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Do JWST’s Results Contradict The Big Bang?

When it comes to the science of cosmology — the history of the Universe and how it came to be the way it is today — one of the crowning achievements of the past 100 years is the development of a “standard model” of cosmology. The dominant factor in determining how the Universe evolves is gravitation, which is governed by General Relativity and accounts for the expanding Universe as well as the assembly of large-scale cosmic structures. The contents of the Universe have been determined to be dark energy, dark matter, normal matter, neutrinos, and photons. And the Universe as we know it began some 13.8 billion years ago with an event known as the hot Big Bang, with density imperfections seeded by a preceding phase known as cosmic inflation.

Despite all the observational evidence we have supporting this picture, it may not be fully correct. Each time we observe the Universe in a new way, we have to check that what we’re seeing is still consistent with this model. With the recent addition of JWST to the arsenal of tools astronomers have, is this picture in trouble? That’s what many, including Patreon supporter Chad Marler, want to know:


“The newest fad [among armchair physicists] is that the JWST observations of galaxies that are more mature than expected in far reaches of the universe ‘disproves’ the Big Bang. I’m not sure there has been enough time or data accrued to actually make a real account of the results yet, but I sure haven’t heard anyone with any credentials say that, either.”


Certainly, a lot of extraordinary claims have been made, but what’s the full truth? Here’s the current status.

The first thing we have to do is lay out, based on our picture of the Universe, how we expect events to unfold in our Universe. This picture — sometimes called the standard model of cosmology, sometimes called the inflationary hot Big Bang, and sometimes called ΛCDM (because of dark energy, i.e., Λ, and cold dark matter) — has been remarkably successful, explaining features ranging from.

It also predicts that, as we look farther and farther back in time — i.e., to greater and greater cosmic distances — that the galaxies we see will be inherently smaller, bluer, less evolved, less rich in heavy elements, and at some point beyond where we’ve been able to look, we should cease to see stars or galaxies of any type, as we’ll reach the Universe’s “dark ages.”


Galaxies comparable to the present-day Milky Way are numerous throughout cosmic time, having grown in mass and with more evolved structures at present. Younger galaxies are inherently smaller, bluer, more chaotic, richer in gas, and have lower densities of heavy elements than their modern-day counterparts, and their star-formation histories evolve over time. This was not discovered or well-known until the 1960s when we began to see large numbers of galaxies from much earlier in our cosmic history. Credit: NASA, ESA, P. van Dokkum (Yale U.), S. Patel (Leiden U.), and the 3-D-HST Team

But that’s simply a picture of what happens. What we need, if we want to compare theory to observations, is to quantitatively figure out not just what happens, but when it happens and, quantitatively, how much it happens. Even though the laws of physics are well-known, and the “starting point,” or our initial conditions, are also well-known, our best quantitative predictions still come along with a large amount of uncertainty.

From the theory of cosmic inflation and the patterns of fluctuations that we see in the cosmic microwave background, we know that our Universe began, at the start of the hot Big Bang, from an almost-perfectly uniform state. There were the seeds of structure — density imperfections — imprinted atop that near-uniform background, leading to under densities and overdensities at about the 1-part-in-30,000 level, which was almost but not quite the same on all cosmic scales: about 3% larger on size-of-the-Universe scales than on size-of-a-galaxy scales.

We know that early on, these imperfections grew gravitationally, but also had to contend with interactions with and pressure from radiation, like photons, creating a pattern of peaks and valleys in how overdense/underdense various regions were on a variety of cosmic scales.

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