Chapter 29 Exploring the Early Universe

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Chapter 29 Exploring the Early Universe
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Guiding Questions

• Has the universe always expanded as it does
  today?
• What is antimatter? How can it be created, and
  how is it destroyed?
• Why is antimatter so rare today?
• What materials in todays universe are remnants
  of nuclear reactions in the hot early universe?
• How did the first galaxies form?
• How were the fundamental forces of nature
  different during the first second after the Big
  Bang?
• Are scientists close to developing an
  all-encompassing theory of everything?
• How many dimensions do unified models predict?

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The Isotropy or Horizon problem why should the
universe look the same in all directions?
The Flatness problem why should the density of
the universe be just barely enough to prevent
recollapse?
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Before the first second, the universe may have
expanded 1050 times in 10-24 s.
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The newborn universe may have undergone a brief
period of vigorous expansion.

• PROBLEM If the universe is at least 26 billion
  light years across (13 billion in each
  direction), how could both sides have exactly the
  same temperature if they couldnt communicate?
• SOLUTION During the first second, the universe
  underwent a rapid but even expansion, called the
  inflationary epoch, in which it became many times
  larger than its original size.

Inflation also explains the flatness problem.
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During inflation, all the mass and energy in the
universe burst forth from the vacuum of space.

• Quantum mechanics explains the behavior of nature
  on the atomic scale and smaller.
• QM tell us how to calculate the structure of
  atoms and interactions between atomic nuclei.
• Elementary particle physics is the branch of QM
  that explains how subatomic particles interact.
• Heisenbergs uncertainty principle one cannot
  know the exact position and momentum (mass and
  velocity) of a particle simultaneously.
• In cosmology, we cannot simultaneously know the
  energy precisely for every moment in time.

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During inflation, all the mass and energy in the
universe burst forth from the vacuum of space.

• Over brief intervals of time, it is impossible to
  know exactly how much energy or matter exists in
  a particular space.
• Virtual pairs of particles and antiparticles can
  virtually exist momentarily

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As the primordial fireball cooled off, most of
the matter and antimatter in the early universe
annihilated each other.
These pairs of particles are spontaneously
created, and then usually annihilate each other.
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Why didnt all matter annihilate with antimatter?
1 proton survived for every billion protons
annihilated with antiprotons an example of
symmetry breaking
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Nucleosynthesis during the first few minutes of
the Big Bang created most of the Helium atoms in
the universe.
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Galaxies formed from density fluctuations in the
early universe.

• Clumps bigger than the Jeans length can grow.
• LJ pkT/mGrm½
• k 1.38x10-23 J/K
• T gas temperature
• m mass of one particle of gas
• G universal gravitation constant
• rm average density of matter in the gas

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In grand unified theories, all physical forces
had the same strength immediately after the Big
Bang.

• Gravitational force - attraction between any two
  objects with mass.
• Electromagnetic force - attraction/repulsion
  between charges, and forces from currents and
  magnetic fields
• Strong nuclear force - holds protons in the
  nucleus of an atom together.
• Weak nuclear force - governs the radioactive
  decay of neutrons into protons.
• A theory that correctly combines all forces in
  the early universe is known as a supergrand
  unification theory or theory of everything (TOE).

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GUT unifies 3 out of 4 forces. Standard model
explains electroweak unification (2/4).
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Relative strengths of four fundamental forces in
the present time Gravity is the weakest.
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Theories attemting to unify the physical forces
predict that the universe may have 11 dimensions.

• We experience 3 spatial dimensions (up/down,
  right/left, forward/back).
• Plus one time dimension
• 3x 1t 4 D
• Kaluza-Klein theory uses multiple dimensions to
  describe electricity and magnetism.
• String theorists we use 11 D to describe the
  universe
• 10x 1 t 11 D

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Guiding Questions

• Has the universe always expanded as it does
  today?
• What is antimatter? How can it be created, and
  how is it destroyed?
• Why is antimatter so rare today?
• What materials in todays universe are remnants
  of nuclear reactions in the hot early universe?
• How did the first galaxies form?
• How were the fundamental forces of nature
  different during the first second after the Big
  Bang?
• Are scientists close to developing an
  all-encompassing theory of everything?
• How many dimensions do unified models predict?