The rate of expansion of the Universe has baffled and worried researchers for decades. Recent measurements have only added to the mystery and increased concern within the scientific community, suggesting that the current theoretical framework may be missing something important.
Observations suggest that galaxies are separating at a greater rate than scientists have long expected. Many now wonder whether the Standard Model of cosmology can fully explain what is happening.
Dan Scolnic is an associate professor of physics at Duke University. He and his team conducted a new study, published in the Letters from astrophysical journalswhich reinforces the arguments in favor of a mismatch between the data and the predictions.
A century of tracking the expansion of the Universe
Edwin Hubble first identified the expansion of the Universe in 1929. Since then, the rate of expansion – called Hubble constant – has been the subject of countless measures.
Each generation of scientists attempts to determine its exact value, with the aim of understanding how quickly cosmic structures propagate through space.
Some researchers rely on data from nearby galaxies, while others look to the early Universe. Over time, these two groups of measurements revealed a conflict known as Hubble voltage.
“The tension is now turning into a crisis,” said Scolnic, who led the research team.
What exactly is the conflict?
When researchers compare the appearance of the Universe at great distances with how it appears in our own cosmic neighborhood, something is wrong.
Standard theories predict a slower rate of expansion than local measurements show. Scolnic highlights the difference between the first snapshots of the Universe and its current form.
He describes this as building a growth curve: there is a baby picture of the Big Bang and a current picture of our galactic environment, but the curve connecting these two pictures does not match the predictions.
“This means, in some ways, that our cosmological model could be broken,” Scolnic said.
Filling the gaps in the “cosmic ladder”
The scientists used a “cosmic scale» to measure distances to celestial objects for many years. Each rung of the scale calibrates the next, creating a chain of reliable measurements.
In recent work, a project called Dark Energy Spectroscopic Instrument (DESI) provided an expanded set of distances to galaxies, adding more precision to the process.
“The DESI collaboration did the hardest part, they were missing the first rung of their ladder,” Scolnic said. “I knew how to get it, and I knew it would give us one of the most precise measurements of the Hubble constant that we could get, so when their paper came out, I dropped absolutely everything and I’ve been working on it all the time.”
The expansion of the universe and the Coma cluster
One of the ways to secure this first level is to examine Coma cluster. Researchers have debated its true distance for about 40 years.
To precisely measure the distance between the Coma cluster, Scolnic and his team, supported by the Templeton Foundationlooked at 12 light patterns Type Ia supernovae within the cluster.
Think of Type Ia supernovae as reliable flashlights in the dark, because their brightness is constant and directly related to their distance. This makes them excellent tools for determining how far away objects are in space.
Researchers have determined that the Coma cluster is about 320 million light years away. This measurement falls right in the middle of the distances found by other scientists over the past 40 years, which is a good sign that their calculation is accurate.
“This measure is not influenced by our theories about how the Hubble voltage will be resolved,” Scolnic explained. “This cluster is quite close to us and we measured it long before we knew how big it would become. »
Do we need a new Hubble constant?
With a solid anchor in place, the team used the remainder of the cosmic scale to calculate a new value for the Hubble constant: 76.5 kilometers per second per megaparsec.
This number describes the rate at which galaxies are moving away from each other by 3.26 million light years of separation.
It aligns closely with other local measurements, confirming that the nearby Universe appears to be expanding faster than the Standard Model predicted.
“Over the past decade, the community has done many reanalyses to see if my team’s initial results were correct,” said Scolnic, whose research has consistently questioned the Hubble constant predicted using the equation. standard model of physics.
“In the end, even if we exchange a large number of coins, we still get a very similar number. So, for me, this is the best confirmation ever.
Why is the expansion of the Universe important?
Scientists now want to know whether the problem comes from the models or the measurements. Some believe the data is strong, leaving open the possibility that the underlying theory requires adjustment.
Others remain cautious, preferring to test each step of the measurement process to rule out errors. As more powerful telescopes and innovative techniques come online, each new data set fuels the debate.
“We’re at a point where we’re hitting very hard on the models that we’ve been using for two and a half decades, and we’re finding that things don’t add up,” Scolnic said.
“This could reshape the way we think about the Universe, and that’s exciting!” There are still surprises in cosmology, and who knows what discoveries will follow?
Big Questions and Enduring Mysteries
Questions about dark energy, dark matterand other unknowns linger in the background. Many are wondering if there is a missing ingredient that could explain the higher-than-expected rate of expansion.
Some are looking to potential new physics, while others continue to refine measurement techniques for better precision.
Researchers continue to observe numbers from observatories around the world, gathering more evidence to understand how the rate of expansion behaves over time.
Whether it’s slight tweaks to established models or an entirely new approach, cosmic history remains a work in progress, driven by measurements that continue to exceed expectations.
The full study was published in the Letters from the astrophysical journal.
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