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Chapter 33 | Particle Physics 1485
Figure 33.6 The image shows a Feynman diagram for the exchange of a between a proton and a neutron, carrying the strong nuclear force between them. This diagram represents the situation shown more pictorially in Figure 33.4.
The relative strengths of the forces given in the Table 33.1 are those for the most common situations. When particles are brought very close together, the relative strengths change, and they may become identical at extremely close range. As we shall see in GUTs: the Unification of Forces, carrier particles may be altered by the energy required to bring particles very close together—in such a manner that they become identical.
Making Connections: Why You Stay on the Earth, but Do Not Fall Through
You are familiar with gravity pulling you towards the Earth. It's why when you jump, you come back down. In this action, and at distances and speeds that we experience in our everyday lives, gravity is the only one of the four fundamental forces that has such an obvious effect on us.
Electromagnetism is vital for our society to run, but due to your body having the same (or very nearly the same) number of positive and negative charges, it doesn't usually have as much of an effect on us. Except for one very important feature: the electrons in the bottom of your feet experience a mutually repulsive force with the electrons in the material you stand on. This is what keeps us from falling into the planet, and also allows us to push on other objects and generally interact with them.
These electromagnetic forces are dominant in the electron shells of an atom, and also the interaction of the electrons with the nucleus. However, within the nucleus, the electrostatic repulsion of the protons would break the nucleus apart if it were not for the strong force, which holds the nucleus together. At even smaller scales, within nucleons such as protons and neutrons, the weak force is responsible for nuclear decays.
The relative strengths of the forces given in the Table 33.1 are those for the most common situations. When particles are brought very close together, the relative strengths change, and they may become identical at extremely close range. As we shall see in GUTs: the Unification of Forces, carrier particles may be altered by the energy required to bring particles very close together—in such a manner that they become identical.
Summary
• The four basic forces and their carrier particles are summarized in the Table 33.1.
• Feynman diagrams are graphs of time versus position and are highly useful pictorial representations of particle processes.
• The theory of electromagnetism on the particle scale is called quantum electrodynamics (QED).
33.3 Accelerators Create Matter from Energy
Learning Objectives
By the end of this section, you will be able to:
• State the principle of a cyclotron.
• Explain the principle of a synchrotron.
• Describe the voltage needed by an accelerator between accelerating tubes.
• State Fermilab's accelerator principle.
The information presented in this section supports the following AP® learning objectives and science practices: