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Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lectures 8, 9 & 10
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Topic 2: Gravity
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Prep For Today (is now due) – L9
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions
– eCampus quizzes (all 6)
– Unit 1 Revision (if needed): Stage 2
• Let us know if you were misgraded on the
original
– Unit 2 Revision (if desired): Stage 1
• Due date move to Monday. Let us know if you
were misgraded
• End-of-Chapter Quizzes
– Chapter 5, parts a & b
• Paper 1:
– Not yet assigned
Big Bang, Black
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Prep For Today (is now due) – L10
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions
– eCampus quizzes (all 6)
– Unit 1 Revision (if needed):
• Let us know if you were misgraded on the
original
– Unit 2 Revision (if desired): Stage 1
• End-of-Chapter Quizzes
– Chapter 5, parts a & b
• Paper 1:
– Not yet assigned
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Heads Up: Paper 1
• What is the
evidence for
Dark Matter?
• This will be
the topic of
Paper 1
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• In order to
understand the
evidence, we
next talk about
gravity and
Dark Matter
• Will be due 1
week after we
finish Chapter 6
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Papers in CPR/Schedule
Schedule is Like PLRQ since it is in CPR:
Each Paper has 4 (or 6) Steps:
1. Mentioned after we start the chapter (just did that)
2. Assigned after we finish the chapter
3. Submit text 1 week later (Stage 1)
4. Calibrations/Reviews/Self-Assessment due the week
after that (Stage 2)
5. Revision (optional): Stage 1 due one week later
6. If you did a Stage 1, Calibrations/Reviews/SelfAssessment due one week after that
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Style of the Paper
• Explain it to someone who isn’t taking
the class (no jargon)
• ~600 words (This is the equivalent of
both side of a sheet of paper, double
spaced)
• No citations! Use your own words
• Text should be professional. You are
“trusted guide” not a “buddy” or
“comedian”
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Paper Format
• Must follow expected Format
• Usually 5 paragraphs. Needs:
– Introduction paragraph
– 1 paragraph per piece of evidence (3
total?)
– Conclusion paragraph that ties it
together
– http://faculty.physics.tamu.edu/tobac
k/109/WritingAssignments/samplepaper
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.shtml
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Help Available for Stage I
• Submit a draft for feedback from the
TA
– Submit on eCampus in “Rough Drafts
(Optional)”
– Drafts due Sunday at midnight
– If you submit late, we can try to give
feedback but we can’t guarantee it
• We also recommend going to the writing
center
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Biggest reason people don’t do well
1. Read ALL the instructions on CPR
– See the FAQ on papers
2. Don’t forget to submit to
turnitin.com
3. We are NOT giving you the
Rubrics for the papers, but lots
of hints about what the Rubric
questions will contain are in the
Writing
Prompt
and
Goals sections9
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Best Guess Schedule
• Paper
– Due
• Paper
– Due
• Paper
– Due
• Paper
– Due
1:
after
2:
after
3:
after
4:
after
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we finish Ch 6, Feb 25
we finish Ch 8, Mar 2?
we finish Ch 12, Mar 23?
we finish Ch 17, April 8?
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For People in the Honors Section
Stage 0 (not in CPR):
th
Due Feb 25
For details see
http://people.physics.tamu.edu/
toback/109/Honors/
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Outline for Unit 2: Physics We Need
Topics
1. Light and Doppler Shifts  Done
2. Gravity, General Relativity and Dark
Matter Today
3. Atomic Physics and Quantum
Mechanics  After that
4. Nuclear Physics and Chemistry
5. Temperature and Thermal Equilibrium
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Why Gravity Next?
• By looking at photons/light we can
learn about things here on Earth
as well as about inner/outer space
• What else do we need to
describe/understand the Universe?
Quantum Mechanics and Gravity
• To understand the answer to these
questions we need to learn more
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The Two Great Theories
• General Relativity: Chapter 6
(Gravity) Predictions
about the very large,
from sizes of a few
meters to the size of
the universe (1024 miles
across)
Chapter 7
• Quantum Mechanics:
Predictions about the
very small (atoms,
particles,<10-10 m)
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Overview of Gravity for the Course
1. What’s so
important about
Gravity?
2. Newton’s Gravity
3. Einstein’s Gravity
–Curved SpaceTime, and
evidence for it
with Dark
Matter
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Gravity: Why do we care?
• Gravity: The great attraction in
the Universe
• Gravity is the theory that predicts
the attraction and the motion of
BIG things over large distances:
– Planets
– Suns
– Galaxies
– How Galaxies form etc.
