Recap the Creation of the Universe

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Recap the Creation of the Universe

• What are the two possible scientific answers to
  the question How was the Universe created ?
• Explain how matter appeared in the Universe.
• How do you answer the question How many
  Universes are there ?

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The Fate of the Universe

• Possible Universe Models
• Observing the Furthest Galaxies
• Galactic Masses
• Invisible Masses
• Dark energy
• The history of the Universe

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Possible Universe Models

• Two forces at work the Big Bang expansion and
  the gravitational attraction of the galaxies
• Three possible models
• Open
• Flat
• Closed and Pulsing (or Oscillating)

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Possible Universe Models
constant expansion rate
space
Open
Flat
Big Bang
Closed
age of the Universe
time
Big Crunch
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Hubble Diagram Revisited (I)
The difficulty in using Hubble diagrams to decide
the age of the Universe is related to the
inaccuracy of the cosmic yardstick. Todays
estimates favor an open Universe.
closed U.
openU.
Galaxies speed
flat U. (critical density)
Galaxies distance
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Observing the Furthest Galaxies

• The Cepheids
• The Cepheid variable stars are aged stars are
  known to brighten and dim regularly in a way
  which reveals their instrinsic brightness and
  implicitly their distances.
• Cepheid stars are visible only at relatively
  small distances (best bellow 80 million
  light-years).
• Type Ia supernovas
• provide a more powerful phenomenon which has a
  brightness independent of the galactic size. They
  occur in binary star systems approaching their
  end of life. If one star reaches the white dwarf
  stage and the other the red giant stage, the
  white dwarf will pull material to grow its size.
  When it reaches 1.4 solar masses it explodes.
  This mechanism always happens the same way in
  every galaxy.
• 1992 Alan Sandage and his collaborators at the
  Space Telescope Institute in Baltimore use
  Cepheid and type Ia supernova observations in the
  galaxy IC 4182 to calibrate the supernova-based
  yard stick.
• They gave the Universe an age around 15 billion
  years, in agreement with the fact that the age of
  some stars was close to 14 billion years.

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From Closed to Open Universe

• The answer on the fate of the Universe relies on
  observations on the furthest galaxies at over 10
  billion light-years from us.
• In 1980s Sandage and his collaborators favored a
  closed Universe model based on the belief that
  the gravitational attraction of the galaxies will
  at some point reverse the expansion. He proposed
  a Pulsing Universe model, with a 40 billion
  interval between two Big Bangs.
• Since 1998 the general belief shifted towards an
  open Universe, which has currently has an
  accelerated expansion. In that year two groups,
  the High-Z Supernova Search Team and the
  Supernova Cosmology Project, have analyzed a
  total of 58 very remote type IA supernovas and
  have concluded that for the last 6 billion of
  years the universal expansion was actually
  speeding up.

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Galactic Masses

• The answer to the question of the closeness of
  the Universe could also come from measurements of
  the galactic masses.
• If these masses are large the average density of
  the Universe could be higher than the critical
  density, needed to close the Universe.
• The mass of a typical spiral galaxy is about 109
  solar masses. This result, based on brightness
  observations, is not too accurate for non-spiral
  galaxies.
• A better method is to calculate galactic masses
  from the observations on their dynamics. Our
  Milky Way rotates around its axes in about 200
  million years and its mass is about 5 times
  bigger than the mass of its stars.
• A lot of work was done and today we have complete
  galactic masses studies for galaxies of various
  types, sizes and brightness.
• Those studies were then combined with studies of
  the intergalactic distances and lead to 10-31
  grams per cubic centimeter (31 orders of
  magnitude smaller than the density of water).
  That result is about 0.7 of the critical
  density, that would close the Universe.

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Invisible Matter

• Intergalactic material
• Using hydrogens characteristic 21 cm radiation,
  one can map not only our galaxy but also some
  intergalactic clouds approaching the Milky Way.
• X ray observations confirmed the existence of the
  intergalactic material which can be charged and
  moving at high speeds.
• In addition to the intergalactic clouds it is
  conceivable that the Universe contains plenty of
  isolated black dwarfs, neutron stars and black
  holes.
• Neutrinos
• Photonic and neutrinic radiation is dense.
• While photons have zero mass, neutrinos seem to
  have a small but significant mass.
• V.Liubimov in Russia and F.Reines in U.S. lead
  groups which in 1975 announced a neutrino mass
  between 25-35 eV.
• That in itself would make the invisible mass 19
  times larger than the visible mass !
• The existence of other elementary particles, such
  as the supersymmetric particles, is still a valid
  speculation.

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Dark Energy

• The latest estimates support a model where the
  visible and invisible matter account for 27-40
  of the critical density of the Universe.
• Knowing that the Hubble diagram measurements
  indicate a density close to the critical density,
  the dominant component in the mass in this
  Universe is a mysterious dark energy.
• Whatever it is, the new component of the
  matter/energy of the Universe must be dark and
  gravitationally repulsive (it does not influence
  individual galaxies motion).
• The existence of this dark energy would make the
  Universe older than without it.
• Explaining dark energy
• the vacuum energy (with virtual particles
  production) or
• on the quintessence theory (A.Lindes chaotic
  inflationary model).
• still far from a precise explanation

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Short History of the Universe

• The radiative stage
• The inflationary mechanism
• A few tens of thousands of years old Universe is
  dominated by ponderal matter.
• For about 9 billion years the Universe expanded
  under the original push of the Big Bang and
  slowed down by the intergalactic gravitational
  attraction.
• In the last 6 billion years as the vacuum between
  the clusters of galaxies increased the dark
  energy became dominant and dictated an enforced
  acceleration.
• The fate of the Universe is different in the
  vacuum or in the quintessence scenario. New
  observations are needed to decide which model
  provides the correct scenario. In the Superstring
  Cosmology one has to also account for the fact
  that by increasing the size of the 5-dimensional
  bubble, in time, all galaxies will become
  invisible from our glaxy.

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Einsteins Cosmological Constant

• The main theoretical model in cosmology is
  Einsteins general relativity. When he formulated
  it he introduced a cosmological constant which
  was adjusted to make the Universe stationary.
• When observations showed that the Universe is
  actually expanding, Einstein declared that the
  cosmological constant was his greatest blunder.
  
• However, his constant returned as a possible
  explanation for the missing mass and for the
  distribution of galaxies.
• Since 1998, we know that the universal expansion
  is accelerating in agreement with the existence
  of a non-zero cosmological constant (see C.Hogan
  et al in Scientific American, January 1999).
• The cosmic constant changes its value in time.