though special relativity basically says that that's impossible.
This quantity is cubed in the denominator of the formula for the Abraham-Lorentz force, and the time-averaged Poynting vector divided by this quantity gives radiation pressure. Beta is equal to velocity divided by this quantity. (*) Cherenkov radiation occurs when this quantity is exceeded in a medium, and vacuum permittivity times permeability gives this quantity squared. This quantity is constant in all reference frames, and a 2013 experiment apparently showed this value being exceeded, though special relativity basically says that that's impossible. For 10 points, name this "universal speed limit," a value symbolized by lowercase c.
This quantity is cubed in the denominator of the formula for the Abraham-Lorentz force, and the time-averaged Poynting vector divided by this quantity gives radiation pressure.
speed of light (accept obvious equivalents but prompt on “lowercase c”; Ed’s note: if anyone’s wondering why Cherenkov radiation says this quantity is exceeded, and then we say it’s impossible, it’s because it’s exceeded in a medium)