From our current understanding of the laws of physics, the universe is estimated to be 13.8 billion years old. However, as I mentioned in my July 23' NS post, recent James Webb Space Telescope (JWST) data has indicated that the universe could be twice as old as that initial estimate. 

Rajendra P Gupta is the scientist making this claim, estimating a new age of 26.7 billion years – that's almost double the current accepted value! This comes following the publication by Labbé et al., who found galaxies with JWST at huge distances (redshifts) which we're seeing as they were 13.5 billion years ago. This would mean that, theoretically, these galaxies existed only 300 million years after the birth of our universe. When we estimate the mass of these strange galaxies (from stars), they seem to be too big – i.e., there hasn't been enough time elapsed at that point in the universe's existence for there to be that many stars. In Gupta's paper, he looks at different models of the universe which could fit the JWST data better.

The current best model of the universe we have is what's known as the ΛCDM model. "CDM" stands for "cold dark matter", and lambda refers to the accelerating expansion of the universe. As radiation travels through the expanding universe, its wavelength gets stretched (and frequency is compressed) to redder wavelengths. ΛCDM (paired with Einstein's equations) is also responsible for the theorised 5% - 27% - 68% visible matter - dark matter - dark energy distribution within our universe. While ΛCDM fits many observations we've made so far, it also has some issues.

A concept which is confusing to many is how redshift can correspond to "how old was the universe when this particular object existed?" If you're receiving light from some object which has been redshifted by some factor, you can calibrate that redshift with the time that light has been travelling for. After all, when you look up at a star or galaxy in the sky, you're looking into the past. A redshift of 10 corresponds to a "lookback time" of 13.3 billion years, when the universe was just 500 million years old. Gupta's paper proposes that this redshift calibration might be off slightly – what if the expansion of the universe isn't the only thing which contributes to redshifting? He suggests that this additional contributing factor could be something known as "tired light." The idea is this – as light travels through the universe and collides with stuff, it loses energy, and since photon energy is inversely proportional to wavelength (as I'm sure we all remember from our quantum physics class), the wavelength increases when this energy exchange takes place. This idea was first proposed by Fritz Zwicky in 1929, but was quickly shut down in favour of the expanding universe model for reasons I don't really understand. Gupta did exactly what came to my mind when I first discovered the tired light theory – why not just combine both models? By creating this hybrid model, it seems that it fits the JWST data better than the other popular models (including ΛCDM).

If we have two contributions to redshift (tired light and expansion), then the expansion rate must be lower to allow for a tired light contribution for a given redshift. However, if the expansion rate of the universe is lower, then it must mean that the universe older than currently thought for it to have reached the size it is today. In Gupta's hybrid model, a redshift of 10 is a lookback time of 21 billion years rather than the 13.3 billion years by ΛCDM.

If we assume that this model is correct, then it solves the problem outlined earlier of JWST detecting galaxies which are too massive. It also would explain how we get supermassive black holes in the early universe. This all sounds so good! Sadly, there is a catch. This research ignores many important observations made in astronomy so far, such as measurements for the oldest stars and star clusters. In addition, the large redshift estimates in the paper published by Labbé et al. also have huge uncertainties, so we should take those age and mass estimates with a grain of salt. Based on the current available evidence, Gupta's cosmological model falls short in many aspects and creates more mysteries than it solves. 

So, what should we make from all this? Well, I suppose that's down to you. I personally think this research is super exciting as it perfectly embodies a new era of astrophysics researched birthed by the launch of JWST. Whether Gupta's model leads to anything significant in the future will be revealed – well – in the future... While I probably sound like a broken record at this point, this is just how research is intrinsically, especially in a field like astrophysics. I understand how this may be annoying to some, but, in my eyes, it just adds to the excitement. After all, life would be a bit boring without a chase and some imagination, right?

published: 11/09/23 by kaan evcimen