In causal set theory, spacetime is not a smooth sheet but a web of tiny points connected by arrows of cause and effect. A point is linked to another only if the first can influence the latter. In such a web, a black hole is described differently: its horizon, the boundary from which signals cannot return, must be redefined.
To find the horizon, researchers weave chains of causally related points through the web: they resemble light rays, only spun from causality. Near the horizon, something unexpected happens: an indicator that measures the divergence of these chains switches sign. It’s as if a thread in the web suddenly changes its tension, exposing an invisible edge.
For large horizons, the method was improved with “blurred” chains that span multiple paths at once. Thus, for the first time in this discrete world of causes, a sign of the horizon has been detected, a step continuing the path of Stephen Hawking.
In the causal web, the horizon isn’t set in advance: it only reveals itself in the shifting behavior of the chains, like an invisible crack in the web’s pattern.
In Interstellar, the tesseract built from threads of causality — perhaps that’s exactly how spacetime appears if you peer inside the web.