Scientists simply can’t agree on how fast the universe is expanding

It’s one of the leading puzzles in cosmology. Why two different approaches used to calculate the rate at which the cosmos is expanding don’t produce the same result. Branded as the Hubble tension, the conundrum suggests that there could be something erroneous with the standard model of cosmology used to explain the forces in the cosmos.

Now, recent observations owing to the new James Webb Space Telescope (JWST) are fueling the debate on how close the mystery is to being resolved.In February, Adam Reiss (the Nobel prize-winning physicist), published a new paper. It informed that new observations of distant stars using the JWST matched those acquired using the Hubble Space Telescope.

These stars, termed Cepheids, are used in one method of calculating the rate at which the cosmos is expanding. Branded as the local distance ladder, or cosmic distance ladder, this technique has been around since observations were first made by Edwin Hubble himself in 1929. And it generally gives out a rate of expansion of around 73km per second per mega parsec.

But a second technique, using predictions of the CMB (cosmic microwave background) radiation left over by the Big Bang, has persistently arrived at a different number for the rate of expansion of the cosmos: 67km per second per mega parsec.Reiss opined that when the fresh data confirmed the earlier observations from the Hubble Space Telescope, the gap between the figures remains unresolved. “What remains is the real and exciting possibility that we have misunderstood the universe,” he said.

A few months later, nevertheless, some more data from the JWST, presented by a physicist at the University of Chicago, Wendy Freedman, using observations from a separate set of stars, arrived at 69km per second per mega parsec, a figure closer to the cosmic microwave background figure of 67. Freedman is thrilled that the figures seem to be converging.

Fascination with Hubble tension among astrophysicists is universal. Bernard Jones (an emeritus professor of astronomy at the University of Groningen in the Netherlands) and VicentMartínez (former student of Bernard Jones and presently a professor of astronomy and astrophysics at the University of València in Spain)too are fascinated by the Hubble tension. Jones says, “The fundamental basis of science, what distinguishes science from science fiction, is our ability to verify the information we are getting.” Martinez says,that’s the reason why the mystery of the Hubble tension is still driving people.