Big Bang, Black Holes, No Math - Texas A&M...

Physics We NeedTopic 1: Light and Doppler Shifts

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David TobackLectures 6 & 7



Prep For Today (is now due) – L7• 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 Quiz Part 4 (Peerceptiv): Will assign at the end of class today• Pre-Lecture Reading Questions:

– Unit 2 Question Submission: • First submission were due already. Grades posted• Pass/Revise assignment:

– Grades posted: 10 = Pass, 5 = Revise– If you don’t pass, follow the instructions in the PLRQ handout. Post your revised set of

questions to “PLRQ Unit 2 Revision”. If you don’t pass a second time, submit to “PLRQ Unit 2 – Revision 2”

– Currently due Monday before class. Let me know if you need an extension– Unit 2 Quiz:

• Open now if you have passed. Will assign today• Will open up for you in eCampus AFTER they are graded and you get a Pass. Also requires

you to have attempted Unit 1 and passed EOC 3. Final due date not yet assigned• End-of-Chapter Quizzes

– (Chapter 4)• Honors Section:

– In a heavy reading period, “Stage 0 idea” should have been Submitted– First meeting 3:30PM Friday. Will find a separate time for people who can’t meet then. – Need to hear from you at least once every 7 days 3



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The Topics• Some stuff we need to 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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Outline for Light

1. Light is a wave…2.…and a particle3. Light is REALLY fast,

but does have a finite speed

4.Doppler effect



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PhotonsWhat do we know about

photons?• Photons are a type

of fundamental particle– Like an electron

or a quark• Higher energy

smaller wavelength• Has no mass, but

does have energy– Aside for those of

you who are interested: It has momentum



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What Does This Have to do with Light?

• Since both sound and light are waves, the Doppler “Effect” applies equally to both – Normally can’t see this effect for light since its wavelength is small and its speed is fast

• Can in special cases:– Things need to be moving really fast, like stars and galaxies

– Need really good measuring devices like the ones Astronomers have



Doppler Effect and LightBlue Shift Sees light

with a smaller

wavelength

Red Shift Sees light

with a larger

wavelength

Galaxy moves to the

right

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• The light from galaxies moving away from us will appear to have longer wavelength light– The light is more Red, or

shifted to the Red side of the light spectrum

– “Red Shifted”• The light from galaxies

moving towards us will appear with shorter wavelength– The light is more Blue, or

shifted to the Blue side of the light spectrum

– “Blue Shifted”

Look at Light from Galaxies



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The Doppler Effect in Action

Doppler Effect



Three ObserversWhat does an object emitting light look like to

different observers when it is 1) Not moving2) Moving

Doppler Shift

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Look at some casesNext lets look at two cases where an “explosion”

occurs and things move away from that location

1. I stay at the explosion point, but the other stuff goes off into space (I’m at the “center” of the explosion)

2. I’m just one of the things that got blasted into space. I move along with them

1. How would this look to an outside observer?

2. How it would look to me in my reference frame?



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What it looks like when I’m stationary (or in my reference frame)

Case 1: Two Objects as they move away from an Explosion (I’m at the explosion site)



What it looks like when I’m moving relative to the

objects

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Case 2: Two Objects and Me Moving Away from the Explosion site (seen by someone else)



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Case 2: Two Objects and Me Moving Away from the Explosion Site (from my perspective)

Why were these cases important?Sorry… you’ll have to wait until we look at galaxies sending us light



Doppler Effect and Light: Summary

Compare the light coming from a car that’s parked and one that’s coming towards you

If a car is coming toward you with its lights on

1.The color of the light changes2.The speed of the light does

not! 42



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Putting It All TogetherSince stars can be billions of light-years away, and are moving quickly, we can use the Doppler effect on light to measure the speed and direction of all objects in the night sky – More in Chapter 10(Can also use it to tell us what Stars are made of, but for that we need to learn about quantum mechanics…)



Lecture on Chapter 5 now complete

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Outline for Unit 2: Physics We Need

1. Light and Doppler Shifts Done

2. Gravity, General Relativity and Dark MatterNext

3. Atomic Physics and Quantum Mechanics

4. Nuclear Physics and Chemistry5. Temperature and Thermal

Equilibrium


Physics We NeedTopic 2: Gravity

Heads Up: Paper 1• What is the evidence for Dark Matter?

• This will be the topic of Paper 1

• In order to understand the evidence, we next talk about gravity and Dark Matter

• Text will be due 1 week after we finish Chapter 6

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How the course is organized

Next few slides are on course organization,

grades etc…http://people.physics.tamu.edu/toback/109/CourseOrganization.pdf

(Pages 46-55) Andhttp://people.physics.tamu.edu/toback/109/ClassSchedule.pdf

• Paper Stuff

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Big Bang & Black Holes Course Organization Document

Papers

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Paper Topics and Due Dates• Papers will be announced before we start the chapter• Assigned after we finish the chapter• 4 Papers

– Paper 1: Evidence for Dark Matter• Assigned after Chapter 6, Typically week 5

– Paper 2: Evidence Stars are made of Atoms• Assigned after Chapter 8, Typically week 7

– Paper 3: Evidence Universe started with a Big Bang• Assigned after Chapter 12, Typically week 10

– Paper 4: Evidence for Black Holes• Assigned after Chapter 17, Typically week 14

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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 sides of a sheet of paper, double spaced)

•No citations! Use your own words•Only use information from the book•Text should be professional. You are “trusted guide” not a “buddy” or “comedian”

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Paper Format• Must follow expected Format

– Like the case a trial lawyer will make• Each paper is usually 5 paragraphs:

– Introduction paragraph that outlines the evidence• Lawyer’s opening statement

– 1 paragraph per piece of evidence (often, but not always, three)• Testimony from the expert witnesses

