chapter17_the beginning of time
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Chapter 17The Beginning of Time
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How far/back in time can we see with our current telescopes?
What is the farthest we could in principle see?
Only until 380,000 years after the beginning
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Our Goals for Learning
What were conditions like in the early universe?
What is the history of the universe according to theBig Bang theory?
17.1 The Big Bang
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What were conditions like in theearly universe?
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Universe
must have
been muchhotter and
denser early
in time
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The early
universe must
have beenextremely hot
and dense
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Photons converted into
particle-antiparticle pairs
and vice-versa
E = mc2
Early universe was full of
particles and radiationbecause of its high
temperature
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Today, In the labs we created conditions up to 10-10 seconds
after the Big Bang.
And we have a theory for up to 10-38 seconds after the big bang.
The very instant of creations we do not know how to describe.
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What is the history of the
universe according to the BigBang theory?
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Lets step back:
There are four known forces in universe:
Gravity:
Electromagnetism:it acts among charged particles, in atoms and
molecules, and is responsible for all chemical and biologicalinteractions.
Strong Force:important only on very small distances, binds nuclei
together.
Weak Force:important in nuclear fusion and fission. There are
some particles which interact only through this force (and gravity).
Like neutrinos and WIMPs (dark matter).
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Thought Question
Which of the four forces keeps you from sinking to thecenter of the Earth?
A. Gravity
B. Electromagnetism
C. Strong Force
D. Weak Force
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Thought Question
Which of the four forces keeps you from sinking to thecenter of the Earth?
A. Gravity
B. Electromagnetism
C. Strong Force
D. Weak Force
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Do forces unify at high temperatures? (think about ice, liquidand vapor as just a various states of water)
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Do forces unify at high temperatures?
Yes!
(Electroweak)
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Do forces unify at high temperatures?
Yes!
(Electroweak)
Maybe
(GUT)
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Do forces unify at high temperatures?
Yes!
(Electroweak)
Maybe
(GUT)
Who knows?
(String Theory)
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Planck Era
Before Planck time
(~10-43 sec)
Random fluctuation
of
energy/particle/space- we have no theory
of quantum gravity.
At the end of Plank
era, gravity froze out
separated from
other forces.
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GUT Era
Lasts from Planck
time (~10-43 sec) toend of GUT force
(~10-38 sec).
At the end of GUTera strong force
froze out.
There are some theories proposed which link GUT forces. Stillunconfirmed, but at least we have some idea how that could work.
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Since this time, space was field with photons (radiation) and all
elementary particles we know of (electrons, quarks, and their
anti-matter counterparts).
Universe was extremely hot and photons had enough energy to
produce even the heaviest particles (most of these particles do
not exist as free particles today). Particles would then annihilate
back to photonsthe universe consisted of the matter-radiation
sea (soup).
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Electroweak Era
Lasts from (10-38
sec) to end ofelectroweak force
(10-10 sec).After
this instant all
forces becameforever distinct in
the Universe.
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We have direct experimental evidence of the transition from
electroweak force to two separate forces: electromagnetic and
weak. We probed in the lab physics of the Universe when it was
just 10-10 seconds old!
To get a better idea: Temperature at the end of this era (10
15
K)was 100 million times hotter than in the Sun!
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Particle Era
In particle era it became cool
enough so that quarks hadcombined producing protons
and neutrons!
The era ended when universe
became too cold (1012 K) for
photons to produce protons
and neutrons. The total
number of protons and
neutrons (and antiprotons/
antineutrons) was sealed at
that time. Photons were stillproducing electrons, and
neutrinos, and got produced
back by their annihilation
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Universe consisted of protons, neutrons, on one hand, and the
soup of photons producing electrons, neutrinos on the other.
But, amounts of matter (protons/neutrons) and antimatter
(antiprotons/antineutrons) was still nearly equal.
How much anti-matter is left in today's Universe?
If the Universe had exactly the same amount of protons and
antiprotons how would it look like today?
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Era of Nucleo-synthesis
There were roughly 1 extra proton
for every 109 proton-antiprotonpairs!
This era begins with matter
annihilating remaining antimatter
at ~ 0.001 sec.
What was left was universe
containing only matter, as we know
it today!
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After that, pand nbegan to fuse, making He and some deuterium and Li.
This era ended when Universe was 3 minutes old. All elements the Universestarted off with (75% H, 25% He, trace amounts of deuterium and Li) where
made in the first 3 minutes!
The Universe expanded so much by than, that p&n, became to far apart, and
synthesis of nuclei ceased.
Why elements heavier than He did not form in the early Universe?
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Era of Nuclei
After the era of
nucleosynthesis the Universeconsisted ofp, He nuclei and
free electrons.
(no neutral atoms existed yet)
Photons were bouncing off
these charged particles, never
managing to travel long
between collisions (in what
layer of the Sun does the
similar condition exists?)
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Era of Atoms
Universe has cooled enough, at
age of ~ 380,000 years, so that
atomscould form (and photons
had not enough energy to ionize
them again).
The Universe suddenly became
transparent for photons, theydidnt have any free charged
particles to bounce from anymore.
They justflashed through the
Universe, and amazingly enough,
we still can see this photons today.All Universe is bathed in this, so
called, cosmic microwave
background radiation. It arrives
to us from every point in space.