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Newton and Gravity
1. Everything moves in a
straight line unless acted
upon by a force
2. Gravity is a force
– Every object in the
universe attracts every
other object in the
universe
– The further the distance
between the objects, the
smaller the attraction
– The bigger the mass, the
Physics 201
bigger the attraction
or 218
•
Light
is
massless

not
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affected
by
gravity
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Large Number of Scales
Kinda amazing!
Gravity covers the attraction
between
– An apple near the Earth
– The Earth and the Moon
– The Earth and the Sun
– The Sun and our galaxy
– Our galaxy and the universe
– Every particle in the
universe and an apple
– The Earth and you
– Bevo and Reveille
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Gravity continued…
The force of Gravity
makes the Moon
“fall” towards the
Earth
 Call this an orbit
– Does a great job
of explaining how
Without gravity, the
the planets move
Moon would fly off into
around
the
Sun
space and ignore the
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Topic 2: Gravity Earth completely
What’s next?
Tell you the different, and
surprising, way that Einstein
describes space, time and
gravity
Then tell why his description of
why the Earth goes around the
Sun is better than Newton’s
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Einstein in the 1910’s
• In the early 1910’s Einstein
was thinking about some
recent experimental results
that didn’t make any sense
to him using Newton’s
theories
• Decided we need new ways of
thinking about space, time
and Gravity
• Einstein says that Newton’s
Laws aren’t really quite
right…
• Einstein’s theory is known as
the “General Theory of
BigRelativity”
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2nd year Grad
School Course
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Observational Fact
Light *ALWAYS* moves at the
speed of light to all observers
So what?
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What happens if I’m
driving a car moving at
half the speed of light
and I turn the
headlights on?
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Two observers get different
answers
The light
is one foot
ahead of
that car!
The light
is two feet
ahead of
me!
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What happens if I’m driving a car
moving at half the speed of light
and I turn the headlights on?
Einstein says
“it’s relative”,
both observers
are correct
Space and Time
are more
related than
we thought
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Start with Space-Time
Can’t think of Space and Time as
separate
– Space (measured with a ruler)
– Time (measured with a clock)
 Single combined entity which we
call four dimensional space-time
– If the four dimensions are
related, unexpected things that
we’re not used to can happen
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Other Weirdness
• Space and time are not
only more related than we
thought, Space can Curve
• Need to talk about what
we mean by Curved
Space-Time
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We’ll start by using the
strange “new” words of
General Relativity in an
example about why we
care, and THEN explain
them a bit more
Space-Time and Gravity
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Newton vs. Einstein
Newton: The Earth moves around
the Sun because of “the force of
gravity” is pulling it
Einstein: There is no “force” of
Gravity, the Earth moves in a
“straight line” around the Sun in
the curved space-time created by
the Sun
This is a VERY different way of
thinking about things…
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Curved Space?
An analogy is to
think of
curved spacetime as looking
like one of
those gravity
wells you’ve
seen
downstairs
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1st floor of the Mitchell
Physics building (MPHY)
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Moving in Curved Space: Analogy
• Let’s say my friend and I are
at the equator and we both
start working due North
– Exactly parallel to each
other
• We will notice that we
“mysteriously” are getting
closer to each other, and will
eventually bump into each
other
• Is there a Force drawing us
together? No… moving in
curved space time LOOKS like The rules of geometry are different in
curved space
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http://en.wikipedia.org/wiki/Parallel_(geometry)
force
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Another Weird Thing: Mass
Curves Space-Time
Think of each of the
heavy things in the
universe (stars,
planets etc.) like a
ball in the middle of a
taut rubber sheet
that represents
space-time
The weight of the ball
will make it sink into
the rubber sheet,
creating a cone
Bigshaped
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Mass Curves Space
The heavier the ball the
bigger the dent in space-time!
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Mass in curved space-time
A mass moves in a
“straight line” in
curved space-time
In this example, this
straight line in
curved space makes
the path of the
small ball look like
something is pushing
it toward the big
ball in 3-dimensions
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The Earth and the Sun
Newton: The Earth moves around the Sun
because of “the force of gravity” is pulling it
Einstein: There is no force, the Earth moves
in a straight line in four dimensions, but the
curved space around the Sun makes it go in
orbit
space
dimensions
Bigan
Bang,
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The way the Planets go Around
the Sun in General Relativity
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Ok…
• Both Newton and Einstein correctly
predict how the planets go around the
Sun
– Actually mostly their predictions for
the locations of the planets at any
given time are almost identical
• How do we decide if one is right and
one is wrong?
