Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lectures 20
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
1
Was due Today – L20
• Reading:
– (Unit 4)
• Pre-Lecture Reading Questions:
– Unit 4 Revision (if Desired): Stage 1, due Wednesday
• End-of-Chapter Quizzes:
– Chapter 13
• Papers:
– Paper 2 Revision (if desired): Stage 2 due Wednesday
– Paper 3: Stage 1, due today
• Honors Papers:
– (Stage 2)
– Final paper due on the last day of class
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
2
A Big Bang Occurs… Then What?
Universe goes through a phase
of being hot and small with
lots of high energy particles
in thermal equilibrium
Then the Universe gets bigger
and cooler
As it gets bigger, it “evolves”
Evolution of the Universe
Big Bang, Black
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3
Universe cools down as time passes
The History of the Universe
10 billion degrees
1 degree
1 second
10 billion years
Evolution
of theexpands
Universeas time passes
Big Bang, Black
Universe
Holes, No Math Topic 2: After The First Three Minutes
4
Various Times
Explain what happens during each of a
number of different periods in time
– The VERY early universe
Chap 13
– The first three Minutes
– The next 300,000 years
Chap 14
– The next billion years
– ~13 billion years later (now) } Chaps 15-17
– The ultimate fate
}
}
of the universe?
} Unit 6
• The first four will take a couple of
lectures
Evolution of the Universe
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5
Where are we now in the history?
3 Minutes
Evolution of the Universe
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After the First Three Minutes
• At about the 3 minute mark the
temperature of the Universe is
about 1 billion degrees
• Electrons and positrons have mostly
annihilated each other
– No particles energetic enough to
produce new ones
~1 electron for every proton
Evolution of the Universe
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What else?
• The temperature drops so
that the photons, on
average, can’t even break
up deuterium
–Easier to start building up
the heavier nuclei
Evolution of the Universe
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8
Forming Heavy Nuclei in the Early Universe
Proton
Proton + Proton
 Deuterium + Electron + Neutrino
Electron
Nuclear
Reaction
Proton
Deuterium
Neutrino
Evolution of the Universe
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9
Nuclei and Low Energy Photons
At the 3 minute mark, low
energy photons only “bump”
nuclei
Deuterium
Low Energy
Photon
Evolution of the Universe
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Can Now Build Heavier Nuclei
Deuterium
Proton + Deuterium  3He + Photon
Nuclear
Reaction
Photon
3He
Proton
Evolution of the Universe
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11
Creating Stable Helium
3He
3He
+ 3He  4He + 2 Protons
Replenishes the hydrogen in the Universe
Nuclear
Reaction
Proton
4He
3He
Evolution of the Universe
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Proton
12
Why so few atoms Heavier than Helium?
Nuclear Physics
Can build up
Hydrogen and Helium
one at a time
 Next
possibility, 5He or
5Li, isn’t stable
So What? Since 5He and 5Li
decay quickly they don’t have
enough time to find another
proton to become 6Li and be
stable
Almost no elements
heavier than helium are
produced
Evolution of the
Universe in the early 13
Big Bang, Black
Three Minutes
Holes, No Math Topic 2: After The First
Universe
The Helium Story
• Able to predict the fraction of the atoms in the
Universe that are Helium
– 75% of atomic mass in hydrogen
– 25% of observed mass in helium
• Same as saying about 91% of the atoms are
hydrogen
• Helium is the same in every direction because it was
created everywhere
– Entire Universe had the same temperature
everywhere
– If it was created mostly in stellar cooking we’d see
it coming from the directions where there are more
stars
• I.e., the direction of galaxies
• More on this in Chapter 16
Evolution of the Universe
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14
Time marches on…
• Universe continues to expand
and cool
• Number of protons goes up
and number of neutrons goes
down
– Why? Neutrons can decay
into protons
Evolution of the Universe
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15
Neutron Decay
Neutron  Proton + Electron + Neutrino
Electron
Decay
Proton
Neutrino
Neutron
Evolution of the Universe
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The End of an Era
• For the next couple hundred
thousand years things don’t
change much
• Nuclear processes eventually
stop making new heavy nuclei
since the Universe gets so big
• But it’s still MUCH too hot
for
atoms
to
form
Evolution of the Universe
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The beginning of a new Era
• From 200,000-700,000 years the
universe expands and cools
• All the protons, neutrons and
electron combine to form atoms
– Translation: Universe cools until
the photons in the universe can’t
knock all the electrons out of the
atoms any more
Evolution of the Universe
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Atoms in a Lower Temperature Universe
Proton
At these lower
temperatures photons can’t
easily break up atoms
ElectroMagnetic
Reaction
Electron
Hydrogen
Atom
Photon
Evolution of the Universe
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Where are we now in the history?
