Quantum theory is concerned with explaining how particles of a matter or the tiniest part of a thing like wood, stone, water, etc can interact within themselves and with energy. Unlike classical physics which is concerned in the description and behaviour of objects in large scale. Quantum theory describes all fundamental forces-except gravity-that physicist have found in nature. In other words, the theory was developed to account for sub-atomic behaviour called quantum mechanics or wave mechanics. It started in 1923 with the postulate of de Broglie, that all particle have both wave and particle properties nature. This is referred to as the wave particle. Simply put, all particle behave just like light (which a form of waves ) and as particles. Related to the above principles of quantum theory is another one called intrinsic angular momentum or spin discovery by Wolfang Pauli in 1925. Simply put, tiny particles of matter do not stay fixed in one position but move and spin around at the same time. Imagine a ball that is thrown from one distance to another. As it is moving it is also rolling around itself; this is how particles behave, and that is why the principle is called spin or intrinsic angular momentum. Additional important concepts have been incorporated into quantum mechnics. These include the discovery of uncertainty principle by Heisenberg in 1927. The principle asserts the existence of a nature limit to the precision with which certain pairs of physical quantum can be known. Simply put, one cannot exactly specify the location of particles as they keep moving constantly. The uncertainty principle, such as an electron, with precision. The principle, also referred to as the indeterminacy principle, further states that a fmore accurate determination of one quantity will result in a less precise measurement of the other. The implication of this is that in quantum mechanics, calculations are probabilistic, instead of being deterministic as in classical mechanics. The 3 main concepts deduced from this theory are;
1. **wave particle duality **means that particles behave in two ways, as a wave and as particle
2. **intrinsic angular momentum or spin **means that particles move from one point to another while turning round and round at the same time as they move.
3. **Uncertainty principle**means that one cannot exactly specify the location of particles they keep moving constantly.
Thus, a different and statistical approach developed in modern physics as a result knowledge in quantum theory. The fully deterministic cause-effect relations produced by Newtonian mechanics were supplanted by predictions of future events in terms of statistical probability only.