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A pendulum chooses how to swing on its own. If you give it a strong push, it quickly returns to a smooth rhythm. If you hold it at its extreme position, it will stay there, but as soon as you let go, it resumes its usual motion. The universe behaves in much the same way in a new mathematical model, where its expansion is described not through specific physical forces but through the geometry of expansion itself, so-called cosmography.

The authors turned cosmographic parameters (numbers describing how quickly the rate of expansion changes) into dynamical variables, as if the position and velocity of a pendulum had a life of their own. It turned out that the rapid inflation of the early universe, when it grew faster than light could cross it, is a natural 'attracting' regime. The state where everything is compressed to the limit (like a taut spring), on the other hand, repels the system. This ordering explains why inflation was almost an inevitable start.

To describe the transition to the familiar expansion with radiation and matter, two ingredients were added to the system: radiation itself and a mechanism for the gradual 'melting' of what caused inflation. As a result, the model shows that after the violent beginning, the universe inevitably settles into a phase dominated by radiation: that hot soup of particles from which atoms would later assemble. This is similar to how a boiling kettle, once turned off, eventually cools to room temperature: that is the final destination.

This approach does not require guessing what the 'dark energy' of the early universe was made of. It provides a general framework that can be checked against observations and shows that the key stages of our history, from inflation to ordinary expansion, are not accidental but deeply embedded in the very geometry of the cosmos.