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Toss a handful of glitter into a river, and some flakes will drift straight while others spin in tiny eddies. Galaxies in the universe do something similar: they don't just recede due to cosmic expansion: they also swirl in giant currents, like wood chips caught in invisible whirlpools. These whirlpools, the vorticity of cosmic gas and dark matter, are a crucial trace of how the universe grew and became more complex. But seeing them directly is nearly impossible: that would require knowing the sideways motion of galaxies, whereas telescopes only measure velocity "toward us" or "away from us."

The authors of the new work took a roundabout route. They used detailed computer simulations, where every motion is known in advance, and trained a neural network to infer the three-dimensional flow from a flat map of galaxies. Then they fed it real data from the Sloan Digital Sky Survey — a vast census of one and a half million galaxies. The network reconstructed the velocity field and, for the first time, produced a map of cosmic vorticity. Familiar features emerged: filaments, clusters, and voids, but now highlighted by motion — spiral flows in clusters, whirlpools in voids.

The verification showed that the reconstructed picture is statistically indistinguishable from the predictions of the standard model. Moreover, when these velocities were used to remove the distortions caused by cosmic expansion, the three-dimensional map of galaxies became almost perfectly homogeneous — exactly as expected. This is independent confirmation that our model of the universe is correct.

So the invisible whirlpools have become visible. The neural network acted as a translator, converting the flat language of photographs into the three-dimensional language of the forces that shape the cosmic web. And it turns out that this web doesn't just hang there: it flows, winding galaxies into slow, majestic spirals. Astronomers now have a new tool to look where only formulas could reach before.