A new measurement of the speed at which the universe is expanding confirms that we don’t understand anything (and that’s good news)

The universe is expanding and it is expanding faster and faster. In other words, the space between two galaxies increases, even though they themselves are not moving. The great challenge for contemporary cosmologists is to determine the speed at which this expansion occurs.

According to scientists’ calculations, based on the cosmic microwave background, the universe should expand at a speed of 67-68 kilometers per second per megaparsec (km/s/Mpc). This cosmic acceleration is called Hubble constant. However, when astronomers used humanity’s most powerful telescope to confirm their theory, they faced one of the main barriers of contemporary cosmology: the speed at which the universe is expanding is greater than what could be expected.

Why are there two values ​​of the Hubble constant?

Measurements of supernovae with the Hubble telescope yielded a Hubble constant greater than the standard model of cosmology predicted. Observational evidence showed that space is expanding at between 70 and 76 km/s/Mpc. The difference in values ​​is too great to be ignored. One parsec is equivalent to 3.26 light years and one megaparsec is equivalent to one million. A scientific dilemma arose from the discrepancy between what was predicted and what was found. Either there was an error in the second measurement of the constant or the universe itself has components that have not yet been discovered.

Dark energy is the big bet to explain this discrepancy. In 2011, Adam Riess, Saul Perlmutter and Brian Schmidt won the Nobel Prize in Physics for confirming that the universe is expanding. They proposed that this phenomenon can be explained by a theoretical energy class large enough to overcome the force of gravity that holds stars together.

There is evidence suggesting the presence of dark energy throughout the universe. There are even some particles “suspected” of being responsible for this expansion. However, the nature of that energy remains elusive. Since it has not been “understood” in the strict sense of the word, the other explanation cannot be ruled out: perhaps there was an error in the measurements made with Hubble. Science cannot ignore either case.

James Webb to the rescue

A decade after being awarded, Adam Riess continues working to increase the evidence on dark energy. For him, this discrepancy between the two measurements cannot be attributed to a measurement error. When he began his observations of supernovae he used Hubble. Now it uses the state-of-the-art James Webb Space Telescope to implement the same procedure.

Riess used data from the last two years of James Webb to recalculate the Hubble constant. In a study published in The Astrophysical Journal describes how he used three different methods to calculate the distances between galaxies that contained supernovae. NASA’s most powerful telescope, which far exceeds Hubble’s capabilities, calculated essentially the same cosmic acceleration of 70 and 76 km/s/Mpc. Riess’ team did not make a measurement error more than a decade ago. The mystery of dark energy is also “palpable” in the James Webb data.

“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. With two flagship NASA telescopes now confirming each other’s findings, we must take this discrepancy very seriously: is a challenge, but also an incredible opportunity to learn more about our universe,” Riess explained in a release from Johns Hopkins University.

Confirming the gaps in our knowledge is a huge step for the advancement of science, the authors believe. Discrepancy in Hubble constant reveals “gaps in understanding of physics.” Of course, the nature of dark energy will remain a mystery, but there is now more evidence to think that it is the best possible path to understanding the behavior of the universe on a large scale.