Transcript Slide 1 - Big Bang, Black Holes, No Math

Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lectures 17 & 18
Big Bang, Black
Evidence for the Big Bang
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
1
Was due Today – L17
• Reading:
– (BBBHNM Unit 3)
• Pre-Lecture Reading Questions:
– PLRQ Unit 3 Revision (if desired), Stage 1 due Wednesday
before class
• End-of-Chapter Quizzes:
– Chapter 11
• Papers:
– Paper 1 Revision (if desired), Stage 1 due before class
• (Text needs to be in turnitin on eCampus)
– Paper 2, Stage 2 due before class
• (Text needs to be in turnitin on eCampus)
• Honors Paper:
– Stage 1 must be approved explicitly
– Stage 2 due Monday March 30
Big Bang, Black
Evidence for the Big Bang
2
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Was due Today – L18
• Reading:
– Unit 4
• Pre-Lecture Reading Questions:
– Unit 3 Revision (if desired), Stage 2 (due before class0
– Unit 4: Stage 1
• End-of-Chapter Quizzes:
– Chapter 11
• Papers:
– Paper 1 Revision (if desired), Stage 2 due before class
– Paper 2 Revision (if desired), Stage 1 due Wednesday
• Honors Paper:
– Stage 1 must be approved explicitly
– Stage 2 due Today
Big Bang, Black
Evidence for the Big Bang
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
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Paper 3: The Assignment
• Abbreviated Description: What
is the evidence for the Big
Bang?
– Explain it to someone who isn’t
taking the class (no jargon)
• Make sure you read ALL the
instructions in CPR
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Overview
Evidence for the Big Bang?
• Finished:
– The Exploding Universe
– Expanding Space-Time
• This Time:
– More evidence for a hot early
Universe?
– Photons and Hydrogen in the
Universe
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Before we begin…
• The Cosmic Background Radiation
provides, perhaps, the most
compelling piece of evidence for
the story of the Big Bang
• Unfortunately, it’s the hardest
to explain to the non-scientist
– Radiation = Photons
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Two Different Pieces of Evidence
When we look at the stuff in the Universe
we see that
1. ~90% of the atoms are hydrogen,
~10% are helium and there are very
little of everything else
– The Earth is very different than the
rest of the Universe in many ways
2. Lots of photons uniformly distributed
with a Temperature of 2.7 Kelvin
– Cosmic Background Radiation
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Prelude to the Story
To understand why the
photons and amount of
hydrogen in the universe
are important, we need to
understand a little about
the Universe changed over
time (the evolution of the
Universe)
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Evidence for the Big Bang
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Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Outline
• A ridiculously brief history of
time
• The Early Universe and its
Particles in Thermal Equilibrium
• Nuclei and atoms and their
reactions in the Early Universe
• The stuff in the Early Universe
• As the Universe expands and
cools
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The Early Universe
If there was a Big Bang, what would
the Universe look like a second
after the Big Bang?
• Very small
• All the particles would have high
energies
• Lots of fundamental particles
Let’s address each of these issues
one Black
at a time
Big Bang,
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Big Question We are Trying to answer
Early Universe
Will say why we think it
started like this in a bit
How did
the
universe
get
from
to?
Today
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Why Small?
If the universe has been
expanding for billions of
years, it would have
been smaller billions of
years ago
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Why High Energy Particles?
• If the universe has been expanding
and stretching the wavelengths of
the particles, this makes them low
energy now
• But back then, when they were
less-stretched, they must have
been higher energy
• Long wavelength  Low energy
• Bang,
Short
theHigh
Big
Black wavelength
Evidence for
Big Bangenergy 13
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Why Fundamental Particles in
The Early Universe instead of
Composite Particles like Atoms?
• This one is harder to
understand
• Need to learn more about
what happens when high
energy particles interact
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Fundamental particles in the
Early Universe
Many things COULD happen if we just had
lots of fundamental particles
Start by describing how they combine
• Quarks could combine to form protons
and neutrons
• Protons/neutrons could combine to form
nuclei
• Nuclei and electrons could combine to
form atoms
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Forming Protons
Quark
qqq  Proton
Nuclear
Reaction
Quark
Proton
Quark
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Forming Heavy Nuclei
Proton
Proton + Proton
 Deuterium + Anti-Electron + Neutrino
Anti-Electron
Nuclear
Reaction
Proton
Deuterium
Neutrino
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Forming Atoms
Proton + electron
 Hydrogen Atom + photon
Proton
ElectroMagnetic
Reaction
Hydrogen
Atom
Electron
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The Story
This is great… you can see that IF there
were lots of fundamental particles in the
early Universe, they could combine to
create the things we see today, like
stars and galaxies
Universe just slowly assembled over time
Lots of atoms combine to form stars, then
galaxies, then us!
