So i was watching this video : And it got me thinking... i began wondering why, when space contracts from someones frame of reference (In the video, this would be the frame of reference of the cat), why is it that the protons dont become black-holes when the space contracts? If the density change has an effect on the electro-magnetic force, why would it not have any gravitational effects? It seems to be contradictory, since from the reference frame of someone stationary, looking at the cat, there is no change in density of the protons in the wire, but instead, we see the cat contract. and we don't see things becoming black holes when moving at or near the speed of light, so i assume that the protons in the wire do not becomes black holes either. So what is the reason length contraction doesn't create black holes in any reference frame?