• Do an experiment!!!
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When do General Relativity and Newton
predict different things?
• Ok… One equation, but I’m guessing
you’ve heard this one
2
E=MC
Ok… what is this equation saying?
Energy and mass may not be the
same, but in Einstein’s theory they
are equivalent Physics We Need
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So what?
What about light?
It has energy, but no
mass
To Einstein, its mass
doesn’t matter, it is a
particle that moves in
curved space-time
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What happens to light as it goes past the Sun?
Path
doesn’t curve
Path
does curve
• Newton’s theory: Only things with “real”
mass “feel” the force of gravity
• General Relativity: Objects move according
to the curve of space-time, regardless of
Big whether
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massWeorNeed
not
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Do an Experiment
1st Experiment:
Looks like
Can see the
its over
star directly
here!
If Einstein is
2nd Experiment:
right, the Sun
Sun in the way
curves the path
If Newton is
of the starlight
right, we won’t
see the star Question: Where
Gross
exaggeration
of sizes
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does the star
appear when you do
Need
the experiment?
41
Physics We
Topic 2: Gravity
The Great Experiment of 1915
Look at a star’s position “behind” the sun
as it “passes” in between us and the star
during an eclipse to block the glare of the
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sunlight
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Another View
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Evidence and More Evidence
• The results exactly agreed with
Einstein’s predictions
– Contradict the predictions of Newton
• Over time, even more compelling
evidence has come in in favor of
General Relativity  observations of
Dark Matter in galaxies
• Next give some of the evidence for
dark matter and that the story hangs
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Evidence galaxies contain
Dark Matter
• Described the Dark Matter in the
Universe and in galaxies in Chapter 2
• In order to better understand dark
matter in galaxies, its useful to show
some evidence that there IS Dark
Matter in galaxies
• Start by considering the case that there
IS no Dark Matter in galaxies
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How stars move in galaxies
• Laws of gravity accurately predict the
orbits of planets and stars as they move
around the solar system and galaxy
• The brightest region of both places is
the center  lots of mass there
• For the solar system, the data agree
perfectly, but for the outer part of
galaxies it should look like stars in orbit
around a massive center
• Problem: This isn’t what the data shows
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The Data
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Does this work for Stars?
Watch how fast a star rotates around the
center of the galaxy…
Simulation without
Dark Matter
Simulation with lots of
Dark Matter particles in
the galaxy
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Data
looks like this
48
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http://bigbang.physics.tamu.edu/Figures/StolenAnimations/galrot_anim.gif
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Data well explained by lots of
“Dark Matter” we can’t see
This is where it gets its name
In some sense, the name is a
statement of almost all we know
about it (it doesn’t interact with
light, and it has mass)
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Another Experiment
Maybe there isn’t dark matter
and General Relativity is
wrong?
Look at the gravitational impact
on light that travels through
the Universe, through a galaxy,
and towards us
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Einstein Ring’s?
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Another view
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Einstein Ring
The “near”
galaxy
The light from
the “far”
galaxy spread
out into a ring
Amount of lensing
explained by
extra mass of
dark matter
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Winner: General Relativity
• Many observations indicate that General
Relativity correctly describes the motion of
light, galaxies and stars in the Universe we
live in  space and time are related
• Space can curve, stretch, change etc.
• Curved space-time will be very important in
later chapters when we talk about the
expansion of the Universe
• Dark matter is an important part of the
evolution of our universe
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Paper 1
• Abbreviated description: What is the evidence for Dark Matter?
