A hologram is a three-dimensional image produced with holographic techniques, which has a physical presence in real space. The term “holography” is used to describe procedures that exploit the wave character of light to achieve a realistic representation. Interference and coherence play an important role here. Colloquially, certain three-dimensional projections are also referred to as holograms. According to Gizmodo, researchers at the University of Sussex have created animated 3D holograms that can not only be seen from any angle, they can also be touched. “The researchers took an approach that was similar to one pioneered by engineers at Utah’s Brigham Young University who used invisible lasers to levitate and manipulate a small particle in mid-air, which was illuminated with RGB lights as it zipped around to create the effect of a 3D image. What’s different with the University of Sussex’s holograms is that instead of lasers, two arrays of ultrasonic transducers generating soundwaves are used to float and control a lightweight polystyrene bead just two millimeters in size.” (Gizmodo, 14 November 2019) A video of the Guardian shows quite impressive examples. Further information is available on the Gizmodo website.