I've was looking into fractional lorentz factors and I stumbled upon this stackexchange thread. I actually winced upon reading it.
https://worldbuilding.stackexchange.com/questions/19745/i-would-like-to-know-if-imaginary-velocity-has-serious-problem
https://worldbuilding.stackexchange.com/questions/19745/i-would-like-to-know-if-imaginary-velocity-has-serious-problem
