Mankind’s current most advanced space telescope, the James Webb, confirmed the measurements of its predecessor, Hubble, regarding the expansion of the universe. The scientific public was not very happy with the result, as we have conflicting measurement data regarding the Hubble constant, which describes the degree of expansion. James Webb Space Telescope measurements could have answered this question, but it didn’t happen that way.
The universe is expanding at an accelerating rate, and there are several ways to measure exactly that. One way is to study the change in residual microwave electromagnetic background radiation after the Big Bang. The other is if we measure the distance to known reference points, for example stars with regularly varying brightness.
In the first method, the expansion speed is 67 kilometers per megaparsec per second (3.26 million light-years per second), and based on the other measurement, this value is 73 km/second/megaparsec.
The reason for the discrepancy in the data is either due to insufficient measurement technique or lack of theoretical background. The difference between the two numbers is called the Hubble stress, but that may just be a euphemism. When the world’s leading physicists met at the Kavli Institute in California in 2019 to clear things up, the deliberations produced headaches rather than wisdom.
We did not call it tension or a problem, but rather a crisis
David Gross, former director of the institute, revived what happened.
The old man was right
In 1928, American astronomer Edwin Hubble was the first to prove that stars are moving away from us at an accelerating rate. (Albert Einstein, who had thought throughout his cosmological theories in terms of a static universe, was only convinced years later by his colleagues’ arguments, and finally called this his greatest mistake.)
The main mission of the Hubble Space Telescope – in addition to producing exciting images of unprecedented quality – was to identify and measure Cepheid-type variable stars. These reference stars are named after the first star discovered in 1784, Delta Cepheid.
In the end, there was a possibility that the cause of the cosmic crisis was that the Hubble Space Telescope, which was built for this purpose, blundered in its mission and due to some glitch measured the Cepheids incorrectly.
Verification was the task of the James Webb Space Telescope, which, examining 320 stars, confirmed that Hubble’s primitive, noisier measurements were correct.
Webb’s measurements demonstrate that systematic error in Hubble’s optical measurements of Cepheids cannot play a significant role in the evolution of Hubble’s tensor.
Adam Ries, an astrophysicist at Johns Hopkins University, summarized the results for Space.com.
By ruling out the error, the ball returns to the theory’s court. According to Reiss, this deepened the mystery, but more exciting solutions remained on the table.
(Science Alert, Space.com website)
