Citizens in the Chinese cities of Jiangxi and Foshan looked up into the sky earlier this month and saw what looked like a "floating city," local news outlets reported.
Here's some (sort of questionable) footage of the phenomenon that's being passed around on Facebook, from China's state-run CCTV:
If the video is real, IFL Science weighed in with probably the most realistic explanation of the phenomenon: that it's a type of mirage called a Fata Morgana, which is caused by rays of light essentially being bent in different directions when they hit layers of the atmosphere that are different temperatures and densities. Wired explains why that can translate as freaky ships floating in mid-air or, in this case what looks like a city in the sky:
But your brain places the object where it would be if the light came to you in a straight path—higher than it actually is. This bending effect can even work with the curvature of the Earth if conditions are just right, which is why some fata morgana images can actually be refracted cities and ships from beyond the horizon.
CCTV said their consultations with meteorologists suggest the video isn't real, because the weather conditions in the region at the time weren't conducive to producing a Fata Morgana.
But these explanations, obviously, have nothing on the speculation that's been unleashed online, which consist of everything from cross-dimentional vortexes and parallel universes to something called Project Blue Beam, a conspiracy theory which, I gather, involves NASA and the Illuminati:
"I have a radical theory about it," wrote one Facebook expert. "In quantum theory, the future determines the past so this sighting just ahead of our LHC experiment to find parallel Universes seem kinda connected to me. If I am correct then we /will/ find evidence of parallel reality and perhaps even make contact. Let's see."
"Project bluebeam is happening in china already, it was all over their news. I'm pretty sure that was just a test. They're gonna use this 3d projection technology to fake the second coming of christ and an alien invasion and this was the beggining of it," wrote another commenter on Facebook.
Another commenter, who called himself a "healthy skeptic" wrote, "Not saying it's definitely a cross dimensional vortex, but that explanation sounds only slightly more plausible than something about swamp gas reflecting the light from Venus."