First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Alex K]

Well, for starters are you able to give this layman a brief explanation of the stong and weak forces? What they? What do? And why?

First of all you have to know that all forces can be seen as the exchange of virtual particles. the electrostatic and magnetic forces for example are communicated by the exchange of virtual photons, the same guys that make up light if you give them some more energy.
What is a virtual particle? Well, that's kind of a technical issue. Think of it as a particle for which there really isn't enough energy present to make one, but which for a short amount of time can defy this hindrance thanks to some sort of uncertainty principle, which allows particles to appear for a short time.
Now, there are many more types of particles in nature which can also cause forces when they are exchanged, but most of them have a much much shorter range than electromagnetism - for different reasons. There are the W and Z bosons, and when they are exchanged one talks about the "weak force". It is actually not weak, but of very short range, because the W and Z bosons are so heavy. This makes it more unlikely that they propagate spontaneously as virtual particles over longer distances, and hence the range is short. The most obvious effect of the weak force can be observed when W bosons are exchanged, because they change the type of particle. They make electrons out of neutrinos and vice versa, and protons out of neutrons, as an example. Therefore, the exchange of a virtual W boson can turn one type of atomic nucleus into another lighter one,  and produce an electron and a neutrino out of the spare energy. That's beta decay.

There are also the Gluons, and they have a somewhat longer range because they are actually massless like the photons, but since they bind to each other, they basically keep themselves from travelling long distances. These guys lead to a very strong binding force between particles which can interact with them - themselves and the Quarks, and the exchange of Gluons can therefore bind Quarks together to form Protons and Neutrons. This is often called the strong force.

But nit just elemdntary particles can cause forces. Pions which are actually pairs of a quark and an anti quark, themselves can be exchanged between protons and neutrons. This isthe force that holds the nuclei of atoms together - even overpowering theelectric repulsion between between protons. This effect is also calledstrong force.

Any clearer?