Time dilation refers to 2 clocks in 2 different frames. Time dilation and length contractions have not been proven in experiments. There exits a preferred frame of reference in the universe. A mass moving at the speed of light becomes energy. Mass is absolute, that is, it has the same value in all reference frames.
All forces have to be contact forces.
The gravitational force is the only natural force. All forces are unique, so none are fundamental. The gravitational force is the strongest force. The gravitational and electromagnetic forces are more fundamental than the strong and weak nuclear forces. Electricity and magnetism are two different forces.