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JWST's test of the Big Bang and modern cosmology

The biggest contribution to cosmology in the past century has been the development of a standard model that describes most of the phenomena observed in the universe to a reasonable degree of certainty. This model of the universe is known as the ΛCDM (Lambda Cold Dark Matter) which postulates three componenets of the universe; Λ, i.e., the cosmological constant which is associated with dark energy, cold dark matter and ordinary matter. This model has been successful in explaining varioius phenomena observed in the universe such as:

  • The afterglow of the Big Bang, i.e., the Cosmic Microwave Background.

  • The large scale structures of the galaxies

  • The internal motion and the relative motion of galaxies

  • The accelerating expansion of the universe inferred from observations of the light received from distant supernovae and many more such observations.

Another prediction that this model makes is that the farther we look back in time, i.e., the farther away we observe the universe, the galaxies should appear to be be less massive, bluer and less rich in heavy elements.

The image above shows how galaxies similar to the Milky Way were in different periods in the history of the Universe. The galaxies formed shortly after the Big Bang (ones on the right) are smaller and bluer than the ones formed many years after (the ones on the left).


With the advent of the James Webb Space Telescope, the question of the evolution of the universe has not remained in the domain of the purely theoretical any longer. Physicists now have access to observational data to better understand the universe. The immense capability of the JWST has allowed us to observe and study the properties of many galaxies formed in the very early stages of the universe. Before the launch of the JWST there was only 1 confirmed galaxy, GN-z11 which estimated to have been formed around 400 million years after the Big Bang and there was another such a galaxy but remained unconfirmned. The JWST has now brought forth more than 100 such galaxies and most have been confirmed to have come into existence during the very early periods of galaxy formation.


There is a catch though. Many of these newly obersved galaxies have properties that they should not have, atleast according to theoretical predictions. These galaxies are,

  • rich in heavy elements

  • very bright

  • very massive

  • still forming new stars

  • very rich in gas

All of these are properties contradict theoretical predictions. According to the current understanding, gas falls into early galaxies and stars feed back some of the gas to keep more gas from falling into them in the future. There is a limit to how fast matter can fall into the stars. The observed properties of the galaxies indicate that something in the current explanation is not quite right.


A large number of people have decried the Big Bang model as a result of the discovery of these new galaxies. The assertion that the Big Bang model is obsolete has been made quite a lot and new laws of physics along with novel physical phenomena and even new particles have been theorized. However the first step should be to consider all the factors that come into play while making obersvations of this kind. Instead of jumping to conclusions what should be done is to check whether the properties exhibited by the galaxies can be predicted by the present model or not. There are various factors that could explain the observations.


The first thing to consider is the fact that even though many galaxies have been observed, the observations themselves have been made in a relatively smaller area (the Cosmic Evolution Early Release Science Survey, CEERS). Another survey, the COSMOS-Web is set to be observing around 50 times more of the present area covered. Hence jumping to conslusions before further observations are made is not a prudent step.


Another thing that could be happening is the heating up of gas due to the supermassive black hole at the centre of the galaxy which makes the galaxies appear much brighter and thus more massive than they actually are. The presence of dust in the surrounding area could also be causing the light from the galaxies to get even more red-shifted giving the illusion that the galaxies are farther away and thus further back in time than they actually are. No conclusive inferences can be drawn till a proper spectroscopic analysis, which is ongoing, of the light received from the galaxies is completed.


Another thing that could be happening is that the JWST is overperforming. This isn't a bad thing and it goes to show the remarkable feat of engineering that this telescope is. However, it could be that the images taken by the telescope may not be properly calibrated thus making the galaxies appear brighter than they are. The last thing to consider is that the theory itself. There could be some flaws in our understanding of how galaxies evolved in the early universe.


As is evident, there are many factors that are to be considered before one has to come up with a different model of the universe. These images are just prelimianaries. Until large, deep field images with proper calibration done and a full spectroscopic analysis is published nothing much can be said. It is entirely possible that present model once modified a little will sufficiently explain the observations

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