to solve across space and time,” Afsordi concluded.
The team’s research appears in the Journal of Cosmology and Astroparticle Physics.
