Introduction to QED Quantum Electrodynamics Part III Double

Introduction to QED Quantum Electrodynamics Part III

$Double Slit Diffraction Interference occurs and probability is between 0% and 4%$

Double Slit Diffraction Interference occurs and probability is between 0% and 4%

When Detectors are Added Interference disappears and probability is always 2%

When Detectors are Fallible

Electron – Photon Interactions • Electrons behave like photons. - On a large scale, they appear to move in straight lines. - On a small scale, they can move anywhere. - Interference becomes important.

Electron – Photon Interactions Three basic actions: - A photon goes from place to place. - An electron emits or absorbs a photon.

Objects Moving from Place to Place

Light’s Probability of Movement • Probability is dependent on only the distance the photon must travel and the time it takes to do so (difference of squares). • Photon moves at c when distance and time components are equal (at a 45° angle). • Photon’s highest probability occurs at speed c.

Light Diagrams

Electron Diagrams

Coupling • An electron has a specific probability to emit or absorb a photon. • Since probability for either to happen is equal, they will be regarded as the same event and be referred to as “coupling. ” • The probability of coupling is the constant “j” (junction number), which is related to the electron’s charge. j » -0. 1

Coupling

Simultaneous Electron Movements

More Possibilities

Photons Moving at Multiple Speeds

Two Photons Exchanged

Diminishing Contribution • The more couplings that are required, the more times the probability must be multiplied by j. • Since j is less than one, the probability of occurrence decreases with every required coupling.

Photon Scattering • Defined as when an electron absorbs and emits a photon, but not necessarily in that order • A photon can disintegrate into an electron positron pair. • An electron and positron can annihilate and become a photon or two.

Photon Scattering

Electrons in an Atom • Electrons are kept in “orbit” by exchanging photons with the protons in the nucleus. • Scattering of photons by electrons in atoms is the cause of numerous optical phenomena.

Hydrogen Atom

Partial Reflection

Partial Transmission

$Index of Refraction • The additional turning of the probability amplitude causes the photon$

Index of Refraction • The additional turning of the probability amplitude causes the photon to appear to be moving more slowly through the material. • The more opaque the material, the more turning occurs and the more slowly the light appears to travel. • The amount of turning by the final arrow caused by the electrons in a material is called the “index of refraction. ”

Stimulated Emission • Photons tend to get into the same state. • The chance that an atom emits a photon is enhanced if some photons are already present. • Principle used in lasers.

Two Photons Moving

When the Points Converge

Electrons and the Exclusion Principle

Magnetic Moment of an Electron • Represents the response of an electron to an external magnetic field • The number changes over time as more possibilities for an electron to absorb a photon are calculated.