physics we need topic 1: light and doppler shifts big bang, black holes, no math 1 big bang, black...

Physics We NeedTopic 1: Light and Doppler Shifts

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David Toback

Lecture 6 & 7



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Prep For Today (is now due) – L6

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

•Pre-Lecture Reading Questions– Boot Camp Quizzes (already

due)– Unit 2: Stage 1 (due before

Class)– Unit 1 Revision (if needed): Will

send email after regrades finished

•End-of-Chapter Quizzes– Chapter 4



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•Reading:–(BBBHNM Unit 2)

•Pre-Lecture Reading Questions–Unit 2: Stage 2 (due before Class)

–Unit 1 Revision (if needed): Will send email after regrades finished

•End-of-Chapter Quizzes–Chapter 4



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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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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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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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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”



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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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Part 1: Light is a Wave

•The light we see is a “wave”, like waves on an ocean

•Best described by it’s wavelength



Why do we believe light is a wave?

•Water and Sound are also both waves–Does light behave like water or sound?

•Can “see” water waves hitting a wall and what happens to them when they hit two small openings in a wall



Water waves moving towards a wall

You are in the sky looking down at the waves as they go by

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Shine light from a laser at two small holes in a wall and see what

comes out on the wall behind itThe waves make patterns on the

wall the same way water waves do (Physics 202 & 208)



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The Wavelength of Light

•Shine white light at a prism and it breaks up into its different colors

•Each color has a different wavelength which we can measure



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Light is more than the colors we see

You may have thought of Radio Waves and X-rays as different things, but they are just light with different wavelengths



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Part 2: Light is a particle

•What if we look at smaller and smaller “amounts” of light?

•The light we see is actually LOTS of particles all moving together

•Call these Photons

Lots of photons where its

brightVery few photons where its

dark



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White Light = Lots of Different Color Photons



Another view…

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The Energy of ParticlesWe can think about Energy in many

ways• One way is the “energy of

motion” – Kinetic Energy in the language

of PHYS 201 and 218• For a particle (with mass) in

motion:– The higher the speed the

particle has, the more energy it has

– The more mass the particle has (the heavier it is) the more energy it has



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Clicker Question for Energy

Which has more energy? (Which will do more damage to a tree?)

1. A) A Prius moving at 10mi/hr or

B) An SUV at 10mi/hr?2. A) An SUV moving at 10mi/hr

or B) An SUV moving with

60mi/hr?3. A) A Prius moving at 60mi/hr

or B) An SUV moving at 10mi/hr?

C) Depends on the masses of the Prius and the SUV



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Photons

What do we know about photons?•Photons are a type of particle

–Like an electron or proton•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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A Particle and a Wave

•Actually it’s really more complicated than that

•Light is both a wave and a particle… can describe it as either… it has properties of both



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Part 3: The Speed of Light

“Not just a good idea, it’s the law!”



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Light has a Finite Speed

Light has been measured to have a specific speed –3 x 108 meters per second –186,000 miles per second–1 foot per nanosecond–Really FAST–The fastest speed allowed



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Maxwell’s Theory•1865: James Clerk Maxwell and others showed light was a wave and calculated its expected speed

•Gave the observed speed of light!–Confidence that his theories were correct

–We can now measure the speed of light to incredible precision

Physics 2082.99792458 x 108 m/s



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A Light-Year

•Some things are so far away that it’s easier to express their distance in light-years–Light travels at 3 x 108 meters/second and there are x 107 seconds/year ~1016 m in a light-year



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Time Machine• The Sun is 8 light-minutes away,

so we are seeing the Sun as it was 8 minutes AGO

• If a star is a light-year away and it must have taken a year for the light to get to us, we are observing the star the way it was a year ago

• If we look at light from something billions of light-years away, we are “observing” things that happened billions of years ago



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Part 4: The Doppler Effect

•1842: Christian Doppler

•What happens to waves when the “thing” creating the waves is moving towards us?–Or we’re moving towards it?

Physics 221



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Example with Sound From a Stationary Car

The sound we hear is actually a wave–Sound waves



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Now the Car is Moving

Things coming at us have their waves “scrunched up”

Things moving away have their waves “stretched”



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The Doppler “Effect” for Cars

Hears a LowerPitched Sound

Hears a Higher

Pitched Sound

A car blaring its horn and going past you will give the famous “Eeeeeeee-Yowwwwww” sound



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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



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Doppler Effect and Light

Blue Shift Sees light

with a smallerwavelen

gth

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



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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 cases

Next lets look at three cases where an “explosion” occurs and things expand from that point

1. I’m stationary and the exploding things are moving away from me (I’m the center of the explosion)

2. I’m moving along with the exploding things

3. Same as case 2, but how it would look to me in my reference frame



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Two Objects Moving Away from Me

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

frame)



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Two Objects Moving Away From Me

What it looks like when I’m moving relative to

the objects



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Same Thing: My Reference Frame

Why were these three cases important?

Sorry… you’ll have to wait until we look at galaxies

sending us light



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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 changes

2.The speed of the light does not!



