What's smaller than the smallest - An Introduction

 People have thought about the existence of particles smaller than the smallest sensible particles of matter from time immemorial. Moreover, a similar philosophy of 'anu' is mentioned in the ancient Indian texts. However, this suspicion had no scientific grounds until one or two centuries ago.

Now, we know that matter is composed of atoms, atoms of nucleons and electrons, and nucleons of quarks. The concept of an atom was first scientifically proposed by John Dalton, which was further developed by Ernest Rutherford and Neils Bohr, although J J Thomson was the first to propose a model after Dalton. While Thomson presented a model of atom in which the electrons are distributed in a positive space as if seeds in a watermelon or plums in a pudding, Rutherford's famous gold foil experiment proved that most of the space inside an atom is empty and that the positive charge is concentrated in a centre called nucleus, and thus proved Thomson to be incorrect. An interesting thing worth noting here is that Rutherford was a research student at Cambridge under J J Thomson. With this view of an atom it is quite tempting to visualise an atom like our solar system in which the electrons are orbiting the nucleus like the planets circuiting our Sun. This was the classical view of an atom. Although this view is in accord with two major pillars of classical physics - Newton's laws of motion and Coulomb's law of electric force, it does not agree with the predictions of electromagnetic theory, which is another major pillar of classical physics, as the electromagnetic theory observes that accelerated electric charges radiate energy in the form of electromagnetic waves. This would mean that the electrons orbiting the nucleus would spiral down to the nucleus, making an atom unstable. An atom, is of course, not unstable.

It was at this point that Neils Bohr blends in quantum theory to Rutherford's model and suggests that electrons revolve in quantised energy levels. Thus, we reach a more acceptable model of atom which conveniently describes it to most of our observations. However, that too wasn't sufficient and further developments were made to reach the quantum theory of atom.