Controversial new theory of gravity rules out need for dark matter | Physics

Dark matter is thought to make up 85% of the mass of the universe, according to conventional scientific wisdom. But proponents of a radical new theory of gravity, in which space-time is “wobbly”, say their approach could render the elusive substance obsolete.

The proposal, outlined in a new paper, raises the controversial possibility that dark matter, which has never been directly observed, is a mirage that a significant part of the physics community has been chasing for several decades. The theory is considered quite fringe and has yet to be tested extensively, but the latest claims are causing a stir in the physics world.

Announcing the X paper, Professor Jonathan Oppenheim, of University College London, said: “My friends, something seems to be 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 are multiple lines of evidence for dark matter, but its nature has remained mysterious and searches by the Large Hadron Collider have failed. Last year, the European Space Agency launched a mission, Euclid, aimed at producing a cosmic map of dark matter.

The last article, published on the Arxiv website and which has not yet been peer-reviewed, raises the question of its existence, drawing parallels between dark matter and erroneous concepts of the past, such as “ether”, a substance invisible supposed to permeate all space.

“In the absence of any direct evidence of dark energy or dark matter, it is natural to wonder whether they are not useless scientific constructs like celestial spheres, the ether or the planet Vulcan , all of which have been replaced by simpler explanations,” he says. “Gravity has a long history of scamming.”

In this case, the simplest explanation offered is Oppenheim’s “post-quantum theory of classical gravity”. The UCL professor has spent the last five years developing this 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 views the fabric of spacetime as smooth and continuous (classical), but inherently wobbly. The speed at which time flows would fluctuate randomly, like a bubbling stream, space would be distorted randomly, and time would diverge in different parts of the universe. The theory also envisages an intrinsic breakdown in predictability.

The paper, written by Oppenheim and Andrea Russo, a doctoral student at UCL, argues that this view of the universe could explain the 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, are expected to rotate more slowly than stars at the centers. But in reality, the orbital motion of stars does not decrease. Astronomers deduced the presence of a halo of invisible (dark) matter exerting a gravitational attraction.

In Oppenheim’s approach, the extra energy needed to keep stars locked in orbit is provided by random space-time fluctuations, which actually add a gravitational hum in the background. This would be negligible in a high gravity interaction, such as Earth orbiting the Sun. But in low-gravity situations, such as at the margins 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 the galactic rotation curves without the need for dark matter or dark energy,” Oppenheim said on further indirect evidence of dark matter, further calculations and comparisons with the data are therefore necessary. But if this is true, it would appear that 95% of the energy in the universe is due to the erratic nature of the dark matter. space-time, signaling either a fundamental breakdown in the predictability of physics, or that we are immersed in an environment that does not obey the laws of classical or quantum theory.

Not everyone is convinced, including well-known theorists Prof Carlo Rovelli and Prof Geoff Penington, who signed a 5,000:1 bet with Oppenheim against proof of the correctness of his theory.

“I think it’s good that physicists are exploring a wide variety of approaches to solving very difficult problems, like combining quantum mechanics and gravity,” Penington said.

“Personally, I don’t think this particular approach is the right one. I have obviously added my words on this subject and there is nothing new in recent newspapers which could make me modify this assessment.

Others are more enthusiastic. “I think the authors are on to something really interesting here, exploring beautiful and new ideas,” said Professor Andrew Pontzen, a cosmologist at University College London. “However, the challenge of replacing dark matter is that there are many different lines of evidence that suggest its presence. So far, they’ve only touched on one of these lines. Only time will tell whether the new ideas can truly explain the wide variety of phenomena that point to dark matter. »

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