(more on this in later chapters, since it’s
not that simple)
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Collisions in the Early Universe
Question: Could the Universe have started with
lots of fully formed galaxies that just have
been moving away from each other since?
Question: What if there was a big bang that
produced lots of lots of fully formed, heavy
atoms? Photons?
Answer: Wouldn’t stay that way! Why not?
• High energy Collisions break apart atoms and
nuclei… we’d end up with fundamental particles
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Atoms in the Early Universe
Proton
High Energy Photon Breaks
up Atoms quickly
 Free electrons and
protons
ElectroMagnetic
Reaction
Electron
Hydrogen
Atom
High Energy
Photon
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Nuclei in the Early Universe
Proton
Nuclear
Reaction
Proton
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Deuterium
Photon Breaks up
Nucleus before it can
find an electron to
create an Atom or find
Highnucleon
Energy
another
to
Photon
form a bigger nucleus
 Free protons and
Evidence for the Big Bang
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Photons and Hydrogen in neutrons
the Universe
Heavy Atoms in the Early Universe
Deuterium
High Energy
Photon
Proton
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Bottom line:
Early Universe has Fundamental Particles
with Really High Energies
• In the early Universe we have many
different types of fundamental particles
because high energy collisions can create
all the different types
• Composite particles could get formed,
but other high energy particles would
bust them apart  we end up with only
fundamental particles
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What else happens in collisions in
the Early Universe?
High energy photons
 lower energy photons
Low energy photons
 higher energy photons
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Thermal Equilibrium
• All these high energy particles are
quickly colliding in a small space
• Eventually all the particles will
(roughly) have the same energy
– Said better: The same
Temperature
– Can think of the universe as being
in Thermal Equilibrium
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Particles in Thermal Equilibrium
Because of the way particles interact
at high energies we get lots of
photons, protons, neutrons and
electrons
Even if the universe didn’t start with
lots of each of these particles,
eventually there would be lots of
them
– Produced in collisions or in the
decay of Evidence
otherforparticles
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the Big Bang
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Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Electron-Photon Soup in the Early
Universe
Electron
Positron
Photon
Electron pairs and
photon pairs interact
and annihilate 
electron and photon
Soup
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Then what happens?
What will happen later?
The Universe Expands and
stretches the wavelengths
of the particles
Universe cools… energies
drop
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Expanding Space Part 1
Photons in Thermal Equilibrium
Early Times  High Temperature,
high
energy
particles
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Expanding Space Part 2
Later Time  Space gets Bigger
Wavelength gets Longer
Temperature is Cooler, lower
energy
particles
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Evidence for
the Big Bang
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Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Expanding Space Part 3
Even later  Red Shifted
32
Even cooler, even lower energies
Big Bang, Black
Evidence for the Big Bang
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Bottom Line
• As time progresses all the
particles, including the photons,
will have lower energies
– Lower temperatures
• The interactions between the
particles are very different at
different energies
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Later Times: Atoms and Low Energy Photons
Proton
Low energy photons
typically only “bump” atoms
or excite them
ElectroMagnetic
Reaction
Electron
Hydrogen
Atom
Low Energy
Photon
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Nuclei and Low Energy Photons
Low energy photons only
“bump” nuclei
Deuterium
Low Energy
Photon
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Can Now Build Up Heavier Heavy Nuclei
Deuterium
Proton + Deuterium  Helium3 + Photon
Nuclear
Reaction
Photon
Helium3
Proton
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Creating Stable Helium
Helium3
Helium3 + Helium3  Helium4 + 2 Protons
This is why we have ~90% hydrogen and
~10% helium. More on this later…
Nuclear
Reaction
Proton
Helium4
Helium3
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Proton
37
Hot Early Universe
The high-energy particles in a hot,
small Universe would break apart
heavy atoms and nuclei, and
explains two pieces of
experimental data
1. So much hydrogen and so little of
other types of atoms except
Helium
2. Lots of photons with the same
temperature
in all directions
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Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Particles in the Universe
• Early times: Protons, Neutrons,
Electrons, Positrons and Photons
• Later times: Photons and atoms
• Much later: Atoms combine to
form stars and galaxies
•More on this later
What happens to the photons?
