The idea of a expanding universe, proposed by Georges Lemaître, finds an unexpected analogy. Space behaves like a piston in a cylinder: dark energy pushes it, much like steam. The relationship between pressure and volume in this 'engine' is strikingly similar to that of a steam boiler.

Most surprising: the cosmic horizon isn't just a boundary; it radiates heat like a warm object.

Scientists tested two models for this cosmic engine: one idealized, setting an unreachable upper limit, and a simpler, more realistic one. Calculations show efficiency always falls below the theoretical ceiling and never exceeds one. Not even the universe can create energy out of nothing.