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Announcements. Abstract of project due: Feb 9 1st midterm: Feb 12 Review session ?????. Lecture 11 Newton’s Cosmology I: Absolute Space and Time. What do you think about the following questions ?. What happened before the universe existed? What is outside the universe?

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announcements
Announcements
  • Abstract of project due: Feb 9
  • 1st midterm: Feb 12
  • Review session ?????

Astronomy 201 Cosmology - Lecture 11

what do you think about the following questions
What do you think about the following questions ?
  • What happened before the universe existed?
  • What is outside the universe?
  • What is the universe like right now ?
  • How did it get there ?

Astronomy 201 Cosmology - Lecture 11

the physical universe
The Physical Universe
  • Proposition: the universe can be understood in terms of natural laws (here: Newton’s laws)
  • physical: anything that can be objectively observed (at least in principle)
  • physical universe: the universe of material objects, of energy, of space, of time

Astronomy 201 Cosmology - Lecture 11

the copernican principle
The Copernican principle
  • Man, Earth, Sun, the Galaxy etc. are not special/are not at a special place in the universe. This a priori does not exclude that there may exist special objects/special places.

Astronomy 201 Cosmology - Lecture 11

quiz quiz quiz quiz quiz quiz
Quiz Quiz Quiz Quiz Quiz Quiz

NameSID

Date

Answer

Signature

Astronomy 201 Cosmology - Lecture 11

slide7
What key ingredient was ignored by Kapteyn and Shapley so they came to opposite conclusions regarding the size of the Milky Way and the location of the Sun ?

Astronomy 201 Cosmology - Lecture 11

slide8
Answer: both ignored the effect of dust.

Astronomy 201 Cosmology - Lecture 11

the anthropic principle
The anthropic principle
  • The weak anthropic principle states that the universe must be compatible with our existence.
  • The strong anthropic principle states that the universe is such as it is because its purpose is to create life.

Astronomy 201 Cosmology - Lecture 11

example
Example
  • Existence of life (as we know it) strongly depends on the presence of carbon
  • If the nuclear force (the force that keeps atomic nuclei together) would have been slightly different, no carbon could have been formed.
  • Why is the nuclear force as strong as it is ?Anthropic principle If it had been different, we wouldn’t ask this question.

Astronomy 201 Cosmology - Lecture 11

a toy universe
constant density

(homogeneous)

boundary

A toy universe

According to Newton, what is going to happen ?

  • The model Universe is going to collapse under its own gravity

Astronomy 201 Cosmology - Lecture 11

newton s universe
Newton’s Universe
  • In order to avoid collapse
    • homogeneous
    • isotropic
    • infinite size
    • no center
  • infinite in time
    • has always been
    • will always be

 perfect cosmological principle

Astronomy 201 Cosmology - Lecture 11

the cosmological principle
The cosmological principle
  • homogeneous: the universe looks the same everywhere on large scales there is no special place (center)
  • isotropic: the universe looks the same in all directions on the sky
  •  there is no special direction (axis)

Astronomy 201 Cosmology - Lecture 11

the perfect cosmological principle
The perfect cosmological principle
  • homogeneous: the universe looks the same everywhere on large scales there is no special place (center)
  • isotropic: the universe looks the same in all directions on the sky there is no special direction (axis)
  • unchanging: The universe looks the same at all times  there is no special epoch

Astronomy 201 Cosmology - Lecture 11

homogeneity and isotropy
Homogeneity and Isotropy

Copernican

Principle

Isotropy

Homogeneity

+

Isotropy around another point

Isotropy

Homogeneity

+

Astronomy 201 Cosmology - Lecture 11

does the cosmological principle apply to our universe
Does the cosmological principle apply to our universe ?

The cosmic microwave

background radiation (CMB)

= afterglow from the big bang.

It’s smooth to 1 part in 105

 yes, the universe appears to be homogeneous and isotropic

Astronomy 201 Cosmology - Lecture 11

does the strong cosmological principle apply to our universe
Does the strong cosmological principle apply to our universe ?

Galaxies today

Galaxies 10 billion years ago

 no, the universe appears to change with time

Astronomy 201 Cosmology - Lecture 11

announcements18
Announcements
  • Abstract of project due: Feb 9
  • 1st midterm: Feb 12
  • Review session ?????

Astronomy 201 Cosmology - Lecture 11

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