From ripples to the cosmic web
From ripples to the cosmic web
Uneven gravitational acceleration stretches and compresses an expanding matter distribution. Follow the first folds, the updated mesh gravity and a saved small wave that you can integrate independently.
L1
How Gravity Builds the Cosmic Web
Follow a patch of matter as unequal compression builds sheets and filaments, then see why crossing streams need both position and velocity.
L2
Measuring Motion with an Expanding Ruler
Separate cosmic expansion from peculiar motion, then convert comoving positions and canonical momenta into distances and velocities.
L2
Why One Position Can Have Several Velocities
Find the first fold in a labelled matter map, calculate its density growth, then count the positive contributions of overlapping streams.
L2
How Mesh Gravity Follows Folding Matter
Follow mass assignment, Fourier gravity and symmetric time stepping to see which forces a finite mesh retains and which structures it smooths.
L3
What a Power Spectrum Remembers
Compute long-wave power from particle phases, test EdS growth and see how different spatial patterns can have the same power.
L3
Give an Exported Initial State to Another Integrator
Independently integrate a full-precision small-wave export in Python, measure particle power and separate time error from finite-grid growth bias.
L4
Choose What You Call a Halo, Then Read Feedback
Use halo definitions and TNG units to read resolution tests, baryonic power responses and residuals in a 2026 feedback preprint.
Run an independent trajectory
Download Python, the exact example and expected results (33189 B)
NumPy and SciPy integrate the exact exported small-wave initial state to its saved epoch. The ZIP contains no browser Engine or TNG data. Python 3.12.12, NumPy 2.3.5 and SciPy 1.17.1 were used for the fresh extracted replay.
SHA-256 and example origin
9334aacf0036834af4e08d102f05e7fa096c71a1ce91b66b8f80b52f6db7c673
The example came from actual Node execution of the frozen model and canonical current-state serializer; it is not a claimed browser download. The guide explains how to substitute your own current-state JSON.
Sources and calculation scope
- Zel’dovich (1970), Gravitational instability: an approximate theory for large density perturbations
All six original pages read. Physical displacement in the original notation is distinguished from modern comoving growth and canonical momentum. We use the pre-crossing map; its discussion of gas shocks is not applied to collisionless matter. The hosted paper remains external.
- Bond, Kofman & Pogosyan, How filaments are woven into the cosmic web (1996), astro-ph/9512141v1
Main text, captions and original Figure 1 inspected. Initial density/tidal correlations organise a network whose contrast nonlinear evolution sharpens. Local first-caustic flattening does not establish a universal sequence in which an entire network first becomes pancakes. Our figure uses our own PM outputs.
- Springel (2005), The cosmological simulation code GADGET-2, astro-ph/0505010v1
Focused reading: Section 2.1, equations 1–3; Section 3.2/3.2.1, equations 20–23; Section 4.1, equations 26–31, with original pages 3 and 11 viewed. Supplies cosmological momentum, PM windows and time-integration context. The teaching calculation specifies its own cutoff and finite gradient and adds no short-range tree force.
- Springel et al., First results from IllustrisTNG: matter and galaxy clustering (2018), arXiv:1707.03397v2
Fixed v2: Methods 2.1–2.2 and original Figures 5–7 read. Figure 6 compares resolution and Figure 7 full-physics/DMO power; the response axes use natural logarithms. Ordered-particle shot-noise limits are discussed in Section 2.2. We inspect published methods and figures, without reproducing TNG runs or downloading snapshots.
- IllustrisTNG official data specifications
Header MassTable, dark matter Coordinates/Velocities and group spherical-overdensity definitions checked on 12 November 2026. Snapshot and group velocity conventions differ; each field needs its own conversion. Numerical unit exercises use hypothetical values, not extracted particles. No TNG data or original assets are redistributed.
- Zhang, Baryonic feedback suppression of the matter power spectrum (2026), arXiv:2609.00807v1
Submitted 1 September 2026; version labelled for submission to JCAP at the 12 November reading. Focused sections 2–5, Figures 1–4 and Table 1 inspected in the actual PDF/primary HTML. Absolute response residuals, single-/three-parameter differences and the low-matter-density stress exception are retained. No independent reproduction or demonstrated weak-lensing posterior is claimed.
- SciPy solve_ivp official reference and installed 1.17.1 documentation
DOP853, tolerances and returned success information checked. The live manual was 1.18.0 when read; the actual replay uses pinned 1.17.1, whose installed solve_ivp documentation and source were separately read. The replay receipts report its real package versions.
- Original finite-mesh calculations and independent small-wave Python replay
Original accepted kernel/linear, nonlinear and five-preset F64 calculations support the teaching figures and calibration. This small public ZIP contains only an exact current-state small-wave fixture, an independent NumPy/SciPy trajectory replay and expected output. The fixture was generated through the frozen model and canonical serializer in Node, not downloaded in a browser. Large raw preset archives remain separately retained; no Engine or source paper is included.