200,000-700,000 years
Evolution of the Universe
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20
The Transition From a Hot Universe to
a Cool Universe
Some Time
Passes
Evolution of the Universe
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The Universe at ~700,000 Years Old
• At a temperature of about
3000K, photons, on average,
can’t knock apart atoms
• We can now have stable atoms
and all the electrons become
part of atoms
• The atoms are now free to form
into
stars
and
galaxies
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
22
Give this special time in history a name
Call this time
“Recombination”
Crappy Word!
Atoms are
combining for
the first time,
not
recombining!
Evolution of the Universe
Big Bang, Black
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Atoms in the Universe
Early Universe
A couple hundred
Thousand Years Later
These days
Evolution of the Universe
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Before and After the Creation of Atoms
Protons and electrons
combine to form
atoms
Universe becomes
transparent for
photons
Lots of electrons and
protons in the Universe
Photons scatter from
charged particles
Evolution of the Universe
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Transparent Universe
The Universe now LOOKS different!
• The light (photons) have no free
electrons to interact with
• Since all the electrons are in atoms,
because of Quantum Mechanics,
they largely ignore the photons
• Photons just travel in a straight line
 Like traveling through glass
Evolution of the Universe
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Atoms in the Universe
Early Universe
Photons bust
apart atoms
Hydrogen
A couple hundred
Thousand Years Later
Photons can only
excite atoms
These days
Universe is
transparent
to photons
High energy
photon
Evolution of the Universe
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A Cartoon…
+
+
+
+
+
+
+
+
After
Before
Recombination:
Photonsignore
Atoms
interact
withphotons
the
charged
particlestravel in
Photons
Scatter and
straight
lines
change directions
forever
Evolution of the Universe
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Cosmic Background Radiation
• The photons we see in the
cosmic background radiation are
essentially the photons AFTER
they interacted with their last
charged particle
• Well… they’ve been traveling for
awhile so they’ve changed a
little
Evolution of the Universe
Big Bang, Black
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Photons in the Universe
After recombination, photons
can travel freely through
space
Their wavelength is only
stretched (red shifted) by
cosmic expansion
Observe most photons as as
the cosmic background
radiation!
 Also can observe photons
emitted from Galaxies a
billion years ago (just
reaching us now) as being
red-shifted
Evolution of the Universe
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Looking Back at the Early Universe
The more
distant the
objects we
observe, the
further back
into the past
of the universe
we are looking
Evolution of the Universe
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The next few billion years
After less than ~0.5 billion
years, the first stars form
 Stars produce heavy
elements (“Stellar Cooking”)
Evolution of the Universe
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A Neutral Universe
• After the electrons and protons
combine to form atoms the Universe is
almost completely neutral i.e., neutrally
charged
• Why is this so important? All the
particles in the Universe stop attracting
each other due to their electric charge
– Not completely true, just true outside
the atoms
– Basically can ignore electric charge
from
here
on
out
Evolution of the Universe
Big Bang, Black
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The Transition From a “Charged”
Universe to a “Neutral” Universe
Some Time
Passes
Evolution of the Universe
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Aside on Dark Matter
• Dark matter is a BIG part of this story
because there is 5 times more mass in
the Universe in dark matter than in
atoms
– Will come back to this in Chapter 15
• However, the story doesn’t change much
with Dark Matter since we think it is
just another neutral particle
Evolution of the Universe
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Holes, No Math Topic 2: After The First Three Minutes
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A Gravity Dominated Universe
• The only thing left is gravity!
• The gravitational attraction
between massive things ONLY
makes them move towards each
other
• Any single atom would be most
attracted to the closest place
with lots of mass
Evolution of the Universe
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Wait a Half Billion Years
• As the years go by, mass
clumps together
• By a half a billion years after
the bang, most of the mass is
in one of a large number of
“clumps”
• Billions of these clumps, each
becomes a galaxy!
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
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Fast Forward…
• Fast forward 13 billion years
– Temperature of space is now ~3
degrees
– Cosmic Background Radiation
• We get people…
• More on Stellar and Galaxy
Formation next
Evolution of the Universe
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Looking Forward
• Finished Unit
–Evolution of
• Starting Unit
–Big Objects
Holes
4
the Universe
5
and Black
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
39
For Next Time – L20
• Reading:
– Unit 5
• Pre-Lecture Reading Questions:
– Unit 4 Revision (if Desired): Stage 1
– Unit 5: Stage 1
• End-of-Chapter Quizzes:
– Chapter 14 (if we finished Chapter 14, else just 13)
• Papers:
– Paper 2 Revision (if desired): Stage 2 due Wednesday
– Paper 3: Stage 2 due Monday before class
• Honors Papers:
– (Stage 2)
– Final paper due on the last day of class
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
40
Full set of Readings So Far
•Required:
–BBBHNM: Chaps. 1-15
•Recommended:
– TFTM: Chaps. 1-5
– BHOT: Chaps. 1-7, 8 (68-85), 9
and 11 (117-122)
– SHU: Chaps. 1-3, 4(77-93),
5(95-114), 6, 7 (up-to-page 159)
– TOE: Chaps. 1-3
Evolution of the Universe
Big Bang, Black 41
Holes, No Math Topic 2: After The First Three Minutes
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
42
Clicker Question
Why can we only see so far back
into space?
