The space we live in appears three-dimensional. But when physicists try to reconcile gravity with quantum mechanics, familiar dimensions start behaving strangely. In a new study, scientists showed that to describe a massive particle while accounting for quantum gravitational effects, it is natural to add two more dimensions.
At the core lies an idea by Indian physicist Thanu Padmanabhan: at very small distances, space itself ceases to be smooth. A minimal possible length emerges — a quantum of space. The usual propagator (a mathematical object describing a particle's motion from point to point) stops working. Padmanabhan proposed a new, "duality-invariant" propagator that accounts for this graininess. The authors translated this construction into field theory language, and found that it is equivalent to an ordinary free massive particle, but in a space with two extra dimensions.
This approach does not require introducing complex interactions or new physics — only expanding the arena. It is similar to how the shadow of a three-dimensional object on a wall can look complicated, but in full volume everything becomes simpler. Here, the "wall" is our familiar space, and the "volume" is a world with two extra dimensions. The model is limited to corrections of the order of the square of the minimal length, but it already shows how quantum gravity might manifest in low-energy effects.
The idea of extra dimensions is not new: as early as the 1920s, Theodor Kaluza and Oskar Klein attempted to unify gravity and electromagnetism by adding a fifth dimension, curled up into a tiny loop.
In Alexander Gromov's novel "The Black Man," characters use extra dimensions for instantaneous communication — similar to how extra dimensions here serve as a channel for quantum fluctuations.