Transcript Slide 1

Big Bang, Black
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ASTR/PHYS 109
Dr. David Toback
Lecture 5 & 6
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Prep For Today (is now due) – L6
• Reading:
– BBBHNM Unit 2 (Chapters 5-9)
• Pre-Lecture Reading Questions
– eCampus Quizzes 1-6
• Check these, some were fixed and
changed scores
– Unit 2: Stage 1
– Unit 1 Revision (if needed) Stage 1:
Due Wed before class
• End-of-Chapter Quizzes
– Chapter 3
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Next Topic: Scientific Methods
Unit 1:
1. Introduction  Done
2. Going Big  Done
3. Going Small  Done
4. Evidence and the Scientific
Method
Today we move on to the Questions
and How we go about answering
them
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Plan for the Next Few Weeks
1. More on the Questions
and How we go about
answering them
2. Some of the history to
teach us about the
Today
method
3. Need to learn some
physics
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}
Next
Unit
4
Next few Weeks Continued…
To learn Cosmology will need to learn a bit
about:
1. Light and Doppler Shifts
2. Gravity, General Relativity and Dark
Matter
3. Atomic Physics and Quantum
Mechanics
4. Nuclear Physics and Chemistry
5. Temperature and Thermal Equilibrium
Won’t spend too long on these, just
enough to get back to the big picture…
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Evidence and The Scientific Method
• What are the clues at the scene of the
crime?
• How can we use the clues to figure out
what happened? Any WHY?
• Scientific Method
– How do we know what we know?
– What is the evidence for some of the
“true things” we heard growing up?
• E.g .Earth goes around the Sun
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How do we know what we know?
• We have a lot of experience in the
world around us
• Unfortunately, our experience is
really lousy in guiding us to really
understanding the bigger (and smaller)
world around us unless we’re really
careful
– We can misinterpret the clues
• As you’ve already seen, the world is
incredibly complex and much of it is
different from what we experience
– Good clues are hard to find,
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sometimes
hard
to interpret
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Single example to Show the
Scientific Method in Action
• People have watched the sky and
noticed that the stars (the dots of
light in the sky) basically all move
together over the course of the
night and over years
• Five of them behave differently
– Start this story in the 2nd century
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Fun Videos of Just the Stars
Start with things you can see
with your own eyes!
Video of stars moving with
Polaris (north star) at the
center
https://www.youtube.com/watch?v=XTTDWhky9HY
Video of stars moving, including
the Milky Way (from Chile)
https://www.youtube.com/watch?v=JEHm-XUHwNw
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Ptolemy’s Universe (2nd century)
The Sun, Moon and Stars go
around once a day, but a few
(the planets) change their
position relative to the other
stars a little every night
Every so often the planets
move backward through the
stars for awhile
Hypothesis: They orbit the
Earth in mostly circular paths
Best guess: these are miniorbits way out there
(epicycles)…
Hmmm…
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Looking at Mars in the Stars
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How Ptolemy envisioned it
• The big circle is the main orbit,
and the little circle is the
epicycle
• This explains why the planets
seem to go back and forth out
there in space (retrograde motion)
every so often
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/ptolem
y.model.swf
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Cracks in the `early cosmology’
In 1514, Copernicus hypothesized
that Planets and Earth orbit the
Sun
Much simpler in some ways
 no epicycles
More complicated in others
 Says Earth is rotating
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Epicycles???
A more modern view of the
motion of the Earth and Mars
and the stars behind them
(from the point of view of the
center)
How would this explain the
epicycles that people saw?
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/mars_r
etrograde_motion.swf
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If we lived in the 1500’s, should we
believe Copernicus?
The Earth isn’t at
REST and rotates?
• Shouldn’t we FEEL
this?
• If the Earth is
rotating, why don’t we
fall off like an ant on
a bicycle wheel?
• Why don’t we feel a
wind as we rotate?
• Why doesn’t it rotate
under us when we
jump?
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Cracks in the `early cosmology’
Should his view have just “been
accepted”?
Perhaps his theory was just a
“different interpretation” of
the same data?
– Both models are consistent
with observations
Need more evidence!
Need a better TOOL to test,
experimentally, which is
correct
Early 1600’s: Kepler and Galileo
started gathering data from
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Big telescopes
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Data Provides Evidence
• Discover moons orbiting Jupiter! 
Solid evidence that not
EVERYTHING orbits the Earth!
