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NEWS: Higgs and Englert are awarded Nobel Prize in Physics 2013.

 INTERACTIONS

 Particle responds to a force due to the presence of another particle because both two have the same kind of charge. This charge is a quantity carried by particles that determines their participation in an interactions process. A particle with electric charge has electrical interactions; one with strong charge (or color charge) has strong interactions, one with weak charge (isospin or hypercharge) has weak interaction and inertial charge (mass) determines gravitational interaction. One consequence of Heisenberg's uncertainty principle is that the energy and duration of a particle are also characterized by complementary uncertainties. There is always, at every point in space and time, even in a perfect vacuum, an uncertainty in energy and an uncertainty in duration, and these two complementary uncertainties cannot be reduced to zero simultaneously. ΔE·Δt ~ ℏ ⇒ ΔE~ ℏ/Δt ⇒ Δm·c2~ ℏ/Δt Δm ~ ℏ/(Δt·c2)   (1) A particle with mass = Δm can exist if its duration is less than Δt . The meaning of Heisenberg's uncertainty principle is that "something" can arise from "nothing" if the "something" returns to the "nothing" after a very short time—an interval too short in which to be observed. These micro-violations of energy conservation are not only allowed to happen, they do, and so "empty" space is seething with particle-antiparticle pairs that come into being and then annihilate each other again after a very short interval. The figure shows an interaction beetwen two electrons "using" a virtual photon (Feynman diagram). Although these particles -VIRTUAL PARTICLES- cannot be observed individually , their existence can be demonstrated.
 According (1), the more energy  virtual particle ‘borrows’ from de vacuum (so the more mass they have) the shorter the time they can exist. For each interaction there is a carrier particle (fundamental boson) associated with quantum excitations of the force field corresponding to that interaction. They are virtual particles that form out of vacuum field, as it was said above. Because photon and graviton are massless the electromagnetic and gravitational interaction can reache infinite distance. However, the big masa of carrier particles for weak interaction implies very short duration and very short distance. The case of strong interaction is different and it's related to the special characterisitics of the strong charge. Gluons are carrier particles for strong interactions (color force fields), photons are carrier particles of electromagnetic interactions,  the W and Z bosons are carrier particles for weak interactions, and gravitons are proposed as carrier particle for gravitational interaction. The next animation shows a muon decay through a virtual W :

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