On the Fringe: String Theory

It all started with Newton. In a world where Aristotelian philosophy dictated that objects in motion slowed down and came to a halt because they were tired, and heavy objects fell faster than lighter ones, Newton started crunching the numbers while picking up objects around him to observe how they really worked. His laws of motion revolutionized the scientific world and laid the foundation for modern physics.

Then Einstein came around and discovered that Newton's model, while amazingly accurate in the world we normally inhabit, broke down when applied to extremely large objects like the bodies of our solar system. He devised his theory of General Relativity^[1], which not only explained the physics of every day life, but succeeded in putting a quantified value on the force of gravity, which accurately predicted the motion of planets, stars, and galaxies.

But even as this revolution occurred, physicists the world over were making extremely bizarre discoveries about the world of the extremely small. In 1897, the electron was discovered^[2], proving for the first time that the atom, which literally means "indivisible," previously thought to be the absolute smallest physical building block in the universe, could be broken down into even smaller particles. From 1905 to 1917, Einstein observed that light is made up of particles called photons^[3], ostensibly conflicting with Thomas Young's famed double-slit experiment^[4] in 1803 proving that light was a wave. However, far from invalidating Young's research, it instead gave rise to the peculiar but true notion that light is both a particle and a wave.^[5] In 1927, Werner Heisenberg realized that is impossible to simultaneously determine the location and velocity of an electron, giving birth to the Uncertainty Principle.^[6]

Over the span of many years, a convoluted and hopelessly unintuitive system of Quantum Mechanics^[7] took form, being able to very accurately predict the behavior of sub-atomic particles. However, there was a catastrophic problem with this: It is entirely conflicting with Einstein's General Relativity. General Relativity is useless at defining the motion of sub-atomic particles, and Quantum Mechanics is likewise laughably wrong when attempting to describe the behavior of anything larger than an atom. Both theories cannot possibly be 100% correct, and yet they are both phenomenally accurate when applied to their respective domains. This causes a central conflict^[8] in the world of physics, which poses some problems. For the most part, physicists can simply use the physics model that best applies to their subject of research: if they're examining celestial bodies they use General Relativity, and if they're working in particle physics they use Quantum Mechanics. However, any areas of research which combine the two domains – most notably, the state of "singularity" at the point of the Big Bang,^[9] and the core of a black hole^[10] – can only be explored in a very limited fashion due to physicists' current impossibility to effectively merge the two theories. This leaves a lot of "unknowns" in the physical world which includes the very birth of our universe as we know it. Thus, the quest to find a Unified Field Theory which brings the two systems together in a manner which makes sense has become the Holy Grail of physics.

In all of physics, there are four observable forces: gravity, which is described by General Relativity, the strong nuclear force, the weak nuclear force, and electromagnetism.^[11] By describing all of matter as being made up of a large number of elementary particles, the Standard Model^[12] was pioneered, successfully uniting the latter three of these forces into a single unified theory which was able to accurately describe the interaction of particles based on those forces. However, this model leaves out gravity, thereby being unsuccessful as an attempt to truly bring the theories of physics together under one grand unification.

Enter String Theory. In 1968, a particle physicist named Gabriele Veneziano stumbled upon a mathematical equation called the Euler beta-function. The formula was an obscure, two-century old problem devised with no particular intention to ever be useful to the field of physics, but coincidentally, Veneziano discovered something rather startling: The equation perfectly described certain aspects of the strong nuclear force.^[13]

In 1970, a young American scientist named Leonard Susskind, attempting to discover the reason behind this seemingly accidental relation, had the idea to model elementary particles as one-dimensional, vibrating strings instead of the zero-dimensional point particles used in the Standard Model.^[14] The math added up. String Theory was born.

The fundamental idea behind string theory is that each elementary particle - the building blocks of atoms – is actually, counter to the normal visualization of small pieces of matter as spherical orbs, a miniscule, vibrating string. Much in the way that the length, thickness and tension of a string in a musical instrument causes the string to vibrate at a certain frequency, creating a tone or a music note, the different vibration patterns produced by string particles result in different types of elementary particles. If true, String Theory would mean that all of existence could be described as a grand symphony of notes, playing in profound harmony with one another to form our universe.