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Another Piece of Evidence
• Can understand the phases of
the Moon because of the
locations of all three
• Not eclipses
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Venus
• Consider the two different versions of how
Venus is predicted to move in space
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The Phases of Venus
• Venus has a
full set of
phases, like
the moon
• Sunlight
shining off
Venus and
to our eyes
• No good way
to explain this
if Venus goes
around the
Earth
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More data
• With better data Kepler realizes an even
better description of the data is that all
planet orbit the Sun in an ellipse, not a
circle
• Sun-centered model now agrees with the
high-quality observed data, Earth
centered does not
• No good REASON for ellipses though…
then again, no good reason they should
be circles (except people LIKE circles,
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and
they
are
more
“perfect”)
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The next generation…Newton
• Newton puts forward his
theory of Gravity and
describes it as a Force
• So what? The same force
that pulls an apple to the
ground from a tree ALSO
pulls the planets towards
the Sun and keeps them in
orbit
• This “explains” why both
the orbits are ellipses
AND why we don’t fall off
spinning
Earth Introduction
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Isaac Newton
1687
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Scientific Method
The history is fun, but we have
a problem:
• How do we separate true
stories from stories we’d like
to believe, but aren’t actually
true?
• Need EVIDENCE and a good
Scientific THEORY
– Good hypothesis testing
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Outline for Unit 2: Physics We Need
Topics
1. Light and Doppler Shifts
2. Gravity, General Relativity and Dark
Matter
3. Atomic Physics and Quantum
Mechanics
4. Nuclear Physics and Chemistry
5. Temperature and Thermal Equilibrium
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PLRQ Unit 1 Grades
• Criteria for Pass/Revise grades for CPR Unit 1
are described in the FAQ and the Lecture
notes
• Will post the grades in eCampus after we are
done with re-grade requests
• You should go to eCampus to make sure you
got the grade you think you did. Many
people are surprised.
• Let us know if you think you were misgraded or
we gave you the wrong grade
• What do you do if your eCampus grade says
“Revise”?
– See
http://people.physics.tamu.edu/toback/109/
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Topic 4: Scientific Methods
Holes, 109FAQ.shtml#CPRGrades
No Math
Prep For Next Time – L5
• Reading:
– Required: BBBHNM Unit 2 (Chapters 5-9)
– Recommended Reading:
• See P3 of
http://people.physics.tamu.edu/toback/109/Syllabus.pdf
• Pre-Lecture Reading Questions
– Stage 1 for Unit 2 due before Class
– Stage 1 in CPR for Unit 1 Revision will be
assigned after grades are posted
• End-of-Chapter Quizzes
– If we finished Chapter 4 then End-ofChapter Quiz 4 (else just Chapter 3)
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Prep For Next Time – L6
• Reading:
– BBBHNM Unit 2
• Pre-Lecture Reading Questions
– eCampus quizzes (all 6)
– Unit 1 Revision (if needed): Stage 1
before Class
• Let us know if you were misgraded
– Unit 2: Stage 2 due before class
• End-of-Chapter Quizzes
– If we finished Chapter 4 then End-ofChapter Quiz 4 (else just Chapter 3)
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Clicker Quiz
A muon is observed to decay into an electron
and two different neutrinos. Is a muon
considered a fundamental particle?
a) No, because it has the electrons and
neutrinos inside it so it can't be
fundamental.
b) Yes, because it isn't composed of electrons
and neutrinos, it just decays into them
c) No, because fundamental particles can't
decay
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Clicker Quiz
Q: What does it mean for an electron to be
"stable?"
a) It is balanced with exactly one proton
b) Its orbit ring exists in one plane (no
wobble)
c) It has reached minimum size (10-19 m)
d) Undisturbed, it can go on living forever and
ever
e) They don't appear to be made of anything
smaller
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Paper 0 Stuff
• Want feedback before turning it
in?
– Post it in eCampus in .doc (or
.pdf) for comments by the TA
by 5PM Friday
– Make sure you polish it
• If you have lots of grammar
and spelling mistakes we’ll just
make you resubmit
it
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PLRQ Concerns
• Many people don’t seem to realize that there
were two different PLRQ assignments
– In eCampus: Quizzes 1-4
– In CPR: Submit questions (Stage 1) and do
all the Review parts (Stage 2) in CPR
• Let us know if you think you were misgraded
• How to tell if you need to do a Revision
– Only the grade in eCampus matters
– Why didn’t I pass? What do you need to do
if your eCampus grade says “Revise”?
