Going into the sixth year of the new millennium physicists are consistently getting closer to discovering a theory of everything, known as String Theory. The question as to how the universe works has perplexed some of the greatest minds in human existence, and thus far all have failed to come up with a comprehensive, water tight answer. The principal reason is that in order to do so physicists must construct a framework that transcends unimaginable scales of size, time and dimension.

The universe is a place of extremes. On a larger scale it is dominated by huge clusters of stars bound together by gravity. Our galaxy, the milky way, is just one of countless millions. Like stars galaxies themselves bond to form clusters and super clusters which extend out far into the observable universe. On a small scale it is another realm entirely, composed of atoms and sub atomic particles (electrons, protons and quarks) glued together by strong and weak electro magnetic forces.

Amongst the greatest achievements of Albert Einstein was his ability to fathom the working of the universe on a grand scale.  In 1905 Einstein published his 'special theory of relativity', the crux of which was a new way of perceiving space and time. Einstein announced that space and time are not separate (as was previously believed), but rather are woven together–they are one and the same. He called this 'spacetime.'

Put simply special relativity binds together not three but four dimensions, three for space (forward–backward, up–down and left–right) and the fourth being time. We move through all of these dimensions everyday of our lives. Einstein proposed that whichever of these dimensions we are moving through, the sum total of the velocities of all of them must always be equal to the speed of light. In this sense space and time are similar dimensions and we can think of the objects speed through time in a similar manner as its speed through space. As you move around here on earth you do so through the three dimensions of space, but only at a fraction of the speed of light. But remember your speed through all four dimensions must always equate to the speed of light. To compensate for your pathetically slow speed on earth you move through time at quite a jog, relatively speaking. In fact almost all of your speed is given over to your movement through time.

Of course Einstein's theory provokes an intriguing paradox. If you were traveling through space close to the speed of light you would no longer be traveling so fast through the dimension of time because you are already fulfilling the rule of light speed travel. Special relativity states that when traveling at velocities very close to the speed of light the time dimension element of the sum equation becomes smaller. Hence the faster you travel through space, the slower time passes as seen from a stationary observer (for whom time passes more quickly). hen traveling through space at the speed of light the passage through the time dimension is zero–time stops completely. Therefore as photons (of which light is composed) travel at the speed of light, time does not exist for them, they are as young as the day they were created (big bang?) billions of years ago.

The reason as to why we find the implications of this theory so difficult is because we live in an incredibly slow world, one that blocks out the true mechanics of spacetime. Special relativity is therefore a theory that requires us to look at the universe in a way that we are not accustomed. However in doing so it reveals the true nature of space and time, and in doing so dismantling Newton's 'clockwork universe' in which time and space are separate entities.

GENERAL RELATIVITY AND WARPED SPACE

Einstein's keen perception and ultimate understanding of relative motion and time led him to formulate his elegant special theory of relativity. Yet it threw up a further conflict, clashing again with the work of Isaac Newton–this time Newton's sacrosanct theory of gravity. Newton correctly theorised that a body exerts a gravitational pull on another body with a force determined by two properties–the mass of their bodies and the distance apart. Newton then surmised that if you were to change one parameter for one body, the other body would instantly feel a change in the way its tugged: the pull of gravity would instantly change. But special relativity states that nothing can travel faster than the speed of light.....

                                    E = mc2

In this equation E represents an infinite amount of energy, which is needed to accelerate mass (m) to the speed of light (c).

Based on special relativity where nothing can travel faster than the speed of light, including the effect of gravity, it follows that if the sun were to suddenly disappear earth would not be affected by the loss of the suns gravitational pull. However as Newton's understanding of gravity implied, the loss of the sun would be felt a little after eight minutes–the time it takes light to travel the 93 million miles between the two bodies. This conflict led Einstein to the formulation of his general theory of relativity.  With general relativity Einstein once again revolutionised the understanding of space and time. He showed through mathematics that space is warped by mass–the greater the mass the greater the warping of space. I would use the analogy of placing a bowling ball on the surface of a trampoline, which will dent its surface, and so the mass of the sun (or any other mass) dents the fabric of spacetime. The earth orbits the sun as it is trapped on the limb of the warped space, mass dictates how space is warped, the manifestation of this warping is the force we call gravity. Furthermore since space and time are interwoven, warping space warps time.

THE QUANTUM WORLD

Put simply quantum theory describes the workings of the universe at the tiniest level. If we were to shrink down to the atomic and sub atomic world it is very different from the world we experience. The essence of quantum theory (also known as quantum mechanics) is that matter at sub atomic levels takes on a Jeckyll and Hyde personality, having both wave and particle properties.

