When we hear of any great inventions or creative ideas we only hear the part that is easily digested or the better halves of it. With the rapid advancement in social media and news platforms it is not common that only good sides of the theory are reflected. Here we will discuss, one of such, The story of “String Theory”.
The origin of string theory can be dated back to 1960s when this theory came as a theory to describe the nature of the strong nuclear forces. Then later it was applied in the quantum chromodynamics. Finally scientists tried to develop this theory to unify quantum mechanics and general relativity as a single entity called quantum gravity.
String theory is basically developed on foundations of assuming the classical point like particles of quantum field theory in 0 dimension as strings in 1 dimension. The interaction of strings occurs by generalizing the perturbation theory for vibration of strings in 1 dimension in the quantum field theory. The strings can be open end strings or closed loop strings. The vibrational states of the strings then determine what the particle is or the state of the particle. But unlike quantum field theory, it does not have a clear non perturbative definition.
The earliest version of the theory is the Bosonic String Theory which described the interactions of bosons. As, this theory only described the bosons more versions of the theory were developed called the superstring theories to incorporate fermions. One fundamental mathematical aspect of the theory was the supersymmetry. The superstring theory had many versions : Type I, IIA, Type IIB, and two versions of heterotic string theory. All these theories used different kind of strings and different symmetries. Also these theories required extra dimensions of the space to be mathematically fit. Thus with the 4 dimensions of space and time in observable universe, extra dimensions were added which were unobservable but played a part in the interaction of the strings.
Even there were different versions of the theory one important component that linked all of them was the duality. This is a concept that describes that in some way or the other the particles in the same physical reality would be similar or can be converted to one another. Based on this concept along with other Edward Witten in 1994 thus proposed that all other string theories were the sub cases of a theory with 11 dimensions called the M theory. Further addition to the theories were done by a number of scientists and till this date the theory of evolving. The theory is supposed to describe the various anomalies of physics once it is fully understood but as in the present time it is able to describe only a few aspects of folds in physics on fields of quantum gravity, quantum chromodynamics, black holes, particle physics and others.
No matter how many scientists, mathematicians and physicists spend their countless hours a theory is not complete until it can described the observed properties of particles or phenomenon it tends to describe. String theory is also being highly criticized for such reasons. Some of the criticisms are:
- The string theory has described the low value of cosmological constant in terms of large number of vacuum states and which are significantly diverse from each other. This lead to a problem that these vacuum states lead to many number of universes also called the multiverse theory. One of the believer of the multiverse theory is Leonard Susskind, who describes that we live in a system of multiverses one within the another where our universe is only in 4 dimensions and access to other universe requires one to jump to other dimensions of the space. This theory is highly controversial in aspects that such existence could never be experimentally verified.
- One of the beautiful part of string theory is that general relativity fits well within it. But as general relativity is background independent, string theory is not. In string theory a fixed reference geometry must be specified for a spacetime and all other possible geometries are described as perturbations on this fixed one. Thus this basic difference between the string theory and general relativity may be the cause why it cannot incorporate gravity to quantum field theory , scientists believe.
Although it may be highly criticized , the supporters of the theory believe that this theory is just beginning to unfold. It will take time before it could be fully understood and conclusions can be drawn. Also, the mathematical problems involved in the theory are complex and thus these mathematics have not been fully formulated which would make the scientists make sense of things within the theory in new way. What today is, is just the infancy of physical intuitions towards describing the universe, origin of it, black holes and fundamental particles of matter all with a single theory of physics and making it the “Theory of Everything”.