It isn't unknown, and it isn't new. Isaac Newton got interested in light after buying a prism at a county fair. Seperation of white light into colors by a prism depends on the same effect: a frequency-dependent speed of propogation of light through some materials. Many devices in wireless technology (example: SAW filters) depend on the same type of phenomenon; light and radio are both EM waves (photons).
That’s not what I’m being skeptical about. It’s easier to believe that they’ve set up the experiment in such a way as to elicit a new behavior from photons rather than believe they’ve actually created a pocket of static time in the universe.
It’s possible, but I won’t believe it until a couple other labs have reproduced and confirmed the finding.
It’s an incredible claim and that requires some serious proof.