New data from the James Webb Space Telescope has confirmed the ongoing, perplexing observation that the universe is expanding at a faster rate than expected, sparking further questions about the role of dark energy and dark matter in this anomaly.
After two years of data collection, NASA’s James Webb Space Telescope has validated earlier findings by the Hubble Space Telescope, which showed that the universe is expanding approximately 8% faster than anticipated, based on our understanding of the cosmos’ initial conditions and evolution. This discrepancy is referred to as the “Hubble Tension.”
The Webb observations, from the most advanced space telescope ever launched, seem to dismiss the idea that previous data from the Hubble Space Telescope was flawed due to instrument errors.
Astrophysicist Adam Riess of Johns Hopkins University, lead author of the study published in the Astrophysical Journal, commented on the significance of the new findings: “This is the largest sample of Webb data – its first two years in space – and it confirms the puzzling finding from Hubble that we’ve been grappling with for a decade: the universe is expanding faster than our best theories can explain.”
Riess, who shared the 2011 Nobel Prize in Physics for the co-discovery of the universe’s accelerating expansion, further stated, “Our understanding of the universe is missing key elements, particularly dark matter and dark energy, which make up 96% of the universe. This is a substantial gap in our knowledge.”
Siyang Li, a Johns Hopkins doctoral student and co-author of the study, added that the Webb results might suggest a need to revise current models of the universe, although pinpointing exactly what’s missing remains difficult.
Dark matter, which accounts for around 27% of the universe, is a theoretical form of matter that cannot be directly seen but is inferred from its gravitational effects on visible matter, such as stars and planets, which make up roughly 5% of the universe. Dark energy, believed to make up about 69% of the universe, is a hypothesized form of energy that counteracts gravity and drives the universe’s accelerated expansion.
As for the reason behind the faster-than-expected expansion, many hypotheses have been proposed, including the involvement of dark matter, dark energy, dark radiation (such as neutrinos), or even exotic properties of gravity itself.
The researchers used three different methods to measure distances from Earth to galaxies containing pulsating Cepheid stars. The data from Webb and Hubble were consistent with each other.
The universe’s expansion rate, known as the Hubble constant, is typically measured in kilometers per second per megaparsec, a unit of distance equal to 3.26 million light-years. Under the standard cosmological model, this rate should be about 67-68, but the data from Hubble and Webb indicate an average of about 73, within a range of 70-76.
The Big Bang, occurring 13-14 billion years ago, initiated the universe’s expansion, which has continued ever since. In 1998, scientists discovered that this expansion is accelerating, with dark energy proposed as the driving force behind it.
The new study analyzed Webb data covering about one-third of the galaxies that Hubble had previously studied, and interim Webb data from 2023 had already supported Hubble’s findings.
To resolve the Hubble Tension, Riess emphasized the need for more data to better understand the discrepancy: “We need more data to characterize this clue—how large is the mismatch? Is it at the lower end, around 4-5%, or the higher end, 10-12%? Over what cosmic time range does it persist? These details will guide further investigations.”
