don't panic, but our universe might be just a little bit broken...
New data from the James Webb Space Telescope says that we'll need to rethink our model of the universe, and scientists are very excited.
Matter. Energy. Dark Matter. Dark Energy. Billions of years ago, the four realms didn’t live in harmony because if they did, there would be no Big Bang, or inflation, or stars, or galaxies, or life. But then dark energy attacked anyway, driving galaxy clusters ever farther apart from each other, doing so at an accelerating pace. Why? Because why not, sometimes things just happen and we deal with them the best we can because that’s simply how reality works.
We’ve consigned ourselves to living at the dawn of the universe that will eventually fly apart into tiny, galaxy sized bubbles and die in darkness. In 100 billion years, the last new star will be born. In a quadrillion years, the very last stars will fade. The cosmos will go silent, dark, and frozen. Only black holes and black dwarves — the remains of the last embers of the last stars — will be around, some bizarre things happening on the quantum level inside them, flashing into the empty, eternal void, then fading out, possibly forever. Bleak stuff, even by my ex-Soviet standards.
Yet, it turns out that this idea of how the universe ends may be wrong. You see, when astronomers try to measure how quickly other galaxies are moving from us, they get a different picture depending on where they look. The first observation that all galaxies around us are redshifted — that is, moving away from us, as moving towards us would show a blueshift — was made by Hubble (the astronomer) in 1929 and confirmed by Hubble (the orbital telescope) throughout the last three decades.
How do you do that? You choose objects that radiate consistent light and energy and are all across the visible universe. Type Ia supernovae fit the bill because the energy required for a white dwarf star cannibalizing an ordinary stellar partner until exploding is usually pretty much the same. That means a Type Ia supernova blast will be bright, but predictably so, and you can use its redshift and parallax to estimate its distance, then plot it against what Hubble (the astronomer) predicted to get a measure of how quickly the universe is expanding in all directions with Hubble (the telescope).
Initially, that number should have been 68 kilometers per second per megaparsec, or 68 kilometers per second for every 3.26 million light years. In some observations, the number came out to 72 km/s/Mpc. In others? 69.8 km/s/Mpc. A few hit 74 km/s/Mpc. All in all, that means the universe is expanding at 5% to 9% faster than it should if the rate of inflation was constant, which was a bit of a head-scratcher for scientists since that number is called the Hubble Constant and should be, umm, well, constant.
now it’s just a universe we used to know
There’s an even bigger problem here because all these different observations should yield the same value from the different parts of the universe around us, and yet they don’t. The most accepted view of the cosmos in astrophysics is that space itself is isotropic and homogenous, which is a very fancy way of saying that every big enough chunk of the universe should look more or less like every other chunk, and they need to be expanding at the same rate, at the same time, in all directions at once.
All right universe, fine. Challenge accepted. After launching the world’s most intricate and expensive origami project, the James Webb Space Telescope — or just JWST to friends and family — about a million miles away, astronomers decided to take another look to see if they can clear up the measurement errors because a 2 km/s/Mpc error over the 93 billion light years of the observable cosmos yields entirely different and unexpected physics and models of our reality. But wouldn’t know you it, JWST had a good, long, hard look, and said “Well, shit… Beats me too.”
In other words, we’re pretty sure we’re measuring the rate of expansion accurately as deep into space and time as we can see, but the data we’re getting just refuses to be consistent for one reason or another, and it’s not just because we have bad tools and made faulty assumptions. And new research even says that based on three catalogs of the aforementioned Type Ia supernovae, dark energy isn’t getting stronger, pulling the universe apart faster. The mysterious force may actually be getting weaker.
Confused? So are the scientists who now have contradictory data and models for the way space and time work. General relativity says that as the universe ages, it should slow down its expansion because it’s less dense and there are fewer forces driving it apart. But Einstein also allowed that space itself could have an energy that wouldn’t slow down, but actually speed up, building inertia. He called this “vacuum energy” of sorts lambda (Λ) and immediately hated it, though how much is up for debate.
This is where we get the lambda in the Λ cold dark matter model of the cosmos — or ΛCDM for short — which has so far held up very well against many efforts to disprove it by an endless parade of papers. Dark energy has remained seemingly unassailable because the moment you take it out of your mathematic models of the universe, you end up with things that defy long-standing observations. Gravity turns into gravy, the Sun becomes a glorified ball of lightning, and cats live with dogs — which yes, does happen, but not of their own volition, and anyway, you know what I mean.
scio nōs nihil scire
To be fair, a lot of those papers claiming to answer what dark energy is or totally erase it from cosmology were ridiculous, and the only reason we even know they exist is the power of elevating damn awful papers for clickbait virality. But what we’re seeing here is very different. The inconsistencies in Hubble (the constant) and negative results in measuring the strength of Λ have been known and agonized over for years, the data is collected by careful scientists, and subjected to intense peer review.
Taken together, all the findings suggest we don’t understand something critical about the universe. A key piece of a huge, complicated 3D puzzle is missing, and it’s just our luck to know what that piece is but not what it looks like, or where we can find it.
At the same time, this is exciting. Bleeding edge, pioneering science is made when a giant model that aims to explain everything tries to come together but can’t. You can pretend that the model works and is perfect, but your predictions will always be off so you can’t do it forever, which is why scientists don’t. Books may need to be rewritten, long cherished ideas about the shape of the cosmos and what you can and cannot do in it or with it could end up being thrown out of the window.
And we didn’t even mention the universe’s Axis of Evil, and the fact that all views of the cosmos have a line going through them, a line on one side of which the objects are closer and brighter than we expect and further and dimmer on the other. Hell, someone could snag a Nobel Prize or three before we’re back to a consensus model again with all the strange stuff we’re noticing the more we study the time and space we occupy. But, again, this is why we do science.
Science is not about knowing stuff so you can dictate it from on high to admirers who gather to hear you spread the infallible truths. (That’s religion) It’s a system constantly asking why or how something is the way it is, and encourages others to discover the answers, which in turn yield more questions.
Having trouble nailing down the behavior of dark energy, scratching your head about the rate of the universe’s expansion, and being unsure why our view is kind of oddly lopsided just shows us how much we still have left to learn, and always will. Which is why it’s so exciting. There are so many possibilities and discoveries just waiting for us everywhere we look, and will be as long as humanity exists.
See: Riess, Adam, et al. (2024) JWST observations reject unrecognized crowding of Cepheid photometry as an explanation for the Hubble tension at 8σ confidence, ApJL 962 L17, DOI: 10.3847/2041-8213/ad1ddd