Hot Big Bang
The early hot, dense, expanding thermal phase of our universe. It does not by itself specify what produced that state.
Inflation
A period of accelerated expansion, usually driven in simple models by an energy component with negative pressure.
Reheating
The conversion of inflationary energy into particles and radiation, connecting inflation to the hot Big Bang.
E-fold
A logarithmic measure of expansion. One e-fold multiplies the scale factor by e.
CMB
Cosmic microwave background: relic radiation released when the universe became transparent.
nₛ
Scalar spectral index describing the scale dependence of primordial scalar perturbations.
r
Tensor-to-scalar ratio: the primordial tensor amplitude relative to scalar perturbations.
False vacuum
A metastable local minimum of a field potential that can decay quantum mechanically.
Coleman–De Luccia transition
A semiclassical vacuum-decay process including gravity, described by an Euclidean bounce.
Hawking–Moss transition
A de Sitter vacuum transition associated with the field reaching the top of a potential barrier over a Hubble-scale region.
Eternal inflation
A regime in some models where inflation continues globally because some regions remain inflating while others exit.
Pocket / bubble universe
A reheated or nucleated region with its own local cosmological history inside a larger model-dependent spacetime.
Particle horizon
The largest comoving distance from which signals could have reached an observer since an initial time.
Event horizon
A future causal boundary: beyond it, events can never send a signal that reaches the observer.
Bounce cosmology
A cosmological history where contraction reaches a minimum scale or density and transitions to expansion.
Cyclic cosmology
A class of models with repeated phases of contraction and expansion.
Quantum cosmology
Application of quantum principles to the universe as a whole, often formulated through a wave function and a Hamiltonian constraint.
Wheeler–DeWitt equation
A quantum-gravity constraint equation schematically written ĤΨ=0 in canonical approaches.
Multiverse
An umbrella term. In this project it primarily means a model-dependent ensemble of causally separated cosmic regions or vacua, not simply everything beyond today's telescope horizon.