Classical mechanics involves the study of familiar things such as motions, energy, momenta of massive objects that behave in a predictable manner obeying Newton’s laws.

In the micro world, where everything is a bit and where values of energy, momentum, position and perhaps time are all too small to be measured, there are fundamental uncertainties in the measurements. The uncertainties are comparable to the magnitudes of the quantities to be measured themselves. They are all governed by probabilities rather than certainties.

The fundamental laws of quantum mechanics are then laws of probability rather than laws of certainty. For example, in contrast to the Bohr's theory, which confines the position of the electron in the ground state of hydrogen to points of fixed distance in a plane, quantum mechanics predicts that the electron can be found in spherical region surrounding the nucleus.

Quantum mechanics has extended man’s power of prediction and quantitative description of the subatomic world. However, instead of two sets of physical principles, one for macro world and the other for micro world, there is only a single set included in quantum mechanics. Classical mechanics turns out to be just an approximate version of Quantum mechanics.

Key Terms

• Quantum mechanics
• Uncertainty principle
• Wave function
• de Broglie wavelength
• Quantization
• Principal quantum number