– More detail on CPR, you REALLY need to read ALL the
instructions
• Explain it to someone who isn’t taking the class (no jargon)
• Follow the required Format:
– Introduction paragraph
– ~1 paragraph per piece of evidence
– Conclusion paragraph that ties it together
• Help:
– Example of good paper
http://faculty.physics.tamu.edu/toback/109/WritingAssignments/sample
paper.shtml
– The first 9 Rubric questions
http://people.physics.tamu.edu/toback/109/WritingAssignments/PaperRubrics_9Questions.pd
f
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Outline for Unit 2: Physics We Need
Topics
1. Light and Doppler Shifts Done
2. Gravity, General Relativity, and
Dark Matter Done
3. Atomic Physics and Quantum
Mechanics  Next
4. Nuclear Physics and Chemistry
5. Temperature and Thermal
Equilibrium
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Prep For Next Time – L8
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions
– eCampus quizzes (all 6)
– Unit 1 Revision (if needed): Stage 2
• Let us know if you were misgraded
– Unit 2 Revision (if desired): Stage 1
• Let us know if you were misgraded
• End-of-Chapter Quizzes
– If we finished Chapter 6 then End-of-Chapter Quiz 6
(else, just through Chapter 5, parts a & b)
• Paper 1:
– If we finished Chapter 6: Stage 1 due Monday before
class
– Can submit a draft for feedback on eCampus if you like
– MUST
submit to turnitin
on eCampus
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Black
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Holes, No Math
Topic 2: Gravity
Prep For Next Time – L9
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions
– eCampus quizzes (all 6)
– Unit 1 Revision: Let us know if you were misgraded
– Unit 2 Revision (if desired): Stage 1
• Let us know if you were misgraded
• End-of-Chapter Quizzes
– If we finished Chapter 6 then End-of-Chapter Quiz 6
(else, just through Chapter 5, parts a & b)
• Paper 1:
– If we finished Chapter 6: Stage 1 due Wednesday before
class
– Can submit a draft for feedback on eCampus if you like by
Sunday night
– MUST
submit to turnitin
on eCampus
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Clicker Quiz
Which of the
following travels
the fastest?
A. Radio waves
B. Gamma rays
C. Red light
D. Blue light
E. They all move at
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the
same
speed
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Clicker Quiz
We observe two objects in space.
From other studies, we can tell
that object X is emitting infrared
light and the object Y is emitting
Ultraviolet light. We observe the
color of the light object X to be
Red and the color of Object Y to
be blue.
Which statement is true?
a) X and Y are moving towards us
b) X and Y are moving away from us
c) X is moving towards us and Y is
moving away from us
d) X is moving away from us and Y
is moving towards us
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Clicker Question
What would happen to the Einstein
ring around a galaxy who's Dark
Matter suddenly wasn't there?
a) Nothing
b) It would get smaller
c) It would get bigger
d) It would disappear
e) None of the above
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Clicker Question
What would happen if you were shot by a gun
that fires "dark matter” bullets which have
the same size and mass as a regular bullet?
a) Your molecules would significantly spread
out from an expansion of space-time
b) A black hole would form inside you
c) Objects behind you would be gravitationally
lensed
d) Your body would barely notice
e) You would die like you would if you got shot
with any kind of bullet
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Clicker Question
Why is dark matter "dark“?
a) Because it is closely linked to
dark energy
b) Because it has no mass
c) Because it is made of black
holes
d) Because it doesn’t interact
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with
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Clicker Question
As far as we know, Dark Matter
exists:
a) Everywhere in the universe
b) Only near black holes
c) Mostly in or around galaxies
d) It doesn't exist
e) We don't know where it
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exists
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Clicker Question
A man shoots a red photon straight up
into the air next to a very tall
building. The photon rises in the air.
Which statements are true:
a) The photon slows down as it rises,
the same way a rock would
b) The photon loses energy, the same
way a rock would
c) The photon gets blue-shifted
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Clicker Question
Instead of throwing a rock into the air, a man shoots a red photon straight up
into the air next to a very tall building. The following question are about the
photon when it reaches the top of the building. Which of the following
statements are true
Question 1: Speed
a) The speed of the photon stays the same
b) The speed of the photon slows down like a rock would
Question 2: Energy
a) The energy of the photon stays the same
b) The energy of the photon gets lower (like the kinetic energy would for a rock)
c) The energy of the photon gets larger (since it is getting closer to outer space)
Question 3: Color
a) The color of the photon stays the same
b) The color of the photon is red-shifted (gets a longer wavelength)
c) The color of the photon is blue-shifted (gets a shorter wavelength)
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Prep For Next Time – L8
• Reading:
– None
• Pre-Lecture Reading Questions
– Let me know if you think you were misgraded
– Unit 1 Revision: Grades will be posted in eCampus
soon, instructions to follow if you didn’t pass
– Unit 2 Revision (if desired): Stage 1 due in CPR
Monday before class
• End-of-Chapter Quizzes
– If we finished Chapter 6 then End-of-Chapter
Quiz 6 (else, just through Chapter 5)
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Prep For Next Time – L9
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you have been misgraded
– Unit 1 Revision: New grades posted soon.
