The early Universe was hot and dense. Within it, like in boiling water, bubbles of a new state of space were born. Usually they are considered simple, but some harbored a gigantic number of hidden 'patterns' — microscopic states, or entropy. It’s like a soap bubble whose surface shimmers not with seven colors, but with billions of shades.
When such bubbles collide, their entanglement does not vanish instantly but instead alters the merger process. This imprints on gravitational waves — ripples in spacetime. Unlike the merger of black holes, where information seemingly disappears, bubbles leave a distinct quantum signature in the waves — an echo of their 'multitude'.
Future detectors, similar to the one created by Rainer Weiss, will be able to capture these signals. Thus we will peer for the first time into the quantum 'personality' of space.
as written by the authors arXiv:2512.13947
Vacuum bubbles, formed in first order phase transitions, have important implications for cosmology. In particular, they source gravitational waves. Usually, it is assumed that, once bubbles are materialized, their state, further evolution and mergers are well-described classically. This paper will show that this intuition breaks down for bubbles which possess high microstate degeneracy. This is generic when the phase transition breaks spontaneously a symmetry. First, the degeneracy enhances the transition rate. Furthermore, the internal quantum state of the bubbles profoundly affects the classical dynamics of their mergers. A bubble, no matter how macroscopic, is born in a maximally entangled quantum state. This state can be viewed as a symmetric superposition of many different would-be classical bubbles. The inner entanglement is largely maintained up until their mergers. The resulting true quantum dynamics of the merger is macroscopically different from any type of classical mergers. These differences are imprinted as macroscopic features in the resulting classical gravitational waves. In this way, the inner microstate entanglement of merging bubbles provides a qualitatively new source of gravitational waves. This phenomenon is quantified and compared with the swift memory burden effect in black hole mergers.
Each bubble was born at once in all possible states — as if a tossed coin landed both heads and tails simultaneously. The complexity of each bubble was astronomical: the number of its microstates exceeds the number of atoms in the observable Universe.
Sci-fi often plays with the theme of multiple universes, but here the 'bubble universes' are also quantum-entangled — as if they share a common memory of the moment of creation.