In today’s bleak media landscape of legitimate news existing alongside rampant chatbot hallucinations and a social epidemic of disinformation, it should go without saying that you can’t believe everything that you read.
But this should especially apply to sweeping claims concerning the entire universe. For example, consider a recent paper that boldly suggests we might live inside a gigantic black hole. While cosmologists are always ready for a new and exciting revelation, and the implications of such a result would be enormous, we have to be extremely careful about jumping to conclusions before there’s enough evidence.
The paper, authored by Lior Shamir, a computer scientist at Kansas State University, appeared in March in the Monthly Notices of the Royal Astronomical Society, an outstanding journal with a prestigious history that stretches back nearly two centuries. And on its face, Shamir’s study seems to make a compelling case. Examining a sample of galaxies from a far-reaching survey conducted with the James Webb Space Telescope (JWST), Shamir found that roughly two thirds of them were rotating in the same clockwise direction as the Milky Way, with the remaining one third instead spinning counterclockwise.
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This is somewhat puzzling because a core tenet of cosmology is that at sufficiently large intergalactic scales, the universe’s properties and structure should be essentially the same in all directions. So we’d expect a roughly even split between clockwise- and counterclockwise-spinning galaxies anywhere we look. The imbalance Shamir has spied, he claims, could be a sign that we live in a rotating universe. While he offers several explanations for what could cause the universe to rotate, he focuses mainly on the hypothesis that it is inside a gigantic black hole. Because black holes naturally rotate, this could give a little spin to the entire cosmos, ultimately cascading down cosmic scales to tweak the twirls of individual galaxies.
Cosmologists would be thrilled to learn that either (or both) of these possible explanations are true: that the cosmos is rotating or that it’s the interior of a giant black hole. Such revelations would open up incredible opportunities for new research and potentially explain vexing problems such as dark energy and the Hubble tension. If nothing else, for most of us, it’d also be really fun to talk about on a date night.
Indeed, astronomers have been toying with both concepts for nearly a century. In 1949 the eminent mathematician Kurt Gödel, a longtime friend of Albert Einstein’s, discovered an exact analytical solution to Einstein’s general theory of relativity that included a rotating cosmos. Interestingly, the spinning universe Gödel constructed allowed for time travel into the past, which he used to poke holes in Einstein’s vaunted theory.
And as soon as astrophysicists realized that black holes weren’t mere theoretical musings but could actually be born from collapsing stars, they started wondering if the universe was trapped inside of one. The similarities are too striking to ignore. As we understand them, black holes have a singularity—a point of infinite density—at their heart. If you rewind the cosmic clock, the universe has a singularity of sorts, too: a point of infinite density at the big bang. Black holes have an event horizon, an invisible one-way boundary at their edge that not even light is fast enough to escape. The universe has a cosmological horizon, a limit beyond which we cannot see that is set by its finite age, light’s finite speed and cosmic expansion.
But unfortunately, that’s where the similarities end. The big bang singularity is not a location in space, unlike the singularities of black holes. It’s a point in our past. And inside a black hole everything is crushing toward that singularity, whereas our universe is of course expanding.
One way to make a black hole sort of look like the universe is to modify the equations of general relativity. One such modification known as Einstein-Cartan theory can avoid black hole singularities altogether by introducing an extra source of repulsive gravitational force caused by torsion. Most of the time, this torsion goes unnoticed. But in the extreme conditions of a collapsing star, the singularity never forms, and instead the black hole becomes a bridge to a white hole—a black hole’s bizarro twin. Whereas a black hole prevents any exit, locking its contents away for eternity, a white hole is a region of space that cannot be entered and is forever spewing out its contents.
The problem with white holes, however, is that they’re catastrophically unstable. They still have gravitational attraction, but material can never enter them. So as soon as even a speck of dust wanders too close, the energy of the system runs amok, and the white hole converts into a black hole. This is one reason why we don’t think white holes exist in the universe—they just can’t stick around.
Then again … maybe our expanding universe is itself some sort of stable white hole, birthed from the formation of a black hole in another cosmos. And even though white holes are regions of extremely curved gravity, maybe there’s some way to make them look flat once they grow to cosmological scales. The maybes keep piling up from there for this fanciful idea, which may I remind you has no solid supporting evidence, but the universe has surprised us before. So if the evidence leads us in that direction, then we’ll just have to admit we were wrong and find a way to cope with living inside a black hole.
The evidence doesn’t lead us in this direction at all, however.
Cosmologists have been seriously mapping the large-scale universe since the late 1970s. In that time, they’ve developed sophisticated techniques to image as many galaxies as possible. With our latest surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and Euclid, by my very rough estimation, we’ve taken pictures of somewhere around 100 million galaxies out of the two trillion or so estimated to exist in the entire observable universe.
Shamir’s paradigm-shattering conclusion relies on 263 of them.
To be fair, it’s not easy to estimate galaxy rotation, and some selection has to be done. Shamir developed a technique that took data from one galaxy survey—JWST’s Advanced Deep Extragalactic Survey (JADES)—selected a region near the pole of the Milky Way’s axis of rotation, picked out spiral galaxies that were face-on from our point of view and filtered out those whose direction of rotation could not be discerned.
Unfortunately, this kind of extreme selection introduces many opportunities for bias to creep in. When we test a new idea in cosmology—indeed, in all of science—we work to make our conclusion as robust as possible. For example, if we were to change any of these filtering steps, from the selection of survey region to the threshold for deciding whether to include a galaxy in the analysis, our results should hold up or at least show a clear trend where the signal becomes stronger. But there isn’t enough information about such methodological checks in Shamir’s paper to make that judgment, which casts doubt on the validity of the conclusions.
This is not the first study to tackle the question of a rotating universe. Others, using far larger samples of galaxies from different regions of the universe, have failed to turn up anything. And when some evidence has cropped up, later research has found that to be a case of human-caused selection effects, not some newfound fundamental property of the universe itself.
The reality of a rotating universe would be fun to explore because it would have deep implications not just for galactic rotations but also for the formation of cosmic structure as a whole (not to mention Gödel’s tantalizing possibility of time travel).
Even a rotating cosmos has only a weak connection to the universe-inside-a-black-hole idea, however. Yes, black holes (and white holes) rotate, but it’s not straightforward how that rotation would manifest on cosmological scales, let alone how it would trickle down to cause a slight asymmetry in the rotations of galaxies.
Even if the universe isn’t a giant black hole (or white hole), that doesn’t mean that we can’t use their similarities to explore cosmological questions. Famed astrophysicist Stephen Hawking studied the close connection between black hole event horizons and cosmological horizons and what that implied for fundamental physics.
It does not seem likely that we live inside a rotating universe, let alone a black hole. We can’t rule it out completely, but so far there is no compelling evidence. Still, these ideas serve as useful foils for several reasons. One is that we should always assess the assumptions that go into our models. No theory, no matter how powerful and storied, is above reexamination. We must continually test our long-standing ideas against new data.
The other reason to always entertain these ideas is that we never know what surprises may be in store. Modern cosmology faces legitimate questions that cannot yet be answered, such as the nature of dark matter and dark energy. We don’t know where the solutions may lie. Sure, we probably don’t live inside a black hole, but perhaps research in that direction may give us a surprising clue.
For those reasons alone, these ideas are worth keeping around, even if they don’t work out.
At least, that’s my spin on this, anyway.