I built **Spacetime Lab**, an open-source platform for exploring
exact solutions of General Relativity in the browser, ranging from
the Schwarzschild horizon to the modern resolution of the Hawking
information paradox via the island formula.
**Live:** https://spacetime-lab.vercel.app
**Code (MIT):** https://github.com/christianescamilla15-cell/spacetime-lab
Each of the seven physics pages corresponds to a pip-installable
Python module, with shared conventions (Lorentzian (-,+,+,+), Wald;
geometric units; LaTeX paired with every numerical result). The
canonical results are pinned by a 690+ pytest suite at machine
precision against literature values (Wald, MTW, Brown-Henneaux 1986,
Strominger 1998, Bardeen-Press-Teukolsky 1972, Page 1976,
Hartman-Maldacena 2013).
**Pages currently live:**
* Schwarzschild — sliders for M, V_eff for circular orbits, ISCO,
photon sphere, Hawking T
* Kerr — (M, a/M); ergosphere splits from horizon, ISCO into
prograde/retrograde branches, third-law T → 0 at extremality
* Reissner-Nordström — (M, |Q|/M); cosmic censorship enforced;
closed-form horizons + photon sphere; numerical ISCO
* Kerr-Newman — three-parameter (M, a, Q); all three limits cross-
checked bit-exactly; ISCO via numerical R = R' = R'' = 0
* BTZ — Strominger-Cardy match recomputed client-side and gated
* AdS — implicit (used by holography page)
* de Sitter — Λ-only, static patch, Gibbons-Hawking T
* Geodesic explorer — Three.js Kerr scene, multiple simultaneous
trajectories, click-pick on equatorial disk, conservation panel
* Penrose diagrams — Minkowski + Schwarzschild four-region; pan/zoom
* Holography — Page curves (eternal BTZ + evaporating Schwarzschild)
side by side
**What's explicitly NOT in v3.2** (specs in `docs/` for each):
* Real LIGO ringdown inference (deferred — needs Bilby + GWOSC + endorser)
* Full FLRW with arbitrary equation of state (deferred — Friedmann ODE)
* HRT (covariant Ryu-Takayanagi) for time-dependent backgrounds
The arXiv preprint draft is in `docs/arxiv-draft.md`. Feedback,
"your physics is wrong here" reports, and PRs all welcome.
(Backend is on Render free tier so the first request after idle
takes 30-60 s to spin up.)