The Guide to the Field Guide to Particle Physics

<p>Frequently asked Questions about Elementary Particles</p><p><strong><br>What is a particle?<br></strong><br></p><p><br>A <strong>particle</strong> is a small packet of energy. It’s nature’s organizational scheme for energy, and energy - so far as we can tell - is never created or destroyed. But it can change forms.</p><p><br>Particles can exist for a moment or for an eternity, but they don’t really have a distinct existence. Unlike birds, trees or people have that their own distinct features or personalities, particles of the same species are completely indistinguishable. For example, it is physically impossible to tell one proton from another. </p><p><strong><br>How big is a particle?<br></strong><br></p><p><br>Particles may or may not have a definite size, although it’s usually fine to think of them as extremely small. A particle’s size is usually a determined by their inner workings, by their constituent components. For example, an atom is only as big as the size of its electrons’ orbit, where as a proton is almost a million times smaller! Elementary particles, like electrons, don’t appear to have any internal structure. Those particles don’t even have a well-defined size!</p><p><strong><br>What is a charge?<br></strong><br></p><p><br>Particles are constantly pushing and pulling on each other. A particle’s charge determines how strong it can push or pull. A great example is the electric charge: opposite charges attract and like charges repel. Electrons and protons have equal and opposite electric charges, which is why they attract to form atoms.</p><p><br>Charges are associated with the forces of nature, like the <strong>electromagnetic force</strong>. There are also the <strong>strong</strong> and <strong>weak</strong> <strong>nuclear forces</strong>, and each has its own kind of charge. In some sense, the mass is the charge for the force of <strong>gravity</strong>. Incidentally, <em>force </em>is just a word for another kind of particle, and we’ll learn all about them in this guide.</p><p><br>Tw