In physics, there are two theories which explain the working of the universe-
Einsteins ‘theory of relativity’ dealing wth the working of large bodies.
Quantum mechanics deals with the working of quantum particles.
As every large body (stars, planets, galaxies etc.) is made up of small subatomic particles, therefore, there cannot exist two theories for the same thing. The laws working behind small particles should be also applicable to the working of large bodies.
The reason that general relativity doesn’t work at the subatomic level is because the equation mistakenly includes a figure for point-like particles. Modifying the equation to include a representation of loops of string, instead, makes the equation work.
There should be a single theory which should explain the system of the universe as a whole. To achieve this either Einstein’s theory needed to be revised or the quantum theories. But there were no problems with the current theories in their respective fields. These two frameworks had proven to be sufficient to explain most of the observed features of the universe, from elementary particles to atoms to the evolution of stars and the universe as a whole.1
In spite of these successes, there are still many problems that remain to be solved. One of the deepest problems in modern physics is the problem of quantum gravity.2
This means that a new theory was needed to bridge the gap between the two. If such a theory is developed, it should be regarded as the parent theory of the two existing theories.
Let’s have a look at this new theory known as the string theory. Originally developed in the 1970s by Leonard Susskind (Father of The String Theory).
The String Theory
In physics, string theory is in which the point-like particles of particle physics having zero-dimension are replaced by one-dimensional objects called strings.
Four fundamental forces of the universe are-
Gravitational Force, Electromagnetic Force, Strong Force and Weak Force
These forces work in different ways and maintains the relationship between the different matter particles in the universe. Each one is understood as the dynamics of a field. The gravitational force is modelled as a continuous classical field. The other three are each modelled as discrete quantum fields, and exhibit a measurable unit or elementary particle.
Strings have many properties that some physicists expect to hold in a fundamental theory of physics. Most notably, a theory of strings that evolve and interact according to the rules of quantum mechanics will automatically describe quantum gravity. Which can give birth to the Einstein’s dream i.e. Unified Field Theory (UFT). This also means that a new theory will bridge the gap between the two existing theories.
In addition to the problem of developing a consistent theory of quantum gravity, there are many other fundamental problems in the physics of atomic nuclei, black holes, and the early universe. String theory is a theoretical framework that attempts to address these questions and many others.
In string theory, there is only one kind of string, it can vibrate in different ways. In this way, all of the different elementary particles may be viewed as vibrating strings.
String theory depicts strings of energy that vibrate, but the strings are so tiny that you never perceive the vibrations directly, only their consequences. Nature of vibration can be better understood by the type of wave called a standing wave.
Types of Vibrating Strings | Quantum Gravity
The strings may be Open (forming a segment with two endpoints) or Closed (forming a loop like a circle) called Type I strings and may have other special properties. Interactions between open strings always result in closed strings. One of the vibration modes of a closed string can be identified as the graviton.
In string theory, one of the vibrational states of the string gives rise to the graviton, a quantum mechanical particle that carries gravitational force. Thus, string theory provides a better answer to the quantum gravity.
Studies of string theory have also yielded a number of results on the nature of black holes, gravitational interaction and extra-dimensions.
11 Dimensions of String Theory
According to Einsteins theory of space-time, we live in the world of 4 dimensions. Space containing three dimensions (x,y,z) and fourth dimension is time.
Consider a point, it has no length, width or height so, it has no dimension.
A line has length but no width or height so, it has one dimension.
Square has length and width but no height so, it has two dimensions.
Cube has length, width and height so, it has three dimensions.
String theory states that there is a possibility of higher dimensions. There can be the existence of 7 more dimensions in the universe. These different dimension together or individually can hold their universe like our universe made up of four dimensions. However, no higher dimension is yet found.
It is almost impossible for us to explore other dimensions as they are too small to get detected. Therefore, it becomes impossible for us to jump into the other dimensions.
Everything Vibrates in the Universe
According to the theory, all particles are actually tiny vibrating strings and each type of vibration manifests a different particle. The different particles are like the different notes that can be played by plucking a violin string. However, the strings of string theory almost certainly would not look like violin strings.3
Bosons are force carrier particles. Fermions are usually associated with matter. In fact, matter itself is seen as the manifestation of standing waves on strings. Different vibrational modes give rise to different particles!
Whether it’s a heavy particle that is part of an atom or a massless particle that carries light, is due to its resonant pattern, or how it vibrates.4
Read More (External Sources)
References[1,2] Becker, Becker, and Schwarz 2007, p. 1
 “What is string theory?| Explore | physics.org.” 2009. 8 May. 2016 <read>
 “NOVA | Elegant Universe | Resonance in Strings | PBS.” 2003. 8 May. 2016 <read>