The James Webb Space Telescope has confirmed controversial Hubble Telescope measurements that seemingly contradict the standard model of cosmology, giving rise to what is known as the ‘Hubble Tension,’ according to new findings involving the most extensive study of the universe’s expansion ever conducted.
Confirmation of the decades-long Hubble Tension, which reveals that the universe is expanding faster than cosmological models predict, has sent astrophysicists back to the drawing board in search of previously unknown physics that could account for the measurements, potentially rewriting the standard model.
“The discrepancy between the observed expansion rate of the universe and the predictions of the standard model suggests that our understanding of the universe may be incomplete,” explained Nobel laureate and lead author Adam Riess, a Bloomberg Distinguished Professor and Thomas J. Barber Professor of Physics and Astronomy at Johns Hopkins University in a statement.
“With two NASA flagship telescopes now confirming each other’s findings, we must take this [Hubble tension] problem very seriously—it’s a challenge but also an incredible opportunity to learn more about our universe.”
The findings follow a March study led by Riess, which showed that the discrepancies found by Hubble could not be attributed to calculation errors. “With measurement errors negated, what remains is the real and exciting possibility we have misunderstood the universe,” Riess said at the time of that study.
James Webb Space Telescope Confirms the Hubble Tension
In 1929, Edwin Hubble published his first version of Hubble’s Law, which showed that galaxies seemed to expand faster the farther away from Earth they were. In recent decades, measurements from the telescope named for the acclaimed scientist helped confirm this theory, showing that the universe’s expansion rate was increasing.
However, unlike cosmological models that predicted this expansion should be around 67-68 kilometers per second per megaparsec (Mpc), the readings from Hubble showed a mean expansion of around 73 km/s/Mpc. Several attempts have been made to shrink this discrepancy enough that it could be blamed on instrument errors or other faults in the model. Those efforts have failed, leading to the puzzle called the Hubble Tension.
Based on studies supporting the universe’s accelerating expansion, Dr. Riess was part of a team that won the Nobel Prize for their research, which attributed that expansion to a mysterious “dark energy” permeating large parts of the cosmos. This latest study employed state-of-the-art instruments aboard the JWST to confirm the Hubble Tension and, as a result, confirm the likely existence of a form of dark energy.
The study employed three different methods to calculate the universe’s expansion rate, known to produce the “most precise local measurement” of distances between galaxies. The first method considered the “gold standard” of measuring cosmic distances, involved an analysis of pulsating stars known as the Cepheid variable.
This analysis included samples of Webb data from two groups unaffiliated with the study that work independently to refine the Hubble constant. One is from the SH0ES (Supernova, H0, for the Equation of State of Dark Energy) team led by Riess; the other is from the Carnegie-Chicago Hubble Program and other teams. The researchers say these combined measurements “make for the most precise determination yet about the accuracy of the distances measured using the Hubble Telescope Cepheid stars, which are fundamental for determining the Hubble constant.”
The other two methods used to check the Cepheid variable findings involved carbon-rich stars and the brightest red giants across the galaxy. As hoped, all three readings from Webb aligned nearly perfectly with those from Hubble.
“All galaxies observed by Webb together with their supernovae yielded a Hubble constant of 72.6 km/s/Mpc, nearly identical to the value of 72.8 km/s/Mpc found by Hubble for the very same galaxies,” a
ccording to the researchers.
Time for Theorists to Get Creative
Although the initial readings from Hubble have often been criticized due to the success of the standard model in other areas of cosmology, the team says that the JWST’s discovery of almost identical discrepancies with its more advanced instrumentation is a huge blow to critics of the Hubble Tension.
“The Webb data is like looking at the universe in high definition for the first time and really improves the signal-to-noise of the measurements,’’ said Siyang Li, a graduate student working at Johns Hopkins University on the study.
Of course, the new findings will not completely resolve the controversy. Still, the study authors believe that theoretical physicists may have to try again to make sense of the data using something other than the standard model, but that doesn’t violate physics altogether.
“One possible explanation for the Hubble tension would be if there was something missing in our understanding of the early universe, such as a new component of matter—early dark energy—that gave the universe an unexpected kick after the big bang,” said Marc Kamionkowski, a Johns Hopkins cosmologist who helped calculate the Hubble constant and has recently helped develop a possible new explanation for the tension but who was not involved in the new study.
“And there are other ideas, like funny dark matter properties, exotic particles, changing electron mass, or primordial magnetic fields that may do the trick,” Kamionkowski added.
“Theorists have license to get pretty creative.”
The study “JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H0” was published in the Astrophysical Journal.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.