In the 19th century James Clerk Maxwell formulated the field theory of electromagnetism, and in the early 20th century, Albert Einstein developed a field theory of gravitation. The last three decades of Einstein‘s life was then consumed trying to combine electromagnetism and gravity into a single theory, but he was ultimately unable to reconcile these forces.
Later physicists have similarly tried to combine all the fundamental forces of nature (gravity, and the three forces acting on the atomic scale of electromagnetism, weak nuclear force, strong nuclear force) into a single Unified Field Theory, but even today they are yet to discover a successful theory of quantum gravity. Consequently, we are still far from developing a unified framework which will allow us to clearly understand how the universe works the way it works, or even being able to frame the “why” questions.
Unified Field Theory
The Unified Field Theory was an attempt to combine General Relativity (laws of large space and how gravity works) with Quantum mechanics (laws of very small space). However, the large ordered world is in direct conflict with the small, erratic world, and the UFT tried to formulate a theory which would unite these two frames and would describe all the forces which rule our Universe.
Everything in the Universe consists of 4 forces interacting with matter. Specifically the four forces that scientists are trying to unify are Gravity (G) as described by Relativity, and the other 3 forces of Quantum Mechanics, namely Electromagnetism (Em) which produces light, electricity and magnetic attraction; and the two Nuclear Forces which are either strong (S) and binds protons and neutrons together to form the nucleus of an atom, or weak (W) which is responsible for radioactive decay.
Traditionally, atoms had always been thought of as balls or points, but according to the Standard Model of Particle Physics, at the heart of atoms are electron-like particles called leptons orbiting a nucleus made of protons and neutrons, which are both made of quarks. Quarks then bind together through the strong nuclear force to form protons and neutrons, while leptons only interact through the electromagnetic and weak nuclear forces. Particle accelerators have been concerned with exploring the behaviour of microscopic particles by smashing them together and studying these collisions. In the shower of particles produced many new particles have been discovered, and scientists have not only discovered these building blocks of matter, but also predicted that the fundamental forces of S, Em and W are mediated by fields known as particles of force or messenger particles. Physicists predict that the exchange of messenger particles between particles of matter creates what we feel as force.
So now we identify the exchange particles that mediate the Strong nuclear force as gluons, Electromagnetic force as photon, Weak nuclear force as W boson. Gravity (G), however, was ignored in these predictions as gravity was seen as a special case.
String Theory is an eloquent theoretical framework which suggests that instead of thinking of atoms or smaller particles as balls or points, everything actually consists of smaller particles made from strings of vibrating energy. The different way the strings vibrate give particles their unique properties such as charge or mass, and the only difference between particles is the way these strings vibrate. String theory also claims to unify all forces and matter in the universe, including Gravity (G), and identifies an hypothetical particle called a graviton, which transmit gravity at the quantum level and explains how gravity works at that sub atomic level.
In addition to the 4 dimensions we know, string theory allows for an additional 6 dimensions or degrees of freedom for the strings to move in. That’s ten dimensions, as opposed to the three dimensions of space and one of time we humans are familiar with. This explanation of a grand cosmic symphony has helped resolve the conflict between the jittery space of the quantum scale, and the large smooth picture of space on a large scale, but still remains just a theory.
Confusingly for a unified theory, string theory had 5 different models. Ed Witten then introduced M theory which helped to unify these models and he did this by adding an extra dimension to bring the total to 11. This extra dimension allowed a string to stretch into a membrane or brane which could even grow to the size of the universe. These membranes also helped keep other dimensions or alternate realities from each other.
It has been noted by physicist that gravity was a weaker force than other forces and they didn’t know why. M theory suggests this has to do with the shape of strings. They now think that everything around us such as matter or light is made from open ended strings, with the ends of each string tied down to our 3 dimensional membrane. However, one kind of closed loop string being studied is the graviton. With closed loops there are no ends to tie down to the membrane of our perceived reality, and so gravitons are free to escape to the different dimensions, thus diluting the force of gravity and making it appear weaker.
Interestingly, no experiments or observations can be done which would prove string theory wrong, and this has prompted many to ask whether it should be considered as physics or instead a part of philosophy.