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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 l.jpg

Announcements

  • Abstract of project due: Feb 9

  • 1st midterm: Feb 12

  • Review session ?????

Astronomy 201 Cosmology - Lecture 11


Lecture 11 newton s cosmology i absolute space and time l.jpg

Lecture 11Newton’s Cosmology I: Absolute Space and Time

Astronomy 201 Cosmology - Lecture 11


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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


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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


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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


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Quiz Quiz Quiz Quiz Quiz Quiz

NameSID

Date

Answer

Signature

Astronomy 201 Cosmology - Lecture 11


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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


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Answer: both ignored the effect of dust.

Astronomy 201 Cosmology - Lecture 11


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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


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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


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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


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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


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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


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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


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Homogeneity and Isotropy

Copernican

Principle

Isotropy

Homogeneity

+

Isotropy around another point

Isotropy

Homogeneity

+

Astronomy 201 Cosmology - Lecture 11


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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


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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


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Announcements

  • Abstract of project due: Feb 9

  • 1st midterm: Feb 12

  • Review session ?????

Astronomy 201 Cosmology - Lecture 11


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