If everything is relative to something else, who's frame of reference is actually correct? For example an observer moving at 99.9%c will use the exact same laws of physics we use and determine without any doubt whatsoever that Earth is flat... flat as a pancake! So who's frame of reference is correct? Is the Earth actually flat or is it spherical? I don't quite understand this. If it's dependent on the observer then doesn't that ultimately mean both are 100% true... Secondly imagine some object of height h at rest and directly facing a slot of height h/2. Obviously at rest the object cannot fit through the slot but at 99.9%c the object can fit through the slot. So according to the physics of the observer moving at 99.9% it will fit, but clearly to the stationary observer it won't fit... who is right? Does it fit or does it not fit?