Planets, stars, and galaxies all spin along an axis of rotation. But does the universe itself also whirl around an axis, or several, albeit on a much larger scale? If it did, it would fly in the face of scientists' most basic assumptions about the cosmos we inhabit. Now, one researcher believes his latest observations may provide evidence for this possibility.
This notion that our universe was born with a spinning structure has been floated by scientists for years, but it is heavily debated because it could violate a fundamental idea in established physics: the cosmological principle. This principle holds that the same physical laws apply everywhere in the universe, adding up to an essentially random mishmash of stuff on cosmic scales of hundreds of millions of light years. A rotating universe would likely cause structural anisotropies and asymmetries to arise on cosmic scales, therefore violating this principle.
A new study by Lior Shamir, a computational astronomer at Kansas State University, is bound to reinvigorate the debate over this weird model of a rotating universe. Shamir presented potential evidence for a spinning universe this week at the meeting of the American Astronomical Society, which is being held virtually due to the Covid-19 pandemic.
The basic premise behind this dizzying model is that the early universe rotated somewhat like an enormous and complex galaxy, and that it transferred this momentum to both ancient and more modern galaxies.
What’s more, if signs of this cosmic rotation become more pronounced at larger distances, and thus further back in time, it may suggest that the early universe had a more consistent structure that it has been steadily losing as it ages. That would mean we live in a time of increasing chaos—not just on Earth, but in the cosmos at large.
Shamir investigated this hypothesis using an algorithm that categorized the spin directions of roughly 200,000 spiral galaxies observed by two different telescopes. The results “agree with previous observations that show asymmetry between galaxies with opposite spin directions” which “can be an indication of a rotating universe,” according to his study, which is published on the preprint server arXiv and has not yet been peer-reviewed.
“According to the cosmological principle, everything is a random blend of galaxies and matter, and you’re not supposed to see any structure,” said Shamir in a call. “Here, we see structure and the scale is much, much larger than any astrophysical structure that we know of. The statistical signals and patterns are very clear.”
However, Shamir cautioned that this rotating universe model, which seems to fit a quadrupole (four-pole) structure, is a “rather exotic” interpretation of the observational data that he studied. He outlines a few other explanations for the asymmetry and that “do not violate the basic cosmological assumptions,” such as primordial gravitational waves, in the study.
“If the universe was born spinning, there should be some evidence to that,” Shamir said, noting that his study presents a potential datapoint for this rotational cosmic model. But the new study is “not very decisive evidence” and should not be regarded as “ultimate proof that the universe was born spinning.”
In other words, much like other challenges to the cosmological principle that have been proposed over the years, it will take much more research to upend our current well-corroborated isotropic model of the universe.
That said, Shamir’s research expands upon previous observations that show asymmetries between the ratio of galaxies that spin clockwise and counterclockwise, which could point to a broader spin of the universe itself. If the universe is isotropic on large scales, as the cosmological principle suggests, then galaxies should have 50/50 odds of spinning in either direction.
Shamir tested out this idea by feeding huge observational datasets collected by the Sloan Digital Sky Survey (SDSS) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) to Ganalyzer, a galaxy-sorting algorithm that he developed. Ganalyzer combed through this material and found 88,273 clockwise galaxies and 86,075 counterclockwise galaxies in the SDSS survey and 16,508 clockwise galaxies and 16,520 counterclockwise galaxies in the Pan-STARRS survey.
While those results may seem relatively even on first glance, they produce an overall ratio of about 51/49 in favor of clockwise galaxies, as opposed to the expected 50/50. Given that some 200,000 galaxies were studied in total, these small differences matter—Shamir said that the odds of such a ratio emerging by chance are fewer than one in a million.
Even so, next-generation telescopes will collect far more detailed and expansive datasets that could either confirm or conflict with these results. For instance, the Euclid space telescope or the Vera C. Rubin Observatory in Chile, “will allow much more powerful data collection” of galaxy spins that “can be studied in higher resolution to provide more accurate profiling,” according to Shamir's study.
Of course, the slight asymmetry in galaxy spin directions could also be explained by the far-out idea of a spinning universe. The rotating cosmos model is also bolstered by recent observations of galaxies unexpectedly spinning in the very early universe, which defies predictions that suggest it should take several billion years for these galaxies to gain spinning momentum.
“Last year, it was rather crazy to say that a galaxy would be observed spinning 1.5 billion years after the Big Bang,” Shamir said. “But now we see them, and they are not even that rare.”
What’s more, Shamir found that the spin asymmetry within his survey of galaxies is more pronounced at larger distances and timescales, hinting that this speculative rotational fabric of the universe is diminishing as the universe ages. If that’s true, it means that the universe is getting less structured and more disorderly over time.
Ultimately, the notion of a rotating universe that violates the cosmological principle will have to be contextualized by new and better observations and models—just like any other challenge to established physics.
“It’s a rather wild theory,” Shamir concluded. “But everything in cosmology is really wild.”