Archive for November 13, 2019

Midair holograms! Who knew?

November 13, 2019 2 comments

Sometimes it’s cool to be wrong.

One thing that’s been a longtime pet peeve of mine in science fiction film and television is free-floating midair “holograms” — volumetric (3-dimensional) images made of light that just miraculously appear in midair. Star Wars holograms are a familiar example, but they’re a common trope throughout SF media. But they annoy me because they make no sense. Light can’t just appear in midair. It has to be emitted by something or reflected off of something. Actual holograms, things that literally use the phenomenon called holography, are flat sheets of photographic film encoded with laser light that’s polarized in such a way that you see a different angle on the photographed subject depending on the angle at which you view the sheet, so that a 2-dimensional film image contains 3-D information. But the image is “inside” the sheet rather than floating in midair. And the things sometimes used in the entertainment industry or museums that are called “holograms” are really just flat film images reflected off of half-silvered glass positioned in such a way that they look like ghostly images hovering behind the glass, but are still just flat projections, so the label is a total misnomer. So the sci-fi conceit of a 3-D shape made of light hovering in midair has always seemed silly to me.

But just now, I read about a prototype system that comes pretty close. It’s called the Multimodal Acoustic Trap Display, and you can see it in action here:

Pretty impressive, huh? Now, the light in this display is still reflecting off a solid object, but it’s a small white bead that’s levitated and moved through the projection volume by precision sound waves, so fast that it blurs out and creates persistence of vision, and is illuminated by multicolored laser light as it moves. Together, the moving bead and the shifting colors function sort of like an old cathode-ray TV screen with scan lines, except it can actually create 3-D shapes that hover in midair. The abstract published in Nature cites movie/TV-style “holograms” as the inventors’ inspiration, and they’ve actually come pretty close to duplicating them, allowing for the fact that the image still has to be contained inside a sort of C-shaped box so that it isn’t quite floating free. (The scan lines make it seem very Star Wars-y.) But it’s just the prototype, so who knows how it can be refined over time?

Of course, there still is a physical object (or several, since it can levitate multiple beads) that the light is reflecting off of, but because it’s just one or a few tiny beads swooping around really fast, most of the volume actually is empty space, with the perception of a continuous shape resulting from persistence of vision. So this is probably just about as close to the standard intangible, free-floating sci-fi “hologram” as we’re likely to get, allowing for further refinements like maybe a system that uses more and smaller beads. I’ve read before that there are some volumetric displays that project light off of a mist of fine particles, but that doesn’t seem to have the same degree of control as this, though maybe it and the acoustic-trap technology could be merged somehow. Anyway, because the beads are constantly moving around and their positions are controlled by the acoustic waves, someone could wave their hand through such a hologram or walk through it, and as long as they didn’t knock out the beads directly, they could just pass through the image without doing more than briefly disrupting it, as often shown in fiction.

So I now have to rethink my contempt for floaty midair holograms as a sci-fi trope. There would still have to be some physical object there for the light to bounce off, and it would still probably have to be confined within some kind of projector stage rather than moving freely through an area like the holograms in a lot of sci-fi (including Star Trek: Discovery). But to an extent, many of the floaty holos in sci-fi are at least somewhat more credible now. Who knows? Ryuji Hirayama and the other developers of this device have solved a number of the engineering problems that I was skeptical could be solved, so maybe they can solve others. So we may see more realistic and versatile volumetric projections in the future (and I guess we’re stuck with them being called “holograms” even though they’re nothing of the kind).

Which means that maybe I should be more open to incorporating translucent midair holos into my own SF writing, rather than going for alternatives like soligrams (shapeshifting smart-matter gel that morphs into solid lifelike objects) or the anamorphic projections I featured in “Murder on the Cislunar Railroad.” Although I rather like avoiding the standard cliches in my writing. But if science makes those cliches real, then continuing to avoid them would be…

(puts on sunglasses)

…a holo gesture.

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