Here's the link: https://sciencebulletin.org/researchers-develop-way-to-control-speed-of-light-send-it-backward/

Here's the line that makes no sense to me: Abouraddy and study co-author Esat Kondakci demonstrated they could speed a pulse of light up to 30 times the speed of light...

Need some help on this one.


You're right, it makes no sense.

It's bad reporting, and I'd go so far as to say that the researchers involved failed to make it clear that what they demonstrated was not a way to make anything actually go faster than $c$. What they showed is crudely analogous to standing on the Earth and zig-zagging a laser beam back and forth across the moon a few hundred times per second. Sure, the point where the beam illuminates the moon moves some tens of times faster than $c$. But nothing is conveyed from point A to point B on the moon in that scenario. Instead, light is conveyed from the laser on Earth to point A and to point B. Make light travel backwards? Easy: just sweep the laser from B to A.

In the paper, the authors do say "The group velocity here is the speed of the wave packet central spatio-temporal intensity peak, whereas the wave packet energy remains spread over its entire spatio-temporal extent.". Their definition would equally well describe a laser spot flying across the Moon. It definitely does not describe a situation where energy flows from point A to point B.


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