String theory - A Taste








 String theory is a theory that attempts to answer everything...everything that we observe in the universe, both on a large scale and sub atomic scale. In attempting to do so the theory must account for the unique behaviour of the fundamental particles and the four fundamental forces that have been measured. It must unify the theories of general relativity and quantum mechanics, and it must explain the birth of the universe and all that we see within it.

Let us first look at the world of physics where it appears that all is not well.....on the one hand we have general relativity, which describes the larger scale workings of the universe, and on the other quantum mechanics, which gives us a framework for understanding the sub atomic scale. The problem is that they just do not fit neatly together like two pieces of a puzzle, which would complete a complete puzzle.....a theory of everything.

The problem arises because general relativity, which explains how gravity works, breaks down at a subatomic level. Effectively the subatomic world is an arena of uncertainty, it is full of fluctuations that apply not only to the position of sub atomic particles but to spacetime as well.  The smooth geometric fabric that Einstein described (a little like the surface of a trampoline) decays into a see of writhing foam, one that becomes more chaotic the closer you look.  Predictably is something that no longer exists.....

This fundamental conflict between the theory of general relativity and quantum mechanics has resulted in many psychopathy taking up the challenge of resolving such an issue. For many they choose not to lose sleep over the fact that these two theories only fail to fit at minuscule scales, yet this is the typical attitude of so many people....lets bury our heads in the sand and kid ourselves that these two theories coherently explain everything. However for those that have striven to find answers there is at last light at the end of the tunnel in the form of 'string theory,' a theory that stems from a revolution in the perception of the minutia.

The essence of string theory is that, unlike previous thinking, the smallest elements of matter are not point particles. Actually there is a much smaller elementary ingredient from which all matter is ultimately made....strings. These strings are extremely small....if an atom could be scaled up in size to represent the size of the universe then a single string would only amount to the size of a house!! Given such a scale there is no chance that we can observe such strings with our current technology...and so this theory is a conceptual one.

The strength of string theory is in its ability to link two opposing theoretical foundations on which modern physics was built...general relativity and quantum mechanics. The fundamental issue in linking these two theories is that the strings are not point particles, they are loops of vibrating matter or energy. Furthermore, and just as important, is the fact that these strings vibrate, much like the strings of a guitar when they are plucked. Effectively these strands of matter oscillate constantly, and just like a guitar string each elementary string appears to smear owing to its own vibration. unlike point particles, there spatial extent is increased by virtue of their vibrating. Think of looking at a photograph of a vibrating guitar string...the image will look blurred and the spatial extent of the blur will be greater than that of a single string at rest. The same is true of elementary strings....which has extremely important consequences for uniting general relativity and quantum mechanics.

The problem with the idea that point particles constitute the smallest fundamental elements of matter is that they exist at a scale where quantum chaos rules...where the devastating effects of the uncertainty principle come into play. But the theoretical understanding that strings are vibrating and are smeared means they do not succumb to the weirdness of the uncertainty principle because of their increased spatial extent. With string theory the quantum chaos that arises from the uncertainty principle becomes redundant and the quantum foam can be tamed. In fact with string theory the quantum foam never exists. The uncertainty principle arose from the necessity to formulate a framework for quantum mechanics and general relativity with elementary particles that were considered to be point particles, of zero spatial extent. When seeing particles to be point like objects with no spatial extent, physicists only considered properties of the universe on arbitrarily short distance scales. In considering these tiniest of distances physicists ran into the uncertainty principle, and this uncertainty has arisen because they were unaware of the limits of scale and were led by a point particle approach to overstep the bounds of physical reality. However if all matter is composed by strings, the extended nature of the string eradicates the ultra short distance behaviour responsible for the dilemma of uncertainty.....

Okay so string theory is still a conceptual theory, yet it does offer to provide the link needed to bind the theories of general relativity and quantum mechanics, and furthermore it offers a powerful paradigm for the workings of the universe. However string theory also offers a tangible understanding of the way things actually behave in the universe.

Galaxies, stars, you, me and everything around us are all composed of just a handful of types of elementary particles, such as electrons, muons and quarks. These elementary particles are the building blocks of atoms. Each type of elementary particle has its own characteristic profile, a specific mass and electrical charge. These particles interact with each other by the workings of an even smaller number of 'messenger' or 'force particles,' which constitute the four fundamental of the universe....weak, strong, electromagnetic and gravity. From this point of view the universe appears to be incredibly finely tuned in the sense that the numerous processes that occur within it (i.e. the formation of black holes and the explosive force of a supernova) can be explained in terms of the actions of a handful of elementary particles and the four fundamental forces. If however these parameters were to be changed by even a minuscule amount then the grand structure of the universe would be completely different. The key question here is what dictates the precise parameters of these particles and forces? Of course it is possible for us to measure their physical properties, but no one knows why they are the way they are.

