The Universe is still expanding, the expansion of the Universe is still accelerating and our understanding of the cosmos remains solid.
Those are the key claims of a new study of the Universe that, the authors say, has debunked a separate, earlier study that had apparently disproven the theory of dark energy.
The team behind the paper say the Universe is behaving exactly as expected and dark energy is still accelerating the expansion of the Universe.
However, the mystery of dark energy remains, they say, meaning astronomers have yet to solve perhaps the most significant conundrum in all of science.
More on dark energy
A primer on dark energy
In 2011, the Nobel Prize in Physics was awarded jointly to astronomers Brian Schmidt, Adam Riess and Saul Perlmutter.
Two independent studies had calculated that not only was the Universe expanding, but that the expansion of the Universe was speeding up.
That was a major revelation, as previous theories had suggested the expansion of the Universe should slow down over time, because the gravitational pull of all matter in the Universe would halt and eventually reverse the expansion.
One key method for determining the acceleration of the Universe's expansion was by looking at Type Ia supernovae.
These are a specific type of exploding star that occur in binary star systems, where a white dwarf star syphons material from its companion.
This eventually leads to the white dwarf star exploding. And because the white dwarf star always reaches the same mass when it explodes, that means it always explodes with the same brightness.
Therefore, astronomers can observe a Type Ia supernova and compare how bright it appears from Earth with how bright it really is.
They can then use that observation to determine how far away it must be, effectively creating a tool for measuring distances across the cosmos.
Yet while astronomers calculate that the Universe's expansion is speeding up, they don't know why.
Some mysterious, unknown force must be driving that acceleration. That force has been given the name 'dark energy'.
An extraordinary claim
In late 2025, a team of astronomers from Yonsai University in South Korea put out a study that provided evidence dark energy was weakening and the expansion of the Universe was no longer accelerating.
You can read our interview with astronomer Young-Wook Lee here to find out more about that study.
The study suggested the methods being used to measure the Universe's expansion using supernovae were flawed.
Now a new study led by Dr Phil Wiseman from the University of Southampton in the UK says the debate that followed the 2025 study was a result of a scientific misunderstanding.
The new study has looked again at the data and says the Universe is behaving exactly as expected.
The paper authors include Professor Adam Riess and Professor Brian Schmidt, the astrophysicists who won the Nobel Prize in 2011.
Wiseman says "the previous and well-accepted measurements were, in fact, fine and our current understanding of the fate of the Universe remains robust.
"Thankfully we have averted this crisis, but the mystery about why the Universe is still accelerating in size remains.
"By proving our measurements are correct, we can get back to trying to understand what dark energy actually is, rather than wondering if it exists at all."
If the 2025 claims were true, it could call into question the nature of dark energy and our entire understanding of the Universe.
So what's going on?
"Extraordinary claims require especially careful testing," says Professor Adam Riess.
"What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent."
The team looked closely at Type Ia supernovae.
The 2025 study claimed that as the Universe aged, these supernovae had different maximum brightnesses.
That, said the paper, caused it to appear as though the Universe's expansion was accelerating when it was actually slowing down.
But the new study says there was an error in how the ages of the stars was estimated.
They say their paper proves the 2025 findings incorrectly assumed the age of a galaxy was the same as the age of the star that exploded.
And they say the 2025 paper failed to account for the mass of host galaxies.
"This is how progress is made," says Professor Mark Sullivan, also from the University of Southampton.
"Although this idea did not turn out correct, it has opened up new ways of thinking about how supernovae explode and how we can measure dark energy more accurately."
Paper co-author Dr Brodie Popovic added: “We've recently been really focused on astrophysics of the explosions and how they impact cosmology.
"This was a good opportunity to go back and go over all of our assumptions. It turns out, yes, we do understand this stuff and we're accounting for it in our cosmology measurement."
Read the full paper via the monthly notices of the Royal Astronomical Society
