Quantum all the way

"Newton’s three laws provide a framework for describing the motion of things under the influence of a force. The first law describes what happens to an object when no forces act: the object either just sits still or moves in a straight line at constant speed. We shall be looking for an equivalent statement for quantum particles later on, and it’s not giving the game away too much to say that quantum particles do not just sit still – they leap around all over the place even when no forces are present. In fact, the very notion of ‘force’ is absent in the quantum theory, and so Newton’s second law is bound for the wastepaper basket too. We do mean that, by the way – Newton’s laws are heading for the bin because they have been exposed as only approximately correct. They work well in many instances but fail totally when it comes to describing quantum phenomena. The laws of quantum theory replace Newton’s laws and furnish a more accurate description of the world. Newton’s physics emerges out of the quantum description, and it is important to realize that the situation is not ‘Newton for big things and quantum for small’: it is quantum all the way."