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Life as a Photon in the Universe
• If a photon is high enough energy to break a
part an atom it will
• Any photon that isn’t high energy enough won’t
interact again and will thus just travel forever
• Thus, the last thing a typical photon in the
universe interacts with is an atom
• Why does that matter? Essentially, they are
unchanged since the time of “last interaction”
except to be stretched by expanding space
– Tells us about the Universe when they last
interacted
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What
happens to
the Photons?
The photons
simply “cool” as
space expands
 Lower
Temperature
Now  Longer
Wavelengths
Then
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Why should we believe this Story?
Should be able to observe
this “remnant” of the Big
Bang
Any evidence for photons
with energies that look like
a low temperature?
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A Great Experiment
Arno Penzias and
Robert Wilson in 1964
were doing high
precision
measurements of
photons for radio
waves
Noticed “noise” in their
system that turned
out to be photons with
a temperature of
about 3 degrees above
absolute zero
Not looking for these
photons… but won the
Nobel Prize anyway
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The same Temperature in all directions?
Look at the full
Temperature Map
(i.e, different colors correspond to
sky in a single map
different temperatures)
Stretch out a
sphere onto a flat Incredibly Uniform!
page
2.78 degrees Kelvin
44
Big Bang, Black
Evidence for the Big Bang
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Conclusion from the data?
• Data is exactly consistent with a
Universe that was small and hot
a long time ago… what we would
expect with a Big Bang!
• No other reasonable explanation
for where lots of photons with a
specific temperature would come
from, and be the same in all
directions
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Summary
1. We observe galaxies moving away
from us in a manner that is
consistent with an expansion of
space-time
2. Most of the atoms in the universe
are hydrogen and helium and not
much else
3. We observe photons (the cosmic
background radiation) uniformly
distributed in all directions that
have a temperature consistent with
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cooling
for
~13.7
billion
years
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Fun Way to think about things
• Look at things “far away” in space  Backward in time
• Can see stars from millions of years ago
– Look like stars today
• Look at galaxies from billions of years ago
– Look like galaxies today
• Look at galaxies from about 13 billion years ago
– Look like baby galaxies forming
• Look even “farther back”
– No galaxies at all since they haven’t even formed
• Look further still… See the “white noise” of the cosmic
background radiation and no evidence of any galaxies
– Looking back at the earliest times we can “see” without the
photons going through the “fog” of the early universe… Can’t
see through the fog to earlier times… Then again, there isn’t
much
time before that
anyway
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Holes, No MathTopic 3: Photons and Hydrogen in the Universe
How far can we look back in time?
All we can see is back a
certain distance in TIME
We can’t see anything “past”
the background radiation
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What’s Next?
Unit 4: Evolution of the
Universe
• The Early Universe
• After the First Three
Minutes
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Paper 3: The Assignment
• Abbreviated Description: What
is the evidence for the Big
Bang?
– Explain it to someone who isn’t
taking the class (no jargon)
• Make sure you read ALL the
instructions
Big Bang, Black
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For Next Time – L17
• Reading:
– Unit 4
• Pre-Lecture Reading Questions:
– Unit 4: Stage 1
• End-of-Chapter Quizzes:
– If we finished Chapter 12, then Chapter 12 (if not, Chapter 11)
• Papers:
– Paper 1 Revision (if desired), Stage 2 due Monday before class
• (Text needs to be in turnitin on eCampus)
– Paper 2 Revision (if desired): Will open after re-grade requests
• (Text needs to be in turnitin on eCampus)
– Paper 3: If we finished Chapter 12, Stage 1 due Wednesday
before class
• Honors Paper:
– Stage 1 must be approved explicitly
– Stage 2 due Monday March 30
Big Bang, Black
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For Next Time – L18
• Reading:
– (Unit 4)
• Pre-Lecture Reading Questions:
– Unit 4: Stage 2
• End-of-Chapter Quizzes:
– If we finished Chapter 12, then Chapter 12 (if not,
Chapter 11)
• Papers:
– Paper 2 Revision (if desired): Due Wednesday before class
– Paper 3: If we finished Chapter 12, Stage 1 due Monday
before class
• Honors Paper:
– Stage 1 must be approved explicitly
– Stage 2 due Monday March 30
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Full set of Readings So Far
• Required:
–BBBHNM: Chaps. 1-13
• Recommended:
– TFTM: Chaps. 1-5
– BHOT: Chaps. 1-7, 8 (68-76), 9
and 11 (117-122)
– SHU: Chaps. 1-3, 4(77-86),
5(95-114), 6, 7 (up-to-page 159)
– TOE: Chaps. 1 & 2
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Evidence for the Big Bang
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Clicker Question
Let’s say you were the person observing
the galaxies, but each other person in
the room were a galaxy. Which person
in the room is moving away from you
most quickly?
