Mini review of where we

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Mini review of where weve come from CMB, SNe
Ia, And Clusters tell us the universe is mostly
dark energy and will expand forever. Plus that we
need CDM Escape Equation and adiabatic expansion
show how why we want to measure H, Wm, WL, plus
how k, R, t, etc are all related. Didnt derive
how t depends on Wm, WL, etc, did argue by units
that 1/H gives approximate age
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Defined de-acceleration parameter as W/2 for L
0, matter dominated era, but a different
physical concept. Showed static universe
naturally requires dark energy. This gives a
negative pressure for positive matter and k 1.
We can see from dU -pdV this causes
expansion From de-acceleration definition and
that q Wm/2-WL for measured values of WL and Wm
we can see the universe is accelerating today
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• Big Bang pretty good
• BB was invented to explain several things
• We know we need more (CDM and L) but
• Theres more
• Inflation is needed ( maybe, you be the judge)

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Classical BB was based on laboratory (confirmed)
physics. Do next. We can use R(t) and t versus
1z and T T0(1z), I never proved in detail
comes from radiation density (rr) proportional to
T4 and rr goes as rr0(R(t0)/R(t))4 Also use r
ro(R(t0)/R(t))3, for matter
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• First a review of what BB does explain
• And how
• We will put in detail!
• Logical progression from the escape equation math

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The Big Bang Explains

• Why the sky is dark at night (Olbers paradox).
• Why the Universe is old.
• Why the Universe is mainly hydrogen and helium.
• The existence of the CMB.
• That the Universe is expanding.

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Olbers Pardox

• If the Universe were infinite
• AND UNEVOLVING
• uniform in density of stars (or galaxies)
• then we would be burned to crisp.
• From simple geometry
• The apparent brightness of objects falls off as
  one over the distance squared.

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Olbers Pardox, cont.

• Number of objects per unit volume in a shell at a
  distance goes as the distance squared.
• Exactly cancels the one over distance squared
  dimming of an individual star or galaxy.
• The sum of all the brightness adds to infinity if
  the Universe is static, un-evolving, uniform in
  density, and infinite.

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Olbers Pardox, cont.

• The BB defeats Olbers Paradox by
• Expanding universe
• Star formation had a beginning.
• Stars to evolve.
• Expansion is not necessary, however, only that
  stars live for a finite time is.

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• The BB says the Universe expands
• And we observe expansion
• Our models with the escape equation give
  expansion
• The observation of distant objects plus (time it
  takes light to travel implies a large age)
• The CMB (universe has been cooling) fits with
  expansion model and observations
• Model says the Universe is about 15 billion years
  old.

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BB Explains Hydrogen Heliumso called BB
Nucleo-synthesis

• The Big Bang starts the Universe off with a hot
  big bang!
• The initial universe was then hot and dense in
  the first 3 minutes (or so) to burn (fuse)
  hydrogen into helium.
• Expansion prevented heavier elements from being
  formed in any significant quantities.

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• Universe in first 3 minutes not too hot to break
  up He and not too cold or under dense to fuse H
  into He.
• Works if we start at 1 second with a reasonably
  high T (about 1 million K).
• We can estimate this T and density (r) by
  extrapolating back from the brick wall
• know T, r, 1z of brick wall when becomes
  transparent from simple atomic physics

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• 1z R(t0)/R(t)
• t AR(t)2 A constant
• applies in radiation dominated era
• about 100,000 years before brick wall becomes
  transparent.
• know t, know T at brick wall transparent
• Extrapolate back to t 1 second
• using T T0(1z) gt at 1 second
• T 1 million K , OK!

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• We also know the physics of radiation , matter
  etc. well enough to do this back to 1 second, at
  least. See the book, page 376, figure 13.7
• Key players are protons, neutrons, electrons
  and neutrinos.
• Neutrons decay into protons, electrons, and
  neutrinos.
• the reverse can happen as long as the temperature
  and density are high enough.

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• gt density and temperature fall and a
  significant number of free neutrons have
  decayed, the fusion process halts.
• Half of all of free neutrons will decay in about
  10.6 minutes
• Net effect is that after about 3 minutes process
  stops
• The higher the density, the higher the
  probability the neutrons and protons will join up
  and eventually make He.

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• An intermediate step join of proton to neutron
  deuterium D.
• The simple process is then p n gt D
• D p gt light He (with only 1 neutron) written
  3He.
• 3He 3He gt 4He (ordinary, super stable helium)
  stuff
• The denser the material, the more D is burned
  into He at faster rate than D is made.

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Baryonic matter
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gt Higher He/H tracks with lower D/H
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The Net Result cont.
gt A measure of the ratio of He/H and or D/H is
the most direct method we have of determining Wb.

• gt A measure of the ratio of He/H and or D/H is
  the most direct method we have of determining
  Wb.
• Therefore a major goal of some people is to go
  out and measure these quantities while others
  make sure the theory is correct.

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• Neutrinos are so penetrating that
• IF we could detect them
• we could see back to about the 1st second
• Very exciting

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• The BB model then starts out hot and dense to
  explain He/H and D/H.
• The Universe expands and cools until the brick
  wall becomes transparent.
• gt What is the brick wall made of and how to we
  predict transparency?
• The brick wall is mainly hydrogen gas but before
  it becomes transparent, the hydrogen is nearly
  totally ionized.
• Electrons and protons are free of each other in a
  weird state we call a plasma.

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The CMB more details now

• As the Universe expands,
• Both the hydrogen gas and the photon gas cool.
• If hot enough, the photons can separate
  electrons from protons that might have joined
  together to make ordinary hydrogen gas.
• And at the same time electrons are very efficient
  at absorbing or scattering photons.
• So the photons cant travel far and we have
  brick wall.

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The CMB more details now

• Eventually, however, the gases (photons,
  electrons, and protons) cool so much
• that the photons dont have enough energy to free
  bound (to protons)
• not enough to even to excite the atom by being
  absorbed. (Nature has conspired so that
  electrons can only circle the proton in certain
  specific orbits and if there isnt enough energy
  for an orbital transfer, the photon cant be
  absorbed be the atom.)

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The CMB more details now

• So gases cool down to point where hydrogen
  becomes atomic hydrogen and the gas suddenly
  becomes transparent. The photon gas then streams
  away on its own to reach us today as the CMB.

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The BB doesnt really say why started out hot or
expanding but

• The model is consistent with this much of the
  data.
• Using only laboratory physics
• We already know some problems smoothness of
  CMB, CMB fine structure, SNe Ia, and clusters.
  But some say we need more gt enter Inflation