Dark matter, the elusive 'missing' mass that makes up a staggering 85% of the universe, just can't seem to catch a break—not even from gravity. But here's where it gets controversial: while we've long suspected dark matter is influenced by gravity, new research not only confirms this but also hints at the possibility of a mysterious fifth force that could upend everything we think we know. Could this be the game-changer astrophysicists have been waiting for, or a cosmic red herring? Let’s dive in.
A groundbreaking study published in Nature Communications on November 3 takes a deep dive into galactic redshifts—the shifts in light wavelengths as galaxies move away from us. The researchers combined data from the first three years of the Dark Energy Survey with 22 additional data points from spectroscopic surveys. Their goal? To see how well this cosmic data aligns with the gravitational force and Euler’s equations, the mathematical tools astrophysicists use to account for general relativity.
The findings are both reassuring and tantalizing. On one hand, the study provides strong evidence that dark matter, like everything else in the universe, plays by gravity’s rules. But here’s the twist: the researchers also detected a small, intriguing possibility of a fifth force. If real, this force could dramatically reshape our search for dark matter—though its existence remains far from certain.
To uncover these insights, the team focused on gravitational wells—massive 'dips' in spacetime caused by the gravity of celestial bodies. By tracking how these wells affect the velocity of galaxies (as seen in redshift data), they tested whether dark matter behaves like ordinary matter. According to Camille Bonvin, a physicist at the University of Geneva and co-author of the study, 'If dark matter isn’t subject to a fifth force, galaxies—which are mostly dark matter—should fall into these wells just like ordinary matter, guided solely by gravity.'
But what if dark matter is exempt from gravity? The paper suggests galaxies would interact with gravitational waves in entirely different ways. Fortunately, the team’s calculations confirmed that galactic motions follow general relativity and Euler’s equations, strongly implying that dark matter does, too. And this is the part most people miss: while the study leans toward gravity as the dominant force, it doesn’t completely rule out the fifth force—a detail that could spark heated debates in the scientific community.
Speaking of the fifth force, the study cautiously entertains its possibility. So far, physicists have confirmed four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces. But could dark matter be governed by something entirely new? Lead author Nastassia Grimm, an astrophysicist at the University of Portsmouth, admits the findings leave room for a 'maybe.' If such a force exists, its strength would be no more than 7% of gravity’s, or we’d have already seen its effects.
Yet, even a slim chance of a fifth force could have monumental implications. As the paper notes, it would 'not only break Euler’s equation but also reshape our understanding of density fluctuations and gravitational potentials.' In other words, it would force astrophysicists to rewrite the rulebook on how galaxies are studied. Nightmare or scientific revolution? Only time—and more data—will tell.
The researchers are already looking ahead, eager to analyze the next wave of data from the Vera C. Rubin Observatory and the Dark Energy Survey. Until then, the debate rages on. What do you think? Is the fifth force a real possibility, or just a cosmic mirage? Let us know in the comments—this is one conversation you won’t want to miss!