a) Because before recombination the
light in the universe was
scattering off most of the
particles
b) Because there are too many things
in the way which block our ability
to see
Evolution of the Universe
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Holes, No Math Topic 2: After The First Three Minutes
Clicker Question
Which of the following requires
the highest energy photon?
a) Breaking apart a Proton
b) Breaking apart a helium nuclei
c) Breaking an electron out of a
hydrogen atom
Evolution of the Universe
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Holes, No Math Topic 2: After The First Three Minutes
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Clicker Question
Order the following in the order of highest
required energy to lowest required energy
A. Breaking apart a Proton
B. Breaking apart a helium nuclei
C. Breaking an electron out of a hydrogen atom
a) A>B>C
b) A>C>B
c) B>A>C
d) B>C>A
e) C>A>B
Evolution of the Universe
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f)
C>B>A
Holes, No Math Topic 2: After The First Three Minutes
Clicker Question
What was the last thing a typical
photon in the universe (part of the
Cosmic Background Radiation) did
before we detected it?
a) Broke apart a Proton
b) Broke apart a helium nuclei
c) Broke the electron out of a
hydrogen atom
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
46
Clicker Question
Why do the photons in the universe
appear to be in thermal equilibrium?
a) Because they all have exactly the
same energy
b) They are in thermal equilibrium
c) The universe was in thermal
equilibrium, and the photons are just
one of the particles in the Universe
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
47
Clicker Question
Why is hydrogen the most abundant
element in the universe?
a) It is the lightest element
b) Any heavy elements that might
have been present would have
been broken apart by high energy
photons in the early universe
c) Both of these contribute
Evolution of the Universe
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Clicker Question
Q: Which of the following statements is MOST
correct?
a)
b)
c)
The photons in the cosmic background
radiation are there because the Universe
has been expanding for ~13 billion years
The photons in the cosmic background
radiation are there because the universe
was in thermal equilibrium
The photons in the cosmic background
radiation are there because photons can
exist forever
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
49
Papers
• Papers:
– Paper 0 Revision: Still working on re-grades.
Will post in eCampus by Wednesday
– Paper 1 Revision: Let us know if you were
misgraded
– Paper 2:
• Bad Rubric fixed (everyone given credit
for low-quality calibration)
• Working on re-grades
– Paper 2 Revision: Changed due date to
Wednesday before class
– Paper 3: Text due Wed before class
Evolution of the Universe
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Holes, No Math Topic 2: After The First Three Minutes
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Prep for Today (Is now due) – L19
• Reading:
– BBBHNM 14
• Reading questions:
– Chapter 14
• End-of-Chapter Quizzes:
– Chapter 13
• Paper Stuff
– Paper 2 Revision: Text was due before
class. Calibrations and Review due Monday
– Paper 3: Text was due before class.
Calibrations and Review due Monday
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
51
For Next Time – L19
• Reading:
– Unit 5
• Pre-Lecture Reading Questions:
– Unit 4 Revision (if Desired): Stage 1 Due Monday before
class
– Unit 5: Stage 1 due Monday before class
• End-of-Chapter Quizzes:
– Chapter 14 (if we finished Chapter 14, else just 13)
• Papers:
– Don’t forget that ALL papers must be submitted to
turnitin.com
– Paper 2 Revision (if desired): Stage 2 due Monday before
class
– Paper 3: Stage 2 due Wednesday before class
• Honors Papers:
– Stage 1 Revision
Evolution of the Universe
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Holes, No Math Topic 2: After The First Three Minutes
Prep For Next Time – L21
• Note: May change depending on how
far we get in lecture
• Reading:
– BBBHNM: All reading through
Chapter 16
• Pre-Lecture Reading Questions:
– All reading questions through 16
• End-of-Chapter Quizzes:
– If we finished Chapter 14 then endof-chapter quiz 14 (else just through
Chapter 13)
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
53
Prep for Next Time – P19
• Reading
– BBBHNM 15
– Recommended:
• SHU: 4(87-93)
• TOE: 3
• BHOT: 8(76-85)
• Reading questions
– Chapter 15
• End-of-Chapter Quizzes
– If we finished Chapter 14 then end-of-chapter quiz 14
(else just 13)
• Papers
– Paper 2 Revision: Text was due before class. Calibrations
and Review due Monday
– Paper 3: Text was due before class. Calibrations and Review
due Monday
Evolution of the Universe
Big Bang, Black 54
Holes, No Math Topic 2: After The First Three Minutes
Prep For Next Time – L9
• Note: May change depending on how far we get in lecture
• Reading:
– BBBHNM: All reading through Chapter 17
• Reading Questions:
– All reading questions through 17
• eLearning Quizzes:
– If we finished Chapter 14 then end-of-chapter quiz
14 (else just through Chapter 13)
• Papers:
– Paper 3 text due in CPR and turnitin.com on
Wednesday
– Paper 3 calibrations, reviews and self-assessment
before next class
– Paper 2 revision: Text due Monday before class (if
desired)
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
55
Papers
• Papers:
– Paper 0 Revision: Still working on re-grades.