String theory does however offer us an explanation for the way these particles and forces behave. Traditionally elementary particles and the fundamental forces have been classified on the basis of their uniqueness. It would therefore seem sensible to suppose that for example, electrons are made of a different material from quarks because their weight and electric charge are different. Once the connection was made that all particles of all types could be made of strings , string theory revealed that the characteristics of each fundamental particle could be a product of the unique vibration of each string.

Essentially the fundamental particles of the universe are not made of different material, but the same. The reason that they display different characteristics is due to their internal strings vibrating differently, and if this is correct the sum total of the unimaginably small vibrating strings equates to the harmonic symphony of the universe we see around us.

Whilst particles and forces are identifiable as separate entities today, most theorists believe that at extreme temperatures and pressures, such as those experienced within the big bang, all particles and forces would have been united. This might have worked in much the same way as ice cubes unite to form the same pool of water when heated. This idea is what is known as the standard model. In order for this type of model to be viable it must be able to accommodate the workings of all the known particles and forces. This is one of the reasons as to why scientists want unification between general relativity, where the forces of gravity dominate, and quantum mechanics, where the three other fundamental forces dominate. All forces must 'get along' since they are at the heart of everything in the observable universe.

If we had point particles as the basic structure of everything then at the beginning of the universe everything would have been compressed down to some form of infinitely tiny distance scale. Furthermore the temperature would have been essentially infinite. It is therefore extremely difficult to describe the birth of the universe within a theory that only has particles and doesn't have strings as the fundamental quantities. With strings this infinite behaviour evaporates and is replaced by something that is finite...everything was compressed to a small size but it was not infinitely small...temperatures would have been high....but not infinitely high. So we are provided with hope of actually calculating what actually happened at the beginning of the universe.

For the first time the mathematics of vibrating strings, the heart of string theory, successfully describes what the theory of point particles could never do, the behaviour of a force particle for gravity...the graviton. By theorising that gravity is mediated by a force particle, which itself is a result of a vibrating string, string theory allows the harmonious merger of general relativity with quantum mechanics...without gross distortions of spacetime. From this point of view string theory offers a very powerful argument in claiming to be a theory of everything.

According to Einstein's equations space and time are curved. I would use the analogy that the universe is like a sheet of rubber, and when a piece of mass is placed in a place it dents the rubber and causes things to fall in, and that is analogous to how gravity works. If you were to take that same piece of mass and jiggle it back and forth, what would happen to the sheet of rubber? Very quickly you would build up ripples on the sheet of rubber as you take the mass point and jiggle it back and forth. Those ripples are in fact the graviton, so it's the waves of gravitational energy in spacetime that are responsible for communicating the gravitational force.

Okay so thus far we have put paid to quantum uncertainty and succeeded in tying gravity into the world of the minuscule. However whilst this sounds logical and common sense nothing in life could be that simple. If everything is made from string vibrations why should there only be a set number of particles? Why not an infinite number of string vibrations leading to an infinite number of particles and forces. The hub of the theory is that the way strings vibrate is dictated by the geometry in which they are contained. Different fundamental particles reflect different string vibration patterns that in turn are dictated by different geometries...or different dimensions. One way of understanding this is to imagine that you are locked in a box and that you wriggle in an attempt to break free. If the box you are in is a long thin box you will wriggle in a long thin way. However if you are in a big square box you will wriggle in a big square way. The wriggling movements that you will make will be dictated by the shape of the box, just as a strings vibrations are dictated by the dimensions in which they exist.


To make the maths of string theory work there is one more leap of faith required. strings operate in a world that contains ten dimensions, one time dimension, three space dimensions and six unknown ones. These extra dimensions are needed to explain the existence of all the particles that have been observed in atom smashes. Having these extra dimensions means that a single string can vibrate in many different directions and therefore can produce the large variety of particles that have already been observed.

Four of these dimensions are familiar to us...