– See
http://people.physics.tamu.edu/toback/109/
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109FAQ.shtml#CPRGrades
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Prep For Today (is now due) – L5
• Reading:
–None
• Pre-Lecture Reading
Questions
–Unit 1: Grades posted.
•End-of-Chapter Quizzes
–Chapters 2 and 3
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Prep For Next Time – L5
• Reading:
– Required: BBBHNM Unit 2 (Chapters 5-9)
– Recommended Reading:
• See P3 of
http://people.physics.tamu.edu/toback/109/Syllabus.pd
f
• Pre-Lecture Reading Questions
– Unit 1 Revision (if Needed): Stage 1 in CPR due before
class
• Let me know if you think you were misgraded
• Must do entire assignment if your grade in eCampus
says “Revise”
– Unit 2: Stage 1 due before class
• No more eCampus stuff for PLRQ
• End-of-Chapter Quizzes
– If we finished Chapter 4 then End-of-Chapter Quiz 4
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Some words; “It’s a theory…”
• Theory: “A set of rules that relate
quantities in a model to observations
we make”
• Hypothesis: “A tentative assumption
that is useful in that it predicts the
outcome of an experiment; can be
tested”
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Science
• For us to “believe” in a theory, or
said better, to think it might
correspond to truth, we agree that
it has to be tested in such a way it
can be tested over and over again
such that the results must always
confirm the theory
• Does the world function in a
“predictable” manner?
• What happens when you test a
hypothesis?
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What Makes a Good Theory?
Two requirements:
1. It must accurately describe a large class of
observations, clues, or other pieces of evidence.
– For example g, the acceleration due to gravity.
Same everywhere on the Earth?
2. It must make DEFINTE PREDICTIONS about the
results of FUTURE (not yet done) observations or
experiments
• Creates testable hypotheses
• An astronaut hits a golf ball on the moon. Can
we predict its path?
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Yet more on Scientific Method
• It also must be falsifiable
• If we do an experiment and the results
disagree with the predictions of the theory,
then the theory is wrong or has to be
modified
– It has been said that “even the most
beautiful theory can be slain by a single ugly
fact”
• If the theory makes predictions for a new
experiment and the data agrees then it gives
us really good reason to believe there really
are underlying principles in the world we live in
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What science does not promise
Science does not promise eternal
truths
Only promises the systematic
elimination of false hypotheses
and the establishment of what is
currently the most likely
explanation of an aspect of
reality…
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Everyday Conversation
• Explanations that stand the test of time
and LOTS of experiments are what we
call Theories
– Gravity, Quantum Mechanics etc.
• When someone says “Well… It’s a
theory” we know what they mean. They
mean “it’s a hypothesis”
– We don’t yell at them for the same
reason we don’t get upset when
someone says the
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Better experiments…
At some point our experiments
get so good that we can
“observe” things that our
eyes can’t see directly
– The very small
– The very faint and/or far
away
What happens if the theories
that explain what we can see
with our eyes don’t explain
what we see in a microscope?
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Weirdness…
Have to try new weirder theories
• What if we come up with a theory
that accurately “predicts” the
results of both the experiments we
can do with our eyes AND the
really sensitive ones we can do with
really special microscopes?
• What if that theory is counter to
our intuition?
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More weirdness
• What if our weird theory then makes further
weird predictions?
• What if it predicts that if we do a simple
experiment we will get crazy results?
• What if we DO the experiment and GET the
crazy results?
At what point do start believing there is some
“truth” to the theory?
Do we change our mind if we don’t LIKE the
implications of the theory? (The Earth isn’t
the center of the universe)
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Fact is Stranger than Fiction
• Typically we have confidence in theories that
do a good job of predicting the results of
experiments have some basis in reality
• In the 1920’s scientists starting coming up
with such theories: General Relativity and
Quantum Mechanics are good examples… Stood
up to 90 years of experiments
– Will talk in the next unit about what’s weird
about them, and what weird things they
predict and explain
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Another Piece of Evidence
• Can
understand
the phases
of the Moon
because of
the locations
of all three
• Not eclipses
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The Phases of Venus
• Venus has a full set of phases, like the moon
– Sunlight shining off Venus and to our eyes
• No good way to explain this if Venus rotates
around the Earth
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Class trip to Cyclotron
Clicker question
• Any interest in a class trip to the
Cyclotron? If so, which day would
you be most interested
• A = Wednesday
• B = Friday
• C = Other day please!!!
