by By Will Dunham
WASHINGTON (Reuters) – New confirmation of the startling observation that the universe is expanding faster than expected has scientists pondering the cause – possibly an unknown factor related to the mysterious cosmic components dark energy and dark matter.
Two years of data from NASA’s James Webb Space Telescope have now confirmed the Hubble Space Telescope’s earlier finding that the universe’s expansion rate is faster – by about 8% – than expected based on what astrophysicists know about the initial conditions in the universe Knowledge of the cosmos would be expected and its development over billions of years. The discrepancy is called the Hubble voltage.
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The observations from Webb, the most powerful space telescope ever deployed, appear to rule out the idea that the data from its predecessor, Hubble, were somehow flawed due to an instrument error.
“This is the largest sample of data from the Webb Telescope – the first two years in space – and it confirms the Hubble Space Telescope’s puzzling discovery that we have been wrestling with for a decade: the universe is now expanding faster than our best theories “can explain,” said astrophysicist Adam Riess of Johns Hopkins University in Maryland, lead author of the study published Monday in the Astrophysical Journal.
“Yes, it seems that something is missing from our understanding of the universe,” added Riess, winner of the Nobel Prize in Physics in 2011 for co-discovering the accelerated expansion of the universe. “Our understanding of the universe includes a lot of ignorance about two elements – dark matter and dark energy – and these make up 96% of the universe, so this is no small matter.”
“The Webb results can be interpreted to mean that a revision of our model of the universe may be needed, although it is currently very difficult to determine exactly what that is,” said Siyang Li, a Johns Hopkins doctoral student in astronomy and Astrophysics and co-author of the study.
Dark matter, thought to make up about 27% of the universe, is a hypothetical form of matter that is invisible but is suspected to exist due to its gravitational effect on ordinary matter – stars, planets, moons, anything on Earth will cover about 5% of the universe.
Dark energy, thought to make up about 69% of the universe, is a hypothetical form of energy that permeates vast areas of space, counteracting gravity and driving the accelerated expansion of the universe.
What could explain the anomalous expansion rate?
“There are many hypotheses linking dark matter, dark energy, dark radiation – for example neutrinos (a type of ghostly subatomic particle) – or gravity itself to some exotic properties as possible explanations,” Riess said.
The researchers used three different methods to measure a certain telltale metric – distances from Earth to galaxies where a type of pulsating star called the Cepheids has been documented. The Webb and Hubble measurements agreed.
The universe’s expansion rate, a number called the Hubble constant, is measured in kilometers per second per megaparsec, which is a distance equivalent to 3.26 million light years. A light year is the distance that light travels in a year, namely 5.9 trillion miles (9.5 trillion km).
According to the Standard Model of cosmology – basically the conventional wisdom about the universe – the value of Hubble’s constant should be around 67-68. The Hubble and Webb data give an average value of about 73, with a range of about 70-76.
The universe was created by the Big Bang 13 to 14 billion years ago and has continued to expand ever since. Scientists revealed in 1998 that this expansion was actually accelerating, with dark energy suspected to be the cause.
The new study examined Webb data covering about a third of Hubble’s entire list of relevant galaxies. In 2023, researchers announced that previous preliminary Webb data confirmed the Hubble results.
So how might this Hubble tension mystery be solved?
“We need more data to better characterize this evidence. How big is it exactly (the discrepancy)? Is the deviation at the low end – 4-5% – or at the high end – 10-12% – of what the current data allows.” “In what region of cosmic time does it exist? These will provide further ideas,” said Riess.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
