Aristotle believed that everything in the world was composed of four basic elements – earth, water, fire and air. He also suggested the nature of forces that acted upon these elements, gravity – which caused earth and water to sink, and levity – which caused fire and air to rise. No matter how primitive and vague his concept was, it is still very consistent with our division of particles of the universe into matter particles and force particles. Aristotle believed that matter particles were continuous and there was no stopping point at which they could not be divided further. Democritus and Leucippus on the other hand, considered matter to be discrete and being composed of small units called atom (atom in greek means indivisible).

For centuries there was no hard evidence to prove whether matter was continuous or discrete. In 1803, a British physicist John Dalton came up with an idea that chemical compounds always combining in certain proportions could be the reason of atoms reacting with each other in numbers to form units called molecules. By 1897, another British physicist, J. J. Thomson discovered the existence of negative charge in matter particles with his cathode ray tube experiment. Even though it was apparent at this point that atom, indeed, was not the smallest unit, the structure of atom was still vague as no one could comprehend the origin of such negative charge.

One of the important pieces of physical evidence was provided by Einstein in 1905 in his paper, “On the Movement of Small Particles Suspended in Stationary Liquids Required by the Molecular-Kinetic Theory of Heat”, where he pointed out that what was called the Brownian motion could be the effect of atoms of the liquid colliding with the dust particles. For his groundbreaking theory on special relativity and photoelectric effect published in the same year 1905, his paper on Brownian motion isn’t as celebrated. Later in 1911, another British physicist, Ernest Rutherford corroborated the existence of elementary particles within an atom. From his alpha-particle bombarding experiment, he proposed the existence of nucleus, describing it as a very small and dense region within the atom, and comprising of positive charge – the positive charge was later discovered to be proton having the same magnitude of charge as the electron. After James Chadwick discovery of neutron in 1932, the structure of atom became much more explicit, with proton and neutron forming the nucleus and electron spinning around the nucleus – the solar system model.

An amusing, yet logical feeling that I inadvertently summon while I cogitate over these historical advancements is how little these scientists knew about the particle that make up everything, before 1930. Yet, the most profound and far reaching theories of thermodynamics, relativity, quantum mechanics, in fact the whole of science, were proposed before that date and is still consistent and relevant to this day. So if these theory deem to be true, are the experiments performed to verify them being influenced by our prior knowledge or do we really don’t need to know much to understand and revolutionize the world?

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