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33.1 The Yukawa Particle and the Heisenberg Uncertainty Principle Revisited

- The story is not complete because quarks and electrons may have smaller structures.

- The basics of particle physics are covered in this chapter.
- Particle physics is evolving with an amazing convergence of topics.
- Nature on the smallest scale may have the greatest influence on the large-scale character of the universe.
- It is an adventure that surpasses the best science fiction because it is real.

- Hideki Yukawa came up with the idea of particle physics in 1935.
- The concept of fields, such as electric and magnetic fields, was very useful to physicists who had long been concerned with how forces are transmitted.
- The force of the object through space is carried by a field.
- Yukawa was interested in the strong nuclear force and was able to explain it in an ingenious way.
- His idea is a blend of forces, particles, and quantum mechanics.
- The force is transmitted by the exchange of particles.

- The particles are in the field.

- The creation and exchange of a pion is how the strong nuclear force is transmitted.
- The pion is created through a violation of mass-energy and travels from the protons to the neutrons.
- It's called a virtual particle because it's not directly observable.
- The Heisenberg uncertainty principle limits the range of force because the pion can only exist for a short time.
- The larger the mass of the carrier particle, Yukawa used the finite range of the strong nuclear force to estimate it.

- The pion can only be created by violating mass-energy.
- The Heisenberg uncertainty principle allows this if it occurs for a short period of time.

- For a period of time, no process can detect a violation of mass-energy.
- The temporary creation of a particle of mass can be done.
- The shorter the time it can exist, the bigger the mass.
- The force can only travel a limited distance in a finite amount of time.

- The pion cannot be directly observed because it would amount to a permanent violation of mass-energy-conservation.
- Yukawa used the range of the strong nuclear force to estimate the mass of the pion.

- Taking the range of the strong nuclear force to be about 1 fermi, calculate the approximate mass of the pion carrying the force, assuming it moves at nearly the speed of light.

- The calculation is approximate because of the assumptions made about the force and speed of the pion, but also because a more accurate calculation would require the sophisticated mathematics of quantum mechanics.
- The Heisenberg uncertainty principle is used to calculate the time that the pion exists, given that the distance it travels is about 1 fermi.
- The mass of the pion can be determined from the Heisenberg uncertainty principle.
- Since we are often considering converting mass to energy and vice versa, we will use the units of mass.

- It's about 200 times the mass of an electron and one-tenth the mass of a nucleon.
- There were no known particles when Yukawa made his proposal.

- The method of force transfer proposed by Yukawa is intriguing.
- It would be possible to free the pion from the nucleus if enough energy was present.
- Energy greater than 100 MeV is required to conserve both energy and momentum.
- In 1947, pions were observed in cosmic-ray experiments, which were designed to supply a small amount of high-energy protons.
- The pions were created in the laboratory under controlled conditions.
- Three pions were discovered, two with charge and one neutral, and given the symbols.

- The pions, or -mesons as they are also called, have mass close to those predicted and feel a strong nuclear force.
- The idea of implosion for plutonium bombs was originated by one of the discoverers of the muon.
- The particle predicted by Yukawa was thought to be the mass of a muon.
- The muons do not feel the strong nuclear force and could not be Yukawa's particle.

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