Will the James Webb Telescope Redefine Cosmology?

Cosmology is at a potential turning point, with NASA’s James Webb Space Telescope (JWST) poised to address long-standing questions in the field. For many years, the standard cosmological model has been the gold standard, explaining the composition of the universe as 68% dark energy, 27% dark matter, and 5% ordinary matter. The model has provided accurate predictions for the structure and distribution of matter in the universe, but recent observations have challenged its assumptions.

Hubble tension

According to an article published in The Conversation, one important issue is the “Hubble tension,” which stems from different measurements of the expansion rate of the universe. Observations using Cepheid variables indicate that the expansion rate is 73 km/s/Mpc, while theory predicts 67.4 km/s/Mpc. This 8% difference has sparked debate about whether current measurements are biased or whether cosmological models need to be revised. Despite its advanced capabilities, the James Webb Telescope has not yet completely resolved this contradiction.

The researchers are currently considering measurements of other types of stars, such as the tip of the red giant branch (TRGB) stars and the J-region asymptotic giant branch (JAGB) stars, which have provided mixed results.

Tensions at S8

Another challenge is the “S8 tension,” which involves the predicted versus observed clumping of matter in the universe. The Standard Model suggests matter should be more clumpy than observed, resulting in a discrepancy of about 10 percent. One potential solution is to revise our understanding of dark matter, perhaps to incorporate fast-moving particles or to account for the effects of galactic winds on the distribution of matter.

Looking ahead

JWST also found that early galaxies were unexpectedly massive, which could indicate new physics or reflect limitations of current measurement techniques. Future observations, including those from the Dark Energy Spectroscopic Instrument (DESI) and the Vera Rubin Observatory, will be critical to resolving these questions.

All in all, while the James Webb Space Telescope has yet to provide definitive answers, cosmology is clearly at a crossroads. In the coming years, either existing models will be strengthened or new physics will emerge that could change our understanding of the universe.