Delayed Phase Transition Baby Universe
Our universe may be a baby universe formed inside a primordial black hole during a delayed first-order phase transition.
Looping ambient scene for Black Hole Genesis. A black hole and a Big Bang both involve singularities; perhaps they are two sides of the same event. The collapse of a sufficiently massive object in a parent universe can produce a new expanding region of spacetime, which from the inside looks like our universe began with a Big Bang.
§1 · The claim, in one sentence
Coleman-De Luccia-style bubble nucleation in a supercooled first-order phase transition can produce inflating baby universes that appear externally as super-critical primordial black holes.
§2 · Why it might be true
Cao and collaborators show that if the early universe undergoes a delayed first-order phase transition, bubbles of true vacuum can nucleate and inflate into self-contained baby universes.
From outside, each such bubble appears as a primordial black hole of super-critical mass. Our universe could be the interior of such a bubble, observed as the cosmos we see while existing as a PBH from the parent universe's perspective.
The family stance
A higher-dimensional parent universe existed before ours. Something collapsed in that parent universe, and the gravitational singularity at the center of the resulting black hole became the seed of our universe. We live inside that black hole.
§2.5 · Evidence
- Cao et al. (2025) provide explicit calculations showing the mechanism is consistent with Coleman-De Luccia formalism and produces observationally testable PBH signatures.
§3 · What you'd need to test it
- Super-critical primordial black hole population in parent universes
- Specific gravitational wave signatures from the delayed phase transition that could be detected in cosmological surveys
§4 · Where it breaks
- Requires a specific delayed first-order phase transition in the early universe, which is model-dependent.
- The PBH signatures predicted are at the edge of current observational sensitivity.
Go deeper
Builds on Coleman-De Luccia bubble nucleation formalism from Quantum Vacuum Mechanism family. See arXiv:2505.23007 for the detailed calculation.
The mechanism requires the phase transition to be sufficiently delayed relative to the Hubble rate that supercooling drives the energy density of the false vacuum well above the radiation energy density at nucleation. When this condition holds, bubbles of true vacuum nucleate inside a parent region that is itself still undergoing rapid expansion, and the bubble interior inherits enough vacuum energy to undergo its own inflationary phase before reheating. From outside the bubble, the inflating interior is causally disconnected and gravitationally bound, appearing as a black hole whose Schwarzschild radius exceeds the cosmological horizon at the time of nucleation, hence super-critical. The predicted PBH mass spectrum depends on the nucleation rate and the duration of supercooling, which are set by the shape of the scalar potential driving the transition. LISA and pulsar timing array measurements of the stochastic gravitational wave background from such a transition would constrain these parameters and, if a signal is detected, distinguish this scenario from inflation-driven PBH formation by the spectral shape of the gravitational wave spectrum.
Variants in this family
▸§5 · Who built it, and when(1 source, 1 established)
Also appears in
This variant answers questions in other chapters too. It is canonically housed here.
Up next
Spotted an error? Have a source to add?
Prefer email?
You can also send a prefilled email with the variant URL already filled in.