Applied Quantum Mechanics

One distinct feature of quantum mechanics concerns the quantization of physical quantities. According to quantum mechanics, some physical quantities such as the energy of the hydrogen atom can have only certain discrete values, contrary to the prediction of classical physics. However, the most striking feature of quantum mechanics involves the statistical nature of its predictions. The outcome of a single experiment cannot, in general, be predicted exactly. All one can do is to determine the probabilities for the various possible outcomes of the experiment. A quantum physicist cannot tell exactly the direction in which a photon would be scattered after colliding with an electron. He can only tell the probability for the photon to be scattered in this or that direction. Despite such apparently looking shortcoming, quantum mechanics has spectacular success in explaining a host of experimentally observed facts.