Albert Einstein’s dream of a single theory to explain every event of the universe from atoms to galaxies is what string theory aims at. According to string theory point particles like electrons, quarks etc. are not spheres but (around 10-35 m) vibrating loops of energy. They are billions and billions of times smaller than an atom, this could be imagined from the fact that if an atom is increased to the size of the solar system, a string would not be bigger than a tree. It all started with a search for a mathematical framework that which could describe the strong forces but it showed physicists a completely new face of the universe.
The idea was first put forward by Leonard Susskind(Stanford University) in 1968. But it was in 1985 that Michael B. Greene(Cambridge University) and his co-worker John H. Schwarz(Cal Tech) brought the theory in light. They were successful to remove the mathematical anomalies. The sub-atomic particles ‘tachyons’ which travels faster than light can have an existence according to the string theory. The difference in pattern of vibrations in the strings is responsible for the formation of different particles and their properties. The theory was later divided into 5 new theories which once seemed to challenge its validity. It was Edward Witten from the Institute for Advanced Studies, Princeton who in 1995 put a view, that the 5 theories were a result of looking differently towards the same aspect of the single theory. He named it the ‘M Theory’ where M (for mother of all or whatever) is still a mystery.
We generally experience only three dimensions of space but string theory believes that the there are 10 dimensions including time whereas according to M Theory there exists 10 spatial plus one time. Physicists believes that these hidden dimensions were not able to expand after the big bang. M theory changed the view from strings to branes or membranes which can be more than 3 dimensional. It shows that our own universe is like a slice and there may be many beyond our own and there exists a possibility of there existence just at distance of 1 mm from us. One can’t see them as they are rolled up in a very complicated manner. The theory also says that gravitons(the spin 2 subatomic particles) which are responsible for the existence of gravitational force are closed branes and may leave the slice(much like sound waves leaving from a pool table), this explains the weak nature of the gravity. The theory also agrees with the creation of the worm holes, which according to the general relativity are impossible as the formation of the space and time cannot be distorted.The success of string theory can be very useful in understanding the black holes where a very heavy mass constricts to a very smaller size. It could also solve the mystery of what the universe would have been in the first 10-43 s after the big bang theory. It showed that the big bang was not a very special event. According to one idea the bang took place when the parallel universes collided and the same may occur again and again.
The concept of hidden dimensions goes all the way back to 1919, when the Polish mathematician Theodor Kaluza came close successfully extending general relativity to include electromagnetism by postulating an extra dimension to provide a structure to every point in ordinary space. Kaluza’s proposal was further developed by the Swedish Physicist Oskar Klein, but some conclusions of the resulting theory, such as the ratio between charge and mass of the electron, disagreed with measurements. Consider an electric wire at a considerable distance from you, to you its only a one dimensional line. But now consider the situation from from the perspective of an ant, for ant there is an additional spacial dimension excluding the known three that surrounds the wire just like a circle, the ant can move in it either clockwise or anticlockwise. If we constrict to the size of sub-atomic particles, we will find an extra circular dimension at each point in space.