a)
b)
c)
d)
Back left
Back right
Front left
Front right
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Clicker Question
Which of the following is the best ranking for
the speeds (from fastest to slowest) at which
galaxies A, C, and D would be moving away
from an observer in galaxy B?
a) A > C > D
Early
Universe Some Time
Universe
Later
b) D > A > C
E
c) C > D > A
E
C
C
D
D
d) D > C > A
B
A
B
A
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Clicker Question
Are the Earth and Sun moving away from each
other since space-time is expanding?
a) Yes. It is just a matter of time before the
Earth will leave the Sun's orbit.
b) Yes, but the gravitational attraction
between the two keeps them at the same
distance
c) No, because the Sun is big enough to
prevent space-time from expanding locally
d) No, because the only thing that matters is
that the Earth is attracted to the Sun
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Clicker Question
Let's say I have two galaxies in space and
they are exactly stationary relative to each
other. What will happen next?
a) Since they are so massive that they will
attract each other by gravity and start
moving towards each other.
b) Since space-time is expanding, the distance
between them will grow as space-time
expands so they will start moving away from
each other.
c) It depends on the overall distance between
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them.
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Clicker Question
If space-time is expanding, is our galaxy
expanding?
a) Yes. Everything in the universe is moving
away from everything else.
b) No. It isn't expanding because the
gravitational attraction of masses pulls the
galaxy back together again
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Clicker Question
If space-time is expanding, are
atoms expanding?
a) Yes. Everything in the universe is
moving away from everything else.
b) No, they aren't expanding
because the electric charge
attraction and quantum mechanics
keep the atoms the same size in
space
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Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Clicker Question
For the most distant
galaxies, which is true?
a) Most of the red-shift
of their spectral lines is
because they are moving
very fast through space
b) Most of the red-shift
of their spectral lines is
because space is
expanding
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Clicker Question
Why is hydrogen the most abundant
element in the universe?
a) It is the lightest element
b) Other elements were broken apart
by high energy photons in the
early universe
c) Both of these contribute
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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 hydrogen atom
b) Broke apart a helium nuclei
c)Bang,
Broke
apart
a forProton
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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
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Clicker Question
If the universe stated contracting, which of the
following would be evidence for it?
a)
b)
c)
d)
e)
Distant galaxies would be less red-shifted
The CMB would have a lower temperature
We would start seeing distant galaxies have
blue shifts
The Earth would start getting closer to the
Sun
Atoms would start shrinking
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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
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1 Paragraph Essay Question
Why are there so many
more hydrogen and
helium atoms in the
universe than any other
type of atom?
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Clicker Question
Why do we think that the Universe is an
expansion of space-time and not an explosion?
Fix me.
a) Because distant galaxies are moving away
from us.
b) Because the farther away a galaxy is, the
faster it is moving away
c) Because hydrogen and helium are most of the
atoms in the universe
d) Because of the Cosmic Background Radiation
e) Not great...
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Clicker Question
Which of the following statements is MOST correct?
•
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
The
•
•
•
•
•
•
•
Universe needed to be in thermal equilibrium for atomic hydrogen to keep accumulating in the early universe
True
False
Is the CMB in thermal equilibrium?
CMB cold and getting hotter or cold and getting colder?
What happens to the energy of photons as the universe expands?
•
They energy of the photons don’t actually change because photons always move at the speed of light. It’s
just an optical illusion.
•
The energy of the photons is converted to the potential energy of the universe
•
The energy of the photons is converted to mass
•
Need other good options… that could be correct and test students conceptual understand. What do they
THINK happens to the photon energy?
