Newtonian mechanics was found to be inadequate in the early years of this century- it’s all right in “everyday life”, but for objects moving at high speeds (near speed of light) it is incorrect, and must be replaced by special relativity (introduced by Einstein in 1905); for the objects that are extremely small (near the size of atom) it fails for different reasons, and is superseded by quantum mechanics (developed by Bohr, Schrödinger, Heisenberg, and many others). For objects that are both very fast and very small (as in common in modern physics), a mechanics that combines relativity and quantum principles is in order: this relativistic quantum mechanics is known as quantum field theory.