But more than just being a beautiful but otherwise equivalent alternative to the Standard Model, String Theory accomplished something much greater. Early on, certain peculiarities immediately manifested themselves. While many of the vibration patterns indicated by String Theory could be directly corresponded to the properties of known particles, the model also predicted other, extraneous vibrations corresponding to massless particles never seen in experiments, which seemed to be irrelevant to the makeup of reality. As further research was done to explain these anomalous patterns, it was found that there was, in fact, a particle whose hypothetical properties could be accurately defined by these odd vibrations. It's true that this particle had never been experimentally discovered, but many scientists had previously predicted its existence. That particle is the Graviton.¹⁵ String Theory, as a mathematical model, had successfully bridged the gap between Quantum Mechanics and General Relativity.

However, at its conception, String Theory had a number of nontrivial problems which kept it from being taken seriously by the scientific community at large. It predicted "Tachyon" particles, or particles which could not possibly exist due to the fact that they travel faster than the speed of light.^[16] It described a spacetime continuum made up not of four dimensions, but upwards of ten. But most fatally, there were a number of mathematical anomalies which would need to be resolved for String Theory to be plausible.

In mathematics, an anomaly is not merely a peculiarity, or something yet to be fully understood. An anomaly in mathematics is a quantitative contradiction between two equations whose very existence falsifies the theory. If one equation says x = 13 and another one says x = 8, you have an anomaly. Determined to solve these problems, two of String Theory's pioneers, Michael Green and John Schwartz, labored for hours on end one day in 1984 to reframe the theory in a way that would resolve the anomalies without compromising the theory's integrity. By the end of the night, they had a theory free of mathematical anomalies.^[17] String Theory was 100% internally consistent.

However, even today, String Theory is still fraught with problems. To start? There are at least five of them.^[18] Yes, that's right, five separate theories, all differing from one in another in some way, yet all of which are equally valid and internally consistent. So which one of them is the correct one? Well, therein is our second problem. No experiment has yet been devised which can test the unique predictions of String Theory. What does this mean? Any theory, to be accurately classified as science, must be falsifiable. There must be some test, some experiment or observation, that when made, has the potential to disprove the theory, and if it can withstand these falsification attempts, it is considered a valid scientific theory supported by empirical evidence. Until such time as a theory is tested, it can be considered little more than speculation, or in this case, an elegant mathematical framework. For these reasons, much of the scientific community is skeptical of String Theory, with some, such as physicist and Nobel Laureate Sheldon Glashow going as far as to say, "There are physicists, and there are string theorists. ...we don't listen to them, and they don't listen to us. We can't understand them, and what we do is not of any direct interest to them."^[19]

So where does String Theory stand? Is it science? Is it at all relevant or useful to our understanding of the universe? Only time will tell. One thing is certain: As an idea, a mathematical framework which seeks to bring together the fundamentally conflicting theories of General Relativity and Quantum Mechanics, it is a phenomenal and very promising leap forward. But until such time as it can be tested experimentally, it lies squarely on the fringe of science as we know it.

References:
[1] http://en.wikipedia.org/wiki/General_relativity
[2] http://www.aip.org/history/electron/jjhome.htm
[3] (PDF) http://www.cipi.ulaval.ca/fileadmin/template/main/publications/review/Fall_2005/Context.pdf
[4] http://www.juliantrubin.com/bigten/youngdoubleslit.html
[5] http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html
[6] http://www.aip.org/history/heisenberg/p08.htm
[7] http://en.wikipedia.org/wiki/Quantum_mechanics
[8] http://www.infoplease.com/cig/theories-universe/quantum-mechanics-vs-general-relativity.html
[9] http://www.big-bang-theory.com/
[10] http://cosmology.berkeley.edu/Education/BHfaq.html
[11] http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
[12] http://www-donut.fnal.gov/web_pages/standardmodelpg/TheStandardModel.html
[13] http://en.wikipedia.org/wiki/Gabriele_Veneziano
[14] (PDF) http://xxx.lanl.gov/PS_cache/hep-th/pdf/0007/0007118v3.pdf
[15] http://en.wikipedia.org/wiki/Graviton
[16] http://scienceworld.wolfram.com/physics/Tachyon.html
[17] http://www.superstringtheory.com/theatre/stringmovie.html
[18] www.superstringtheory.com/basics/basic5.html
[19] http://www.pbs.org/wgbh/nova/elegant/view-glashow.html

See Also:
http://www.SuperStringTheory.com