EARLY-UNIVERSE COSMOLOGY · OPEN RESEARCH NOTEBOOK · 2026

What happened before the hot Big Bang?

I work backwards from the relics we can measure — the microwave background, primordial perturbations and large-scale structure — and ask which earlier histories can actually generate them.

WORKING SYNTHESIS Inflation → reheating

The strongest end-to-end bridge implemented in this project between a pre-hot state and the hot, structured universe we observe. This is a working scientific synthesis, not proof of a unique beginning or of a multiverse.

Start the study guide Open data observatory

Biswajit Jana Equations + simulations Planck · ACT · SPT · SPT-3G

Conceptual visualization of luminous bubble universes in an inflating background

OBSERVEDCMB + structure CALCULATEDn_s, r, a(t), reheating OPENInitial-state selection

MODEL CHAINpre-hot → inflation → reheating

OBSERVATIONAL BRIDGECMB → LSS → parameter constraints

MULTIVERSE STATUSmodel-dependent · not directly observed

THE PHYSICAL STORY

Start with what survived. Reconstruct what could have come before.

The narrative is deliberately ordered from measured relics back toward progressively more model-dependent physics.

The standard hot-Big-Bang model begins with an already hot, dense, expanding state. The sharper problem is therefore: what physical process can generate that state and still leave the relics we measure today?

Inflation supplies accelerated expansion. Quantum fluctuations become curvature perturbations. Reheating transfers energy into particles and radiation. The calculation then enters the thermal history tested by the CMB.

OBSERVEDCMB, expansion, structure

CALCULATEDa(t), n_s, r, reheating

MODEL-DEPENDENTEternal inflation

OPENWhy this initial state?

Notebook-style scientific sketch showing inflation, reheating, hot Big Bang, CMB and structure formation — Inflation → reheating → hot Big Bang → CMB → structure.

Scientific visualization connecting primordial fluctuations in the CMB to the cosmic web — Primordial fluctuations seed later structure: the bridge that makes early-universe theory testable.

COSMOLOGY DATA OBSERVATORY

CMB power spectra across multiple experiments, with live residual diagnostics.

The data interface loads NASA/LAMBDA plotting tables for TT, TE, EE, gravitational lensing and B-mode measurements. Measured data, numerical calculations and conceptual illustrations are kept visibly separate.

ROWS LOADED—

EXPERIMENTS—

ℓ RANGE—

SOURCENASA/LAMBDA

TT: CMB-only temperature bandpowers. Residuals are standardized against a smoothed Planck reference for visual consistency checks; they are not likelihood residuals.

Connecting to NASA/LAMBDA…

INFLATION MODEL ↔ DATA LAB

Move the e-fold count and watch model predictions move through n_s–r space.

Number of e-folds N = 60

Quadratic φ²

Starobinsky plateau

Compressed benchmark used in this project: n_s ≈ 0.9682 ± 0.0032 and r < 0.034. This panel is a transparent first-order model diagnostic, not a full MCMC parameter inference.

Illustrated scientific constraints plot in scalar spectral index versus tensor-to-scalar ratio space — **Illustrative constraint map.** The interactive canvas above is the quantitative site calculation.

Scientific infographic showing observational probes for testing the earliest universe — Observational roadmap: polarization, large-scale structure, 21-cm cosmology and gravitational waves.

COMPETING HISTORIES

“Before” is not one theory.

Inflationary extension, bounce/cyclic histories and quantum-boundary proposals answer different questions and carry different assumptions.

01 · WORKING LEAD

Inflation + reheating

Accelerated expansion followed by transfer of energy into radiation. It supplies a physical route into the hot Big Bang and observable perturbations.

nₛ ≃ 1 − 6εᵥ + 2ηᵥ · r ≃ 16εᵥ

02 · ALTERNATIVE

Nonsingular bounce

A contracting phase reaches a finite-density turnaround. The difficult tests are high-density completion, perturbation stability and distinctive signatures.

H² ∝ ρ(1 − ρ/ρc)

03 · ALTERNATIVE

Cyclic cosmology

Repeated contraction and expansion can replace an absolute classical beginning, but entropy and transition physics must remain controlled.

a(t): contraction → transition → expansion

04 · QUANTUM BOUNDARY

Quantum cosmology

No-boundary and tunnelling proposals replace an ordinary earlier classical phase with a quantum boundary prescription.

ĤΨ = 0

Four early-universe model paths — Four broad origin paths considered in the research framework.

Scientific comparison of inflation, bounce, cyclic and quantum cosmology — Model comparison: mechanisms, observables and unresolved physics.

Triptych comparing inflationary extension, bounce and cyclic cosmology — Three classical-history interpretations of “before”.

FALSE VACUUM → BUBBLE INTERIOR

If bubbles matter, the tunnelling calculation comes first.

The project treats bubble universes as field-theory objects: specify a potential, solve the Euclidean problem, estimate the action, then ask what happens inside the nucleated region.

False-vacuum decay and bubble nucleation — False-vacuum decay: a semiclassical transition, not decorative bubble art.

Conceptual landscape of vacuum states — Vacuum landscape: model-dependent theory space, not a map of observed universes.

Evolution inside one bubble universe — Inside one bubble: nucleation → reheating → thermal history → structure.

SEMICLASSICAL NUCLEATION Γ / V ∼ A e^−B/ℏ

The repository implements thin-wall, Hawking–Moss and Euclidean trajectory diagnostics as controlled toy calculations.

