The Universe The by yurtgc548


									The Universe

 Origins and Change
“If we do discover a unified theory of
the universe, it should in time be
understandable in broad principle to
everyone, not just a few scientists. Then
we shall all, philosophers, scientists, and
just ordinary people, be able to take
part in the discussion of the question of
why it is that we and the universe exist.
If we find the answer to that, it would
be the ultimate triumph of human
reason- for then we should know the
mind of God”.         Stephen Hawking
“There is a theory which states that
if ever anyone discovers exactly
what the Universe is for and why it
is here, it will instantly disappear
and be replaced by something even
more bizarre and inexplicable. There
is another theory which states that
this has already happened.” - The
Hitchhiker's Guide to the Galaxy by
Douglas Adams
         The Big Bang
• Current theory of how universe
  was formed
• All matter concentrated in a
  single point called a singularity
• Matter exploded outward
• Universe has continued to
  expand ever since
Monsignor Georges Henri Lemaître (July 17, 1894 – June 20,
1966) a Belgian Roman Catholic priest, proposed what
became known as the Big Bang theory of the origin of the
Universe, which he called his 'hypothesis of the primeval
atom‘ in 1927
 Big Bang Model
   Universe expanded from an extremely dense and hot state
    and continues to expand today
   Like raisins in a rising loaf of bread
   The graphic scheme above is an artist's concept
    illustrating the expansion of a portion of a flat Universe
• Expanded from a hot and dense initial condition
  called the singularity
• Approximately 13.7 billion years ago and continues
  to expand to this day
Misconception Revealed

• The Big Bang theory cannot and does
  not provide any explanation for such
  an initial condition; rather, it describes
  and explains the general evolution of
  the Universe since that instant
Physical Cosmology
  PART 1 History
•In 1912 Vesto Slipher
     •measured the first Doppler shift of a
     spiral galaxy
     •discovered that almost all such galaxies
     were receding from Earth.

                         In 1924, Edwin Hubble developed a series of distance
                         indicators, using the 100-inch Hooker telescope at
                         Mount Wilson Observatory. This allowed him to
                         estimate distances to galaxies whose redshifts had
                         already been measured, mostly by Slipher.

                         In 1929, Hubble discovered a correlation between
                         distance and recession velocity—now known as
                         Hubble‘s Law validating Lemaître Big Bang Theory
         Underlying assumptions
• The Big Bang theory depends on two major
  assumptions: the universality of physical laws, and
  the Cosmological Principle. The Cosmological
  Principle states that on large scales the Universe is
  homogeneous and isotropic. (uniform is all
 FLRW metric
• General relativity describes space-time by a metric,
  measuring distances that separate nearby points
  (galaxies, stars, or other objects)
• A coordinate chart or "grid" is laid down over all
Horizons and Big Bang Space-Time
An important feature of the Big Bang
 space-time is the presence of
The Universe has a finite age and light
 travels at a finite speed
   there may be events in the past whose
   light has not had time to reach us
This places a limit or a past horizon
 on the most distant objects that can
 be observed
Horizons and Big Bang Space-Time
• Conversely, space is expanding and
  more distant objects are receding more
   – light emitted by us today may never "catch
     up" to very distant objects.
   – This defines a, future horizon. (limiting the
     events in the future that we will be able to

 In general relativity, an event horizon is a boundary in space-
 time, most often an area surrounding a black hole
                   Doppler Effect
• Doppler effect changes the pitch of a sound coming from something
  moving toward you, or away from you (police siren, an ice cream
  truck's music, a mosquito buzzing)
• Sounds moving toward you are a higher pitch because the sound
  waves are compressed together, shortening the wavelength
• Sounds moving away from you are a lower pitch because the sound
  waves are stretched apart, lengthening the wavelength
• Light behaves in the same way
          Continuous Spectrum

• A rainbow is an example of a continuous spectrum
• Most continuous spectra are from hot, dense objects
  like stars, planets, or moons
• The continuous spectrum is also called a thermal
  spectrum, because hot, dense objects will emit
  electromagnetic radiation at all wavelengths or colors
• Any solid, liquid, and dense (thick) gas at a
  temperature above absolute zero will produce a
  thermal spectrum
Which way the spectral lines are shifted tells you if the object is moving
toward or away from you.

Blueshift - toward you the waves are compressed, so their wavelength is
Redshift - away from you the waves are stretched out, so their
wavelength is longer.
• This explanation also works if you are moving and the object is
  stationary or if both you and the object are moving. The doppler effect
  will tell you about the relative motion of the object with respect to you.
  The spectral lines of nearly all of the galaxies in the universe are
  shifted to the red end of the spectrum. This means that the galaxies are
  moving away from the Milky Way galaxy and is evidence for the
  expansion of the universe.
• You can also see
  this effect with
  the light bulb
  wired to a
  dimmer switch.
• Dim bulb will
  have an orange
  color and as you
  make it brighter,
  the bulb will turn
  yellow and even
        Absorption and Emission
                                       All matter is
                                       concentrated in
                                       a single space
                                       called a
                                       singularity. It
                            Proto-     explodes
                                       outward. As
                                       the universe
                                       expands the
              Explosively              gas cools into a
              expanding                cloud.
              cloud of                 Sections of the
                                       cloud collect
                                       under the force
                                       of gravity and
                                       form proto-
    Gases in the
    continue to
    cool and
    collect as
    Inside the
    nebula stars
    are born

