Introduction Topic 4: Scientific Methods Big Bang, Black Holes, No Math 1 Big Bang, Black Holes, No...

IntroductionTopic 4: Scientific Methods

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David Toback

Lecture 5 & 6



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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 Today (is now due) – L6

•Reading: –BBBHNM Unit 2 (Chapters 5-9)

•Pre-Lecture Reading Questions–Unit 1 Revision (if needed): Stage 1–Unit 2: Stage 1

•End-of-Chapter Quizzes–(Chapters 2 and 3)



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/109/109FAQ.shtml#CPRGrades

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Next Topic: Scientific Methods

Unit 1:1. Introduction Done2. Going Big Done3. Going Small Done4. Evidence and the Scientific

MethodToday 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 method

3. Need to learn some physics

}Today

}Next Unit



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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 Matter3. Atomic Physics and Quantum

Mechanics4. Nuclear Physics and Chemistry5. Temperature and Thermal

EquilibriumWon’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 Questions and how do we go about answering them?

• Scientific Method–How do we know what we know? –What is the evidence for the

“facts” we heard growing up?•E.g .Earth goes around the Sun

–Observation (looking at the heavens)



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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

•As you’ve already seen, the world is incredibly complex and much of it is different from what we experience



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 10



Fun Videos of Just the Stars

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Start with things you can see with your own eyes!Video of stars moving with Polaris (north star) at the centerhttps://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 mini-orbits way out there (epicycles)… Hmmm…



Looking at Mars in the Stars

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How Ptolemy envisioned it

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/ptolemy.model.swf

•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)



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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???

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/mars_retrograde_motion.swf

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?



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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 telescopes



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Data Provides Evidence

•Discover 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 versions of

how Venus is predicted to move in space

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The Phases of Venus

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•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



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…

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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” the orbits are ellipses (and why we don’t fall off a spinning Earth)

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



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…



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 “Sun is setting”

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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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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



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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.pdf

• 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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Clicker QuizA 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 QuizQ: What does it mean for an electron to

be "stable?"a)It is balanced with exactly one protonb)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 evere)They don't appear to be made of

anything smaller



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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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



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



Phase I, Phase II and Phase IIIPhase 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 gradePhase 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 – L9faculty.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)



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? 56



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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

Introduction Topic 4: Scientific Methods Big Bang, Black Holes, No Math 1 Big Bang, Black Holes, No...

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