This simulator emits two light pulses in opposite directions from a single event and then re-expresses those same events in the coordinates of an observer who moves along the same line. Because the Lorentz transformation changes both the distance and the time of each photon event, the moving observer still measures a speed of exactly c for both pulses.
• A 3D scene with the emission event, a right-going photon, a left-going photon, a moving observer and a laboratory coordinate rail measured in light-seconds. • One velocity control for the observer (-0.9c to +0.9c) and an optional toggle for explanatory moving markers. • Live readouts: Lorentz factor, current pulse age in the lab, the right photon's transformed x′ and t′, and the right and left photon speeds divided by c. • Tabs for curves and measurements, two experiments (chase the right pulse at 0.8c, reverse the observer), a model-check bench, a timestamped event log and a short quiz.
The transformation is x′ = γ(x − βct) and t′ = γ(t − βx/c) with γ = 1/√(1 − β²). A photon on the path x = ct therefore has x′ and t′ that shrink by the same factor, so x′/t′ stays equal to c. The left-going photon keeps −c even when the observer moves toward it. The lab shows this directly rather than asking you to assume it.
The model is one-dimensional, inertial and in vacuum. The emission experiment repeats every 4 animation seconds, pulse age resets while overall runtime continues, and the source, observer and distance scales are illustrative. It says nothing about light in glass or other media, where propagation needs additional physics.
Because space and time coordinates transform together under the Lorentz transformation. The photon's distance x′ and time t′ both change by the same factor, so their ratio stays c. The simulator shows x′, t′ and the resulting speed live as you change observer velocity.
γ = 1/√(1 − β²) measures how strongly the two frames' coordinates differ. At β = 0 it is 1 and the frames agree; at β = 0.8 it is 5/3, and the transformed photon coordinates shrink accordingly while the speed stays c.
Its transformed velocity is still −c. Set a negative observer velocity (the Reverse the observer experiment uses −0.8) and the roles of the two light paths swap without changing either speed magnitude.
No. The lab models vacuum light in one dimension only. Light in a medium travels slower than c, and explaining it requires additional physics that this model does not include.