Theory of Everything

 

In physics, particles are considered as points moving through space, tracing out a line called the World Line. Unfortunately, there are a great number of different fundamental particles, which makes the construction of a 'Unified Theory' difficult.

In String Theory, the myriad particles are replaced by a single loop, a `string'. As the string moves through time it traces out a tube, the 'World Sheet'. The string is free to vibrate, and different vibration modes on the string represent the different particle types. One mode of vibration makes the string appear as an electron, another as a photon. There is even a mode describing the graviton, the particle carrying the force of gravity. This is an important reason why String Theory has received the attention it has. There was hope that the String Theory will be able to 'unify' all of the known forces and particles together into a single 'Theory of Everything'.

 

Extra dimensions
One of the most famous predictions of String
Theory is that space-time has ten dimensions!

This may be seen as a reason to dismiss the theory altogether, as we obviously have only three dimensions of space and one of time. If it is assumed that six of these dimensions are curled up very tightly, then one may never be aware of their existence. Having these so-called compact dimensions is very beneficial if 'String Theory' is to describe a 'Theory of Everything'. It is assumed that the extra dimensions are wrapped up on six circles.

 

Questions and more Questions

Despite all the progress that has taken place in our understanding of Superstring Theory, There are many important questions whose answers are still unknown. It is unclear how many important discoveries still remain to be made before it will be possible to answer the 'ultimate question' that we are striving towards -- 'why does the universe behave the way it does'?

What is the best way to formulate the theory? How and why is super symmetry broken? Why is the cosmological constant, which characterizes the 'energy density of the vacuum', so 'small' or 'zero'? How can a realistic solution of the theory be chosen from the myriad of possibilities? What are the cosmological implications of the theory? What predictions can be made?