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Clicker Question
Are the Earth and Sun moving away from each
other since space-time is expanding?
a) Yes. It is just a matter of time before the
Earth will leave the Sun's orbit.
b) Yes, but the gravitational attraction between
the two keeps them at the same distance
c) No, because the Sun is big enough to prevent
space-time from expanding locally
d) No, because the only thing that matters is
that the Earth is attracted to the Sun
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70
Clicker Question
Let's say I have two galaxies in space and
they are exactly stationary relative to each
other. What will happen next?
a) Since they are so massive that they will
attract each other by gravity and start
moving towards each other.
b) Since space-time is expanding, the distance
between them will grow as space-time
expands so they will start moving away
from each other.
c) It depends on the overall distance between
Big Bang,
Black
Evidence for the Big Bang
71
them
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Clicker Question
If space-time is expanding, is our
galaxy expanding?
a) Yes. Everything in the universe is
moving away from everything
else.
b) No. It isn't expanding because
the gravitational attraction of
masses pulls the galaxy back
together again
Big Bang, Black
Evidence for the Big Bang
72
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Clicker Question
If space-time is expanding, are
atoms expanding?
a) Yes. Everything in the universe is
moving away from everything else.
b) No, they aren't expanding
because the electric charge
attraction and quantum mechanics
keep the atoms the same size in
space
Big Bang, Black
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73
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
For Next Time – L17
• Reading:
– (Unit 4)
• Pre-Lecture Reading Questions:
– Unit 3 Revision in CPR (if desired): Stage 2
– Unit 4: Stage 2
• End-of-Chapter Quizzes:
– If we finished Chapter 12, then Chapter 12 (if
not, Chapter 11)
• Papers:
– Paper 2 Revision (if desired), Stage 1
– Paper 3: Stage 1 due Wednesday before class
• Honors Paper:
– Stage 1 must be approved explicitly. Revisions
Big Bang,due
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74
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
For Next Time– L18
• Reading:
– BBBHNM: 14
• Pre-Lecture Reading Questions:
– Chapter 14
• End of Chapter Quizzes:
– Chapter 11
• Papers:
– Paper 0 Revision: Was due before class. Let us know if you
think you were mis-graded. Still working on re-grades.
– Paper 1: Still working on re-grades.
– Paper 1 Revision: Was due before class if you wanted to
submit. If you want an extension let me know in email ASAP
– Paper 2: Was due before class. Let me know if you think
you were misgraded
– Paper 2 Revision: If you want to do a revision, text is due
one week from today before class
Big Bang, Black
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75
For Next Time– L18
• Reading:
– BBBHNM: 14
• Pre-Lecture Reading Questions:
– Chapter 14
• End of Chapter Quizzes:
– If we finished Chapter 12, then 12, (if not, then just
Chapter 11)
• Papers:
– Paper 0 Revision: Was due before class. Let us know if you
think you were mis-graded. Still working on re-grades.
– Paper 1: Still working on re-grades.
– Paper 1 Revision: Was due before class if you wanted to
submit. If you want an extension let me know in email ASAP
– Paper 2: Was due before class. Let me know if you think
you were misgraded
– Paper 2 Revision: If you want to do a revision, text is due
one week from today before class
– Paper 3: If we finished Chapter 12, then due 1 week from
Big Bang,
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Evidence for the Big Bang
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today
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Was due for Today – L18
• Reading:
– BBBHNM: 13
• Pre-Lecture Reading Questions:
– Chapter 13
• End of Chapter Quizzes:
– Chapter 11
• Papers:
– Paper 0 Revision: Was due before class. Let us know if you
think you were mis-graded. Still working on re-grades.
– Paper 1: Still working on re-grades.
– Paper 1 Revision: Was due before class if you wanted to
submit. If you want an extension let me know in email ASAP
– Paper 2: Was due before class. Let me know if you think
you were misgraded
– Paper 2 Revision: If you want to do a revision, text is due
one week from today before class
Big Bang, Black
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77
Was due for Today – L19
• Reading:
– BBBHNM: 14
• Pre-Lecture Reading Questions:
– Chapter 14
• End of Chapter Quizzes:
– Chapter 11
• Papers:
– Paper 0 Revision: Still working on re-grades.
– Paper 1: Still working on re-grades.
– Paper 1 Revision: Text was due already.
