The world around us seems to be made up of some minuscule fundamental particles. However, which particles are regarded as fundamental, varies with time. This goes back to Greeks who had a credence that all matter was composed of small indiscrete particles, they called these particles as ‘atoms’.
Their argument hinged on the inkling that it is impossible to keep dividing matter for infinity and therefore the matter must be made up of minute particles. They believed that these particles were too tiny for human senses to detect.
Eighteenth-century chemist John Dalton too had a belief that atoms can’t be subdivided. But the notion that atoms are indivisible, ultimate particles of the matter was discarded when English physicist J. J. Thomson discovered electron, the first subatomic particle.
And soon the proton and the neutron were discovered. Now atom seemed to be composed of three fundamental particles i.e. protons, neutrons, and electrons.
But wait! This is not the complete tale. Things are not nearly so straightforward as they seem. The advent of big bulky machines called “particle accelerators” has completely changed this depict. Hundreds of other particles have been discovered in high energy collisions carried out in these machines. These collisions can reveal the deep structure of matter.
In Last quarter of the twentieth century there came a profound view of the universe: that the material universe of today has emerged from a hot Big Bang, and that collisions between subatomic particles are capable of recreating momentarily the conditions that were present at that early epoch.
Thus today we view these collisions as a means of studying the phenomena that ruled when the universe was newly born.
The theories and discoveries of thousands of physicists since the 1930s have resulted in a remarkable insight into the fundamental structure of matter: everything in the universe is found to be made from a few basic building blocks, governed by four fundamental interactions (electromagnetic interaction, weak interaction, strong nuclear interaction and gravitation).
Our best understanding of how these particles and the forces are related to each other is encapsulated in the Standard Model of particle physics.
Developed in the early 1970s, it has successfully explained the experimental results and precisely predicted a wide variety of phenomena.
There are seventeen named particles in the standard model which include all the known constituents of matter -six leptons and six quarks, the particles that govern the behaviour of fundamental interactions of nature - w boson, z boson, gluon, photon and the recently discovered Higgs Boson popularly known as the God Particle.
Even though standard model is currently the best description there, of the subatomic world but it too has many loose ends, it incorporates only three out of four fundamental interactions omitting gravitation and falls short of being a complete theory of fundamental interactions.
It does not fully explain baryon asymmetry or accounts for accelerating expansion of universe as possibly described by dark energy.
Thus if one looks beyond the laboratory to the cosmos, there is a clear need for new physics beyond the standard model.
Theoretical physics continues to strive towards a theory of everything, a theory that could fully explain and link together all known physical phenomena, and predict the outcome of any experiment that could be carried out in principle.
The goal in this regard is to develop a theory which would unify the Standard Model of particle physics with Albert Einstein’s famous theory of General Relativity. Among various noteworthy attempts in this direction is Supersymmetry according to which each particle in the Standard Model would have a superpartner known as “sparticle” whose spin differs by half from the ordinary particle. Due to the breaking of supersymmetry, the superpartners are much heavier than their ordinary counterparts.
Another important candidate which can come to the rescue and be the basis of a final theory of everything is String Theory. According to this theory, leptons, quarks, and field bosons are not points in the four dimensions of spacetime but vibrating loops of string in a space of ten dimensions.
In the new experiments at the world’s largest atom smasher, the Large Hadron Collider-LHC at CERN in Geneva, physicists will be on the lookout for signs of particles ‘spontaneously’ appearing or vanishing.
If such a phenomenon is found to occur in some systematic way, this could provide evidence that we are indeed like flatlanders and that there are dimensions in nature beyond the three space and one time that we currently experience.
We have reached a point where it is beginning to be hard to distinguish science fact from science fiction. But a century ago, much of what we take for granted today would have been beyond the imagination of H. G. Wells. A hundred years from now there will be material in the science textbooks as yet undreamed of.