Announcements

• Exam 1 will be returned next time

• Dark Sky Observing Night Wednesday night. Set-up starts at 7:45pm. Meet at “The Farm”

Foundations of Modern Cosmology

Colored Card QuestionWhich of the following would be an example of an anthropomorphism?a) Attributing the annual migration of birds as a

signal for the change of seasons.b) Considering the daily motion of the Sun, stars

and planets to be caused by the universe revolving around the Earth.

c) Imbuing the stars with powers over the daily lives of people.

d) Using the annual motions of the stars as a means to keep time.

Another Colored Card Question

One of the most important properties of any scientific theory isa) it can proven to be true.b) it can be proven false.c) it is widely accepted by the scientific

community.d) it is used by scientists for centuries.

The Anthropic Principle

The properties of the universe are “just right”. Why? Is it because we are here or are we here because they are just right?

Cosmological Myths

Creation myths reflect the culture

The Australian aborigine Dreamtime

Symbols found in Dreamtime art

Most creation myths involve

anthropomorphism

Most creation myths give humans and Earth a central role

Anthropocentrism

If things didn’t go well for humans it was because of a vengeful god

The Christian Genesis and

the expulsion of Adam & Eve

from the Garden of Eden

The snake is given human-like characteristics and the vengeful God punishes the transgressors for eating the apple of knowledge

Hindu Cosmology involves lots of creation, destruction and sacrifice

The Celtic peoples were hunters so their myths involve lots of animals

Egyptian creation myths involved many gods and battles between them

Mesoamericans were big on sacrifice and wars between the gods

The Raven and Sedna were part of the Inuit creation myth

The modern creation myth

The Scientific Method

The Scientific Method is based on induction rather than deduction

Induction is to extrapolate the general principle based on limited observations. Deduction is to start with a general principle and attempt to apply it to specific cases. Because the process starts with induction, no scientific theory can ever be proven true, it can only be proven false.

The scientific method is a closed cycle, it doesn’t have an end

An example of the never ending cycle: the theory of gravity

The five characteristics of a “good” scientific theory

1. RelevanceMust be relevant to the field. A theory that is

irrelevant to astronomy may be relevant to biology, geology or some other field.

A theory on how the pyramids were built may be relevant to archeology but it is irrelevant to cosmology (though there may be some astronomical relevance).

2. FalsifiabilityA scientific theory must be capable of being shown false.

The theory that the moon is made of green cheese is a valid scientific theory. It was proven false by the Apollo missions.

The theory that a supreme being rules over the universe is not scientific. Unless we can prove He doesn’t exist, the theory cannot be shown to be false.

3. Consistent

A scientific theory must be consistent with the existing science.

Example: Einstein’s Special Theory of RelativityIt is consistent with Newtonian mechanics if the relative velocity is small compared to the speed of light.

4. Simplicity

What is simple to one may be complex to another. Apply Occam’s Razor: all things being equal, the simpler theory is more likely correct.

5. PredictabilityA good theory must be able to predict behavior that has not yet been observed. Closely related to fasifiability.

Einstein’s theory of General Relativity predicted gravitational lensing. It was first observed in the total solar eclipse of 1919. It has since been observed many times.

Homework for next time

MesoamericanBabylonian

Hindu

Chinese Australian

In groups of two, prepare a short (7 or 8 min) presentation on the origin myth of one of the ancient cultures

Chapter 2: Cosmology Becomes a Science

To the early Greeks, the universe was small and centered on the Earth

They observed that all the planets moved in a band near the path of the Sun: the Ecliptic. The earliest models kept the planets on the ecliptic. Later models had the planets moving slightly off the ecliptic.

The Greeks: Plato• 427-347 BCE

• More philosopher than astronomer

• Codified the requirement of circular motions in the heavens

• Theory is truth, observations are subject to human frailties

The Greeks: Eudoxus• 400 – 347 BCE

• Student of Plato

• First to use nested spheres to explain planetary motions

• Took 27 spheres to explain observed motions

The Greeks: Aristotle• 384 – 322 BCE

• Like Plato, his teacher, more philosopher than astronomer

• Developed a cosmology similar to Eudoxus but with 55 spheres

• Codified “Physics”Terrestrial realm obeys different physical laws than celestial realm and is made of different stuff: earth, air, fire & water versus quintessence

Despite being wrong, most people “believe” the physics of

Aristotle

“All motion is either Natural motion or Forced motion. Falling is a natural motion. All bodies fall at a constant speed. The

speed of a falling body is proportional to its mass”

The arrow is given an impetus by the bow. The impetus provides the force as it flies through the air but it is used up as the arrow pushes the air out of the way