**String Theory- Is It Valid?**

Abstract

I discuss the theories of quantum mechanics, general relativity, and the Standard Model, and analyze possible theories of everything, specifically string theory. I address the recent developments of string theory and assess its most pressing problems.

Introduction

The prediction of the quantum by Max Planck and the developments made by Einstein, Bohr, Heisenberg, Dirac, Schrodinger, and Pauli rushed in a new era of physics: quantum physics. The first thirty years of the quantum revolution introduced newer, more accurate theories of physics that have transformed the way physicists think and the technology available to us today. In these years, Einstein created his brilliant general theory of gravity. General Relativity has been verified on many occasions by experimentation and observation, but it is not a quantum theory. A multitude of explanations and hypotheses have been thought up to combine these two theories, the majority of which have not been successful. There is another problem, which seems to arise from the four fundamental forces. The electromagnetic, weak nuclear, and strong nuclear forces have enjoyed successful amalgamation with quantum mechanics; gravity, the last of the four fundamental forces, has not [1].

The Constituents of String Theory

String theory is a quantum mechanical theory that addresses the crux of theoretical physicists’ problems; general relativity remains incompatible with quantum mechanics in some areas, gravity has not yet been quantized (fitted to quantum mechanics), and there are infinities caused by perturbative calculations for particles that require the complicated method of renormalization. String theory is based on the idea of vibrating strings at the Planck scale (where, at the Planck length, classical gravity is thought to break down) that make up all matter [2]. Different types of strings vibrate differently and cause different characteristics of the elementary particles, which include spin and charge. There are five separate hypotheses in string theory: E(8)E(8) heterotic, SO(32) heterotic, SO(32) Type I, Type II A and Type II B. Type I strings are strings consisting of a single free segment attached to “D-branes”, and the Type II A and Type II B strings are strings that are “closed”, and form loops [1].

The Standard Model is a set of very successful quantum field theories that describe all the elementary particles in nature and unite three of the four fundamental forces in the cosmos: Electromagnetic, Weak, and Gravity. Gravity is the only force that has eluded the successful joining of the other forces. The so called “theory of everything” is an all-encompassing theory that would unify the four forces and combine general relativity with quantum field theory. String theory combines gravity with the three other forces, general relativity with quantum mechanics, and removes infinities in some calculations. It has appeared to offer a gravity that is compatible with quantum mechanics. Physicists were elated by this new, promising hypothesis.

The Problems with String Theory

String theory cannot make predictions about the cosmos that can undergo experimentation; therefore, the hypothesis is essentially useless. Most of the major theories made that describe the cosmos can calculate a prediction of what will happen, which is tested at high energy colliders, to see if the theory agrees with the experiment. Traditional mathematical methods of calculations seem to be insufficient for string theory, and the lack of solid predictions causes trouble with experimentation. Though some beautiful mathematics can be derived from string theory, the overall evidence for string theory is overshadowed by its problems.

String theory predicts a new particle, a massless boson (an elementary particle that has integer spin) with spin 2 that is not included in the Standard Model and that requires such high energies to be experimentally found, that it will most likely never be experimentally confirmed [3]. This particle seems to be a gauge boson that carries the force of gravity; thus, it was aptly named the graviton.

String theory also requires the existence of ten or eleven dimensions, most of which are unobservable and “compactified,” or rolled up like a cylinder [1,2]. These extra dimensions complicate the mathematics and may not be a good enough solution to the numerous problems of string theory. String theory leads to the existence of an infinite amount of universes, a preposterous idea that can barely be proven.

Originally, the hypothesis had only applied to bosons, so string theorists incorporated fermions (elementary particles with half integral spin). Hence, the equations of string theory are “required to be invariant under half-integer changes in spin” [3]. From this, supersymmetry was born. Supersymmetry is a crucial hypothesis that predicts that there is a supersymmetric “superpartner” for each of the Standard Model elementary particles. For example, the electron, spin ½, has a superpartner of spin 0, called “selectron.” Supersymmetry predicts a plethora of new particles that have not yet been discovered and that do not appear in the Standard Model [3].

As I discussed earlier, string theory has five main hypotheses within itself. So the natural question comes to mind: which one is correct? Certainly, if the “theory of everything” is to embody all the laws of physics, one must be correct. To tie up these theories, some symmetries known as dualities (such as T-duality and S-duality) have been proposed [4]. Even though most of the problems of string theory have been cleaned up nicely, the fact remains: string theory can make no predictions and cannot be directly proven. String theory has therefore been described many times as “not even wrong,” which were the famous words of Wolfgang Pauli.

Where String Theory Stands

As I have shown, string theory has been a revolutionary hypothesis that has been successful in unifying the four forces, and reconciling general relativity with quantum field theory. However, string theory has run into a myriad of problems which has caused even the most ardent string theorist to be instilled with doubt.These problems caused the assistance of other hypotheses, such as brane-theory (which is more successful, because it can explain anomalies in black holes, and can even describe certain problems within string theory). Today, there are many possible hypotheses that can solve string theory’s problems, but string theory itself has only one piece of evidence of it being correct. That evidence is mathematical beauty. String theory has not been proven, and will most likely never be proven. Thus, in order to progress with more accurate physics, we must not waste time on string theory, but we must look back at the old quantum physics and make a new theory that is beautiful, yet can make predictions. A new theory of everything will be made; but it is not string theory.

References:

[1] Duff, M. (2003, May 1). The Theory Formally Known as Strings. Retrieved February 10, 2015. web.b.ebscohost.com or www.scientificamerican.com

[2] String Theory. Retrieved February 9, 2015. http://web.b.ebscohost.com/

[3] Ruetsche, L. (2006). String Theory. In D. M. Borchert (Ed.), Encyclopedia of Philosophy (2nd ed., Vol. 9, pp. 267-270). Detroit: Macmillan Reference USA. http://ic.galegroup.com/

[4] How are string theories related? The Official String Theory Website. Retrieved February 10, 2015. http://superstringtheory.com/

Dimitrios Kidonakis