– Unit 2 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– If we finished Chapter 6 then End-of-Chapter
Quiz 6 (else, just through Chapter 5)
• Paper 1:
– Stage 1 due Monday before class
– Can submit a draft for feedback on eCampus if
you like
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–
MUST
submit
to
turnitin
on
eCampus
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PLRQ 1 Revision
• We still have a number of people
who haven’t passed all the parts
yet
• I opened Stage 2 to let people
finish it, thus the updated grades
have not been posted on eCampus
• When they are done, I will send
an email with new instructions –
We will have a special way for
student who need a third try
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Back to Our Example
Gravity well analogy:
• In Relativity: It’s
not that there is
something “pulling"
towards the center,
instead space is
curved and the
penny is just moving
in a straight line in
curved space
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Starting to think about “Curved Space-Time”
Analogy in 3 dimensions
General Relativity talks
about 4-dimensional
space-time
Our eyes can only see in
3 space dimensions
To us something moving
in a “straight line” in
4-dimensional curved
space time “looks” like
its moving in a curved
path in the 3dimensional space we’re
used
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Black
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Prep For Next Time – L5
• Note: May change depending on how far we get in
lecture
• Reading:
–BBBHNM: All reading through Chapter 9
• Reading Questions:
– All reading questions through 9
• eLearning Quizzes
– If we finished Chapter 6 then end-of-chapter
quiz 6 (else just up to Chapter 5)
• Paper 1
– Revisions if needed
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Prep For Next Time – L9
• Reading:
– BBBHNM: Chapter 7 (already assigned)
• Pre-Lecture Reading Questions:
– Chapter 7 (already assigned)
• End-of-Chapter Quizzes:
– Did not finished Chapter 6, so just Chapter 5
(already due)
• Paper:
– Paper 0: Submit to CPR and turnitin on eCampus
by Friday
– Calibrations after that
– Will assign Paper 1 next time since we will finish
Chapter 6
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Prep For Next Time – L9
• Note: May change depending on how far we get in
lecture
• Reading:
– BBBHNM: Chapter 7 (already assigned)
• Pre-Lecture Reading Questions:
– Chapter 7 (already assigned)
• End-of-Chapter Quizzes:
– If we finished Chapter 6, then Chapter 6. If not,
just Chapter 5 (already due)
• Paper:
– Needed to be submitted to CPR and turnitin on
eCampus
– Be working on Calibrations.
– Due Wednesday
– Paper
1 coming up, Physics
will beWe
due
one week after we
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finish
Chapter
6.
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Prep For Next Time – L10
• Note: May change depending on how far we get in
lecture
• Reading:
– BBBHNM: Chapter 7 (already due)
• Pre-Lecture Reading Questions:
– Chapter 7 (already due)
• End-of-Chapter Quizzes:
– If we finished Chapter 6, then Chapter 6. If not,
just Chapter 5 (already due)
• Papers:
– Paper 0 due to CPR and turnitin on eCampus on
Friday
– Be working on Calibrations
– If we finished Chapter 6, Paper 1 will be due
next Wednesday before
class
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Was Due For Today– L8
• Reading
– BBBHNM: None
• Pre-Lecture Reading Questions:
– None
• End-of-Chapter Quizzes
– Chapter 5
• Paper Stuff
– Paper 0 in CPR and turnitin.com
before class
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Was Due For Today– L9
• Reading
– BBBHNM: Chapter 7
• Pre-Lecture Reading Questions:
– Chapter 7
• End-of-Chapter Quizzes
– Chapter 5 was already due
• Paper Stuff
– Will talk about this today
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Was Due For Today– L10
• Reading
– BBBHNM: Chapter 7 (already due)
• Pre-Lecture Reading Questions:
– Chapter 7 (already due)
• End-of-Chapter Quizzes
– Chapter 5 parts A&B (already due)
• Paper Stuff
– Working on Paper 0, due Friday
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Paper 0, Questions 1-5
1.
2.
3.
4.
5.
Does the paper make it easy to understand what question is being answered, what the answer is, and how
it will be answered? If anyone of those are missing, or if you can't follow the argument, then choose No.
If the argument is clear, but not said very well (or is wordy), then you should still give a Yes. If the
paper is clear to you, but would not be clear to someone who hasn’t taken the course choose No. Being
easy to read isn't a good enough reason to give a Yes. Having a sentence or two that are hard to
understand (or poorly written) within a basically clear paper is fine, and can still deserve a Yes if it is
otherwise ok.