CAUSAL STRUCTURE

“Outside our universe” is not automatically a meaningful coordinate.

Ordinary FLRW cosmology can contain regions beyond our present particle horizon without those regions being separate universes. Eternal-inflation “pockets” are a different, model-dependent construction.

χ_p(t) = c ∫ dt′ / a(t′)

A horizon is a causal boundary, not a material shell.

Nested cosmological horizons and model-dependent pocket universes — Observable region, causal horizons and a model-dependent inflating background.

WHERE THE MULTIVERSE ENTERS

A conditional consequence of some dynamics — not the starting assumption.

Some inflationary potentials can enter a stochastic self-reproduction regime. Local regions may reheat while other regions continue inflating.

Conceptual illustration exploring a many-universe analogy — **Author analogy:** Earth turned out to be one world among many; the project asks whether “our universe among many” can be a useful theoretical analogy while keeping analogy and evidence separate.

ℛ_EI ≃ 3H³ / (2π|V_,φ|)

When this local diagnostic exceeds unity in a suitable part of field space, stochastic fluctuations can dominate classical drift. Eternal inflation may then occur in that model.

Evidence boundaryNo other pocket universe has been directly observed. There is no astronomical coordinate pointing to a confirmed external universe.

Observable universe within a larger model-dependent multiverse perspective — Observed, extrapolated and model-dependent layers separated explicitly.

Close visualization of bubble universes in an inflating background — Conceptual close-up — not observational evidence.

EVIDENCE LEDGER

Keep the extrapolation visible.

OBSERVED

CMB anisotropies, cosmic expansion and large-scale structure in our observable universe.

CALCULATED

Stochastic self-reproduction criteria can be evaluated for specified inflationary potentials.

MODEL-DEPENDENT

Causally separated reheating regions or vacuum bubbles can arise in particular eternal-inflation constructions.

NOT OBSERVED

No second universe or external pocket has been directly detected.

Speculative higher-dimensional perspective outside a bubble universe

COULD THERE BE AN “OUTSIDE” PERSPECTIVE?

A useful speculative question, but standard cosmology does not give the whole universe an ordinary outside.

Some higher-dimensional or brane constructions embed lower-dimensional spacetimes in a larger mathematical geometry. That can make an external embedding meaningful inside a specific theory.

It does not imply literal beings outside our universe, nor does current evidence establish an external observing vantage point.

SPECULATIVE / MODEL-DEPENDENT

THE LONG HORIZON

The future of a universe is also a causal-structure problem.

Accelerating expansion changes what remains observable, how information is partitioned by horizons, and which regions can ever communicate.

01CMB polarization and tensors 02Non-Gaussianity and primordial features 03Large-scale structure and 21-cm cosmology 04Stochastic gravitational-wave backgrounds

Conceptual far future of a bubble universe and its horizons — Far-future causal structure in an accelerating bubble universe.

STUDY THE SUBJECT · FROM BEGINNER TO RESEARCH LEVEL

Learn multiverse cosmology in the order the physics actually connects.

This project now has a searchable study layer as well as the visual research story. Each guide starts with the plain-language question, then moves through the mechanism, equations, observational status and what is still unknown.

01FOUNDATIONS

Big Bang → inflation → reheating

What the hot Big Bang actually says, why inflation is introduced, and how reheating creates a hot particle-filled universe.

02OBSERVATIONS

CMB evidence & inflation tests

Acoustic peaks, polarization, primordial perturbations, nₛ, r, and what the data can — and cannot — establish.

03MULTIVERSE

Eternal inflation & bubble universes

How self-reproduction can arise in some potentials, what a pocket universe means, and why this remains model-dependent.

04FIELD THEORY

Vacuum decay & bubble nucleation

Coleman–De Luccia tunnelling, Hawking–Moss transitions, vacuum landscapes and the physics behind “bubble universe” language.

05ALTERNATIVES

Bounce, cyclic & quantum cosmology

What alternatives to a simple inflationary extension try to solve, their equations, and the empirical problems they must face.

06CAUSAL STRUCTURE

Horizons and “outside the universe”

Observable universe versus whole universe, particle and event horizons, extra dimensions, and what “outside” can mean mathematically.

Want the complete path?Open the full curriculum with equations, glossary, references and chapter order.

Open the Multiverse Study Guide ↗

LONG-FORM RESEARCH REPORT

A chapter-by-chapter LaTeX monograph.

The report expands the website into a readable research narrative: first the hot Big Bang, then inflation, quantum fluctuations, reheating, CMB evidence, model discrimination, vacuum decay, horizons, bounce/cyclic alternatives, quantum cosmology, the multiverse branch and the higher-dimensional “outside” question.

18 chapters 20 conceptual figures equations with layman explanations primary literature cited throughout

Read the monograph PDF ↗ Read as web chapters ↗ LaTeX source ↗

Infographic showing how observations can test the earliest universe — Evidence roadmap used in the long-form report: CMB polarization, large-scale structure, 21-cm cosmology and gravitational waves.

AUTHOR'S SYNTHESIS · 2026 If I compress the investigation to one word: INFLATION followed by reheating

The deeper frontier — what selected the inflating state, and whether its global completion contains other universes — remains open.

Nine research questions ↗ Integrated report ↗

DATA + PRIMARY LITERATURE

01NASA LAMBDATT, TE, EE, lensing and B-mode plotting data 02Planck 2018 XInflation constraints 03Inflation at the End of 2025Current nₛ and r synthesis used by the project 04ACT DR6Public analysis notebooks