Calibrations/Reviews/Self-assessment due before class on
Wed
– Paper 2: Working on re-grades
– Paper 2 Revision: Will be posted soon, checking the
calibrations/rubrics for potential problems
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Prep For Next Time – L8
• Reading:
–BBBHNM: All reading through Chapter 14
• Reading Questions:
– All reading questions through 14
• eLearning Quizzes:
– End-of-chapter quiz 12
• Papers:
– Paper 2 text due in CPR and turnitin.com by
Tuesday at Midnight
– Paper 2 calibrations, reviews and self-assessment
due Monday before class
– Paper 3 text due in CPR and turnitin.com before
Big Bang,next
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Evidence for the Big Bang
79
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Prep for Today (Is now due) – L16
• Reading:
– BBBHNM 13
• Reading questions:
– Chapter 13
• End-of-Chapter Quizzes:
– Chapter 11
• Paper Stuff
– Paper 2: Was due Monday
– Paper 3: Will be assigned after we
finish Chapter 12
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80
Prep for Today (Is now due) – L17
• Reading:
– BBBHNM 13
• Reading questions:
– Chapter 13
• End-of-Chapter Quizzes:
– Chapter 11
• Paper Stuff
– Paper 2 Revision: Due 1 week from day
(same time as paper 3)
• Need to do text, calibrations and
reviews
– Paper 3: Due 1 week from today
Big Bang, Black
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81
Prep For Next Time – L8
• Note: May change depending on how far we get in
lecture
• Reading:
–BBBHNM: All reading through Chapter 14
• Reading Questions:
– All reading questions through 14
• eLearning Quizzes:
– If we finished Chapter 12 then end-of-chapter
quiz 12 (else just through Chapter 11)
• Papers:
– Paper 3 text due in CPR and turnitin.com before
Wednesday!
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82
Prep for Next Time – P15
• Reading
– BBBHNM 13
–
Recommended:
•
•
•
TFTM: 4 & 5
SHU: 5 (104-114), 7 (154-159)
BHOT: 8 (68-76)
• Reading questions
– Chapter 13
• End-of-Chapter Quizzes
– If we finished Chapter 12 then end-of-chapter quiz 12
(else just 11)
• Papers
– Paper 2: Calibrations and Reviews due tonight
– Paper 3: If we finished Chapter 12, then paper 3 is due 1
week from today
Big Bang, Black 83
Evidence for the Big Bang
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Prep for Next Time – P16
• Reading
– BBBHNM 13
• Reading questions
– Chapter 13
• End-of-Chapter Quizzes
– If we finished Chapter 12 then end-ofchapter quiz 12 (else just 11)
• Papers
– Paper 2: Was due on Monday
– Paper 3: If we finished Chapter 12, then
paper 3 is due 1 week from today
Big Bang, Black 84
Evidence for the Big Bang
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Paper 3 Organization Stuff
• Due 1 week after we finish Chapter 12
• Want feedback before turning it in?
– Post it in eLearning in .doc (or .pdf) for
comments by the TA
– Make sure you polish it
• If you have lots of grammar and spelling
mistakes we’ll just make you try again
• Will be due in CPR and turnitin.com at the
same time
• Calibrations will be due 1 week after
submission
dateEvidence for the Big Bang
Big Bang,
Black
85
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Big Bang Produces Fundamental Particles
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86
What are the Fundamental Particles?
The Big Bang Produces lots of
particles
• Electrons and anti-electrons
• Photons
• Quarks and anti-quarks
– Others… More on this later
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87
Back then… and Today
• What would the objects in
Thermal Equilibrium in the Early
Universe look like today after
space has expanded?
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88
The Reading So Far and For Unit 4
Reading for next time:
• BBBHNM 13
• TFTM: 4 & 5
• SHU: 5 (104-114), 7 (154-159)
• BHOT: 8 (68-76)
Full reading so far:
• BBBHNM: Chaps. 1-14
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-122)
• SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6, 7 (upto-page 159)
• TOE: Chaps. 1 & 2
Lecture prep: Turn in on eLearning
Two questions from Chapter 13
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89
Paper 1 Stuff
• Done with grades for both original and Revision
– Graded unfairly? Let us know!
