big bang, black holes, no...

IntroductionTopic 4: Scientific Methods

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David TobackLectures 6 & 7



Prep For Today (is now due) – L7No one in back 4 rows and no laptops or cellphones• Reading:

– BBBHNM Unit 2 (Chapters 5-9): Was due before class– Recommended Reading:

• See P3 of http://people.physics.tamu.edu/toback/109/Syllabus.pdf• Warmup Quizzes:

– (Warm-up Quizzes Parts 1-3)– Warm-up Quiz Part 4 (Peerceptiv): Will assign soon

• Pre-Lecture Reading Questions:– (Unit 1 Quiz)– Unit 2 Text Submission, 4 questions to TurnItIn:

• Submission due today. Will post grades soon. Need 4 (and only 4) Excellent questions to pass.

• Pass/Revise assignment. If you don’t pass we will set up dates for Revisions after you get Feedback

– Unit 2 Quiz: Will assign today• End-of-Chapter Quizzes:

– Chapter 3: Was due before class

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Next Topic: Scientific MethodsUnit 1:1. Introduction Done2. Going Big Done3. Going Small Done4. Evidence and the Scientific

Method TodayToday we move on to the Questions

and How we go about answering them

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Next few Weeks Continued… The tools in our toolbox… Learning some PhysicsTo learn Cosmology will need to learn a bit about:1. Light and Doppler Shifts 2. Gravity, General Relativity and Dark

Matter3. Atomic Physics and Quantum

Mechanics4. Nuclear Physics and Chemistry5. Temperature and Thermal Equilibrium

Won’t spend too long on these, just enough to get back to the big picture…



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Copernicus’s “Hypothesis”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_retrograde_motion.swf



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If we lived in the 1500’s, should/would we have believed 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 the rotating Earth move under our feet 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 telescopes



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Early Data Provides EvidenceDiscover moons orbiting Jupiter! Solid evidence that not EVERYTHING orbits the Earth!



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 predictions of how

Venus moves 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 more accurate data Kepler realizes an even better description of the data is that all planets orbit the Sun in an ellipse, not circles

• Sun-centered model now agrees with the high-quality observational data, Earth centered model does not

• No good REASON for ellipses though… then again, no good reason they should be circles (except people LIKE circles, and they are more “perfect”) 21



Need to Separate the Issues• The fights at this point were about HOW the planets move

• There was no good explanation of WHY they move that way

• If someone could explain WHY they move that way, then maybe we can learn something close to the truth about the universe/nature

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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 a spinning Earth

Isaac Newton 1687



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Scientific MethodThe 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



Lecture on Chapter 4 now complete

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Outline for Unit 2: Physics We Need

Topics1. Light and Doppler Shifts2. Gravity, General Relativity and Dark

Matter3. Atomic Physics and Quantum

Mechanics4. Nuclear Physics and Chemistry5. Temperature and Thermal Equilibrium

Physics We NeedTopic 1: Light and Doppler Shifts


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Next Set of Topics: Physics We Need

Finished our introduction• Big and small things in the Universe

• Evidence and the Scientific Method

Next we move on learn some of the physics we need in order to understand why scientists have confidence in the Big Bang Theory



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Back to the Big Picture

Questions we’re trying to answer:• How did the Universe come into being?

• How did it evolve into what we know today?

• What is the evidence for all of this?



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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 Topics• Some stuff we need learn a little about:

1. Light and Doppler Shifts2. Gravity, General Relativity and Dark

Matter3. Atomic Physics and Quantum Mechanics4. Nuclear Physics and Chemistry5. Temperature and Thermal Equilibrium

• We won’t spend too long on each, just enough to get back to the big picture…

• Since there is no perfect way to present them (they all tie into each other) we’ll just start somewhere and get going…



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LightWhat we know about the universe comes from multiple places

One of the most important is from looking at both outer space and “inner” space

Need to know more about the “light we see”



Prep For Next Time – L7No one in back 4 rows and no laptops or cellphones• iClicker:

– Make sure to register by clicking on the link in eCampus (will be in the Home area)• Reading:

– BBBHNM Unit 2/Chapters 5-9: Was due already– Recommended Reading:

• See P3 of http://people.physics.tamu.edu/toback/109/Syllabus.pdf• Warmup Quizzes:

– (Warm-up Quizzes Parts 1-3)– Warm-up Quiz Part 4 (Peerceptiv): Will assign soon

• Pre-Lecture Reading Questions:– Unit 2 Text Submission: Will push due date to Friday before class

• Submit your 4 questions to TurnItIn in eCampus (under Turnitin Assignments). • Will post grades soon. Need 4 (and only 4) Excellent questions to pass.• Pass/Revise assignment. If you don’t pass we will set up dates for Revisions

after you get Feedback– Unit 2 Quiz: Will open up for you in eCampus AFTER they are graded and you get a

Pass. Also requires Unit 1 and EOC 3. Final due date not yet assigned • End-of-Chapter Quizzes

– EOC 4: Due before next clas

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