What is a real hologram, anyway?

The word 'hologram' originally meant something specific: an image reconstructed by interfering coherent light with a recorded interference pattern. Dennis Gabor invented it in 1947 and won a Nobel for it in 1971. By the canonical definition, very little of what is marketed as 'holographic' today actually is.

The most common impostor is Pepper's Ghost — a 19th-century stage trick that uses an angled sheet of glass to reflect a flat image into apparent space. It is the technique behind almost every 'concert hologram' you have seen on the news. It produces a single sightline, requires a darkened venue, and contains no parallax — walk around it and the image collapses.

A second impostor is volumetric LED, where a swept array of LEDs paints an image in a rotating volume. These can be impressive at scale, but they are not holograms in the optical sense — there is no light-field reconstruction, just a high-frame-rate persistence-of-vision trick.

The third — closest to the real thing — is light-field display, where a panel reconstructs the angular distribution of light such that different viewing positions see geometrically correct images. This is what Nexa builds. It is a true holographic display in the sense that the optics matter and the math is correct: the light arriving at the eye is the light that would arrive from a real object.

Why does this matter? Because the difference is the difference between a stunt and a medium. A stunt impresses once; a medium becomes invisible because it works. We are building toward the second category.