Two coherent wave sources create a pattern of alternating bright and dark bands — constructive and destructive interference. This is the experiment that proved light is a wave in 1801 and the principle behind holograms, radio antennas and quantum mechanics.
Each source emits circular waves: η(r,t) = A·sin(kr − ωt)/r. At any point the amplitudes add linearly (principle of superposition). Where crests meet, amplitude doubles; where crest meets trough, cancellation. The resulting pattern of nodal lines follows δ = nλ.
Drag the two sources closer or farther apart. Adjust Frequency to shrink or widen the fringe spacing. Increase Phase shift between sources to shift the pattern. Toggle to a single source to see the radial pattern alone.
Thomas Young's 1801 double-slit experiment was considered 'unpatriotic' in England, as it challenged Newton's corpuscle theory of light. When quantum physicists fired single electrons through two slits 120 years later, the interference pattern still appeared — each electron interferes with itself.