QED: The Strange Theory of Light and Matter Vocabulary

Vocabulary flashcards covering the concepts, particles, and mathematical rules of Quantum Electrodynamics (QED) based on Richard Feynman's lectures.

Quantum Electrodynamics (QED)

The strange theory of light and matter, specifically describing the interaction of light (photons) and electrons.

Photomultiplier

An instrument designed to be sensitive enough to detect a single photon; it produces audible clicks of uniform loudness when hit by light of a given color.

Photon

Each little lump of light, also known as a particle of light; they behave like raindrops of the same size if the light is all one color.

Monochromatic Light

Light of one color, such as red or blue, produced by instruments such as lasers.

Frequency

A number used to describe the scale of light; as numbers get higher, light moves from red to blue to violet to ultraviolet, then to X-rays and gamma rays.

Partial Reflection

The phenomenon where a surface reflects only a percentage of photons; for example, an average of $4$ out of $100$ photons (or $4\%$) are reflected by a single surface of glass.

Probability Amplitudes

The technical term for the little arrows drawn on paper used to calculate the probability of an event; the probability is equal to the square of the length of the final arrow.

Adding Arrows

The general rule for calculating the final arrow if an event can happen in alternative ways; one arrow is drawn for each way and they are combined by hooking the head of one to the tail of the next.

Multiplying Arrows

The process of successive shrinking and turning of arrows, used for events consisting of a sequence of steps or independent things happening concomitantly.

Interference

A phenomenon in which probabilities vary (amplify or turn off) due to the addition or subtraction of amplitude arrows; for example, partial reflection from two surfaces of glass ranges from $0\%$ to $16\%$ based on thickness.

Diffraction Grating

A mirror that has been etched or scratched in specific places (grooves) to ensure only arrows pointing in a certain direction are added, resulting in a strong reflection where none was expected.

Focusing Lens

A piece of glass of varying thickness that slows down light on shorter paths so that the light for all paths takes exactly the same time, producing a large final arrow (high probability) at a single point.

Iridescence

The phenomenon of colors produced by the partial reflection of white light by two surfaces, seen in soap bubbles, oil films on mud puddles, and the feathers of peacocks.

Action #1 (QED)

The fundamental action where a photon goes from place to place in space-time, represented as a wiggly line.

Action #2 (QED)

The fundamental action where an electron goes from place to place in space-time, represented as a straight line.

Action #3 (QED)

The fundamental action called a 'junction' or 'coupling' where an electron emits or absorbs a photon.

Space-time

The stage on which actions take place, represented by graphs showing location on the horizontal axis and time on the vertical axis.

c

The speed of light, represented as a $45$-degree angle on a space-time graph where the horizontal distance is equal to the vertical distance.

j

The amplitude for an electron to emit or absorb a photon, valued at about $-0.1$; it represents a shrink to about one-tenth and half a turn.

Virtual Photon

An exchanged photon that never appears in the initial or final conditions of a physical experiment but occurs between interaction points.

Positron

An electron going backwards in time which appears to have a positive charge; a sister particle to the electron and an example of an anti-particle.

Exclusion Principle

A principle stating that no two electrons with the same polarization can be at the same point in space-time, which accounts for the variety of chemical properties in atoms.

Index of Refraction

The degree to which there is extra turning of the final arrow as light goes through a material (like glass or water), caused by electrons scattering the light.

Magnetic Moment of the Electron

The response of an electron to an external magnetic field, measured experimentally at $1.00115965221$ with a high degree of precision matching QED theory.

Renormalization

A 'dippy' but effective mathematical process used to find the theoretical values $n$ (rest-mass) and $j$ (coupling) by stopping calculations before the distance between coupling points reaches zero.

Quantum Chromodynamics

The theory of strong interactions involving quarks and gluons that hold the nucleus together.

Quarks

Fundamental spin $\frac{1}{2}$ particles that come in flavors such as 'd' (down) and 'u' (up) and colors 'Red', 'Green', and 'Blue'.

Gluons

Spin $1$ particles that carry the 'color' force between quarks, allowing them to bind together to form protons and neutrons.

Beta Decay

A slow form of radioactivity where a neutron changes into a proton as one 'd' quark changes into a 'u' quark.

W-intermediate-boson

A search for a very heavy particle (mass of about $80,000\,\text{MeV}$) that couples with electrons, neutrinos, and quarks during weak interactions.

Muon

A particle discovered by Carl Anderson in 1932 that acts exactly like an electron but is about $206$ times heavier, with a mass of $105.8\,\text{MeV}$.