Aristotle’s World
Joshua Lande
Aristotle (384 BC – 322 BC)
• Born of a well-to-do
family in the Macedonian
• In 384 BC.
• At 17 he went to Athens
to study at Plato’s
Academy.
• He remained for the next
20 years.
Aristotle’s Physics
• Is amazingly plausible,
coherent, and common
sense.
• Lacks Mathematical rigor
• “Mathematics was
concerned with unchanging
objects that lacked reality,
while his natural philosophy
focused upon changing
objects with a reality of
their own.”
• Almost fully accepted until
the Copernican revolution.
The Qualities
• Four fundamental quantities
– Hot, cold, dry, & wet
• Hot & cold are active quantities
• Addition or subtraction will change things
• Wet & Dry are result of action of active
quantities
• Fundamental qualities can be combined in
only 4 ways to create the 4 elements
Material Science
• Four main elements
make up the terrestrial
world:
• earth, air, water and
fire.
• Earth=Dry + Cold
• Water = Wet + Cold
• Fire = Dry + Hot
• Air = Hot + Wet
• Earth is not the same as
earth!
The Periodic Table of the Elements
• 4 elements roughly
correspond to 4 states
of matter
– Solid, Liquid, Gas,
Plasma.
• Heavy material like
rocks and Iron made up
mainly of earth
• Lighter objects like
wood contain more
water and air
This Can Explain Lots of Observations
• Example – Boiling
• The addition of heat to
a wet object.
• The heat draws the
wetness (water/air) out
• The resulting substance
is thicker (more earth)
• The separate wetness
(water/air) is lighter so
rises
Theoretical Issue
• Ice is dryer and colder
than water - contain
more earth.
• But earth is attracted
downwards more
strongly.
• Strangely ice floats in
water?
Human Biology
• Humans consist of a
complex mixture of all the
elements:
– Earth gives strength and
weight
– Fire provides warmth
– Water for blood and bodily
fluids
– Air fills lungs and breath of
life.
• Each human has a
different composition
making us all unique.
The Universe Has a ‘Cosmic Graph
Paper’
• In the center of the
graph is the geometric
center of the universe.
• The center of the
universe is where all the
radial lines converge.
Natural State
• The natural state of
objects is at rest
• This is obvious from
terrestrial observations
• All things put in motion
eventually stop
Natural Place
• All mater has a natural
place it wants to go to
• The natural ordering is
Fire, Air, Water, and
Earth
• Earth wants to “go
down” more than
water.
• Lightning is fire in the
sky.
Dynamics
• Natural motion caused by objects seeking
their natural place
• Motion is straight up / down in radial lines
• Explains why rocks sink in water but air
bubbles rise up
• Fire rises through air.
Details
• Natural motion, proportional to weight.
• Explains why rocks fall faster than feathers
• The speed of fall depends inversely on the
density it falls through.
• Explains water resistance, etc
• Because of this, there can be no vacuum
• Things would move infinitely fast through it
Why the Earth is Round
• The way for most earthy
material to get as close
as possible to the
center.
• The water rest on
surface because it
wants to be further
from center.
The real world is more complicated.
• Our world isn’t in equilibrium
• Water somehow gets pulled up into the
atmosphere for a while (clouds) before eventually
falling to earth
• Fire trapped in things like trees eventually
released during burning
• Volcanoes occasionally spew earthy and watery
and fiery junk into the atmosphere
• It lingers for a while before moving back toward
its natural place
Violent Motion
• Only way for an object to move unnatural (in
non-rectilinear motion up/down) is violently.
• Violent motion happens when one object acts
directly acts upon another causing it to move.
• So motion only happens when a force is
involved.
• This explains pushing a boulder up a hill,
walking, etc.
• Speed of violent motion proportional to force
– If you push something harder it moves faster
Impossibility of Heliocentric Universe
• Imagine a bird taking off and flying
• After leaving the ground, it would come to
rest
• But rest is moving quickly away from the earth
• So the bird would leave the earth.
Projectiles
• Hard to explain
• Continues to move in the
air instead of immediately
falling towards earth
• Explanation is that the air
in front of the object
became disturbed by the
movement
• Air swirls behind it
pushing it along.
• This tendency weakens
with time
Cosmology
• Everything in the sky move
round in circles.
• Other than that, it doesn’t
really change.
• But our terrestrial world is
always in flux.
• Therefore, the heavens
must be made of an entirely
different substance.
• This substance is aether, a
pure, completely different
perfect substance
Aether
• The main difference
between aether and
matter is that aether’s
natural state is circular
motion
• Circles are the most
perfect geometric
shape
• Aether means always
running
The Moon
• The Moon marks the
boundary between the
Earth and the Heavens
• It is mostly aether.
• Small amounts of earth
accounted for the visible
imperfections on its
surface.
• All imperfect celestial
objects such as comets,
nova, and meteors are
sublunar.
Cosmology
• Heavenly objects move
in celestial spheres.
• Center is Earth, then
moon, then planets,
then stars.
• Agreement with rough
observations.
Imperfect Planets
• The planets & sun drift
relative to the stars
• This is an imperfection
• Closer bodies are
increasingly corrupt by
terrestrial elements
• E.g. The sun probably
contains some fire in it.
Dynamical Connection Between
Heavens and Earth
• Rotation of the outer sphere of stars mechanically
responsible for all the other motion in the universe.
• The rotation of the stars pulls the planets around
• In turn pulls the Sun around
• In turn pulls the Moon around
• In turn communicates motion to sublunar region.
• Plausible
– The tides correlates with the motion of the Moon and Sun
– So does the daily warming and cooling of the Earth
– And yearly progression through the seasons.
Questions?