When a light source moves toward you, its waves compress — shortening the wavelength toward the blue end of the spectrum. When it moves away, wavelengths stretch toward red. This is the Doppler effect applied to light, and it's one of astronomy's most powerful tools: redshift tells us galaxies are receding; blueshift reveals approach. In the simulation, particles born at the wormhole's edge glow red (moving away from the exit) and shift through orange, yellow, and cyan to blue-white as they accelerate toward the singularity — a continuous colour-coded velocity map.

Your cursor acts as a gravitational singularity. Mass curves spacetime, and light (modelled here as particle streams) follows that curved geometry rather than travelling straight. The deflection angle scales with how close a particle passes to the singularity — particles nearby are bent sharply; distant ones barely deviate. This replicates the Einstein ring effect seen when a massive galaxy precisely aligns between Earth and a distant quasar, bending the quasar's light into a perfect ring. The cyan glow around your cursor represents the accretion disk — compressed, brightened matter near the event horizon.

The rotating dashed ring around your cursor marks the event horizon — the boundary of no return. Inside this radius, all particle paths curve inward with no escape trajectory. The intense cyan brightness you see at this boundary replicates accretion disk physics: infalling matter compresses and heats to millions of Kelvin, releasing X-ray radiation. In terms of simulation, the brightness boost for particles within 120 pixels of the cursor models this energy concentration, while the lineDashOffset rotation creates the visual impression of an orbiting disk.

In 1935, Einstein and Rosen showed that GR's field equations permit solutions connecting two separate regions of spacetime through a 'bridge' — what we now call a wormhole. The throat of the wormhole (the spiral tunnel you see) connects an entry black hole to an exit white hole. A white hole is the time-reversed counterpart of a black hole: instead of absorbing everything, it expels matter and light. The simulation follows this journey: particles spiral inward through the throat, and after frame 600, the exit white hole expands in a blinding flash — the transition to the nebula field beyond represents emergence into a new region of spacetime.