Can something a lot simpler explain what astronomers observe in the universe?
According to most astronomers, ordinary matter such as that in people, planets, stars, and galaxies, comprises only some 5 percent of the universe. Dark matter and dark energy make up the rest. But is there another explanation for what we observe?
Credit: Astronomy: Roen Kelly, after NIST
Ask most astronomers, and they’ll tell you that dark matter and dark energy make up more than 95 percent of the universe and that they are the explanations for many of the large-scale phenomena we observe. But a new study published Sept. 12 in the journal “Galaxies” offers a different scenario: that what we see is the weakening of some fundamental forces of nature, such as gravity.
The study was led by Rajendra Gupta, Adjunct Professor in the Department of physics at the University of Ottawa. Its main assertion is that if nature’s forces change over time, they can explain things like the evolution of galaxies and the expansion of the universe.
A new model … for everything
“The universe’s forces actually get weaker on the average as it expands,” Gupta explains. “This weakening makes it look like there’s a mysterious push making the universe expand faster (which is identified as dark energy). However, at galactic and galaxy-cluster scale, the variation of these forces over their gravitationally bound space results in extra gravity (which is considered due to dark matter). But those things might just be illusions, emergent from the evolving constants defining the strength of the forces.
“There are two very different phenomena needed to be explained by dark matter and dark energy: The first is at cosmological scale, that is, at a scale larger than 600 million light-years assuming the universe is homogeneous and the same in all directions. The second is at astrophysical scale, that is, at smaller scale the universe is very lumpy and direction dependent. In the standard model, the two scenarios require different equations to explain observations using dark matter and dark energy. Ours is the only one that explains them with the same equation, and without needing dark matter or dark energy.”
Gupta went on to say, “What’s really exciting is that this new approach lets us explain what we see in the sky: galaxy rotation, galaxy clustering, and even the way light bends around massive objects, without having to imagine there’s something hiding out there. It’s all just the result of the constants of nature varying as the universe ages and becomes lumpy.”
Something other than dark matter
In a previous study, published in The Astrophysical Journal on March 15, 2024, Gupta put forth the idea that we don’t need dark matter to explain things like galaxy rotation curves.
In his new model, Gupta defines a parameter (Alpha) that lets what he calls coupling constants to evolve. The main coupling constant is gravity. So, basically, Alpha acts like an extra component in the gravitational equations. And they produce effects just like the ones scientists say dark matter and dark energy produce.
On cosmological scales, Alpha is a constant. But locally (on astrophysical scale), it’s not. Let’s consider a galaxy as an example of something on the astrophysical scale. Gupta’s theory predicts that where there’s a lot of standard matter —like the region around the core — the extra gravity effect is a bit weaker. But where there’s little matter, it’s stronger. So, rather than adding dark matter halos around galaxies as many theories do, the extra gravitational pull comes from Alpha. This theory nicely explains why stars move faster than expected in the outer parts of galaxies.
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What could this mean?
Gupta believes his theory answers some of astronomy’s big questions better than other theories. “For years, we’ve struggled to explain how galaxies in the early universe formed so quickly and became so massive,” he says. “With our model, you don’t need to assume any exotic particles or break the rules of physics. The timeline of the universe simply stretches out, almost doubling the universe’s age, and making room for everything we observe.”
His expanded timeline makes it easier to explain how big, complex structures like galaxies and black holes appeared so early in the universe. “Sometimes, the simplest explanation is the best one,” he said. “Maybe the universe’s biggest secrets are just tricks played by the evolving constants of nature.”
