A black hole doesn't just swallow everything around it: it also slowly evaporates, like a chunk of ice in the sun. As the hole shrinks, the quantum fields around it start behaving unusually. In a new study, physicists traced how entanglement, a special kinship between particles that persists even when they are far apart, changes.
In an ordinary world without black holes, entanglement between distant patches of a field can flare up again and again, like an echo that returns after many steps. But when an evaporating black hole is nearby, that echo begins to fade. The reason lies in how the hole scrambles information. If the scrambling is slow, the entanglement surges are still visible. If it's fast, they smooth out and disappear. The authors found the point where the surges vanish completely: at that moment, the size of the region covered by entanglement grows exponentially with the scrambling time.
The work connects two extremes: the world of free particles, where entanglement spreads like a wave, and the world of maximal chaos, where any memory of the past is erased almost instantly. It turns out that you can smoothly transition between them just by changing the speed at which the black hole entangles information.
as written by the authors arXiv:2604.26600
We investigate the spreading of entanglement, and entanglement memory effects, in two-dimensional conformal field theory (CFT) propagating on evaporating black hole backgrounds. Memory effects leading to late-time spikes in mutual information for widely separated intervals are well known in CFTs admitting a quasiparticle description. In this work we examine the effect of black hole scrambling on late time mutual information spikes for disjoint intervals in free fermion CFT prepared in a thermofield double state. Late-time entanglement revival is driven by island-induced purification of modes in the union of the intervals. We show across two distinct 2d gravity models, Jackiw-Teitelboim (JT) gravity and the Russo-Susskind-Thorlacius (RST) model, that parametrically dialing up black hole scrambling time smooths out and suppresses entanglement spikes until they disappear at a critical scale, interpolating between free quasiparticle and maximal scrambling pictures. At the critical point, the interval lengths are exponential in black hole scrambling time. We further find a very closely related effect manifest as an entanglement dip for a single interval in a single-sided evaporating RST black hole.
In the quantum world, entanglement doesn't weaken with distance, unlike a radio signal: two particles can fly to the edge of the universe and still remain a single whole.
In Robert Charles Wilson's novel Spin, an alien veil around Earth acts as a giant filter that alters the flow of time — somewhat like how the black hole here filters and quenches quantum memory.