                Nebula   Proto-star   Solar System
     Can You Imagine?
• All the material of the universe
  exploding outward
• As it spreads and cools large clouds
  of gas and dust called nebulae
  begin to coalesce and cool
   –We’re talking millions of light
    years large
• As portions of the nebulae came
  together under the force of gravity,
  stars were born – Nebular Theory
There are billions of
galaxies in the universe
Galaxies are collections of
     billions of stars
Stars are spinning clouds
   of gases that radiate
 electromagnetic energy
     through a fusion
   reactions, changing
  hydrogen into helium
      Lifecycle of a Star
• Stars are born, live and die
• How a star dies is determined by
  its mass
 – Massive stars (7-10X the mass of our
   sun) turn into supernova, neutron stars
   or black holes

 – Smaller stars cool to become white or
   brown dwarfs
         A Star is Born
• Nebula - huge
  clouds of dust and
  gas in galaxies
• Dust and gas
  collects under the
  force of gravity
• If a critical mass
  is reached
  – A fusion reaction
  – Star is born
 Background Information
• Stars’ sizes from .08 to 120
  times the mass of our sun (one
  solar mass)
• For a star to be born the
  internal temperature must
  reach about 10 million degrees
  Kelvin (about 18 million
  degrees Fahrenheit)
• At these temperatures atomic
  nuclei can be fused - a fusion
 The Bigger They Are…
• The more massive the star the
  faster the fusion reaction and the
  more energy emitted
• Our sun will take about 10 billion
  years to fuse its hydrogen to
• A star three times as massive as
  our sun can do the same thing in
  500 million years because of the
  higher rate of fusion
        A Star’s Life
• Produce energy through fusion
  reactions fusing hydrogen to
• Force of fusion reaction pushes out
  against the pull of gravity
• The balance between these forces
  determines the size of the star
• As the star fuses all its hydrogen
  the push of the fusion reaction
  decreases and the pull of gravity
  takes over
Gravity   Fusion   Gravity
        Solar Collapse
• The star lacking
  the push of the
  fusion reaction
  collapses in on
• As the core
  collapses it
  generates intense
  pressure and
  heat, the outer
  gases expand and
  the star becomes
  a red giant
• All stars are born as
  proto-stars, fuse
  hydrogen to helium until
  the hydrogen runs out,
  suffer core collapse and
  become red giants
• At this point what
  happens depends on the
  mass of the star
   Stars Like Our Sun
• Fuse hydrogen to helium
• When the majority of hydrogen is
  used up the core begins to collapse
• There is not enough mass for the
  core to reach the 100 million
  degrees K needed to start fusing
  helium to carbon
• There is enough pressure to cause
  the remaining hydrogen in the
  outer shell to start a fusion
Stars Like Our Sun
• The outer shell expands
  to become a red giant
• When that hydrogen is
  fused, the star fizzles out
  and becomes a white
      Massive Stars
• If it is massive enough, it will build
  up enough pressure and
  temperature during the collapse to
  start a fusion reaction turning
  helium into carbon in the core
• In the outer shell the remaining
  hydrogen will fuse to helium
• Very massive stars can have fusion
  occurring in several shells
    Massive Stars
• For stars of less than 8 solar
  masses this is the end.
  They can not generate the
  heat and pressure required
  to fuse carbon
• Fusion stops and they fizzle
  into white dwarfs
      Shell Fusion
• Stars larger than 8 solar
  masses are big enough to fuse
  carbon to oxygen in the core
• While that is happening the
  temperatures outside the core
  are hot enough to fuse helium
  to carbon
• In the next layer up hydrogen
  is being fused to helium
   The process continues
• With each successive conversion
  the core collapses further into
  itself and becomes hotter
  eventually reaching 3 trillion
  degrees K when the core fuses
  from silicon to iron
• At each stage new shells form and
  convert the lighter elements
• Hydrogen fused to helium becomes
  helium fused to carbon, to oxygen,
  to silicon …..
• The giant star now resembles an
  onion with a core at 3 trillion
  degrees K and multiple fusing
• The iron core absorbs energy as
  other elements fuse to it instead of
  emitting it
• The iron core collapses and
  becomes so dense protons and
  electrons fuse to become neutrons
• The by-product of this process are
• The core continues to collapse until
  the neutrons become so dense
  they begin to repel each other
• The core rebounds violently
• The rebound of the core and the
  neutrinos push the outer shells out
• The explosive force of the
  supernova last only seconds
• The added energy of the
  neutrinos causes fusion of
  heavier elements in the ejected
• The core collapses again to
  become a neutron star
• The shell, a nebula to start the
  process again
A neutron star's magnetic fields radiate as rings of
energy, and accelerated beams of gamma rays
stream out from the star's pole.
• The explosive force of a
  supernova is equal to 10
  trillion, trillion atomic
• That’s
        Neutron Stars
 Returning to the neutron core
 left over from our supernova
 Ifit is less than 3 solar masses the
  force inward of gravity and the
  force outward of the neutrons
  balance each other
 It becomes a stable neutron
          Black Holes
 Ifthe mass of the neutron star is
  greater than 3 solar masses the
  force of the neutron repulsion
  cannot overcome the force of
  gravity and the core continues to
 The core becomes denser and
 smaller until it creates a black
      Newton vs. Einstein
 Newton believed gravity was caused by the
 attraction of all objects to each other

