Indexing the archive…
Your Universe of Digital Possibilities
Light from a hidden scene meets a reference wave on a flat plate, and the plate records only where the two add and cancel — fringes. Dennis Gabor called it the whole picture (1948): the phase of the light is in the fringes, so the plate can be refocused, after the fact, to any depth. The rebuild is handed the plate and nothing else; it finds every point at its depth, a twin it cannot always shake off, and a scene that survives in every fragment of the plate. Turn around when it has finished looking.
A plate records intensity only, but the cross term R*O carries the object wave’s phase, written into the spacing of the fringes. Its conjugate RO* — the twin — is recorded too. In-line the two share every spatial frequency; tilt the reference and they part.
A field is a sum of plane waves — its 2-D spectrum — and each plane wave advances by a known phase. Multiply, transform back, and the field is anywhere you like: run z negative and a plate refocuses to any depth of the scene that lit it.
The near-axis limit of the same propagation: every point of the plate sends a spherical wavelet, approximated as a parabola. It is why one point’s hologram is a zone plate — rings that crowd outward — and why a small piece of plate still holds the point.
The Orfeo Edition’s fourth shadow is the one that keeps the phase. Where The Phase had to infer it from intensities alone, a hologram writes it down by interference — and pays with a twin: the conjugate wave rides in the same record, inseparable in-line, separable only by tilting the reference. The rebuild is blind as ever (the plate, the wavelength, the reference), the best-focus depths are the only numbers it can know, and the depth errors wait behind the veil. The fringes themselves are The Slit’s, and the waves they are made of are The Wavefunction’s.