According to new data from the James Webb Space Telescope, the universe is expanding faster than astronomers can explain. Building on earlier data from the Hubble Space Telescope, it confirms that unknown forces are driving the universe’s accelerated expansion.
It means there’s a glaring gap in what astronomers know about a fundamental fact of the nature of reality.
Incomplete Understanding
“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,” said Adam Riess, a Bloomberg Distinguished Professor and Thomas J. Barber Professor of Physics and Astronomy at Johns Hopkins University, a Nobel laureate and lead author of a study published today in The Astrophysical Journal. “With two NASA flagship telescopes 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 ‘Hubble Tension’ Explained
JWST’s confirmation of Hubble’s expansion rate measurements is huge in astronomy. It also gets slightly confused because the original law — Hubble’s Law — is named after Edwin Hubble, the American astronomer later honored by the space telescope.
Hubble’s Law — also known as the Hubble Constant — says that galaxies are moving away from us at a rate of 67-68 kilometers per second per megaparsec (a megaparsec is 3.26 million light-years). In effect, that’s also the expansion rate of the universe. However, telescope observations give a higher value of 70 to 76 kilometers per second per megaparsec.
The difference between them is too large to explain away through errors or flaws in measurement or observing techniques.
Universe In High-Definition
The new study using JWST used the known distance to a galaxy called NGC 4258 as a reference point to measure the distances to galaxies that host supernovae, Cepheid variables (a star that pulsates predictably) and red giant stars. Its incredible accuracy produced a Hubble constant of 72.6 kilometers per second per megaparsec, almost identical to the 72.8 kilometers per second per megaparsec found by Hubble for the same galaxies.
“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.
Early Dark Energy
Discovering what causes the Hubble tension is critical to astronomers because it means unraveling dark energy and dark matter — two mysterious substances that appear to shape the cosmos — as they attempt to map the structure of the universe and discover what happened just after the Big Bang that brought it into existence.
“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. “And there are other ideas, like funny dark matter properties, exotic particles, changing electron mass, or primordial magnetic fields that may do the trick. Theorists have a license to get pretty creative.”
Wishing you clear skies and wide eyes.
