
Formation and evolution of vacuum bubbles during phase transitions in the early universe.Cosmic bubble nucleation is the process by which vacuum bubbles form and expand during phase transitions in the early universe. In the standard cosmological model, the universe underwent several phase transitions as it cooled, such as the electroweak and QCD transitions. During these events, the universe could have been trapped in a metastable state known as a false vacuum, which then decayed to a lower-energy true vacuum through the quantum-mechanical nucleation of bubbles. These bubbles of true vacuum expanded, collided, and merged, eventually filling all of space and leaving behind the matter and structure we observe today.
The concept was developed in the late 1970s and early 1980s by Sidney Coleman and collaborators, who applied quantum tunneling theory to field theory and cosmology.
The mechanism is analogous to boiling water: the false vacuum is a superheated state, and quantum fluctuations or thermal effects create small bubbles of the stable phase. Once a bubble appears, it expands at nearly the speed of light, converting the surrounding false vacuum into true vacuum. The collision of expanding bubbles releases energy, which can produce particles, gravitational waves, and other observable signatures. The rate of nucleation depends on the energy barrier between the false and true vacua, and on the temperature of the universe at that time.
It is used to model the early universe's evolution, predict gravitational wave backgrounds, and explain the matter-antimatter asymmetry.
The collision of vacuum bubbles in the early universe could have produced gravitational waves that might be detectable by future space-based observatories like LISA.



















