> For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water.
Light travels at about 0.75c in water.
You are both correct, but on different levels.
No, in water, the spacetime is not significantly warped, certainly not warped enough to slow down light. The different speed of light in a medium compared to vacuum comes from the interaction between the photons and the medium. The photon then, effectively, becomes a hybrid "photon-medium excitation" which is an effective particle with an effective speed lower than the vacuum speed of light.
Is there a theory for what "effect" would be
produced by a theoretical object going faster than
light?
Now if you don't mean in a vacuum but in a medium like water, or air, or ice, etc.
What they're doing here is based on the fact that you can make light move at under c if you force it to travel through a dielectric material. The c in E=mc^2 is the speed of light in a vacuum: not necessarily through a carefully designed atomic obstacle course.
https://en.wikipedia.org/wiki/Vacuum_permittivity
https://en.wikipedia.org/wiki/Vacuum_permeability
Free space has an electrical resistance of about 376 ohms.
Impedance, to be precise. If free space had electrical resistance of 376 ohms, our world would be much stranger place than it is now.
The experiment specifically used mediums, where the speeds are not the speed through through the vacuum, the report from which smithsonianmag took the info and provides the link is somewhat more precise:
http://www.livescience.com/57572-ultrafast-camera-captures-s...
"study lead author Jinyang Liang, an optical engineer at Washington University in St. Louis, and his colleagues designed a narrow tunnel filled with dry ice fog. This tunnel was sandwiched between plates made of a mixture of silicone rubber and aluminum oxide powder."
"Then, the researchers fired pulses of green laser light — each lasting only 7 picoseconds (trillionths of a second) — down the tunnel. These pulses could scatter off the specks of dry ice within the tunnel, generating light waves that could enter the surrounding plates."
"The green light that the scientists used traveled faster inside the tunnel than it did in the plates. As such, as a laser pulse moved down the tunnel, it left a cone of slower-moving overlapping light waves behind it within the plates."