Are the pieces of evidence clearly and correctly enumerated in the opening paragraph? This includes the
electrons going around atoms, the Moon orbiting the Earth, and planets orbiting the Sun.
Does the structure of the paper follow the instructions? Specifically: Is there an introduction paragraph,
separate paragraphs discussing evidence, and a conclusion paragraph? If any are missing, choose No. Does
the paper directly address the question and make the argument to answer it? If the paper addresses the
question and makes an argument (right or wrong) to answer it, choose Yes (we will address the wrongness in
a later question). Do not choose No due to a poorly written or confusing introduction. The paper does not
need to have only three paragraphs, and the pieces of evidence can be intertwined within them. Do not
choose No due to missing evidence or more than three paragraphs. Do not choose No just because evidence
is not constrained to these paragraphs. If the paper does not end with a conclusion paragraph, choose No.
Do not choose No due to a poorly written or confusing conclusion.
Is the paper generally free of extraneous evidence? If there is any significant evidence that is off topic
or an argument that has nothing to do with the topic, choose “No.” If there is significant evidence from
outside class, choose No. Do not choose “No” due to evidence that is unnecessary if the evidence is
relevant to the topic.
Does the paper only use language and words that can be understood by the average lay-person? If the
author uses an acronym, like GR, for general relativity that is ok but only if the acronym is clearly
defined. If they use an acronym that isn't defined, then select No. Similarly, just because you saw these
words in a high-school science class does not mean they are understood by the average person. The
average person on the street would know what an atom is, but not know what a spectral line is.
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Paper 0, Questions 6-10
6. Does the essay use language formal enough to give to a statesman? If
the paper uses jokes, slang or other informal language, choose No. Do
not choose No due to poor grammar, spelling mistakes, incomplete
sentences, or poor sentence structure (we will take off points in a
different question for this). Do not choose No due to the use of an
acronym, like USA, since it is common usage and not slang.
7. Is the essay generally free of instances of bad grammar, incomplete
sentences or spelling mistakes? If there are more than two minor
mistakes, choose No.
8. Does the paper make clear how and why the evidence presented relates
to the argument? If the facts are mentioned but show no clear
connection to the argument, then choose No. If the facts are not
addressed throughout the paper, then choose No. If it states the data
without saying why it is evidence then choose No.
9. Do the middle (evidence) paragraphs clearly tie into the overall
structure?
10.Does the paper use the scientific method and evidence based decision
It’s OK if the wordsPhysics
“scientific
Bigmaking?
Bang, Black
Wemethod”
Need and “evidence-based
81
decision
making”
are
not
mentioned
specifically.
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Paper 0, Questions 11-15
11. Does the essay make it clear what the Scientific Method is and
why it is important in this paper?
12.Does the essay clearly tie together the pieces of evidence using
the scientific method in the conclusion?
13.Does this paper say that the Moon orbits the Earth?
14.Does the paper mention explicitly that the Earth is much more
massive than the Moon, and that it is important to why the
Moon orbits the Earth instead of the other way around? If it
mentions that the Earth is more massive, and that this is what
is important, then this is good enough. If it just says that it is
more massive without saying why that is important in some way,
then answer No. If it says "bigger" or "larger" (or that the
Moon is "smaller") that is good enough.
15.Does the paper mention that the Earth or the planets orbit the
Sun? Either is fine. If neither is mentioned, then give a No.
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Paper 0, Questions 16-20
16.Does the paper mention explicitly that the Sun is much more massive than the
things orbiting it, and that it is important to say why they orbit the Sun
instead of the other way around? If it mentions that the Sun is more massive,
and that this is what is important, then this is good enough. If it just says
that it is more massive without saying why that is important in some way, then
answer No. If it says "bigger" or "larger" (or that the planets are "smaller")
that is good enough.
17.Does the paper mention that electrons orbit protons or that electrons orbit a
nucleus? Either one is fine.
18.Does the paper mention explicitly that the proton (or nucleus) is much more
massive than the electron orbiting it, and that it is important to why they orbit
the proton (or nucleus) instead of the other way around? If it mentions that
the proton or nucleus is more massive, and that this is what is important, then
this is good enough. If it just says that it is more massive without saying why
that is important in some way, then answer No. If it says "bigger" or "larger"
(or that the electron is "smaller") that is good enough.
19.Does the essay spend an appropriate amount of time on each topic?
20.Does the conclusion paragraph tie together all the big picture issues discussed in
the other paragraphs? If the conclusion does not summarize the evidence, then
chose No. If the conclusion simply re-states the pieces of evidence, then
Bigchoose
Bang,No.
