QED by Richard Feynman

QED: Quantum Electrodynamics / Quod Erat Dictum

Everyday properties of light:

• goes in straight lines 
• bends when it goes into water 
• when reflected from a surface like a mirror, the angle at which the light hits the surface is equal to the angle at which it leaves the surface 
• light can be separated into colors 
• you can see beautiful colors on a mud puddle when there is a little bit of oil on it 
• a lens focuses light 
• light is partly reflected in some surfaces, such as glass or water

Proven using photomultipliers (which produce an audible click each time a photon hits) and monochromatic (red, green, or blue) light:

• light is made of particles (photons) 
• partially reflective surfaces return an average of 4% of photons 
• as the thickness of a given partially reflective surface increases, the return oscillates between 0 and 8% 
• because glass has two reflective surfaces (front and back), the return oscillates between 0 and 16% 
• this cycle repeats itself at different rates for different colors, so some thicknesses return only red or only blue, or blue and red in different proportions, creating effects like rainbows in oil puddles 

Grand Principle:
The probability of an event is equal to the square of the length of an arrow called the "probability amplitude." An arrow of length 0.4, for example, represents a probability of 0.16 or 16%.

General Rule for drawing arrows if an event can happen in alternative ways:
Draw an arrow for each way, and then combine the arrows ("add" them) by hooking the head of one to the tail of the next. A "final arrow" is then drawn from the tail of the first arrow to the head of the last one. The final arrow is the one whose square gives the probability of the entire event.

Derived from the above findings:

• The arrows correspond to a metaphorical stopwatch hand; their direction is determined by the amount of time it takes for them to travel a given distance. When graphed, outliers cancel each other out, so the center of the distribution has the most influence on the final direction of the arrow / path of the light. Thus, light travels along the shortest path, and the angle of incidence equals the angle of reflection. 
• If the scope of the possible paths is limited too extremely, the time of each revolution of the metaphorical stopwatch is too short, so near-identical paths end up scattering. There is a lower limit to the size of a mirror. 
• Scraping away the parts of a mirror that bias one direction biases the light towards the opposite direction, making a previously unreflective surface reflective. This is called a diffraction grating.

The Four Laws of Thermodynamics

0. About thermal equilibrium
If two thermodynamic systems are separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

1. About the conservation of energy
The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to or removed from the system and teh work done on or about the system. So, we can say (1) “Energy is neither created nor destroyed.”

2. About entropy
The total entropy of any isolated thermodynamic system always increases over time, approaching a maximum value or we can say, “In an isolated system, the entropy never decreases.” Another way to phrase this: Heat cannot spontaneously flow from a colder location to a hotter area— work is required to achieve this.

3. About the absolute zero of temperature
As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as: “the entropy of all systems and of all states of a system is smallest at absolute zero” or equivalently, “it is impossible to reach the absolute zero of temperature by any finite number of processes.” Absolute zero, at which all activity would stop if it were possible to happen, is -273.15°C, or -459.67°F, or 0K.

Lever

From French lever, “to raise”

A rigid object used with an appropriate fulcrum to realize a mechanical advantage.

Archemides said:
“Give me a place to stand, and I shall move the Earth with a lever.”

The ratio of the force applied to each end points of the lever is proportional to the ratio of the length of the lever arm measured between the fulcrum and the force’s application point at each end.

M = Fd

where M is the moment, F is the force,

and d is the distance between the force and the fulcrum

F*L_F = R*L_R

where F is the force, L_F is the distance between the application and the fulcrum

R is the resistance, and L_R is the distance between the resistance and the fulcrum

Class 1: The fulcrum is located between the applied force and the load

Class 2: The load is located between the fulcrum and the force

Class 3: The force is located between the fulcrum and the load

Pulley

Reasons to use a pulley:

• Change the direction of an applied force 
• Transmit rotational motion 
• Realize a mechanical advantage in either a linear or rotational system of motion

Pulleys are composed of a wheel on an axle or shaft
that may have a groove between two flanges along the edge

A rope, cable, belt, or chain usually runs over the wheel and inside the groove
if present.

Belt and pulley systems transmit mechanical power, torque, and speed across axes, and if the pulleys are of differing diameters, realize a mechanical advantage.

Rope and pulley systems transmit a linear motive force (in tension) to a load through one or more pulleys for the purpose of pulling the load.

A fixed pulley has a fixed axle
and is used to change the direction of the force on a rope
and has an MA = 1

A movable pulley has a free axle
and is used to multiply forces
and has an MA = 2

A block and tackle system uses a combination of fixed and movable
and has an MA > 2

Mechanical Advantage

MA = output force / input force

MA = distance over which effort is applied / distance over which the load is moved

Gear

Reasons to use a gear:

• Reverse the direction of rotation 
• Change the speed of rotation 
• Move rotational motion to a different axis 
• Keep the rotation of two axes synchronized 

Gears are read left-to-right when counting ratios (left gear is bigger in a 2:1).

Gears are manufactured such that tooth count is more accurate than circumference in determining gear ratios.

To create large gear ratios, use a gear train.

Worm gears function as “one tooth” gears
and flip the axis of motion 90°.

A planetary gear system uses the same axis for both input and output gear
and is very rugged.

Rotation (Torque)

A twist that causes a perpendicular body to rotate.

Thrust (Force)

A push or pull that causes a free body to accelerate.

Atomic Number

Symbol is Z.

Equals the number of protons in a given atom.

Each unique atomic number corresponds with an element on the periodic table.

Proton

Symbol is p+.

Subatomic particle with electric charge of +1e.

Mass is 1.672621637(83) * 10-27kg.

Exists as a nucleon in all atoms.

Exists independently as the hydrogen atom, H+.

Number in each atom (atomic number, Z) determines its element.

Composed of two up quarks and one down quark.

Quarks

Symbol is q.

From James Joyce, Finnegans Wake

“Three quarks for Muster Mark!”
Three being a natural organizational number for quarks,
color is also employed as a metaphor.

Elementary particle.

Never exist independently.

Up Quark
Symbol is u.

Elementary particle with electric charge of +2⁄3e.

Have gravitational, electromagnetic, weak, and strong interactions.

Stable quarks.



Down Quark
Symbol is d.

Elementary particle with electric charge of -1⁄3e.

Have gravitational, electromagnetic, weak, and strong interactions.

Stable quarks.

The Four Known Fundamental Interactions

Electromagentism
Causes interaction between electrically charged particles
in areas called electromagnetic fields

And binds (negative) electrons to (positive) protons

which together form atoms
which together form molecules
which are categorized as elements
which together form chemicals
which together form everything we see

A changing electric field generates a magnetic field

and vice-versa
in a process called electromagnetic induction

Strong Interaction
Causes the (netural) neutrons to bind to the (positive) protons and form the nucleus

and quarks to bind to gluons and form nucleons, etc
overriding electromagnetism
The strongest of the Interactions

Weak Interaction
Causes radioactivity through beta decay
(the emission of electrons by neutrons or positrons by the protons in atomic nuclei)

And is due to the exchange of the heavy W and Z bosons



Gravitation
Causes dispersed matter to coalesce

And is due to the curvature of spacetime which governs the motion of inertial objects

Newton's simpler, still reliable theory states:

I deduced that the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centers about which they revolve: and thereby compared the force requisite to keep the Moon in her Orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly.