one movie, two worlds — the side you believe you're on decides which direction you see
One movie, two worlds. This is a real 3D simulation of a dotted torus. The dot layout is mirror-symmetric: every dot at ring angle θ has an identical twin at −θ. Because of that, two genuinely different worlds project the exact same movie onto your screen:
· World A — you are above the torus, and it spins clockwise (seen from above).
· World B — you are below it, and it spins counter-clockwise (seen from above).
Both movies are pixel-identical — verified at startup ✓. So the toggle cannot change a single pixel: it only changes which world you believe you're in. One picture, two truths, and your brain silently picks one — that is the illusion.
The red dot is the one dot you can actually track. It crosses the top of its orbit moving rightward. If that top is the far rim (World A), the spin is clockwise; if it is the near rim (World B), the very same motion means counter-clockwise. Click any dot to move the marker and test its orbit.
Resolving the illusion. The solidity slider asks a simple question for every dot: could you see this point if the torus were solid? Dots that the solid body would hide — the back of the tube, the inner walls facing away — fade away. Now the two worlds differ: from above, the red dot survives only along the lower (near) half of its orbit and vanishes behind the solid torus on the upper half; from below it is exactly the opposite — visible above, hidden below. The depth cue adds perspective on top (near dots also grow). Slide both back to 0 and the perfect ambiguity returns.
The central beam. The optional beam is a rod driven through the hole, along the spin axis. It sits exactly on the symmetry axis, so with cues off it too is identical in both worlds — it adds nothing and breaks nothing. But with the torus solid, the body hides the rod's lower stretch when you are above (only its tip re-emerges beneath the torus), and its upper stretch when you are below. Same rod, opposite occlusion — flip the side and the beam tells you instantly which world you are in.
Keys: 1 / 2 world · space pause · R marker · T trail · P path · B beam · click any dot to follow it