• D = Not likely to make it
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Prep For Next Time – L5
• Reading:
–BBBHNM: Chap 5
• Reading Questions:
– Two questions from Chapter 5 or
the recommended reading
• End-of-Chapter Quizzes
– If we finished Chapter 4 then
end-of-chapter quiz 4 (else just
3)
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Prep For Next Time – L4
• Note: May change depending on how far we get in
lecture (some may have already been due)
• Reading:
– BBBHNM: All reading up to Chapter 6
• Pre-Lecture Reading Questions:
– Two reading questions from Chapter 6
• End-of-Chapter Quizzes
– If we finished Chapter 4 then end-of-chapter
quiz 4 (else just 3)
• Paper 0
– Paper 0 has been posted on CPR
– If we finished Chapter 4, then Paper 0 is due one
week from today
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Full set of Readings So Far
•Required:
– BBBHNM: Chap 1-5
•Recommended:
– BHOT: Chap. 1-3
– SHU: Chap. 1-3 (p55-69)
– TOE: Chap. 1
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Prep for Today (Is now due) – L5
• Reading:
– BBBHNM: Chap 4
• Reading questions
–Two questions from Chapter
4
• End-of-Chapter Quizzes:
–Chapter 3
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Phase I, Phase II and Phase III
Phase I: (Paper due 1 week after we finish Chapter 4)
• Turn in a polished draft to eCampus
• TA’s will provide feedback, but not if there are
multiple spelling/grammar mistakes
• Pass/Fail grade
Phase II: (Due one week after Phase I)
• A revised version will be done 1 week later on CPR
• When you submit to CPR (after revision), you will need
to also submit a copy of your to the turnitin.com line
on eCampus
Phase III: (Due one week after Phase II)
• Calibrations and Reviewing due one week after you
submit
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Paper 0 Stuff – L9
faculty.physics.tamu.edu/toback/109/WritingAssignments/
• Phase I: Due last Wednesday
– You will get feedback soon, work on revisions
now
– Email if you need an extension
• Phase II:
– Due in CPR/Turnitin.com Wednesday
• Phase III:
– Will talk more about CPR and reviewing
Wednesday
– Following
Wednesday
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History and Just-So Stories
State of our understanding
2500 years ago: “The
earth is, obviously, flat…”
So, how DID they figure
out the earth is round?
– Ships on the horizon:
Top of the mast first
– Aristotle (340 BC): The
earth’s shadow on the
moon
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Worse…
Actually, it’s even worse
• What we “believe” can deceive
us from understanding how
things actually work
• Unfortunately, our history is
littered with “Just-so stories…”
that have set back our
understanding
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What we “believe” can mislead us
• We “see” the sun/moon go
around the Earth, must be so!
• The Church demanded that
this model be accepted for
Religious reasons…
– Man should be at the center
of the universe
– Circular orbits – Perfection!
• This model was accepted for
nearly 1500 years
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The Church and Science
• It’s easy to pick on the church with
hindsight
• Then again, much of the great
progress in our understanding of the
physical world comes because science
(and lots of other things) were its
beneficiary
• In today’s lingo “The Church” was the
one of the few funding agencies for
hundreds of years…
– What if you weren’t independently
wealthy and wanted to do science?
(Want to learn to read???) And be
able to eat? Either become a priest
or a monk… Maybe work for a King?
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Interesting aside Continued: The backlash…
• These findings contradicted the Church!
• Now scientists have a problem: Galileo was a
leading scientist in Italy (close to Rome!) and
he was Loud!
• The Church spurned this as heretical and set
back science (nearly ex-communicated,
sentenced to life of house arrest)
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Reading Quizzes
• We are not looking for questions
where we could get the answer on
Google (which you could do)
• Wrong questions:
– How big is the largest planet
we’ve found?
– When was the telescope invented?
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Epicycles…
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Copernicus Continued
• This is a test…
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Ptolemy
• Eight “bodies” rotating the earth in
circular orbits (2nd century BC).
• People accepted this theory even
though it had problems (moon should
be twice as big..)
– Church liked it… it stuck and was
largely unquestioned
– It didn’t offend anyone
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Kepler
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Ptolomy
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Brahe
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SHU: Chapter 1
• Eratosthenes (Greek
mathematician)
• Different length shadows at the
same TIME of day.
• Pictures? Pages 22 and 23
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Greek view of the universe
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