OPEN STUDY GUIDE · BISWAJIT JANA · 2026
Multiverse cosmology, from the hot Big Bang to the hardest open questions.
This curriculum is designed to be read in order. Every chapter asks the same five questions: what is it, why is it needed, how does it work, what can we observe, and what is still unknown?
Recommended learning path
CHAPTER 01
What is the multiverse — scientifically?
A beginner-friendly scientific guide to the multiverse: observable universe, inflationary pockets, vacuum landscapes, many-worlds distinctions, evidence limits, and open questions.
CHAPTER 02
Big Bang → inflation → reheating: what is each stage?
Understand the difference between the hot Big Bang, cosmic inflation and reheating, with equations, physical intuition, observational links and open questions.
CHAPTER 03
How does the CMB test inflation?
How the cosmic microwave background tests inflation: temperature and polarization spectra, acoustic peaks, scalar spectral index, tensor-to-scalar ratio and current limits.
CHAPTER 04
How can eternal inflation produce a multiverse?
A scientific explanation of eternal inflation, stochastic self-reproduction, pocket universes, measure problems, evidence limits and what is still unknown.
CHAPTER 05
What is a bubble universe in field theory?
Learn the field theory behind bubble-universe language: metastable vacua, Coleman–De Luccia tunnelling, Hawking–Moss transitions and what is model-dependent.
CHAPTER 06
What alternatives exist to an inflationary prehistory?
Compare nonsingular bounce cosmology, cyclic models and quantum cosmology with inflation: equations, goals, observational tests and unresolved problems.
CHAPTER 07
Is there an “outside” the universe?
What 'outside the universe' means in cosmology: observable horizons, the whole universe, bubble embeddings, extra dimensions, brane models and evidence limits.
REFERENCE
Glossary of multiverse cosmology
Plain-language definitions for inflation, reheating, horizon, vacuum decay, pocket universe, nₛ, r and more.
How to use this project
Start with the definitions page if the word multiverse itself is unclear. Then follow the physical chain from hot Big Bang → inflation → reheating → primordial perturbations → CMB constraints. Only after that move into eternal inflation, vacuum decay and pocket universes. This ordering keeps directly measured cosmology separate from increasingly model-dependent extrapolation.