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Spacetime is often pictured as a smooth fabric. But at the very microscopic level, this fabric might not be continuous; instead, it could consist of individual 'atoms'—events linked by causality. This picture of the world is called causal set theory. In it, the universe is not a field or a wave, but a vast scattering of points, where some events precede others, like beads strung on threads of time.

The problem is that one can dream up infinitely many such scatterings. Some resemble our world — with smooth curves, like a crumpled sheet. Others look like a crystal lattice or a layered cake. How can we tell which universe we are dealing with? The authors of the new work took nine completely different classes of causal sets — from lookalikes of our world to bizarre 'quasicrystals'—and tested whether they could be distinguished using simple measurements. Instead of computing complex geometric quantities like curvature, they used graph properties — networks of points and links. For example, they looked at how many links a point has on average, or what notes sound if you imagine the network as a drum.

The result was surprising: just three indicators — the distribution of links among points, the vibration spectrum of the network, and the abundance of 'intervals' (regions where one point influences another)—were able to clearly separate all nine classes. It's as if, by asking three simple questions about a city (how many streets branch off from intersections, what hum fills the square, and how often you encounter dead ends), you could tell without fail whether you are in New York, Venice, or a stilt village. Especially important is that these questions are almost free of random errors, unlike complex curvature calculations, which often go astray. This approach opens the way to practically exploring the landscape of all possible universes — not in fantasies, but with numbers in hand.