In the first moments of the universe's life, there was not even a hint of dark energy — the very force that today pushes galaxies apart ever faster. But if you look deeper, down to the Planck scale (billions upon billions of times smaller than an atomic nucleus), spacetime ceases to be smooth. It resembles a foam of tiny 'building blocks'—discrete structures from which gravity might emerge.
In their new work, the authors proposed that these 'building blocks' act as defects — quantum-like imperfections that create friction for ordinary matter. A boat gliding on water would move forever without resistance, but the viscosity of the fluid gradually saps its energy. So too here: spacetime defects form a medium in which matter's energy slowly dissipates. This process follows the diffusion equation — the same one that governs heat spreading through a spoon dipped in hot tea.
Calculations revealed something astonishing: if the young universe had no dark energy at all, the gradual 'friction' against defects could have accumulated exactly as much as astronomers observe today. A small positive cosmological constant (a measure of dark energy density) emerges naturally, without extra hypotheses. Thus, the quantum foam underfoot becomes the engine of cosmic expansion.
The Planck length is the scale at which the very concept of distance loses meaning: to 'see' such details, you would need an accelerator the size of a galaxy.
The idea of spacetime as a foam that gives birth to entire universes is explored in Greg Egan's novel 'Schild's Ladder'.