Solving numerical problems in physics was a fun back then in the high school. But, hardly anyone in that age bothers to dig the depth of these equations and those who do are the ones who write new chapters in the history of science.
What do Newton's Laws of Motion tell us about nature? What is the significance of the Law of Gravity? What Maxwell's Equations has to do with reality? Do you ask these questions to yourself?
Imagine a universe with bizarre laws like a ball moves in a horizontal direction instead of upward direction when you through it up or moves in a non-linear path. Imagine a universe where an increase in temperature turns water into ice. Why our universe doesn't work this way? Why it couldn't be that same charges attract each other at one location and repel at another location. or why can't same charges attract and different charges repel?
A small observation yields that nature follows some definite rules which the brilliant minds of the world have been discovering since ages. They decode these rules in the form of mathematical equations. Newton discovered the three Laws of Motion and the Law of Gravity which holds accurate everywhere except the atomic world. Maxwell's Equations can explain everything related to electricity and magnetism.
Einstein was quite offbeat from the mainstream physicists. Even when almost all of the contemporary mainstream physicists were embracing the probabilistic interpretation of Quantum Mechanics, Einstein strongly opposed this idea and defied it till his last breath. Towards the last few years of his life, Einstein discovered a bizarre pattern in the laws of nature. Maxwell had unified electricity and magnetism through his four equations into a single fundamental interaction called Electromagnetism. Newton's Law of Gravity and Laws of Motion apply to both the cases- the falling of an apple from the tree and the revolution of one celestial body around another. This idea of unification greatly inspired Einstein.
Einstein disproved the Newtonian concept of gravity by introducing his General Theory of Relativity in 1915. Einstein proved that gravity is an interaction between mass and spacetime rather than a force that acts between two masses. Let us understand his idea in brief:
According to Newton's picture of gravity, if the sun disappears suddenly, then all the planets in the solar system is disconnected from its gravitational influence and will start moving in the tangential direction of their orbits. And this process is instantaneous. However, according to Einstein's Special Theory of Relativity(1905), the speed limit of the universe is the speed of light. Nothing can move faster than light. Now, the question arises, how could the effect of the absence of sun reach the planets instantaneously as nothing can move faster than light and even the light from the sun takes 8 minutes to reach earth. Einstein cleared this ambiguity through his General Theory of Relativity. Einstein showed mathematically that large masses like the planets and the stars curve the space in the same way a football stretches a plain cloth downwards when the football is placed on the cloth held from its four corners. The planets move around the sun in this curve in space only.
Now, if the sun disappears suddenly, it causes a disturbance in the spacetime and waves of gravity are generated which then moves in all directions. When this wave reaches the planets, then only they experience the absence of the sun. These waves are called the Gravitational Waves which were detected for the first time in 2011 at the LIGO. Einstein calculated the speed of the wave which is surprisingly equal to the speed of light. The equality of the speed of Gravitational Waves and of light(an electromagnetic wave) stunned him. Einstein was convinced that there must be a link between Electromagnetism and Gravity. Einstein spent his later life working on a theory which could unify these two fundamental interactions into a single master equation. But, his dream remained incomplete as he breathed his last in 1955.
The development of Quantum Mechanics during the 1920s led the regime of physics to a different direction. Quantum Mechanics showed that deep under the atomic range, nature is not deterministic rather probabilistic where a particle exists at many locations at the same time until we look for it or it can be in many different states at the same time. Quantum Mechanics led to the discovery of two new fundamental forces namely the Strong Nuclear Force and Weak Nuclear Force. Strong Nuclear Force is a short range force(and the strongest among the four) which binds the nucleons together in the nucleus of an atom and Weak Nuclear Force which is a short range(but the weakest) force allows neutrons to turn into protons and vice versa giving off radiation which is responsible for the radioactivity of the radioactive elements. These four forces i.e. Gravitation, Electromagnetism, Strong Nuclear Force and the Weak Nuclear Force summarize everything about our universe.
The three forces- Electromagnetism, Strong Nuclear Force, and Weak Nuclear Force were unified into a common theory named Unified Field Theory in terms of the laws of Quantum Mechanics during the 1970s. Steven Wienberg, Abdus Salam, and Sheldon Glashow were awarded the Nobel Prize in Physics in 1979 for the development of the Unified Field Theory. This theory put forward the Standard Model of the universe according to which these forces are characterized by the exchange of some fundamental particles known as Guage Bosons. The Gauge Bosons for Strong Nuclear Force is Gluon, for Weak Nuclear Force it is W and Z Bosons and for Electromagnetism it is Photon. The Modern Unified Field Theory considers Graviton as the Gauge Boson of Gravitation which is yet to be proved.
However, Gravitational Force does not fit into the Unified Field Theory. Einstein's General Relativity fails at the quantum level. Thus, the theory which can explain gravity in terms the laws of Quantum Mechanics or in simple words a theory which unifies the laws that govern the large masses and the laws that govern the small masses is known as The Theory of Everything. Hence, the Theory of Everything unifies all the four fundamental forces into a single master equation. But, what is the need of the Theory of Everything? Is it that necessary?
A Black Hole holds the answer to this question. Black Hole is a region of super-dense matter where the gravity of the mass is so strong that it curves the space into an infinitely deep hole. Nothing, even light cannot escape from its pull. It is a region of a large mass in an extremely small dimension. For this reason, both General Relativity and Quantum Mechanics fails in this region which is quite non-sensible. For a theory to be valid it should be applicable everywhere in the universe. To make both of these theories universal, they must be unified into a single theory which could then satisfactorily explain the universe.
A few theories have been proposed as the candidate for The Theory of Everything. The String Theory and the Loop Quantum Gravity are the most popular ones. However, String Theory has been widely accepted by the physics community. String Theory considers the fundamental particles of nature as some extremely small one dimensional vibrating strings of energy. Just like different frequencies of the strings of a guitar give different sounds, different frequencies of these strings characterize different particles. Thus, according to String Theory, the universe is a cosmic symphony resonating with all different frequencies.
But, the validity of String Theory requires a universe with eleven dimensions. Only, four dimensions are known to human beings till now that are the three spatial dimensions and the time dimension. Does the rest of the dimensions really exist? If yes, then where? One possible answer is that these dimensions are so tiny that large masses like the human body cannot move into these dimensions. But, just like an ant can move along the length as well as the curved surface of a wire, the small fundamental particles can move into these tiny dimensions.
The size of the strings is so small that they cannot be detected with even the strongest particle accelerator(LHC) of the present time. One day it may become possible to detect these strings which would finally give us the ultimate theory of our universe- The Theory of Everything.
References:
- Youtube: Einstein & The theory of Everything HD (The Elegant Universe)[Link]
- Youtube: String Theory:Theory of Everything(full documentary)HD[Link
- Ask Ethan: How Close Are We To A Theory Of Everything?[Link]
- CERN: The Standard Model[Link]
- Youtube: What is Space(full documentary)HD[Link]
- Physics.org: What is String Theory?[Link]