There is no denying the amazing predictive power of Albert EinsteinThe 1915 theory of gravity and general relativity – yet the theory still shows inconsistencies when it comes to calculating its effect at large distances. And new research suggests that these inconsistencies could be the result of a “cosmic glitch” in gravity itself.
In the 109 years since general relativity was first formulated, it remains our best description of gravity on a galactic scale; time and time again, experiments have confirmed its accuracy. This theory has also been used to predict aspects of the universe that would later be confirmed by observation. This includes the Big Bang, the existence of black holes, the gravitational lens of light, and tiny ripples in spacetime called gravitational waves.
But like the Newtonian theory of gravity that surpassed them, general relativity may not give us the full picture of this enigmatic force.
“This gravity model 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, at the scale of galaxy clusters and beyond, we encounter apparent inconsistencies with the predictions of general relativity.”
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“Gravity gets weaker by about one percent as it goes to distances in the billions of light years,” Wen said. “We call this inconsistency a ‘cosmic disturbance’. It’s almost as if gravity itself no longer fits perfectly with Einstein’s theory.”
The cosmic disturbance described by the team would require a change in a value called the gravitational constant. This change would occur as calculations approach the “super horizon,” or the maximum distance light could have traveled since 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 known as the lambda model for cold dark matter. Once completed, the addition should eliminate inconsistencies in cosmological-scale measurements without affecting existing successful applications of general relativity.
What is general relativity and can it be wrong?
The discovery of general relativity was so revolutionary because, instead of describing gravity as a mysterious force, it posited that gravity arises from the curvature of the fabric of space and time, unified as a single entity that becomes ‘spacetime’ named. And this curvature, Einstein realized, is formed by objects with mass.
Imagine placing balls of increasing mass on a stretched rubber sheet. A tennis ball would make a small, almost unnoticeable dent; a cricket ball would make a more pronounced dent; and a bowling ball would create a huge curve that probably pulls everything else on the sheet towards it. It’s the same concept with objects in space, although the curvature of spacetime exists in four dimensions, so there are some pretty important differences. Yet moons have less mass than planets, planets less than stars and stars less than galaxies – increasing the gravitational influences of these celestial bodies respectively.
Einstein’s theory of gravity was a successor of sorts to the Newtonian theory, although the latter still functions quite well on an Earth scale and is accurate enough to take rockets to the moon. Yet Einstein’s theory could explain things that Newton’s could not, such as Mercury’s idiosyncratic orbit around the sun.
Newton wasn’t exactly that wrong about gravity – he just wasn’t right about the scales of planets, stars and galaxies.
However, is general relativity wrong?
Well, probably not. As a theory, it has been too accurate in predicting aspects of the universe we knew nothing about. For example, in April 2019, the first image of a black hole captured by the Event Horizon Telescope was revealed to the public. This image was quite shocking because of how closely the appearance of the supermassive black hole M87* resembled predictions of general relativity.
However, scientists are aware that there are a number of problems with general relativity that may require eventual revision. For example, the theory is incompatible with quantum mechanics; the best description we have of physics at fundamental levels smaller than the atom. This is mainly because there is currently no quantum theory to describe gravity.
So it seems that at some point, adjustments to general relativity seem inevitable to “extend” its reach to the smallest scales of the universe – and, according to this team, the largest scales.
For decades, researchers have been trying to create a mathematical model that will help general relativity overcome its inconsistencies, and applied mathematicians and astrophysicists at the University of Waterloo are deeply involved in this quest.
Change general relativity? What!
If the idea of revising general relativity amounts to heresy, consider that this would not be the first time that associated theories have needed to be adjusted.
Shortly after Einstein first introduced the theory, he and others expanded it to develop an equation to describe the state of the universe. Due to general relativity, this equation predicted that the universe would have to change. The problem with this was the scientific consensus at the time that the universe was static. And while Einstein was no stranger to stirring up the status quo, he happened to agree with this unchanging cosmic picture.
To ensure that general relativity predicted a static universe, Einstein added a “fudge factor” that he later described as his “biggest blunder.” This is known as the cosmological constant and is represented by the Greek letter lambda. The constant would be removed from thinking when Edwin Hubble convinced Einstein that the universe is non-static. It is expanding, he argued. And as far as we know today, Hubble was indeed right.
However, Lambda would actually make a comeback. It would take on a different function at the end of the 20th century, when astronomers discovered that the universe was not only expanding, but that it was doing so at an increasingly rapid pace.
“Nearly a century ago, astronomers discovered that our universe is expanding,” Niayesh Afsharid, professor of astrophysics at the University of Waterloo and researcher at the Perimeter Institute, said in the statement. ‘The further away galaxies are, the faster they move, to the point that they appear to move at almost the speed of light, the maximum allowed by Einstein’s theory. Our findings suggest that Einstein’s theory may also be insufficient at that scale.”
The University of Waterloo team’s suggestion of a ‘cosmic disturbance’ changes gravity at large distances and extends Einstein’s mathematical formulas to address this without ‘overthrowing’ the theory.
“Think of it as a footnote to Einstein’s theory,” Wen said. “Once 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 called the cosmic microwave background (CMB), from an event that occurred shortly after the Big Bang, could shed light. about whether a cosmic disturbance in gravity is responsible for the current ‘cosmic tensions’.
This could include the reason that quantum theory gives a value for lambda that is a staggering factor of 10¹²¹ (10 followed by 120 zeros) greater than astronomical observations seem to indicate (no wonder some physicists call this “the worst theoretical prediction in the history of humanity”). physics!”).
“This new model could be the first clue in a cosmic puzzle we are beginning to solve across space and time,” Afshordi concluded.
The team’s research appears in the Journal of Cosmology and Astroparticle Physics.