That Tupac hologram? It wasn't
The 'hologram' that allowed murdered rapper Tupac Shakur to steal the show at the Coachella music festival was a mere theatre trick that has existed for over 150 years.
Snoop Dogg and Dr Dre wowed the crowd as they danced and sung alongside their fallen friend last week with what was described by the projection company responsible for the stunt, AV Concepts, as holographic technology.
However, Dr Lincoln Turner of the Monash University School of Physics reveals that Tupac actually appeared via common stage-craft known as 'Pepper's Ghost'.
This illusion involves an image being projected onto a transparent sheet, known as mylar film, using high-definition video projectors, which are reflected off mirrors below the stage. As long as the stage lighting carefully avoided the plastic film, spectators were unaware that they were watching Snoop Dogg and Dr Dre through a screen.
"Tupac had as much depth as any other 2D projection - none - and the illusion only worked because the audience was too far back to see this," said Turner.
"Everything else on their website has 'holographic' splashed all over it ... they were certainly under no illusions as to how the thing actually works," Turner said.
The distinction between this illusion and real holography is that a projection will record an image, whereas a hologram will record the full wavefield of light falling upon it.
Similarly, a 3D TV merely creates the illusion of depth but lacks 'parallax' - the apparent difference of an object when observed from different viewpoints.
"Deep down your brain knows that it's getting a pretty cheesy illusion ... In a hologram, as in real life, what you see depends on where you look from," said Turner.
So why opt for a cheap trick instead of the real thing?
Holographic technology is still extremely expensive and data-intensive, despite having existed in labs and in science-fiction since the early 1960s.
"The technology works very well, but we haven't yet worked out how to build it into our digital world," said Turner.
The most obvious use for holographic technology in the future is for video calls. "Eventually it would be indistinguishable from being there," said Turner.
However, a single holographic video call on a one-square-metre portal would require a data rate of approximately 200 terabits per second.
The current world record for data transfer speed is 109 terabits per second over a single fibre optic cable, held by the National Institute of Information and Communications in Tokyo. This kind of speed is obviously extremely uncommon and still only half the speed required for a holographic video call.
But the future is not all bleak according to Turner.
"There's little doubt that as bandwidth expands, technologies such as holography will be there to make great use of it".
- Sydney Morning Herald