A                        GLANCE                        TO                        MODERN                        PHYSICS
                        


It was in the IV century A.D when the idea of a particle first came to light. Democritus call it atom meaning indivisible. Nowadays we know that the atom is indeed divisible. By the begining of the XX century, the british physicist Ernest Rutherford realised for the first time that the stucture of the atom contains a nuclei where most of its mass is concentrated. It is also known these days that a cloud of electrons surronds this nuclei. Since early in the XX century attemps have been made to identify the true fundamental particles that conform matter. That is those physical entities which are indivisible.



The CERN accelerator in the Swiss-French Border
In order to investigate the physics related to the elementary particles huge machines have been built. These are the particle accelerators. The end of these accelerators is to make collide beams of particles with a predefined target and sometimes between them. The collision region is surrounded by detection instruments. The function of these detectors is to study the debri produced by the collision in order to identify possible new particles.



Particle tracks coming from a high energy proton-antiproton collision as detected by the UA1 experiment at CERN in 1982. The tracks emerging from the central detector are due to an electron-positron pair coming from the decay of the first Z Boson ever observed. Several British groups were involved in this experiment.

So far the known fundamental particles are:

LEPTONSANTI-LEPTONSQUARKSANTI-QUARKS
electron positronup s-up
downs-down
muon anti-muoncharm s-charm
stranges-strange
taon anti-taonbeauty s-beauty
tops-top

These particles are the basis of all matter from this set all other particles are form. However these are not the only fundamental particles that exists. There exist also the force carriers, these particles are called bosons, and they are the responsible of all the interactions in nature. And the neutrinos associated with each of the three families of quarks. As of this day there are four known forces governing the Universe: the familiar electromagnetic force, the also familiar gravitational force, and the not so familiar weak and strong forces. Actually we can talk of only three forces since it has been proved that the electromagnetic force and the weak force are really just different aspects of a single one: the electroweak force. The bosons carrying these forces are: the photon for the electromagnetic force; the W+, W- and Z0 for the weak force; the graviton for the gravitational force; and the gluon for the strong force.

As you may see this idea of simplicity (to have just one fundamental entity) is far from being achieved. New supersymmetric theories attach another set of particles and antiparticles to each of the fundamental particles mentioned above. In this chaotic scenario, a new theory has recently emerged: the String theory and its supersymmetric counterpart: Superstring theory. These theories are achieving what seemed to be impossible: to have one single entity describing all known matter: the strings!

Strings and Superstrings, just like any violin string, can vibrate and form melodies, the notes of the Strings and Superstrings are different states of matter, some describes for example the gravitons other vibrations describe the quarks, and so on. Thus, these two theories are the best hope we have so far to reach the dream: to have a unique theory describing the very nature of the Universe.

Later on in future editions of this section I will talk more on the fascinating subject of strings and how they differ from the old particle point of view. In the mean time, let us have a look at the Big Bang theory and how the Universe started!





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