 It’s a great theory and it works well on earth,
 but unfortunately it runs into some problems
 in space

 If gravity only attract object to each other
 why hasn’t the moon crashed into the Earth or
 the Earth into the Sun?
 Einstein solved that one by saying that
  space and time are like a fabric
 Massive objects warp the fabric
 Smaller objects travel in straight lines
  around that warp
    Think of a large rubber sheet. Now put a bowling
     ball on it. It creates a warp in the sheet. Absent of
     friction you could roll a marble in a straight line and
     it would orbit around the bowling ball
    Back to Black Holes
 If you put a shot put on the sheet instead of
 the bowling ball the warp would be sharper
 and deeper

 In theory neutron stars do the same thing to
 the fabric of space-time

 They are so small and so dense that a
 teaspoon would weigh as much as 3000
 aircraft carriers or 290 million tons
         Black Holes
 Because they are super dense
  neutron stars, they exert enormous
  gravitational force
 The force is so strong it pulls other
  matter and objects into itself getting
  more dense and of greater mass all
  the time
 It continues to sink deeper into the
  fabric of space and time
         Black Holes
 At some point it becomes so
  massive that not even light can
  escape its gravitational attraction
 With no emissions escaping there is
  nothing for us to detect, hence a
  black hole
 We believe we can detect black
  holes by their event horizon as
  matter accelerates towards the hole
 Remnants of supernovae are rich in
  heavier elements necessary to life
 Matter drifts free of a core and
  eventually begin to cool and collect
 Eventually they clump together and
  begin to collapse again forming new
  stars and planets
 Planets are nebular material not
  massive enough to start a fusion
Organization of the Universe

 Think concentric circles
 Satellites orbit around planets
 Planets orbit around stars
 Stars orbit around the center of a
 Galaxies are zooming through
  space in an expanding universe
 Satellites are natural or man made
  objects that orbit around planets
 Our moon is a natural satellite
 There are thousands of man made
  satellites orbiting the earth
  transmitting radio waves for cell
  phones, pagers, televisions etc.
 The space shuttle and space station
  are satellites
        Solar Systems
 As satellites orbit around
  planets; planets, asteroids and
  comets orbit around stars
 The collection of objects that
  orbit around a star is called a
  solar system
 Galaxies are collections of billions
  of stars which orbit around the
  center of the galaxy
 Galaxies are huge
 Our galaxy The Milky Way is
  120,000 Light Years across
 There are billions of galaxies in the
The Universe
    Geocentric Universe
 Since the time humans walked the
  earth and became aware they
  observed a constant pattern of the
  sun, moon and stars rising in the
  eastern sky and setting in the west.
 Since they had no perception of
  moving it was only reasonable to
  believe all these objects revolved
  around the earth
Greek astronomer Ptolemy
 developed a model for a
 geocentric universe in about
 140 AD
That model was the
 standard until the 1600s
   Heliocentric Universe
 Ptolemy’s model had only one problem
 To make the model work the planets had
  to occasionally make small backward
  circles to adjust their orbit
 These are know as retrograde motion
 Polish astronomer Copernicus proposed
  a heliocentric model in the 1600s
 This model worked without the
 The heliocentric model still
  possessed some irregularities, it
  didn’t work mathematically
 Kepler inherited 20 years of very
  accurate observations made by
  Tycho Brahe, a Danish noble
 Kepler studied planetary
  movement mathematically
        Kepler’s Laws
 Kepler found that the planets
  traveled in elliptical not circular
  orbits (1st)
 Each planet covered and equal area
  in equal time, i.e. did not travel at
  the same speed (2nd)
 The period squared of the planet is
  equal to the cube of its distance
  from the sun (3rd)
  Galileo and Newton
 Galileo used the telescope he
  invented to observe the
 His observations confirmed the
  heliocentric model
 Newton provided the why with
  his Laws of Gravitation
 And so the universe stood until
  the 1900s
   The Speed of Light
 Einstein calculated the speed of
  light at 186,000 miles per second
 His theories state that nothing can
  travel faster than the speed of
 Distances in space are so vast they
  are measured by the distance light
  will travel in a year or a light year
 Let us suppose there is other
  intelligent life in our galaxy.
 The Milky Way is 120,000 light years
 The next closest star (potential solar
  system) is 4.5 light years away.
 If we send out a radio signal how long
  will it take to reach the closest star
  and a response to get back?
 To the other side of the galaxy?

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