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.