In the far reaches of space, there exists a hypothetical object: an ultracold black hole. It is charged and resides in an expanding universe (de Sitter space). Its temperature hovers just above absolute zero — about one trillionth of a degree above it. The thermal motion of particles inside nearly freezes, like tea cooled to the last possible degree.

Physicists attempted to describe such a hole in the language of quantum mechanics. To do so, they used a special model — the double-scaled SYK model (a system of many interacting fermions with random couplings). In a certain limit, it reduces to flat JT gravity (a two-dimensional model where gravity is governed by a dilaton field). But this gravity behaves capriciously as a quantum system: it has infinitely many states with the same energy — the so-called Hagedorn degeneracy. This is like a hotel with an infinite number of rooms on one floor: you can't meaningfully assign guests.

The authors added the first subleading correction to the dilaton potential (a scalar field that determines the strength of gravity in the JT model). This destroyed the infinite degeneracy but did not fix the structural problem. Then they turned to the gauge description of the sine-dilaton gravity model and proposed a new method for quantizing the near-horizon dynamics. As a result, high-energy states (in the spectral asymptotics) are dynamically suppressed, and discrete spacetime emerges, as if reality becomes grainy, like a photograph at high magnification.

The outcome is unusual behavior of the partition function at low temperatures. Instead of a smooth cooling, the system abruptly changes its properties — quite unlike what previous models of cold and Nariai physics predicted. This can be interpreted as a way the quantum system itself ensures that singularities do not peek out.