Why in News? A big open problem in cosmology is the Hubble tension, that is, there are two equally valid ways to measure how fast the universe is expanding, but they have yielded two very different estimates.

How is the Expansion of the Universe Claimed to be Happening? The universe started to expand after the Big Bang event around 14 billion years ago. If it continues to expand unabated forever, it will be an open universe. But if at some point the expansion stops, because of the gravitational forces exerted by the galaxies, the universe could collapse and become closed. If the universe continues to expand, and the rate of expansion (which is currently increasing) eventually starts decreasing (due to the gravitational forces), this leads to a flat universe.

What are the Ways to Study the Universe’s Expansion?

1. Cosmic microwave background (CMB): This is a sea of photons, that are left over from the Big Bang/ its afterglow. The WMAP, BOOMERanG and ’Planck’ are 3 telescopes in space that study the CMB. According to their data, the observable universe is flat with a 0.4% margin of error.
2. Cosmic distance ladder: This is a set of techniques used to measure the distance to objects that are close, further away, and very far away from the earth. One object in particular is the Cepheid variable star. The best way to follow these stars is using the near-infrared radiation they emit. Fortunately, NASA’s James Webb Space Telescope (JWST) can track near-infrared radiation.

What Gave Rise to the Hubble Tension? Researchers found significant differences in the data collected by the Hubble telescope (previously the best space telescope) and JWST. Thus, the Hubble tension is real and its origins remain a mystery.