- High-priced Cummins, Starc face off as IPL enters playoffs
- Iran media says President Raisi died in helicopter crash
- Dominican Republic President Abinader re-elected to 2nd term
- New Taiwan president Lai hails 'glorious' democracy
- New Caledonia separatists defy French efforts to unblock roads
- Timberwolves knock out defending champion Nuggets, Pacers oust Knicks
- Trump biopic hits Cannes Film Festival
- Iran President Raisi's helicopter found, 'no sign of life'
- Three talking points ahead of 2024 French Open
- 'Haikyu!!': Comic heroes fuel Japan Olympic volleyball manga mania
- Timberwolves rally to knock defending champion Nuggets out of NBA playoffs
- London court set to rule on Julian Assange extradition
- Business and Bollywood votes in India election
- Pope calls anti-migrant attitudes at US border 'madness'
- Mexico aims to be big economic winner from US-China tensions
- Uncertain future for thousands after deadly Brazil floods
- Schauffele makes the putt of his life for first major win
- Wirtz returns to help unbeaten Leverkusen chase history
- Search for Iran's President Raisi after helicopter goes missing
- DeChambeau's powerful putting has him excited for US Open
- Taiwan to swear in new president as China pressure grows
- Atalanta can end 61-year wait for trophy in Europa League final
- Schauffele birdies final hole to capture PGA for first major win
- Guardiola casts doubt over long-term Man City future
- Hollywood icons Costner and Demi Moore make Cannes comeback
- Pacers shoot down Knicks to reach NBA Eastern Conference finals
- Schauffele birdies final hole, captures first major at PGA Championship
- McLaughlin powers to Indy 500 pole in all-Penske front row
- Monaco footballer tapes over LGBTQ badge
- Korda wins sixth LPGA title of year with win at Liberty National
- Pacers put on shooting show to down Knicks, reach NBA Eastern Conference finals
- US envoy touts 'potential' of Israel-Saudi deal in Netanyahu talks
- Dominicans vote for president in poll overshadowed by Haiti crisis
- Brest secure Champions League qualification, PSG win without Mbappe
- Mbappe absent as PSG win final Ligue 1 game
- Still exhausted after arrest, Scheffler closes with 64 at PGA
- Brest secure historic Champions League qualification
- France's Macron calls fresh emergency on New Caledonia unrest
- Taiwan swears in new president as China pressure grows
- Schauffele leads as dramatic PGA back-nine battle begins
- Biden faces silent Gaza protest at Martin Luther King Jr's college
- Ten Hag says Man Utd 'must do everything' to win FA Cup after Premier League flop
- Cannes film follows Egypt feminists on brink of adulthood
- Pep Guardiola: Man City manager addicted to winning
- Jackson wins season opener in Marrakesh with all eyes on Paris
- Things get real as imaginary friend flick 'If' tops N.America box office
- Paris seeks to boost sluggish sales for Paralympic Games
- How a French director pulled off Cannes's crazy Mexican narcos hit
- Man City make case to be ranked as England's greatest-ever team
- Hamdy gives Zamalek second CAF Confederation Cup title
The universe's accelerated expansion might be slowing down
The universe is still expanding at an accelerating rate, but it may have slowed down recently compared to a few billion years ago, early results from the most precise measurement of its evolution yet suggested Thursday.
While the preliminary findings are far from confirmed, if they hold up it would further deepen the mystery of dark energy -- and likely mean there is something important missing in our understanding of the cosmos.
These signals of our universe's changing speeds were spotted by the Dark Energy Spectroscopic Instrument (DESI), which is perched atop a telescope at the Kitt Peak National Observatory in the US state of Arizona.
Each of the instrument's 5,000 fibre-optic robots can observe a galaxy for 20 minutes, allowing astronomers to chart what they have called the largest-ever 3D map of the universe.
"We measured the position of the galaxies in space but also in time, because the further away they are, the more we go back in time to a younger and younger universe," Arnaud de Mattia, a co-leader of the DESI data interpretation team, told AFP.
Just one year into its five-year survey, DESI has already drawn up a map which includes six million galaxies and quasars using light that stretches up to 11 billion years into the universe's past.
The results were announced at conferences in the United States and Switzerland on Thursday, ahead of a series of scientific papers being published in the Journal of Cosmology and Astroparticle Physics.
DESI is on a mission to shed light on the nature of dark energy -- a theoretical phenomenon thought to make up roughly 70 percent of the universe.
Another 25 percent of the universe is composed of the equally mysterious dark matter, leaving just five percent of normal matter -- such as everything you can see.
- An inconstant constant? -
For more than a century, scientists have known that the universe started expanding after the Big Bang, 13.8 billion years ago.
But in the late 1990s, astronomers were shocked to discover it has been expanding at an ever-increasing rate.
This was a surprise because gravity from matter -- both normal and dark -- was thought to have been slowing the universe down.
But obviously something was making the universe expand at ever-faster speeds, and the name "dark energy" was given to this force.
More recently, it was discovered that the acceleration of the universe significantly sped up around six billion years after the Big Bang.
In the push-and-pull between matter and dark energy, the latter certainly seems to have the upper hand, according to the leading model of the universe called the Lambda CDM.
Under this model, the quickening expansion of the universe is called the "cosmological constant," which is closely linked to dark energy.
DESI director Michael Levi said that so far, the instrument's early results were showing "basic agreement with our best model of the universe".
"But we're also seeing some potentially interesting differences which could indicate that dark energy is evolving with time," Levi said in a statement.
In other words, the data "seems to show that the cosmological constant Lambda is not really a constant," because dark energy would be displaying "dynamic" and changing behaviour, De Mattia said.
- Slowing down in old age -
This could suggest that -- after switching into high gear six billion years after the Big Bang -- the speed at which the universe has been expanding has been "slowing down in recent times," DESI researcher Christophe Yeche said.
Whether dark energy does in fact change over time would need to be verified by more data from DESI and other instruments, such as the space telescope Euclid.
But if it was confirmed, our understanding of the universe will likely have to be changed to accommodate for this strange behaviour.
For example, the cosmological constant could be replaced by some kind of field linked to some as-yet-unknown particle.
It could even necessitate updating the equations of Einstein's theory of relativity "so that they behave slightly differently on the scale of large structures," De Mattia said.
But we are not there yet.
The history of science is full of examples in which "deviations of this type have been observed then resolved over time," De Mattia emphasised.
After all, Einstein's theory of relativity has withstood more than a century of scientific poking and prodding and still stands stronger than ever.
T.Bondarenko--BTB