Darkness can "travel" faster than light speed
nature.com
nature.com
How can such a thing be detected? And without detection how can speed be measured?
- if you can measure the 'optical singularities' travelling FTL, then surely 'information' is travelling FTL?
- does it matter (i.e. violate relativity) if something is travelling faster than light speed in some medium as long as it doesn't travel faster than light in vacuum?
> if you can measure the 'optical singularities' travelling FTL, then surely 'information' is travelling FTL?
Information is not traveling FTL.
The canonical example is when you have a lighthouse in the middle of a huge circular wall. The light spot may move faster than light when you see it on the wall, but the info moves from the center to the wall, not along the wall.
When the singularities are far away, you can treat them like a single entity, and track the anti-peak and measure it's speed and they will move like 1/100 of the speed of light in this case.
When the singularities are very close together the anti-peak may move at a faster speed (FTL IIUC), but it's just an illusion for tracking the peak. The information moves slower than light.
> does it matter (i.e. violate relativity) if something is travelling faster than light speed in some medium as long as it doesn't travel faster than light in vacuum?
This is totally possible. It's common if you live inside the water pool of a nuclear reactor or a neutrino detector. More info in https://en.wikipedia.org/wiki/Cherenkov_radiation
As I explained in a reply to a sibling comment, the spot on light on a wall can "move" faster than light. Or you can have the inverse setup of a wall that is illuminated everywhere but in a dark spot, and the dark spot can "move" faster than light.
You can imagine the second example like a movie where a dark UFO moves over a light sky. There is an illusion of movement, like in a movie. But the information is not moving FTL from a part of the screen to the other, the information is moving STL from the proyector to the screen.
They measure the point where A=0 on a surface. When the singularities are far away, they behave like particles and it makes sense. In this case the point A=0 "moves" FTL, but it's as fake as the UFO in the movie. Also in some cases it's easier to do the math considering fake objects that move FTL. (just google "phase vs group velocity"). This is a well known problem/trick that is taught in a standard course in the second year of a physics degree.
It looks like the research is interesting, but the groundbreaking "darkness can “travel” faster than light" angle in the article is just nonsense.