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Era of
Galaxies
Galaxies form at
age ~ 1 billion
years.
We have alreadydiscussed the rest
of the story in the
previous
chapters
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Primary Evidence for Big Bang theory
1) We have detected the leftover radiation
from the Big Bang.
2) The Big Bang theory correctly predicts the
abundance of helium and other light
elements.
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What have we learned? What were conditions like
in the early universe?
The early universe was
filled with radiation and
elementary particles. Itwas so hot and dense that
the energy of radiation
could turn into particles of
matter and antimatter,which then collided and
turned back into radiation.
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What have we learned? What is the
history of theuniverse
according to
the Big Bangtheory?
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17.2 Evidence for the Big Bang
Our Goals for Learning
How do we observe the radiation left over from the
Big Bang?
How do the abundances of elements support the Big
Bang?
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How do we observe the radiation
left over fromthe Big Bang?
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The cosmic
microwave
background
the radiation left
over from the
Big Bangwasdetected by
Penzias &
Wilson in 1965.
They noticed that wherever they point their antenna
(designed for satellite communications) to, they get some
unexpected noise, which they tried hard to get rid off. At
the end, they got Nobel Prize, for providing first evidence
for Big Bang theory.
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Background radiation from Big Bang has been freely
streaming across universe since atoms formed at
temperature ~ 3,000 K: visible/IR
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Expansion of universe has redshifted thermal
radiation from that time to ~1000 times longer
wavelength: microwaves(part of radio waves)
Background has perfect
thermal radiation
spectrum at temperature
2.73 K
Corresponds to a temperature of2.73 K
the temperature of the night sky.
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CLICK TO PLAY MOVIE
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COBE detected the seeds of future structure formation: the
temperature of universe varies slightly, by only about 0.01%.
These variations indicate that the density of the early universe did
differ from place to placethe seeds of structure formation were
present during the era of nuclei.
( )
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COBE (1993)
WMAP (2003)
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WMAP gives us detailed baby pictures of structure in
the universe
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How do the abundances of
elements supportthe Big Bang?
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Before the Big Bang theory, the fact that Universe contains so
much He was a puzzle. It meant that the Universe was once hotenough for nuclear fusion of H to He to happen, but people did
not know how.
The fact that the temperature of microwave background is 2.73 K,
tells us precisely how hot was the Universe in the distant past and
exactly how much He should have been made. The result, 25%
He, is another success of this theory.
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Abundances of
other light
elements agreewith Big Bang
model having
4.4% of critical
density ofnormal matter
more
evidence for
WIMPS!
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Thought Question
Which of these abundance patterns is an unrealisticchemical composition for a star?
A. 70% H, 28% He, 2% other
B. 95% H, 5% He, less than 0.02% other
C. 75% H, 25% He, less than 0.02% other
D. 72% H, 27% He, 1% other
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Thought Question
Which of these abundance patterns is an unrealisticchemical composition for a star?
A. 70% H, 28% He, 2% other
B. 95% H, 5% He, less than 0.02% other
C. 75% H, 25% He, less than 0.02% other
D. 72% H, 27% He, 1% other
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What have we learned? How do we observe the
radiation left over from the
Big Bang?
Telescopes that can detectmicrowaves allow us to observethe cosmic microwave
backgroundradiation leftover from the Big Bang. Itsspectrum matches thecharacteristics expected of theradiation released at the end of
the era of nuclei, spectacularlyconfirming a key prediction ofthe Big Bang theory.
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What have we learned?
How do the abundances of elements support the
Big Bang?
The Big Bang theory predicts the ratio of protons toneutrons during the era of nucleosynthesis, and from
this predicts that the chemical composition of the
universe should be about 75% hydrogen and 25%
helium (by mass). This matches observations of thecosmic abundances, another spectacular
confirmation of the Big Bang theory.
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17.3 The Big Bang and Inflation
Our Goals for Learning
What aspects of the universe were originallyunexplained by the BigBang model?
How does inflation explain these features of the
universe?
How can we test the idea of inflation?
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What is cosmological inflation?
A brief period of exponentially fast expansion of the Universe. Theuniverse expanded from to in just seconds!
Do you know for some other period in which universe was
expanding exponentially fast?
It presumably happened at the end of GUT era. When the strong
force separated, the huge amount of energy was released and it
caused this rapid expansion.The idea (like many others) sounds bizzare, but it is useful
addition to the standard Big Bang theory: it helps solve some
features of Universe unexplained by standard Big Bang model.
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What aspects of the universe
were originally unexplainedby the Big Bang model?
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Mysteries Needing Explanation
1) Where does structure come from? (how diddensity enhancements come about)
2) Why is the overall distribution of matter so
uniform?
3) Why is the density of the universe so close to the
critical density? (it could have been whatever
number and it has exactly this, critical density
value)
Inflation can
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Inflation can
make all the
structure by
stretching tinyquantum ripples
to enormous
size.
These ripples in
density then
become the
seeds for all
structures
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How can microwave temperature be nearly identical on
opposite sides of the sky?
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Regions now on opposite side of the sky were close
together before inflation pushed them far apart
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Overall
geometry of the
universe is
closely related
to total density
of matter &
energy
Density =
Critical
Density >
Critical
Density
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