However when working within string theory there are six other dimensions which are so small that we cannot possibly see them. However this aspect of the theory created an argument. With these ten dimensions scientists could only explain string theory mathematically in five different ways, that is the Theory of Everything came in five different forms (or flavours) dependant upon how the properties of the strings are viewed and which fundamental particles you would allow for in your mathematical treatment. too much for a theory of everything I hear you say...the theory cant even agree on one version!!! well that may have been so...until the emergence of one scientist who transformed string theory.

The answer to this problem came in 1995 through what is known as M–theory, and the man who made it possible, Edward Witten. He suggested that the five different 'flavours' were simply different ways of looking at the same problem. He argued that each of the five different string theories can actually be connected to each other by mathematics and are different facets of one all encompassing theory, M–theory. Think about standing in a life that has five different mirrors and looking at your own reflection – yes each reflection is unique, but the image that each mirror is reflecting is of the same object.

However in order to assimilate the five different mathematical versions of string theory Witten had to introduce an 11th dimension. This extra dimension allows greater freedom of movement for the physical behaviour of our minute strings of vibrating matter. The more degrees of freedom our strings have the greater the ability of string theory to explain all of the observed physical properties of the universe. However by adding another dimension a new implication was uncovered.....there may be more than one universe.


Rather than being tiny and restrictive the 11th dimension has a unique quality, it allows a string to be able to expand. An expanded string is known as a 'brane' (short for membrane). Visualising this brane is dependant upon how much energy the string has. Mathematics has shown us that the more energy a string has within the 11th dimension the larger the brane can become.....give it enough energy and it could become the size of the universe. This opens up yet another question...perhaps the universe is a brane and we are living in the skin of a brane. When thinking about this a further question can be posed....Are there other brane's??? This is perhaps a scary question as what I am asking is whether or not there are in fact other universes?? Perhaps there is another brane paralleling our brane....a parallel universe. The laws of physics and the forces that act within any particular brane are considered to be a manifestation of the strings that are attached to that brane, and different brane's may well have different strings, and hence different laws of physics.

However we must remember that this is only a theory based upon mathematical findings. Theoretically all of this is possible, yet testing the reality of such predictions has thus far been incomprehensible. Perhaps the best way to explore this concept is to explore two factors that may suggest this proposal to be a reality...the big bang and gravity.

As we know gravity is one of the four fundamental forces, which are instrumental in the workings of the universe. However if differs from the other three fundamental forces (being weak, strong and electromagnetic) in that it is much weaker. For example gravity is a thousand billion billion billion billion times weaker than the electromagnetic force that holds atoms together. The weakness of gravity has baffled scientists for decades, but string theory may have provided an answer.

Why should gravity be so weak in comparison to other forces in our universe. Well if we return to the prospect that 'our universe' is in fact a brane, string theorists believe that each brane may have its own physical laws. If I went to visit a parallel brane (universe) the physical laws which govern that universe may be substantially different, yet still dictated by the strings that anchor it.

A further question could be directed towards the freedom of such strings...what if some strings were not anchored down to their universe..what if some were free to move?? This is the new thought behind gravity. The string responsible for creating the behaviour of the graviton is thought to be a closed loop, and so because of its shape it is not tied down to any universe. Instead it is free to permeate between brane's. Like sound waves gravity can reverberate around brane's, and also like sound waves gravity gets weaker as it disperses. Gravity may well be as strong as the other fundamental forces, but owing to its ability to permeate through parallel universes it becomes diluted. If such a theory is correct gravity may well be the only way we can communicate with other parallel universes, since it is the only force common to all universes and dimensions.


String theory, which has now become M–theory, is providing a revolution in the way we perceive the cosmos, and indeed our very 'existenz.' Perhaps the ultimate question for me is whether string theory can explain how it all began. The idea of the big bang, the event that created everything in our universe, is neither a new idea or one that is water tight. In fact it has considerable problems. The theory of the big bang states that everything we can observe was born from an infinitesimally small point which rapidly expanded out from a rapidly huge explosion of energy. What caused this event, and indeed what preceded it has never been satisfactorily explained, afterall even I cannot comprehend the fact that a big bang occurred out of nothing.

Some string theorists are toying with the idea that the big bang is a manifestation of the collision of brane's, that is two or more parallel universes colliding, releasing a vast amount of energy and matter which eventually condensed to form the galaxies, stars, planets and even me and you. If we were to use this explanation then big bangs are far from unique, rather they are just the by product of the endless cycles within the cosmos...they have happened before and they will happen again. Perhaps string theory offers an insight into how we got here, and I for one am willing to embrace such a theory in searching for the answers to my own existence.


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