Black
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Clusters of galaxies can smear out the light
from a single galaxy into a long “arc”
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Our best Understanding
• Oversimplified view of a spiral galaxy
In some ways, Dark
Matter surrounds
the galaxy like the
water in a fishbowl
surrounds a fish in
the middle of the
bowl.
Not exactly the
same… denser in the
middle because of
the pull of gravity
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Lensing of Galaxies
Prism
• Dark Matter
“Lenses” the
galaxies behind
them like a
prism or a pair
of bad
eyeglasses
• Evidence that
the light coming
to us is passing
through lots of
matter we can’t
see
directly
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General Relativity and Light
• The large mass
Is here
“Looks” like
of the Sun can
its here
bend the path
of light
• Result: The
apparent
position of a
Light’s path in
star “moved” as
curved
the light passed
space time
from outer
space, past the
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Looking at Light from the Universe
Galaxy
Light from a Galaxy
Hydrogen
Another Galaxy
Cloud
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Looks like a Galaxy
Looks
Lookslike
likea aGalaxy
Galaxy
behind a cloud of
behind a cloud of
heavy “stuff” that
hydrogen
just stars and88
Physicsisn’t
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Topic 2: Gravity
Prep for Today (Is now due) – L8
• Reading:
–BBBHNM 7
• Reading questions:
–Chapter 7
• End-of-Chapter Quiz:
– Chapters 5
• Paper 1:
–Phase II is due Friday at 5:45PM
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Phase I and Phase II in CPR
Phase I: (Due 1 week after we finish Chapter 4)
• Turn it into CRP (online)
• Need to also submit a copy to the version of
turnitin.com on eLearning
Phase II: (Due one week after Phase I)
• Three-Part Calibrations/Reviewing
1. Calibrations, learning to use the Rubrics
2. Grade three other papers
3. Grade your own paper
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Prep for Next Time – P7
• Reading:
– BBBHNM 7
– Recommended:
• SHU: 6 and 7 (up-to page 153)
• BHOT: 9 and 11 (117-122)
• Reading questions
– Two questions from Chapter 7 or the
recommended reading
• End-of-Chapter Quizzes
– If we finished Chapter 6, quiz due before
the next class (else just 5)
• Paper 1
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–
Phase
II
is
due
Friday
at
5:45PM
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Prep for Next Time – P8
• Reading:
–None
• Reading questions
–None
• End-of-Chapter Quizzes
–If we finished Chapter 6, quiz due
before the next class (else just 5)
• Paper 1
–Phase II is due Friday at 5:45PM
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Full set of Readings So Far
•Required:
– BBBHNM: Chap 1-7
•Recommended:
– BHOT: Chap. 1-6, 9 and 11
(117-122)
– SHU: Chap. 1-3, 6 and 7 (upto page 153)
– TOE: Chap. 1
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Overview of Physics We Need
• Cosmology, the Big Bang and
Black Holes are some of the
most interesting things that
can be understood
• However, to UNDERSTAND
them better, and the
EVIDENCE for them, we
need to learn some physics
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The Good, the Bad and the Ugly
Good:
• Both make lots of predictions that are
observed in experiment
– Example: What does Light do and how
does it behave
Bad:
• Don’t always make predictions that are
inconsistent with each other, although wean’t
yet test any of those predictions
– Example: Different predictions for the
center of a Black Hole
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???
• Maybe just need to modify one or the
other (or both?) and combine to make a
“quantum theory of gravity”?
– Could be, but been working on it for
more than 60 years, no luck yet
– Maybe both are wrong?
• Either way, they are our best
understanding at the moment  Lots of
experiments are INCREDIBLY well
described by them  Makes us think
there is SOME truth in there
somewhere…
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Why do we need the world to be this
complicated?
• Data says that light always moves at the
speed of light.
• Einstein says that the laws of physics should
be the same for all freely moving observers,
no matter what their speed
• So What?
• Since nothing can move faster through space
than light (it always moves at the speed of
light) this has enormous implications for the
way both space and time are related
– Space (measured with a ruler)
– Time (measured with a clock)
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The Great Experiment of 1915
• Look at a star’s
position “behind” the
sun as it “passes” in
between us and the
star
• Result: The apparent
position of a star is
different when the sun
is close to the path
• In other words, we
observe that the
gravity of the sun
“bent” the path of the
“no mass” light object
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coming
from the star
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Light’s path in
curved
space time
98
Mass Curves Space
The heavier the ball
the bigger the dent in
Big Bang, Black
space-time!
