The James Webb Telescope has been roaming the vast space since late 2021, bringing us hundreds of fascinating images of the stars, galaxies, and even blackholes; unveiling the secrets of the universe to us. Yet, it could also help end a long-standing debate in cosmology.
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A compiled image of the farthest galaxies taken by the James Webb Telescope lens.
Cosmology is the science that studies the history, development, origin, and, accordingly, the end of the universe, by studying the light emitted from distant stars. The expansion of the universe was one of the predictions of Einstein's theory of general relativity, which explains the motion of large bodies and gravity through the spacetime continuum. Nearly ten years later, Edwin Hubble's measurements confirmed the expansion of the universe; the rate of expansion—or the speed at which the universe is expanding—was named the "Hubble's constant".
How is the Hubble's constant measured?
There are two ways to measure the Hubble's constant. The first method utilizes both the standard cosmological model (also known as the Lambda Cold Dark Matter model), which is the theory that explains how the universe operates and how it originated from the Big Bang. It also attributes the motion of galaxies to the existence of dark matter and dark energy, along with the cosmic microwave background (CMB)—which refers to the radiation left over from the Big Bang that appears to us as heat. According to this calculation method, Hubble's constant is 67.4 kilometers per second per megaparsec (km/s/Mpc).
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History of the Universe according to the standard cosmological model. Source: NASA
The second method for measuring the Hubble's constant uses the Doppler effect to calculate the distances and velocities of nearby stars and galaxies, such as the Andromeda Galaxy. Imagine, for instance, that you are on a boat searching for land. You turn around and see a faint light coming from some distant lighthouse. You will be able to estimate the distance you need to sail to reach land based on the intensity of the light. Now let us replace the sailor with an astronomer and the lighthouse with stars. The farther the stars are, the longer the time light takes to reach us. Light stretches as it travels, causing it to appear redder, which is known as redshift. As it gets closer, it turns blue. This method has estimated that the Hubble's constant equals 73.5 kilometers per second per megaparsec (km/s/Mpc).
While the difference between the two measurements may seem small, it has created a gap of one billion years in the estimated age of the universe; this is where the crisis has risen.
How does the James Webb Telescope relate to the crisis?
The James Webb Space Telescope is the largest telescope ever sent into space; it is the successor to the Hubble Space Telescope. Among Webb's main goals is understanding the history of the universe by exploring the first galaxies that formed after the Big Bang, and understanding the evolution of galaxies and the life cycle of stars. However, some of Webb's observations have deepened the crisis. In 2023, it observed that six of the oldest galaxies have expanded much faster than the Lambda Model of the universe predicted. At the end of the same year, it confirmed the validity of the redshift method measurement of Hubble's constant.
How can the standard model of cosmology be wrong in calculating Hubble's constant and the age of the universe, while it is one of the most important cosmological theories that have successfully explained many other cosmic phenomena? Perhaps we are on the verge of a new physics, or we will witness a change in the standard model of cosmology.
References
You can see the James Webb Telescope observations here.
phys.org
science.nasa.gov
sciencedaily.com/210630091358
sciencedaily.com/230413154323
webbtelescope.org/contents
webbtelescope.org/webb-science