MadSci Network: Physics

Re: I have heard that there is a fifth state of matter. is this true?

Date: Tue Sep 26 10:05:17 2000
Posted By: Dan Mayer, Post-doc/Fellow, Mathematics and Theoretical and Particle Physics, I am currently out of work.
Area of science: Physics
ID: 969668827.Ph

If by the other four states of matter you mean Solid, Liquid, Gas, Plasma, then the answer is yes. There is a state known as quark gluon plasma. To explain this state, I will have to give you a quick introduction to particle physics.

All forces are carried by particles. For example, when two negatively charged particles (such as an electron) repel, they exchange a photon (particle of light) - the carrier of the electromagnetic force. Gravity is thought to be carried by gravitons. There are also two other forces in nature, but they operate over a short range and therefore not apparent in everyday life: these are the Weak and Strong forces.

Atoms are made up of positively charged nuclei surrounded by a cloud of negative electrons. The nuclei are made up of neutral neutons and positively charged protons. Neutons and Protons are both made up of quarks. A neutron is made up of two down quarks and an up quark, while a proton consists of two up quarks and a down quark. An up quark has a charge of 2/3 that of an electron, while a down quark has a charge of -1/3 (This gives Proton Charge = 2/3+2/3+(-1/3) = +1, and Neutron Charge = 2/3- 1/3-1/3 = 0). There are three families of quark, so that as well as up and down, there are charmed (charge 2/3) and strange (-1/3), and top (2/3) and bottom (-1/3) quarks. The type of quark is known as its flavour. All apart from the up and down quarks, however, are heavy and short lived (they very quickly decay into lighter particles). Quarks are held together by the strong force: just as the electromagnetic force has charge, so does the strong force. Quarks can come with a 'charge' nown as colour, of red green or blue (or anti-red, anti-geen, and anti-blue for anti-quarks). Each quark also has an anti-quark. Thus there are six flavours, three colours, and two matter-types of quark, giving 6*3*2=36 quarks. The carrier of the strong force is known as the gluon, and it like colours repel while different colours attract. The physics of quarks is known as quantum - chromodynamics, or QCD.

Just as regular plasma is made up of a sea of positive nuclei and negative electrons held together by photons, Quark - Gluon Plasma (QGP) is a sea of quarks and gluons. However, because the strong force will try to confine quarks into particles such as protons or muons (quark-antiquark pairs), a lot of energy is needed to form a QGP. As the strong force is so strong the energy requirement is massive. There is some evidence that a QGP has been created by colliding very fast-moving electrons and positrons at the LEP at CERN, in Switzerland and France. If not, it will certainly be created when the LEP's replacement, the LHC, opens at CERN by 2005.

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