Transcript Cosmology ppt. - University of Dayton

ORIGIN OF THE UNIVERSE
PIn the beginning, God created the heaven and the
earth; and the earth was without form and void;
and darkness was upon the face of the deep and the
spirit of God moved upon the face of the water.
And God said, "Let there be light," and there was
light. And God saw the light, that it was good.
Genesis 1:1-3
COSMOLOGY
The study of the origin, structure, and evolution
of the universe.
Clues about the Origin of the Universe
PCosmic background radiation
PCosmological redshift
What is cosmic background radiation?
This is background microwave radiation that is
uniform in all directions and indicates a
temperature for the current universe of about 3
degrees Kelvin. This supports the Big Bang
theory.
What is the cosmological redshift?
Photons from distant galaxies are all redshifted.
This is a color shift in the radiation spectrum of
galaxies. The further away the galaxy the greater its
redshift. This redshift is caused by the expansion of
the universe - further evidence for a Big Bang. All
galaxies are receding from each other as a result of
the Big Bang.
Conclusions Based on Observations
• Evidence for expansion follows from the
cosmological redshift
• The expanding universe is probably the
result of an explosion - The Big Bang
• The microwave background radiation is
further evidence for the Big Bang
• The cosmic background radiation implies a
period of “inflation” after the Big Bang
6
What is the Center of the Universe
PThe universe has no preferred center of
expansion.
PWe are not the center of the universe nor is
anything else.
PEvery observer, no matter where in the universe
will see the universe expanding in the same way.
Age of the Universe
PCalculations indicate an age of about 15 billion
years for the age of the universe. No objects older
than this have been observed.
PE.G. the age of the earth is about 4.5 billion years
PThe oldest stars are about 10 billion years.
Beginning of “Big Crunch” ?????????
Now (15 billion years after B.B.)
Dawn of civilization
Big Bang
Radiation and Matter: Origin of
the Universe
Gamma Rays
Particle
Antiparticle
Particle
Gamma Rays
Antiparticle
Radiation and Matter: Origin of the
Universe
After about 1 microsecond
PUniverse was hot and dense
PRadiation converted into protons and antiprotons
plus quarks and anti-quarks and visa versa
PSmall volume, jammed with quarks and
antiquarks annihilating each other by creating
radiation, began to expand.
PThe cooler radiation was no longer hot enough to
create quarks and thus most quarks disappeared
from the universe.
Radiation and Matter: Origin of the
Universe
After about 1 microsecond
PA few quarks survived and combined to make
protons and neutrons.
PWithout this tiny imbalance in quarks (symmetry
breaking) the universe would be void of matter
containing only cosmic radiation.
PSpace was then filled with ordinary matter and
radiation and continued to expand.
Radiation and Matter: Origin of the
Universe
After about 5 seconds
PUniverse still hot enough to create light particles,
electrons and anti-electrons.
PProtons and electrons interact to produce neutrons
PUniverse continues to expand
PUniverse cools to a few billion degrees and the
creation of matter stops.
Radiation and Matter: Origin of the
Universe
About 3 minutes
PExpansion cools the universe to a few hundred
million degrees.
PApproximately 1/4 of the protons are fused into
helium.
PAll of space is now permeated by helium and
hydrogen (about 71% H and 27 % He).
Radiation and Matter: Origin of the
Universe
About a million years
PExpansion cools the universe to about 3000 K
PAtoms can now form by nuclei capturing
electrons - recombination.
PBefore recombination, the universe behaved as a
single blend of radiation and matter.
PAfter recombination, matter and radiation acted as
separate entities.
Radiation and Matter: Origin of the
Universe
The matter Era
PSince matter and radiation are no longer locked
together, radiation just expands with the universe
to become the 2.7 K cosmic radiation of today.
PClouds of matter condense out to form clumps of
matter, galaxies, etc. Formation of galaxies needs
dark matter?
Sequence of Events in the Big Bang
Event
Time
Creation
0
infinite
-44
Heavy-particle era 10
Light-particle era
10
Radiation era
10
Matter era
10
Now
10
Temperature (K) Result
-4
6
10
sec
sec
33
10
10
12
10
sec
10
yrs
3000
yrs
3
?
Photons make massive
particles
Photons make light
particles
Only a few particles left
in a sea of photons
Radiation & matter
decouple
Current picture of
universe
Evolution of Forces in the Big Bang
-43
10 Sec
10-35
-12
10
-6
10
32
10
27
10
15
1013
10
Now
3K
K
Summary of Big Bang
• Is the universe “open” or “closed”
• Open means that it will expand forever
• Closed means that sometime it will stop
expanding and will begin to contract - the
Big Crunch.
• Third possibility is a “flat” universe. This
universe just stops expanding at some point
and remains at that size.
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Summary of Big Bang
Nucleosynthesis
PUniverse begins with “Big Bang” - plasma of
protons & neutrons.
PPlasma cools & forms hydrogen nuclei
PGravity pulls hydrogen together to form stars
PCollapsing hydrogen heats up (for about 10
million years) & the hydrogen becomes fused into
helium, releasing energy.
Summary of Big Bang
Nucleosynthesis
PEventually, the star materials fuse into nuclei
around iron, releasing energy, and the star uses up
its energy.
PThe larger of these dying stars explode into
supernovae.
PThe explosions release lots of neutrons which fuse
with medium weight nuclei makeing heavier
elements.
PThis spreads as dust into the universe eventually
forming planets in some cases.
Questions
PDark Matter - missing mass?
POpen, closed or flat?
POther universes - other dimensions?
PWhy is the universe all ordinary matter, i.e. no
antimatter?
PWhy is the cosmic background radiation so
smooth?
Review Questions:
Why do astronomers believe the universe is expanding?
What is cosmic background radiation and what is its origin?
How was helium formed from hydrogen in the early universe?
What is the approximate age of the universe?
What is dark matter?
What is meant by the big bang and the big crunch?
What is meant by an open and closed universe?