The distance between the bright spot and the central point of the interference pattern. The distance between slits. A double slit interference pattern does not require diffraction. A single slit diffraction pattern does not require interference. Diffraction, refraction, and reflection all can cause the path of light to not be in a straight line.
Polarization involves interference.
Laws are the same only on inertial frames with zero velocity. Laws are the same only in inertial frames moving at low velocities. Laws are the same only on inertial frames moving at near light speed. Laws are the same on all inertial frames. A super fast freight train has a 20 m long box car when measured at rest.