WHAT IS LIGHT?

The idea of this theory stems from a series of discoveries made during the late 19th and early 20th century. In 1905 Einstein solved a riddle that had perplexed the German scientist Max Planck.  Planck deduced that atoms could absorb or emit energy, in the form of electromagnetic radiation (as in light or infra red heat energy) but only in discrete packets. Planck surmised that such an observation was a consequence of the ability of atoms to emit energy only in separate chunks. Then Einstein proved that electromagnetic waves, such as light, are themselves composed of discrete packets of energy, or 'quanta.' Later the quanta were named 'photons.'  If you turn on a light bulb or an electric fire billions upon billions of photons stream out each second to illuminate or heat a room. Einstein had these ideas whilst he was trying to explain an observation called the photoelectric effect. Not only did he shows that light came in photons, but he also came up with the notion that light waves can actually act as if they were light particles.

The photoelectric effect happens when light bombards the surface of a metal, and electrons are ejected from the metal, only when light of a minimum frequency (or energy) is used. Above that frequency increasing the intensity of light increases the number of electrons that are ejected. Hitherto light had been thought of as light waves that bend on hitting a solid surface. But it is easier to imagine that a particle rather than a wave could dislodge an electron from an atom by colliding with it. Once the critical minimum energy or frequency of light is exceeded, the energy content of each photon is enough to cause one metal atom to lose one electron. Below the critical energy no single photon has enough energy to dislodge an electron from an atom, but above it more photons will dislodge more electrons. The governing idea of Einstein's photoelectric effect is that light sometimes has the properties of a wave and sometimes has the properties of a particle...a phenomenon known as wave–particle duality.

WHAT IS MATTER?

In 1923 a French prince (de Broglie) used Einstein's special theory of relativity to reason that since energy, which is propagated through wave motion, and mass (matter) are interchangeable through Einstein's equation, then matter too must display wave–particle duality. If light can be considered to have both wave and particle properties, then why doesn't matter behave in the same way? His assumptions were vindicated a few years later by scientists who demonstrated that electrons, minuscule particles of matter, also behaved like waves. The particles themselves were considered to be point particles, in effect having no spatial extent. This is an important factor when considering the validity of string theory.

Essentially all matter has wave like characteristics, not just electrons. What is important is that this occurs at the smallest sub atomic level, and that all matter has wave like properties, including the particles that make up your computer. Yet there is another twist in the quantum world, one that lies at the heart of quantum mechanics, 'the uncertainty principle.'

WAVES, PARTICLES AND UNCERTAINTY

The uncertainty principle was developed in the 1920s by Werner Heisenberg, and is a result of matter having wave–particle duality. The premise is this–think of a particle of matter, such as an electron. It is a tiny point of matter, and has a position in space. However the electron also has wave properties, and so it is moving, and you can measure where it is and where it is going. But....the two measurements are in direct conflict, if the electron is moving it doesn't have a stable position.  Waves do not have a position in the same sense as particles, they only have a direction and momentum since all mass that moves carries a momentum force.

This shows that mathematically you cannot know both the position and momentum of an electron at the same time. The uncertainty principle states that electrons, and all other point particles, cant be described as being in such a place at such a time with such a momentum. You can measure say the momentum of a particle but not its position. In fact the more precisely you know property, the less sure you can be of the other. Okay so I hear you say that you would be able to know the position of a moving car at an instant in time with a fairly high degree of accuracy. However in the tiny world of quantum mechanics this becomes more difficult as the numbers get smaller. You may be looking at your computer thinking 'I know exactly where my computer is' but on a sub atomic level it is impossible to know instantaneously the velocity and position of any of the electrons that are part of the atoms in the material from which your computer is made.

BRINGING IT ALL TOGETHER

Einstein's general theory of relativity (built upon his earlier formulation, special theory of relativity) is a theoretical framework that describes the universe on a large scale–the interaction between stars, galaxies and clusters of galaxies, space and time.

Quantum theory provides a theoretical framework for understanding the universe on atomic and sub atomic scale. Both general relativity and quantum theory have been vindicated through years of thorough experimentation, but there does remain a problem.....the two theories are incompatible!!!

Effectively general relativity breaks down at a sub atomic level and uncertainty dominates. Not only is the position of particles unpredictable, so is the whole fabric of space time. The perfect geometric shape of spacetime degrades into a chaotic unpredicted foaming mass at the quantum level. whilst the two theories explain the macro and micro universe beautifully, it seems that the two will not join. This has represented the key conflict between 20th century physicists, but a result to provide a link between the two has been sought and found.........in the guise of String Theory.