Twentieth century witnessed great revolution in the field of physics. Previous view of space-time was rejected by new concept of space-time which is also known as theory of relativity. Similarly the microscopic view of science also makes huge progress. Discovery of quantum mechanics rejected previous concept of determinism and shocked many scientists. These are two main breakthroughs of physics of 20th century.
Similarly there was huge progress in cosmology also. Hubble’s find out about expanding universe was also important step. Similarly there was huge research about black holes also. In one part expanding universe demands the matter at highly dense state in past so has black hole.
And to know the property of space time at such a massive state we must combine theory of relativity with quantum mechanics. But there is great problem with this two. General theory of relativity is valid in large distance but quantum theory only works in very small scale. Similarly gravity although weakest force it has great influence in large scale but other force works in small distance only in normal condition both theory can work separately but is dense state such as in big bang there must be combination of these two. Such a theory was quest of Einstein in his later days and still it is considered as a holy grail for physicists. But still scientists are far from reaching this goal.
In search of such a theory scientists have purposed many theories. One of the theories with high influence is superstring theory. According to superstring theory in microscopic world particle will not be dot like as previously considered but they are string like. Like string of guitar they vibrate in different way. This different pattern of vibration forms of particle will be formed. According to Einstein, mass and energy are same. So vibration energy will cause particle with different mass,
But string particle are related with microscopic world. How they will unify physics? Some enthusiastic scientists also give answer of this.
Some scientists including Gabriele Veneziano were researching on strong nuclear force. Surprisingly they found the result matched with 200 year old mathematical equation
. after two year working on this surprising result was obtained. Leonard Susskind and holger nielson revealed that if the strong force between two particles were due to tiny extremely thin almost rubber band like particle then the quantum process that Veneziani had been poring over would be mathematically describes.
Again research on string gives a new result. The result described a new particle with zero mass and spins two. In the beginning scientist rejected this idea because zero mass particle (photon) have spin zero. But finally it was revealed that new particle match property gravitaton. Graviton has also have spin two. So string theory first found in research of strong nuclear force match with gravity. So scientist came in conclusion that string theory ca associate nuclear force and gravity. So in grand unified theory string theory can play vital role.
However these property superstring’s theory is not accepted universally. Because it requires 10 dimensional space. . in calculating this 10d mathematics become very complex. Again string particle are very small. it look like reading this words from thousands of light year away. That is very far from our instrumental resolving power. So strings are still far from our observation capability. So how manipulate mathematically without observing it? The answer is however we cannot see it but it describe all natural phenomenon. So it can not be discarded. And if it describe all p
phenomenon then it will be ultimate  theory of physics

(article prepared for a magazine going to published from Patan multiple college science bloc)