# Escaping from Igorance

*Because the world is round, it turns me on; Because the world is round, Ah…Because the wind is high, it blows my mind; Because the wind is high, Ah…*(The Beatles: Because)

Keplers model of the planetary system.

The hodometer was used by the Romans to measure distances, e.g. along roads. Can you figure out how it worked?

We start with the intuitive ideas of *space* and *time *we all have: We perceive that everthing there is in the physical world, has a place in some form of big container with three independent directions which we call *space*. We further experience that things can* change shape and position in space*, the rate of which we measure using clocks recording *time* by periodic motion.

We will record position in space by and time by , where and represent numbers. Points in space-time can then be recorded as pairs of numbers .

We live in three-dimensional or 3d space and a point can be identified by three coordinates or numbers , and , which we can collect into a *triple* and we can write .

If we restrict the world to two dimensions or 2d, that is to a plane, then we need only two space coordinates and , which we can collect into a pair .

If we restrict the world further to one space dimension or 1d, that is to a line, then just one coordinate is enough and we have .

We start using *rational numbers* expressed as *decimal numbers* like

using the* base* and denoting here multiplication by . As usual , and more generally e.g. , et get.

We recall that a rational number is the quotient of two *integers* and (of the form ) with , and the non-negative integers are called *natural numbers.*

We denote the set of natural numbers by , and the set of rational numbers by .

# SI Standards of Length and Time

The SI Standard of unit of time is *second,* which is the duration of a certain number of oscillationsof a certain caesium atom. More precisely:

- one
*second*is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom at a temperature of 0 Kelvin. Mechanical clock with wheels, gears, escapement

The SI Standard of unit of length is a *lightsecond*, which is the distance traveled by light in one second, and *meter* as

- the distance traveled by light during a time interval of 1/299 792 458 of a second.

Entering into Inner Space Simulation of Köln Concert.

# Coordinate Systems in 1d, 2d and 3d

With a laser-beam we can set up coordinate systems along a 1d line, in a 2d plane and in 3d space.

In 1d, for example a horisontal line, we mark the coordinates in meter using a laser beam and a clock measuring the time it takes for light to pass from a given point, which we called the *origin*, to different points to the right and left marking the points to the left with a minus sign.

In 2d, for example a horisontal plane, we choose two perpendicular 1d directions which we mark separately as in 1d:

In 3d we choose three perpendicular directions and mark each direction as in 1d. We can think of these directions as South-North, East-West, down-up.

# The Time Step

We will denote by a *smallest unit of time*, which can be different in different situations. The smallest we can measure is the time of one oscillation of a caesium atom, about seconds. Depending on the setting, may be one second, minute, hour, day, month, year,…

We will describe as *Newton’s World of Mechanics* the physical world with a smallest as indicated, and by *Leibniz’ World* a mathematical fictional world where is assumed to be smaller than any given finite value, or *vanishingly small*.

We shall find that in Leibniz fictional world with a vanishingly small time unit, many mathematical expressions and formulas become easier to manipulate and easier to understand on a conceptual level, than in Newton’s real world with a finite smallest time unit.

In computational simulations we have to use a finite time step, since the computer can only perform a finite number of operations per time unit.

We shall use tools from Leibniz world when we construct computational digital simulations of Newton’s real analog world, because these are efficient tools, but in the computational simulations effectively use a finite time step or time unit.

Leibniz world is like the ideal world of Plato, which is useful for thinking but untouchable in reality or simulation. IT is like the world we can imagine by using language, which is different from the real world. But we also know that the real world can be more remarkable than any world we may imagine.

Caesium reference clock at NIST Laboratory, Colorado.

The Caesium atom is large and vibrates slowly.It also reacts with water.

# Point, Vector and Distance = Vector Norm

Let , where is the set of triples with , be a point in a 3d coordinate system. We can to the point associate a *vector* also denoted by as the directed straight line segment from the origin to the point , or arrow from to $x$. We write also for a vector .

By *Pythagoras Theorem*, the distance from to the point , which is also the length or *norm* of the vector $x$, is given by

- ,

which we can think of as the length of the straight line from the origin to the point , also referred to as the vector .

# Scalar Product

If and are two vectors in 3d space, that is , then we define their *scalar product* as follows

We will say that if , then the vectors and are *orthogonal* or *perpendicular*. We note that the length of the vector , or distance from the origin to the point is defined in terms of the scalarproduct as follows:

- .

The distance between two points and is then given by , where .

Further, the *angle* between two (non-zero) vectors and (with an arrow with tail at and head at ) is connected to the scalar product by the following formula (which you will derive yourself below):

- .

The central quantities of geometry of distance and angle, are thus computable in terms of the scalar product. Neat!

# Change of Position/Time Unit = Velocity

Velocity is defined as change of position per unit time step , that is,

- .

Nude time stepping down a staircase by Marcel Duchamp.

# Change of Velocity/Time Unit: Acceleration

Accelleration is defined as change of velocity per unit time step , that is,

- .

# Particles and Forces

Everything which happens in physical space can be thought of as an interaction between materialparticles each one occupying a specific point in space at a given time, with the interaction mediated by certain* forces.*

# Newton’s 2nd Law: F=Ma

The most basic law of physics is *Newton’s 2nd Law* stating that

where is *force*, is *mass* and $a$ is accelleration. Since Newton’s 2nd law can be written

- ,

or normalizing to ,

- .

This law connects the world of particles, the world of velocities of particles, with the world of forces.

If we think of the world as consisting of particles interacting by forces, we understand that somehow the effect of forces acting on particles must be specified and Newton’s 2nd is the basic law making this specification.

# How to Motivate Newton’s 2nd Law?

Is it possible to understand why Newton’s 2nd Law holds? Or is it simply a definition of force $F\equiv Ma$? Or a definition of mass ? We will \hyperref[chapterequivalence]{return to this question below}, when we are prepared to give an answer. As of now, let us accept it and use it in our description of the World.

Mixing real reality and virtual reality by Rene Magritte.

# To Think About

- How is length and time measured?
- Is the constancy of the speed of light in vacuum, a definition or a physical fact?
- What is the difference between a definition and physical fact? Or is there no difference?
- What is Planck’s constant?
- Things That Don’t Exist.

# Watch

Max Planck being struck by the idea of quantum of energy.

*When modern physics exerts itself to establish the world’s formula, what occurs thereby is this:the being of entities has resolved itself into the method of the totally calculable*. (Heidegger)*Time is not a thing, thus nothing which is, and yet it remains constant in its passing away without being something temporal like the beings in time.*(Heidegger)

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