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Stars
Space-time is
curved or
“warped” a lot by
stars
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Interesting Aside
Interesting to note
that if Newton’s
laws were even
slightly different,
the orbits of the
planets would not
be circles or
ellipses
Would spiral into
the sun or escape
completely…
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Today’s Lecture
• Today we’ll talk about Gravity and
General Relativity
– If there are questions that you want
answers to then you should write them
down and we’ll get back to you
• Only tell you the things about Gravity
and General Relativity you need to know
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How this “Looks” to us in the Real World
General Relativity talks
about 4-dimensional
space-time
Our eyes can only see in
3 dimensions
To us something moving
in a “straight line” in
4-dimensional curved
space time “looks” like
its moving in a curved
path in the 3dimensional space we
know
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In-Class Writing Assignment
Write down, during the course
of lecture
Two questions you
want to know the
answer to
If you ask them during lecture,
you can still write them down
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2nd Issue for General Relativity
• In General Relativity,
bodies always follow a
straight line in four
dimensional space-time
unless there is a force
– Gravity is not a force
• Compare to Newton:
“Unless there is a force
things move in a straight
line in three dimensions;
gravity provides a force”
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In General Relativity, bodies
always follow a straight line
in four dimensional spacetime unless there is a force
Why is this important?
Better yet,
Why do we care?
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• General Relativity says that
what appears to be the
force of gravity pulling a
mass is actually a mass
moving in straight line in
curved space-time
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This is a BIG statement
This is a VERY different way of thinking. Let’s
spend some on this
• In General Relativity, bodies always follow a
straight line in four dimensional space-time
unless there is a force
– Gravity is not a force
• Compare to Newton: “Unless there is a force
things move in a straight line in three
dimensions; gravity provides a force”
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Einstein and General Relativity
• Laws of physics should be
the same for all freely
moving observers, no matter
what their speed
• Changes our concept of
time…
– There is no absolute time!
• Space is not separate from
time, we need to combine
them into 4 dimensional
space-time
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2nd year Grad
School Course
109
General Relativity
• Gravity is not a
force like other
forces, but rather
the weird
consequence that
space-time is not
flat
• Space-time is curved
or “warped” by the
distribution of mass
and energy in it
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Outline
1. Overview for the next set of
lectures
– Physics We Need
– De-mystifying the strange
theories
2. Overview of Today’s lecture
– Gravity and General
Relativity
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Today’s Lecture
• Today we’ll talk about Gravity and
General Relativity
• I wasn’t planning on going over
EVERYTHING in BHOT because I don’t
think we need it for our story
– Can cover extra questions in
recitation
• Only tell you the things about Gravity
and General Relativity you need to
know
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Next Few Lectures
• De-mystifying the strange theories
• For next time:
– Reading: BHOT 4-6 (Gravity)
– Lecture Prep: Create two multiple
choice questions based on the reading
• Next round of reading after that:
– SHU: 3 (p55-69)
– SHU: 6 and 7 (up-to page 153)
– BHOT: 9 and 11 (117-122)
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Section 2
The reading for the next 5 lectures:
• Today: Gravity
– BHOT: Mostly 4 and 6
• Next lecture
– BHOT: 5 and SHU: 3 (first part,
p55-69)
• After that
– SHU: 6 and 7 (to page 153)
– BHOT: 9
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Outline
• Definitely:
– Doppler shifts
– Spectral lines
– Newtonian gravity
• Might need?
– Quantum Mechanics
– Curved space
• Other stuff
– Atomic model: Electrons that surround a nucleus
– Nuclear model: A nucleus is protons and neutrons that are
held together
– What is the Milky Way?
– Feynman diagrams here?
– What is temperature?
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• Do we need to do atomic
Physics and chemistry first
(textbook?)?
• Speed of light is really
freaking large
• Photons are particles, but also
a wave… have a wavelength…
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BHOT: 4: General Relativity vs.
Quantum Mechanics
• General Relativity
– Gravity and Theory of the very big
• Quantum Mechanics
– Theory of the very small
• Aren’t consistent with each other, but
both are incredibly successful in their
areas
• Looking for a quantum theory of
gravity
• Jonathan: Pictures from BHOT chapts
1-4
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BHOT 6 cont:
• Time runs differently at
different heights in a
gravitational field. Need to
talk about this? Its cool, but
so what…
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