Dark matter is supposed to make up 85% of the mass in the universe, according to conventional scientific wisdom. But proponents of a radical new theory of gravity, in which space-time is “shaky”say their approach could render the elusive substance obsolete.
The proposal, detailed in a new paper, raises the controversial possibility that dark matter, which has never been directly observed, is a mirage that has haunted a significant portion of the physics community for several decades. . The theory is considered quite left-field and has yet to be thoroughly tested, but the latest claims are causing a stir in the world of physics.
Prof Jonathan Oppenheim, from University College London, said during the announcement of the paper on X: “Man, it looks like something is happening. We show that our theory of gravity … can explain the expansion of the universe and galactic rotation without dark matter or dark energy.”
There is various evidence for dark matter, but its nature has remained mysterious and searches by the Large Hadron Collider have come up empty-handed. Last year the European Space Agency launched a mission, Euclidwith the aim of producing a cosmic map of dark matter.
The latest newspaper, published on the Arxiv website and yet being peer-reviewed raises the question of whether it even exists, drawing parallels between dark matter and flawed concepts of the past, such as “the aether,” an invisible substance that supposedly permeates all of space.
“In the absence of any direct evidence for dark energy or dark matter, it is natural to wonder if these might be unnecessary scientific constructs such as celestial spheres, aether or the planet Vulcan, all of which have been replaced by simpler explanations,” it says. “Gravity has a long history of being a trickster.”
In this case, the simpler explanation proposed is Oppenheim’s “postquantum theory of classical gravity”. The UCL professor has spent the past five years developing the approach, which aims to unite the two pillars of modern physics: quantum theory and Einstein’s general relativity, which are fundamentally incompatible.
Oppenheim’s theory envisions the fabric of space-time as smooth and continuous (classical), but inherently unstable. The rate at which time flows will vary randomly, like a bubbling stream, space will be randomly warped and time will vary in different spots of the universe. The theory also envisages an intrinsic breakdown in predictability.
The paper claims that this approach to the universe can explain landmark observations of rotating galaxies that led to the “discovery” of dark matter. Stars at the edges of galaxies, where gravity is expected to be weakest based on visible matter, should rotate more slowly than stars in the center. But in reality the orbital motion of stars does not descend. From this, astronomers deduced the presence of a halo of invisible (dark) matter exerting a gravitational force.
In Oppenheim’s approach, the additional energy needed to keep the stars locked in their orbits is provided by the random fluctuations in spacetime, which in effect adds a background hum of gravitation. This would be negligible in a high gravity interaction, such as the Earth orbiting the Sun. But in low-gravity situations, such as the edges of a galaxy, the phenomenon would dominate – and could cumulatively account for the majority of the energy in the universe.
“We show that this can explain the expansion of the universe and galactic rotation curves without the need for dark matter or dark energy,” Oppenheim said on X. “However, we urge caution as there is other indirect evidence for dark matter, so further calculations and comparison with data are needed. But if this holds, it would appear that 95% of the energy in the universe is due to the erratic nature of spacetime, indicating either a fundamental breakdown in the predictability of physics, or we are immersed in an environment that does not obey the laws of classical or quantum theory.”
Not everyone is convinced, including renowned theorists Prof Carlo Rovelli and Prof Geoff Penington, who have placed a 5,000:1 odds bet with Oppenheim against his theory being proven correct.
“I think it’s good that physicists are exploring a wide variety of approaches to very difficult problems, such as combining quantum mechanics with gravity,” Penington said.
“Personally, I don’t think this particular approach is likely to be the correct one. I obviously put my money where my mouth is on that front and there is nothing new in the recent papers that will make me change that assessment.”
Others are more enthusiastic. “I think the authors are on to something very interesting here, exploring some beautiful and novel ideas,” said Prof Andrew Pontzen, a cosmologist at University College London. “However, the challenge of replacing dark matter is that there is so much different evidence suggesting its presence. So far they have only addressed one of these rules. Only time will tell if the new ideas can really explain the large variety of phenomena that refer to dark matter.”