– Conclusion paragraph that ties it together• Lawyer’s closing arguments

people.physics.tamu.edu/toback/109/WritingAssignments/samplepaper.shtml

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Different than usual…• Each Paper Assignment has 3 Stages, all in Peerceptiv

1. Text Submission• Also submit to TurnItIn

2. Review (evaluate others text)• You are required to do 3 reviews• You can do these as soon as you submit

(assuming others have submitted before you to Review)

3. Back-evaluate your graders• You need to do this for each Review, but it can

only happen after your paper has been Reviewed• Your grade is based on quality of your text (graded on a curve), but you only get a grade if you pass the Review and Back-evaluation portions. If you don’t pass your Reviews the first time you will have to do more

• Actual dates from the Lecture notes50


Help Available for the Writing Stage

• We provide feedback on your paper if you submit a draft on eCampus in “Rough Drafts (Optional)” in TurnItIn– We aren’t going to correct grammar, or

just tell you what are missing to get an A• We have set things up so you can submit a revision (to the same assignment) but you will need to do a full set of Reviews and back-evaluations

• We also recommend going to the Writing Center

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Biggest reasons people don’t do well1. Don’t read all the hand-out instructions on

how to use Peerceptiv http://people.physics.tamu.edu/toback/109/WritingAssignments/Papers_and_Peerceptiv.pdf

2. Don’t read all the paper-specific instructions given in the assignment

• Hints given in addition to requirements3. Don’t do all the Peerceptiv stages and/or

Forget to submit to TurnItIn4. Don’t get help when you need it

• Go to the Writing Center• Submit a draft to the TA• Read the hints on the handouts

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Peerceptiv forPapers

In eCampushttp://people.physics.tamu.edu/toback/109/WritingAssignments/Papers_and_Peerceptiv.pdf

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Why are we using Peerceptiv?• Skills:

– People in the real world need to do multiple drafts of documents, often with others, until they are excellent

– People in the real world need to know how to tell the difference between an excellent document and a mediocre one

– People in the real world need to know how to give feedback on documents others have written that will help them get turned from being mediocre into something that is excellent

• How does this impact you?– You need to get good at this for after you graduate – Learn to better evaluate/improve your own work to ensure it

is excellent BEFORE you submit it for a grade

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Topics1. Light and Doppler Shifts Done2. Gravity, General Relativity and Dark

Matter Today3. Atomic Physics and Quantum

Mechanics After that4. Nuclear Physics and Chemistry5. Temperature and Thermal Equilibrium



What’s Next?

• Now that we have some understanding of photons/light we can use the knowledge to learn more 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

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The Two Great Theories•General Relativity:(Gravity) Predictions about the very large, from sizes of a few meters to the size of the universe (1024 miles across)

•Quantum Mechanics:Predictions about the very small (atoms, particles,<10-10 m)

Chapter 6

Chapter 7



Why Gravity Next?• Gravity tells us about the big stuff in the universe and how the big stuff is held together (plus a whole lot more)

• Also, with an understanding of gravity and light we can provide the evidence for Dark Matter

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Overview of Gravity and Dark Matter for the Course

1. What’s so important about Gravity?

2. Newton’s Theory of Gravity

3. Einstein’s more-correct version• Curved Space-

Time, and evidence for it

4. Dark Matter and Evidence for it



Paper 1

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• Abbreviated description: What is the evidence for Dark Matter? – More detail on Peerceptiv, 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 • Lawyers opening arguments at a Trial

– ~1 paragraph per piece of evidence/talking point• The case at a Trial

– Conclusion paragraph that ties it together• Lawyers closing arguments at a Trial

• Help:– Example of good paper

http://people.physics.tamu.edu/toback/109/WritingAssignments/samplepaper.shtml



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Taken from Peerceptiv for Paper 1



Reminders about Papers

Re-read pages 48-52 of the Course Organization Document

http://people.physics.tamu.edu/toback/109/CourseOrganization.pdf

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Topics1. Light and Doppler Shifts Done2. Gravity, General Relativity, and

Dark Matter Done3. Atomic Physics and Quantum

Mechanics Next4. Nuclear Physics and Chemistry5. Temperature and Thermal

Equilibrium



Prep For Next Time – L7• Reading:

– (Unit 2) • Warmup Quizzes:

– Read http://people.physics.tamu.edu/toback/109/WritingAssignments/Papers_and_Peerceptiv.pdf– Warm-up Quiz Part 4 (Peerceptiv), Quizzes 1 & 2: Due before class Monday

• Pre-Lecture Reading Questions:– Unit 2 Question Submission:

• First submission were due already. Grades posted• Pass/Revise assignment:

– Grades posted: 10 = Pass, 5 = Revise– If you don’t pass, follow the instructions in the PLRQ handout. Post your revised set of

questions to “PLRQ Unit 2 Revision”. If you don’t pass a second time, submit to “PLRQ Unit 2 – Revision 2”

– Currently due Monday before class. Let me know if you need an extension– Unit 2 Quiz:

• Open now if you have passed. Due Monday before class. Let me know if you need an extension

• Will open up for you in eCampus AFTER they are graded and you get a Pass. Also requires you to have attempted Unit 1 and passed EOC 3. Final due date not yet assigned

• End-of-Chapter Quizzes– If we finished Chapter 6 then End-of-Chapter Quiz 6 (else just Chapter 5a&b)

• Papers– Paper 1 will be assigned when we finish Chapter 6

• Honors Section:– In a heavy reading period, “Stage 0 idea” should have been Submitted– First meeting 3:30PM Friday. Will find a separate time for people who can’t meet then. – Need to hear from you at least once every 7 days

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