Baking a universe

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Baking a universe

• Or, how we came looking like this out of the Big
  Bang

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The Big Bang
13.5 billion years ago
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How do we know the universe is expanding?

• Looking at distant galaxies
• They are all moving away from us and form each
  other
• Their speed is proportional to their distance
• Precisely as if they were carried away by an
  expanding universe

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How do we use this to understand the present
universe?

• We mix
• Theory of relativity
• Gravitation
• Thermodynamics
• Particle physics

We get a story and some of the scenes can
be compared with data
As in the theory of evolution, The details of
some periods are heatedly discussed But the
paradigm is not.
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An atom primer
Atoms are made of a small nucleus of radius
10-15m
Surrounded by an electron cloud of darius 10-10 m

The nucleus is made of protons and neutrons

Protons and neutrons are made of quarks

To date no parts of quarks or electrons have
been found
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The earliest fossils
In the earliest times the universe was very
hot Up until 100 microseconds protons and
neutrons could not form The universe was a soup
of quarks, electrons and radiation
At 1s, and a temperature of 9 109 oK
Protons and neutrons formed
At 200s, and a temperature of 8 108 oK
Atomic nuclei formed
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But not all nuclei were created!
For light nuclei
Electric repulsion

• Only
• Deuterium
• Helium
• A bit of Lithium
• were cooked in the early universe
• The amounts are also predicted.

High speed (large temp.)
CONFIRMED
For heavier nuclei
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The earliest light
At 1/3 million years, Atoms formed
Atoms are neutral They interact little with
light From that time on the early-universe
radiation has traveled (almost) unimpeded
As the universe expands the wavelength of the
radiation also expands The current universe is
suffused by a uniform bath of microwaves
CONFIRMED
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If we could see microwaves

• Inhomogeneities in the Early Universe
• z
• Very faint (about 0.001)
• The seeds of clusters of galaxies
• Each has expanded to a region 5 109 light years
  across

Antarctica
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A mysterious matter

• The fate of the universe depends on how much
  matter it contains
• Too much it will expand to a maximum size and
  then re-contract
• Too little it will expand forever
• There is a critical value separating these two
  cases
• (about 1 mass of the Moon in every 30 cubic light
  years)

• Luminous matter about 4 of critical
• From counting galaxies and gas clouds
• From the synthesis of D, He and Li in the early
  universe

Unless there are othrer contributions the
universe will expand forever
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Another way of measuring matter
R 3.8 105 km
Looking at the Moon I can weight the Earth.
To go around the Earth takes me T 27.3 days
0.07479 years
So MEarth 6 1024 kg
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For the planets I get
And I can do the same for a galaxy Measure the
speeds of stars orbiting it. Measure their
distance to the center ) get the mass of the
galaxy
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Can be explained if the force is / 1/r not /
1/r2. Are Newton Einstein wrong? Are we
missing matter?
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Dark Matter
The hypothesis is that the universe has enough of
a new kind of matter to explain the rotation
curves of galaxies. This new matter is called
Dark Matter because it does not shine. Then
the density should be / 1/r2 and its temperature
should be uniform So galaxies would be
surrounded by a dark matter halo Stars orbiting
the galaxy are plowing through a dark-matter
mist
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There is other evidence of Dark Matter If we
observe distant galaxies and there is a lot of
dark matter in between, we should see a
characteristic distortion and we do!
Images distorted perhaps by a great deal of
dark matter
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And then theres the bullet cluster Two
galaxies with few stars and a lot of gas
collided Most of the matter is in the form of
gas The stars were almost unaffected The gas of
each interacts a lot so it stayed in the
middle But the strongest gravitational effects
are localized near the stars not the
gas! Matches perfectly the Dark Matter
hypothesis Hard to explain with other hypotheses
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Update on the cosmic census
Ordinary matter 4 of critical Dark Matter 23
of critical
If there is Dark Matter, Can we detect it in
some way? Is there only one kind? Could it be
that Dark Matter cosmologists are wondering what
that annoying 4 is all about? Could it be
something else?
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Another mystery
The rate of expansion is increasing The universe
is accelerating why?
The best current hypothesis There is a new form
of energy causing this dark energy If so then
it gives about 73 of critical
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The decade of cosmology
Over the next 10-15 years The nature of Dark
Matter will be understood The nature of Dark
Energy will be understood Or else Well have to
revise our understanding of space matter and
gravitation