WATCH THIS SPACE

Nov 27, 2025
5 min read

Updated: Jan 2

While we were all distracted with wars and pandemics, politics and social change, our basic understanding of the universe sprung a whole bunch of leaks; or, that's how I'm choosing to read this while knowing some experts may disagree. Starting roughly around 1998, our best model of cosmology, that branch of astrophysics concerning itself with the universe at its largest scales, has been something given the obscurifying acronym ΛCDM (lambda cold dark matter). But since the adoption of ΛCDM a slew of new tools and techniques arrived for your friendly neighbourhood physics nerds, particularly over the last decade. They figured out how and finally built an observatory to detect gravitational waves, developed new ways to gather and process light and better map the universe, and you might recall the James Webb Space Telescope, Hubble’s predecessor, being completed, launched, reaching its final destination, and beaming back novel images. All that has really paid off. Turns out those deploying and exploiting these new treats and tricks have been very busy — busy breaking everything we thought we knew about what the universe is composed of, how it should behave, and its origins. That sounds like a lot. And it is. This couldn’t be a more exciting time.

Starting around 2010, cosmological observations began getting a little weird. More and more papers showed up with titles and descriptions like “A Giant Arc on the Sky”, “a giant ring-like structure”, and “new data support the existence of a Great Wall”. What they were seeing were clusters, rings, and unimaginably huge walls of galaxies and quasars spanning as much as 10 billion light-years, making these structures by far the largest conglomerations ever observed. (For scale, our solar system is roughly two light years across, our own Milky Way Galaxy is around 100,000, and the whole of the cosmos perhaps 93 billion light years or so.) Obviously, a structure spanning 10% of the observable universe is quite the thing, indeed. None of that had been seen before and was not anticipated by any theories.

These observations and others (showing there are vast voids between ever-larger structures, like galaxy superclusters and web-like supercluster filaments) suggested a real problem with our current understanding. That’s because foundational to cosmology is the principle that the universe cannot be arbitrarily large and, at least at scale, zoomed out enough, it must be homogenous, effectively a uniform soup. Though there may be an intricate lattice or fractal-like structure at some level, like the knit of your shirt or sweater, when observed in its entirety the standard model needs the cosmos to have this uniform, or isotropic, nature. Even if you haven’t done any math or physics you’ve probably noticed or been told there is inherent pattern and symmetry to be found. Those symmetries and the simplifications built upon them, found in Einstein’s work but also tracing back to Copernicus, for example, insist there are no seriously exotic locations or directions in the universe. As you can imagine, if the cosmos was highly weird then no observations would be deeply meaningful or necessarily tell us anything about any other part of the universe, rendering cosmology effectively pointless. So this ultimate uniformity makes the job of modelling the cosmos possible.

As such, finding gargantuan structures, rings and walls, raised some eyebrows and sent more people investigating. Then in 2023, I began hearing of a new set of observations and problems and, suddenly, of cosmology in turmoil. As they do, astrophysicists were using their telescopes to attempt to measure the current expansion rate of all that we see out there, what is called the Hubble constant. That's because different observations have always, most annoyingly, yielded different results for the Hubble constant since the discovery of the universe’s expansion. Discrepancies there were commonly believed to be due to the imprecision of the tools used; hence the need for building much more powerful and precise instruments. Trouble is, in 2023, using those remarkably accurate instruments, new values arrived for the Hubble constant. Once again, those appeared to further clash with the predictions yielded by the standard model of cosmology, while simultaneously killing the comforting, status quo-preserving explanation of weak tools. Weirder still, two different techniques were used to perform separate measurements of the Hubble constant. Both arrived at significantly different results. The universe, it seemed, was giving very different answers to the same question. Most annoyingly, both results were tested and tested again and looked to be correct while both being incompatible with one another and also violating the model we’ve used for generations to make our best and most accurate predictions. Yowza!

This wasn’t some new theory that failed confirmation through observation but the old theory, so very useful and seemingly robust for so long, appearing to fail confirmation using novel observations. As Dr Poulin-Détolle explained in a publication for France’s National Center for Scientific Research, “That’s very exciting because it could mean that our model of cosmology is incomplete and that we need to consider the possibility of new physics.” A review paper published on the matter (with dozens of authors) offered something just as explicit, “While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model.” So all of this was starting to look like we are on the cusp of a Galileo or Copernicus moment.

Then the James Webb Space Telescope started getting in on the fun and offering up its own observations. What it sent back was data on galaxies so bright, massive, and distant that they had to have arisen extremely early in the formation of the universe, only 280 million years after the singularity. Other galaxies were similarly observed, and more still are yet to be formally confirmed. If accurate, these observations would, once again, put a crack in what we know about physics as our best estimates to date have predicted galaxy formation not at slightly different timelines but hundreds of millions of years later, around 500 million years. One review came back offering that “...the extremely high stellar mass of GS-z14 remains an outlier when compared to previous measurements of high-redshift galaxies detected by JWST and our numerical models (even after accounting for cosmic variance).” Another problem for these earlier-than-expected galaxies is that researchers showed they contain heavy elements like nitrogen and oxygen. That’s significant because the standard model tells us the early universe contained only hydrogen and helium, as the forging of heavier elements require the cores of existing stars, and then those stars need to explode in old age to release those heavier elements. So it seems, just to make any sense, generations of existing stars had to pre-date these too-early galaxies; only, our current physics doesn’t allow for even a single generation of low-mass stars to have aged enough to produce things like nitrogen in a galaxy just 300 million years old. Wow!

So, watch this space.

MORE DETAILS:

Guide to ΛCDM

https://astrobites.org/2025/01/06/lambda_cdm

Sloan Digital Sky Survey: “The Sloan Digital Sky Survey: Mapping the Universe”

https://www.sdss4.org

DESI: “mapping the universe”

https://www.desi.lbl.gov/focal-plane-system

LIGO: “About”

https://www.ligo.caltech.edu

A Giant Arc on the Sky

https://arxiv.org/abs/2201.06875