Link?

The basic physics is, there is no known way to project a hologram pixel (as in, a point that looks different from different angles) in mid air without some solid substrate.

Closest approach so far has been projecting voxels on smoke or water mist, that look the same from all angles.

Both of these approaches have been integrated with touch response, yet they still fail the fundamental part of "free standing hologram".

It gets even more pathetic when someone calls "hologram" a 3D model projected onto a 2D display (cough EuroVision 2024 cough).