The Universe Just After the Big Bang

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The Universe Just After the Big Bang
Color represents small variations in temperature.
Temperature of gas tells you its
density. Exaggerated Contrast
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Conclusion

• Previous graph proves the universe obeys flat
  geometry.
• Geometry is determined by the density of the mass
  in the universe, so we now know that density.
• Knowing the density tells us the speed of sound.

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NucleosynthesisA Cosmic Game of Chutes and
Ladders

• We know how protons, neutrons and electrons
  behave when they are hot and dense. We know
  density based on curvature. We know temperature
  based on color.
• We also know what atoms were created so we can
  figure out what reactions took place.

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No Stable Elements With a Mass of 5 or 8

• Possible to get over the gaps (fusion in stars
  does it)
• But you must have a simultaneous 3-way collision
  which is rare.
• That rarity tells us how dense
• the protons and neutrons were.

9Be
8Be 10-17 sec
6Li
7Li
5Li 10-22 sec
8Li 0.8 sec
3He
4He
5He 10-23 sec
1H
2H
3H 12 years
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No Stable Elements With a Mass of 5 or 8

• He-4 is more stable than hydrogen.
• The universe is about 75 hydrogen and 25
  helium.
• Knowing the density of the early universe, how
  long would it take to convert 25 of the hydrogen
  into helium?
• Tells us how long it took the early universe to
  cool below the critical temperature.
• 20 minutes.

3He
4He
5He 10-23 sec
1H
2H
3H 12 years
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• Curves show how much of each element there should
  be (y-axis) if the universe started with a
  density of n (x-axis)
• Horizontal bands are the margin of error on the
  observed amount of each element.
• The yellow band is the only density that works
  for all of the elements.

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Back to the Shape Question

• The size of the WMAP spots tells us the geometry
  of the universe is flat
• The cause of the geometry is the density of
  matter in the universe.
• Ratios of He and Li tell us the density.
• Lets compare the WMAP and the nucleosynthesis
  data.

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Density of protons and neutrons in our universe
Density of total mass needed to make the universe
flat
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Contradiction?

• We know the universe is flat.
• Curvature depends on total mass
• Nuclear reactions depend on protons and neutrons,
  electrons.
• Therefore if they disagree, it must be because
  there is mass in addition to the protons,
  neutrons and electrons.
• But what is that mass?

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Things it isnt / doesnt do

• Isnt Protons, Neutrons, Electrons.
• Isnt Quarks, Muons, Pions, Neutrinos, etc.
• Doesnt give off light
• Doesnt heat up
• Doesnt collide with other particles going
  through it.
• In two slides Ill tell you about neutrinos and
  address your questions.
• Doesnt have any interactions at all except
  through gravity.
• It is in this room right now not interacting with
  us

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Things Near the Center Orbit Faster
Unless there is lots of mass around the outside
that we cant see
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Not Dark Matter, But Similar

• Mean Free Path
• On average, how far does a particle travel before
  bumping into something?
• Depends on density
• Air molecule at sea level
• 65 nm.
• Neutrino traveling through solid lead.
• 1 light year or 5.9 billion miles.
• Thats an average. There are trillions of them
  going through the earth every second, so
  sometimes scientists get lucky and one of them
  hits their detector.
• The only reason you can touch the table is
  protons and electrons interact with each other.
• Neutrinos dont interact with protons or
  electrons (very much).
• Dark matter doesnt interact with protons or
  electrons at all (except through gravity)

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Zombie Mystery

• The mystery that died How will the universe
  end?
• Gravity slows down the expansion. Eventually
  gravity wins and everything collapses back
  together.
• Gravity slows down the expansion, but not enough.
  As things get farther apart, gravity gets weaker
  and the universe expands forever and ever.
• Conclusion Universe will expand forever.

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Zombie Mystery

• The Mystery is Reborn
• Looking far away tells information about long
  ago.
• Long ago, the expansion was slower than it is
  now.
• Gravity should make the expansion decelerate
  (regardless of whether gravity wins or expansion
  wins). Something else is making everything in
  the universe repel each other.
• Observed. Now we just need to figure out why.
• Having too much energy could do this, but we
  dont see the energy just to give it a name,
  lets call it Dark Energy.

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• We dont know what dark energy is, but we know
  how much of it there must be to make the universe
  accelerate.
• We dont know exactly what dark matter is but we
  have ruled out all but a couple options. We have
  multiple ways of measuring how much of it there
  needs to be and that all agree pretty well.

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The majority of the universe is composed of dark
energy.
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Nagging Question

• The CMB started out orange, 3,000 Kelvin, cool
  enough for electrons and protons to make atoms.
• Before that it was much hotter and much dense.
• More density means more nuclear reactions, so why
  did only 25 of the helium get fused into
  hydrogen?
• Before that it was denser still.
• Infinitely dense? Almost infinitely dense?
• Why didnt it make a giant black hole?

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Why Wasnt There More Fusion

• Thousands of degrees electrons cant stay bound
  to protons.
• Millions of degrees nuclear reactions occur
• Billions of degrees so hot that energy (light
  and KE) spontaneously turns into a pair of matter
  and antimatter particles, that then annihilate
  each other and change back into energy (light and
  KE).
• Trillions of degrees too hot for protons to
  form. Matter is exclusively quarks (
• To make a proton or neutron three quarks join.
• Before the universe became a fog of glowing
  orange hydrogen, it was a trillion-degree
  mass/energy/quark soup.

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Why Didnt it Make a Black Hole?

• Really dense means lots of gravity that pulls
  objects toward it.
• Universe was really dense everywhere, so which
  way should the object be pulled?
• Cant make up its mind, meanwhile universe
  expands.