• Passing score: Need ALL of the following
– Text score: more than 21 points (70%)
– Calibrations: more than 15 points
– Reviews: more than 15 points
– Overall score: more than 70 points
• Revision CPR
– Do full CPR grading
Big 90
Bang, Black
Evidence for the Big Bang
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Papers 2 and 3 and Other Stuff
• Paper 2:
– Text was due last Friday at noon
– CPR grading due Friday at Noon
• Paper 3:
– Due March 24th before class
– 1 week after we finish Chapter 12
– Now open
• Elearning:
– Unit 3 in progress
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91
Electron Photon Soup
Electron
Positron
Low Energy photon
Electron pairs
annihilate,
but photon
pairs don’t
create more
electrons!
Not enough
Energy
E=MC2
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92
Writing Assignments
1. Short Assignment 1 did not go well
• Revise your submissions and
resubmit by 5PM on Friday
2. Short Assignment 2 is posted
• Currently Due Thursday Oct 29th
which is one week after we
finish Chapter 12
eLearning:
Unit 2 due before the beginning of
next class
Big Bang,
Black to beEvidence
for the on
Big Bang
93
Need
working
Unit 3
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Paper 1 Feedback
I must have been unclear on what I was looking for in Paper 1
• Your job was to explain the evidence for stars being made of
atoms, not convince people that its an interesting question or that
scientists did something important
– Think lawyer, not lobbyist
• The best papers had 5 paragraphs with an introduction that made
it clear what question was being answered, then outlined the main
pieces of evidence. Then each paragraph gave a different piece
of evidence. The conclusion told how all the pieces tied together
• The common problems were:
1. Using humorous “getting started” words to motivate why the
question is important or interesting.
2. No structure, just started giving pieces of evidence and
stopped when all the pieces had been given
3. Didn’t give all the different arguments needed to make the
case (like nuclear physics to explain atomic fingerprints)
4. Used words like “Spectral lines” but didn’t define them
5. Had a conclusion which essentially praises scientists for
Big Bang,figuring
Black it out
Evidence for the Big Bang
94
Holes, No MathTopic 3: Photons and Hydrogen in the Universe
Papers AFTER Paper 2
Two options
1. Research Paper
• If you want to do the research paper
option you must complete Stage 0 by
Thurs Oct 29th
• 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
Big Bang,class)
Black
Evidence for the Big Bang
95
Holes, No Math
Topic 3: Photons and Hydrogen in the Universe
Soup
So our early Universe is a soup
of:
• Protons
• Neutrons
• Electrons (and positrons)
• Photons
– Others… later
What
happens
to
our
soup?
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96
Two Hypotheses
1. No high energy photons  protons
“cook” into heavy elements  Lots of
heavy elements in the universe today
2. Lots of high energy photons  protons
can’t “cook” into heavy elements 
mostly hydrogen in the universe today
Because of Thermal Equilibrium and the way
particles interact at high energies even if we
didn’t have lots of photons, we’d eventually
get a lot of photons
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97
Lots of High Energy Collisions
In the early Universe there must have
been lots of high energy collisions
If there weren’t lots of high energy
collisions then all the hydrogen would
have been "cooked" into heavier elements
– More oxygen, Nitrogen and Iron, less
Hydrogen
Not what we observe!
The Universe is ~75% hydrogen
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98
Big Toys
Properties of the
noise:
• Point at the
earth? Not
coming from there
• The plane of the
milky way? Nope
• From a nearby
galaxy? Nope
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99
Other Possibilities?
Other things in
the “horn”?
Noise appears
to be the
same and
coming equally
from ALL
DIRECTIONS
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100
What happens to our Soup of Photons?
The photons simply “cool” as spacetime expands  Lower Temperature
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/CMB.swf
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101
Paper 1 Notes
• Class Average: 63
• Good Things:
– Most people got the structure and main
topics for the paper (atomic model,
spectral lines, etc…)
• If you want to improve your grade you may
resubmit your paper 1 by March 25th
– Again on WebCT by the new link
Paper1Redo
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102
Resubmitting? Things to work on
• You must explain these topics fully to a
lay-person, not just make statements
• For example this is not an explanation:
– “The atomic model explained by
quantum mechanics is responsible for
the spectral lines we see.”
• Andy will stay after class if you want
to talk about your paper
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103
Lots of High Energy Photons
In the early Universe there must have
been LOTS of high energy photons
Why? Ask differently… What if this
weren’t true?
Nuclear reactions would have proceeded so
rapidly that a large fraction of the
hydrogen would have been "cooked" into
heavier elements
Not what we observe!
