After the Space-Time Cones, I'd like to share the bigger project behind it, the place where all of this geometry lives. 🌌 Have you ever seen the shadow of a four-dimensional shape? We can't see the 4th dimension directly. But we can see its shadows. A 3D cube held under a lamp casts a flat 2D shadow on the table. In the same way, a 4D shape casts a 3D shadow into our world. Flatten that again and you get a 2D pattern. That's what the Geometry Atlas is: a map of those shadows. 👉 https://allistarcenter.com/geometry-atlas.html What's inside Nine interactive models, each one you can rotate, zoom and look inside: 🔷 The six regular 4D polytopes, the 4D "cousins" of the Platonic solids: • the 5-cell, the 4D tetrahedron and the simplest 4D shape • the Tesseract, the 4D cube • the 16-cell, the 4D octahedron • the 24-cell, a shape that exists only in four dimensions, with no 3D equivalent • the 600-cell and the 120-cell, the largest and most complex of all, built entirely on the golden ratio 🔷 The 600-cell and 120-cell merged into one dual pair. A slider lets you grow one inside the other and watch the exact moment they lock together: when the 120-cell is φ times the 600-cell. 🔷 Nested Platonic solids and nested dual shells: tetrahedron, cube, octahedron, icosahedron and dodecahedron sitting inside one another, layer by layer, each touching the next at exact points. How you can explore them 🔄 Rotate in 3D, and on some models even rotate through the 4th dimension and watch the shadow turn itself inside out. 👁️ Look along the symmetry axes: vertex-first, cell-first, edge-first, face on, and 2-, 3-, 4- and 5-fold views. 🎨 Switch each shell on and off to see how the layers build up from the centre. 📏 Read every rod length in millimetres for the size you choose. Each model is also a parts list for building it physically from copper rods and hubs. The orthographic views: where it gets beautiful When you look straight down a symmetry axis, the 3D shadow flattens into an exact 2D pattern: rings within rings, stars within stars. The 600-cell even produces a 30-fold mandala.