Relativity Hangar
Walk slowly. Cruise near light speed. Look at the same room differently.
Drag to look · Slider cruises along the hangar · WASD walks · Arrows look · Space stops · Home faces forward
Ready. The four wall clocks are synchronized in the hangar frame.
Description
A polka-dot hangar, eight solid blocks, four synchronized wall clocks, and your own clock. Move from −0.90c to +0.90c and look around to explore relativistic Doppler shifts, aberration of light, light-travel delay, time dilation, and length contraction. The hangar is 200 model units across in either horizontal direction, with c = 10 units/second: light takes exactly 20 hangar seconds to cross it wall-to-wall.
Instructions
- Slide to cruise. Positive speed travels along the room’s forward axis; negative speed goes backward along that same axis. Dragging changes where you look without steering your cruise, so you can compare the forward, side, and rear views at the same velocity.
- Walk and look. WASD walks at 0.03c relative to your look direction. Arrow keys look around. Combined walking and cruise speed is capped at 0.90c. Home looks forward; Space or Stop brakes. Walls and blocks brake you automatically. Dragging works on touchscreens too.
- Watch the clocks. Each wall has a giant millisecond-resolution readout. Your clock records your accumulated proper time. One real-time second advances one hangar second; your own clock advances more slowly while you move.
- Compare the two views. “Optical image” shows light arriving at your eyes now, with aberration, spectral color shifts, and delayed wall-clock readings. Click it for “Measured geometry,” a simultaneous slice in your current inertial frame: lengths contract along your velocity, colors stay at rest, and wall-clock readings show relativity of simultaneity. This second view is a coordinate construction, not a photograph.
- Pause to inspect. The pause button freezes time and position while you drag, change speed, or compare views. P pauses, V switches views, and R resets while the canvas is focused. The curved-arrow button resets the room, clocks, and camera.
Why clocks can look faster
Approaching a clock brings its light signals closer together; receding spreads them apart. That optical Doppler effect combines with time dilation. A clock you are approaching can therefore look faster even though moving clocks run slower in a simultaneous frame comparison. In measured geometry at constant velocity, each fixed wall clock advances at 1/γ of your own proper-time rate. Changing velocity changes which distant events count as simultaneous, so those coordinate readings can jump.
Why blocks do not simply flatten
Measured length contraction and visual appearance are different. The optical view traces rays through the exact instantaneous special-relativistic aberration transform before intersecting the stationary room and blocks. Their apparent deformation comes from that geometry; the game does not animate a fake stretch on individual meshes. The measured view instead contracts all room geometry along your velocity by 1/γ.
What happens at 0.90c
At 0.90c, γ ≈ 2.294 and longitudinal measured lengths are about 43.6% of their rest lengths. Light directly ahead is shifted up in frequency by about 4.36×; light directly behind is shifted down to about 0.229×. Some colored dots become dark because their modeled emission shifts outside the visible band. Bright surfaces may wash out under the display’s fixed exposure.
A small experimental universe
The room and all eight blocks remain at rest in one flat-spacetime frame. Speed changes are idealized instantaneous boosts; gravity, acceleration forces, material strain, and biological effects are omitted. At boundaries, automatic braking keeps the observer outside solid geometry. Time pauses while this page is hidden.
Rendering and clock assumptions
This is a 3D ray tracer with a GPU path and a bounded software fallback, so it also works without WebGL. Geometry uses an instantaneous Lorentz boost for each ray. Colors are integrated over modeled spectra rather than hue-shifted RGB: the dots use narrow Gaussian emission bands, while neutral surfaces and clock segments use a 6500 K thermal spectrum. Spectral radiance transforms as I′λ(λ) = D⁵ Iλ(Dλ). Approximate CIE color matching, an sRGB display, a finite spectral lookup table, and tone mapping limit color and brightness precision. These are idealized emitting materials, not a prediction for arbitrary real-world paint.
The giant displays magnify four point clocks located at the centers of the walls for legibility. Each readout shows that point clock’s retarded emission time in optical view, or its simultaneous time in measured view. The face of a giant clock is not itself simulated as many separate, independently delayed emitters. Milliseconds are display granularity; animation is limited by the browser’s frame rate. Static surface positions do not change with emission time. There are no reflections or multiple light paths.
Background: visual observations in high-speed flight; relativistic aberration and optical distortion; length contraction.