The Universe is ~75% hydrogen
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104
Nuclear Cooking
This rapid nuclear cooking
could only have been
prevented only if the universe
was filled with photons having
high energy
requires high temperature
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105
Nuclei in the Early Universe
No high energy photons
 protons “cook” into
heavy elements
Proton
Nuclear
Reaction
Deuterium
A high energy photon can
break apart the Nucleus
before it can find an
electron to create an Atom
or find another nucleon to
form a bigger nucleus
Proton
High Energy
Photon
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106
Advertisement 1
Big Bang, Black
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107
Advertisement 2
Big Bang, Black
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108
• Slide 29
Maps based on 53 GHz (5.7
mm wavelength) observations
made with the DMR over the
entire 4-year mission (top) on
a scale from 0 - 4 K, showing
the near-uniformity of the
CMB brightness, (middle) on a
scale intended to enhance the
contrast due to the dipole
described in the slide 19
caption, and (bottom)
following subtraction of the
dipole component. Emission
from the Milky Way Galaxy is
evident in the bottom image.
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109
Fix this with the flat
background from COBE!
Big Bang, Black
Evidence for the Big Bang
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110
TFTM 3: Cont…
• Equilibrium?
• Like economics: if demand exceeds
supply, then the price will rise (cutting
the effective demand) and encouraging
production. If supply exceeds demand
prices will drop (increasing the effective
demand) and discouraging production.
• Electron and photon soup: If too many
electrons, they will interact until there
are more photons and the two come into
equilibrium. I.e., the market clears.
Big Bang, Black
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111
• Need WMAP pictures of
uniformity
• With Doppler Shift
• Have after Doppler Shift
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112
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113
What are the Fundamental Particles?
•
•
•
•
•
•
•
•
Electrons
Positrons (anti-electrons
Photons
Neutrinos
Proton
Neutrons
Hydrogen
Helium
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114
PHOTON BREAKING A
NUCLEUS
PHOTON
(γ)
HELIUM
(He)
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115
PHOTON BREAKING A
NUCLEUS
PHOTON
(γ)
HELIUM
(He)
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116
PHOTON BREAKING A
NUCLEUS
PHOTON
(γ)
HELIUM
(He)
Big Bang, Black
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117
PHOTON BREAKING A
NUCLEUS
HYDROGEN
(H)
PHOTON
(γ)
HYDROGEN
(H)
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118
• This is some
text…
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119
• Distribution
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120
• How the horn
works…
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121
• What if in the early Universe it
WASN’T in Thermal Equilibrium?
• How would the world look today?
• What would that predict?
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122
Need this part of the story?
• Video with lots of proton and
neutrons forming lots of different
nuclei
– This is the “without” photon
radiation picture
– Creates LOTS of non-hydrogen
• Version where the photons are
constantly breaking it up
– Left with most hydrogen
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123
BHOT 7 cont…
• Since energy is conserved, back
when the Universe was small we had
the same amount of heat but in a
smaller amount of space
• As we saw before, this would be
what we call a high temperature!
• The early universe should be very
hot and dense, glowing white hot
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124
• This is some
text…
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125
The Cosmic Background Radiation
(2)
After recombination, photons can
travel freely through space.
Their wavelength is only stretched
(red shifted) by cosmic expansion.
Recombination:
z = 1000; T = 3000 K
This is what we can observe today as the
Big Bang, Black
Evidence for the Big Bang
background
radiation!in the Universe
Holes, No MathTopiccosmic
3: Photons
and Hydrogen
126
The Cosmic Background Radiation
The radiation from
the very early phase
of the universe
should still be
detectable today
R. Wilson & A. Penzias
Was, in fact, discovered
in mid-1960s as the
Cosmic Microwave
Background:
Blackbody radiation
with
Big Bang, Black
Evidence for the Big
Banga temperature
127
ofinTthe
= 2.73
K
Holes, No MathTopic 3: Photons and Hydrogen
Universe
Looking Back Towards the Early Universe
The more distant the objects we
observe, the further back into
the past of the universe we are
looking
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128
Evolution of the Universe
Before
After
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129
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130
• Diffuse background of radio
static
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131
The Cosmic Background Radiation
The radiation from
the very early phase
of the universe
should still be
detectable today
R. Wilson & A. Penzias
Was, in fact, discovered
in mid-1960s as the
Cosmic Microwave
Background:
Blackbody radiation
with a temperature
of T = 2.73 K
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132