Will post in eCampus by Wednesday
– Paper 1 Revision: Let us know if you were
misgraded
– Paper 2:
• Bad Rubric fixed (everyone given credit
for low-quality calibration)
• Working on re-grades
– Paper 2 Revision: Changed due date to
Wednesday before class
– Paper 3: Text due Wed before class
Evolution of the Universe
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Holes, No Math Topic 2: After The First Three Minutes
56
Part II
In class Quiz
for Next
Time: What is
happening in
each region?
{
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
57
Why not much Heavier than Helium?
Nuclear Physics
Can build up
Hydrogen and Helium
one at a time
 Next
possibility, 5He or
5Li, isn’t stable
So What? Since 5He and
5Li
decay quickly they don’t
have enough time to find
another proton to become
6Li and be stable
Almost no elements
heavier than helium are
Evolution of the produced
Universe
58
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
Aside on Helium
Why is Helium important to the
story?
Explains two things:
1. Why the atoms in the Universe
are mostly Hydrogen and Helium,
and not much else
2. Why the Helium, like the photons
is evenly distributed around the
universe
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
59
The Reading So Far and For Unit 5
Reading for Unit 5:
• BBBHNM: Chaps. 15-17
• SHU: 4(87-93)
• TOE: 3
• BHOT: 8(76-85)
Full reading so far for Unit 5:
• BBBHNM: Chaps. 1-17
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-85), 9 and 11 (117-122)
• SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7 (upto-page 159)
• TOE: Chaps. 1-3
Lecture prep: Turn in on eLearning
Two questions from Chapter 15 you want to
know the answer
Evolution
to of the Universe
Black
Big Bang,
Holes, No Math Topic 2: After The First Three Minutes
60
The Transition From a Hot Universe to
a Cool Universe
Electrons
Atoms
Photons
Photons
Protons
Electrons
Some Time
Passes
Protons
Photons
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
61
Writing Assignments
1. Short Assignment 1
• Want to revise again? Talk to
me. Still not getting it? Need to
get you to the writing center!
2. Short Assignment 2 is posted
• Due Today
eLearning:
Unit 3 now due
Evolution of the Universe
Big Bang, Black
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Need
to
be
working
on
Unit
4
Holes, No Math Topic 2: After The First Three Minutes
Papers AFTER Paper 2
Two options
1. Research Paper
• If you want to do the research paper
option you must turn in Stage 0 at the end
of class today. Must be approved
• Stage 1 due Thurs Nov 5th
• Final paper due the last day of class,
Tuesday Dec 8th
2. Two short papers like the first one
• One on Black Holes (due mid Nov)
• One on Dark Matter (due last day of class)
Evolution of the Universe
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Before 700,000 years: Summary
Photons are incessantly scattered
by free electrons; photons are in
equilibrium with matter
Photons-electron
soup  have the
same temperature
(energy)
Radiation dominated era
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
64
After 700,000 Years: “Recombination”
Protons and electrons combine to
form atoms  universe becomes
transparent for photons
Transition to matter
dominated era
Crappy Word!
Atoms are
combining for
the first time,
not recombining!
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
65
A cartoon of an atom and a photon
Mostly this is happening now since the photons
are low energy
Evolution of the Universe
Big Bang, Black
Holes, No Math Topic 2: After The First Three Minutes
66
The Cosmic Background Radiation
After recombination, photons can
travel freely through space
Their wavelength is only stretched (red
shifted) by cosmic expansion
This is what we can observe today as
Evolution of the Universe
Big Bang, the
Blackcosmic background
radiation!
Holes, No Math Topic 2: After The First Three Minutes
67
Wait a Billion Years
After less than ~ 1 billion
years, the first stars form
 Produce Heavy Elements in
Stellar Cooking
Formation of
the first stars
Evolution of the Universe
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68
The First Three Minutes
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/first3minutes.swf
Evolution of the Universe
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