Antimatter is very much like ordinary matter, but it carries the opposite charge eg an anti-electron (a positively charged electron) or an antiproton (a negatively charged proton). Crashing matter particles together is now a daily occurence in machines like LHC, in many such collisions antimatter particles are produced. The fact that the universe seems to be full of matter and not antimatter is one of the most baffling problems in modern physics. At the time of the Big Bang, matter and antimatter are believed to have been produced in equal quantities. What seems to have happened is that collisions between the two types have destroyed all the antimatter but left a little of the matter behind, from which our universe is made.

Big Bang Science                                                                                                                                            It is thought that the universe began around 15 billion years ago in the Big Bang and that it has been cooling down and expanding ever since. For physicists, the most interesting time was within the very first instant, where the conditions were so extreme that the laws of physics as we know them today didn't apply. After about 0.01 seconds, the universe was cold enough for quarks to stick together, forming protons and neutrons. These formed the first helium nuclei after 100 seconds, but the first atoms didn't appear for 100,000 years. After a few billion years stars began to form, using hydrogen and helium to build the heavier elements that make up the familiar world around us -elements heavier than helium owe their origin to stars. The Big Bang theory correctly predicts that about 75% of all visible matter is hydrogen and about 25% helium. (All other matter accounts for less than 1%.)  

Dark matter

We know from observing the rotation of galaxies that about 90% of the matter they contain is invisible to us. The matter we can't see is called "missing" or"dark" matter. The amount of dark matter contained in the universe is crucial to its fate. If it is greater than a certain amount, the universe will eventually collapse. Below this, and it will keep on expanding for ever. There are many ideas about what dark matter might be, ranging from exotic new particles to black holes.