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Putting It All Together

Since 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(Can also use it to tell us what Stars are made of, but for that we need to learn about quantum mechanics…)



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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 Chemistry

5. Temperature and Thermal Equilibrium



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Prep For Next Time – L6

•Reading:– (BBBHNM Unit 2)

•Pre-Lecture Reading Questions– Boot Camp Quizzes (already

due)– Unit 2: Stage 2 (due before

Class)– Unit 1 Revision (if needed): Will

send email after regrades finished

•End-of-Chapter Quizzes– If we finished Chapter 5 then

End-of-Chapter Quiz 5 (else just Chapter 4)



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Prep For Next Time – L7• Reading:

– (BBBHNM Unit 2)• Pre-Lecture Reading Questions

– Unit 2 Revision: Stage 1 (due before Class)

– Unit 1 Revision (if needed): Will send email after regrades finished

• End-of-Chapter Quizzes– If we finished Chapter 5 then End-of-

Chapter Quiz 5 (else just Chapter 4)



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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



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Clicker Quiz

Which of the following travels the fastest?

A.Radio wavesB.Gamma raysC.Red lightD.Blue lightE.They all move

at the same speed



Clicker QuizWe 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

usb) X and Y are moving away

from usc) X is moving towards us and Y

is moving away from usd) X is moving away from us and

Y is moving towards us

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Paper 0, Questions 1-51. 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.

2. 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.

3. 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.

4. 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.

5. 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 6-106. 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 making? It’s OK if the words “scientific method” and “evidence-based decision making” are not mentioned specifically.

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Paper 0, Questions 11-1511.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. 52



Paper 0, Questions 16-2016.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 choose No.

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Prep For Next Time – L7

•Reading:– (BBBHNM Unit 2)

•Pre-Lecture Reading Questions– eCampus quizzes (all 6)– Unit 1 Revision (if needed):

Stage 1 •Let us know if you were

misgraded– Unit 2: Stage 2

•End-of-Chapter Quizzes– If we finished Chapter 5 then

End-of-Chapter Quiz 5 (else just Chapter 4)



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• Reading: – BBBHNM Unit 2

• Pre-Lecture Reading Questions– eCampus quizzes (all 6)– Unit 1 Revision (if needed):

Stage 1 due date postponed until Monday•Let us know if you were misgraded

– Unit 2: Stage 1• End-of-Chapter Quizzes

– Chapter 4



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• Reading: – (BBBHNM Unit 2)

• Pre-Lecture Reading Questions– eCampus quizzes (all 6)

•Many of you need to check these

– Unit 1 Revision (if needed): Stage 1•Let us know if you were misgraded

– Unit 2: Stage 2• End-of-Chapter Quizzes

– (Chapter 4)



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– Required: BBBHNM Unit 2– Recommended Reading:

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

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

due Monday before class– Unit 2: Stage 2 due Monday before class

• End-of-Chapter Quizzes– If we finished Chapter 5 then End-of-

Chapter Quiz 5 (else, just through Chapter 4)



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– Required: BBBHNM Unit 2– Recommended Reading:

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

• Pre-Lecture Reading Questions– Unit 1 Revision: Let me know if you were

misgraded– Unit 2: Let me know if you were misgraded– Unit 2 Revision (if desired): Stage 1 due

Monday before class• End-of-Chapter Quizzes

– If we finished Chapter 5 then End-of-Chapter Quiz 5 (else, just through Chapter 4)



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Was due today – L7• Reading:

– BBBHNM: All reading through Chapter 6

• Pre-Lecture Reading Questions:– All reading questions through

Chapter 6• End-of-Chapter Quizzes:

– All end-of-chapter quizzes through 4• Papers:

– Should have been working on Paper 0

– Read the “Writing Prompt” and other stuff on CPR



Paper 1 Stuff• I have extended the due date until

Friday at 5:45PM• Want feedback before turning it in?

– Post it in eLearning in .doc (or .pdf) for comments by the TA by 5PM tomorrow

– Make sure you polish it•If you have lots of grammar and spelling mistakes we’ll just make you resubmit it

– Will be due in CPR and turnitin.com in one week 60



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Prep for Next Time – L6

• Reading: – BBBHNM 6

•Recommended: BHOT 4-6• Reading questions

– Two questions from Chapter 6 or the recommended reading

• End-of-Chapter Quizzes– If we finished Chapter 5 then

end-of-chapter quiz 5 (else just 4)

• Be working on Paper 1



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Prep for Next Time – L7

• Reading: – None

• Reading questions– None

• End-of-Chapter Quizzes– If we finished Chapter 5 then

end-of-chapter quiz 5 (else just 4)

• Paper 1– Phase II is due Friday at 5:45PM



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Prep For Next Time – L6• Note: May change depending on how far we

get in lecture• Reading

– BBBHNM: None• Reading Questions:

– None• End-of-Chapter Quizzes

– If we finished Chapter 5 then end-of-chapter quiz 5 (else just up to Chapter 4)

• Paper Stuff– Paper 0 in CPR and turnitin.com before

class– Will talk more about Calibrations next time



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Prep For Next Time – L7• Note: May change depending on how far we

get in lecture• Reading

– BBBHNM: None• Reading Questions:

– None• End-of-Chapter Quizzes

– If we finished Chapter 5 then end-of-chapter quiz 5 (else just up to Chapter 4)

• Paper Stuff– Paper 0 in CPR and turnitin.com before

class– Will talk more about Calibrations next time



Full set of Readings So Far

•Required:–BBBHNM: Chap 1-6

•Recommended:–BHOT: Chap. 1-6–SHU: Chap. 1-3–TOE: Chap. 1

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Prep for Today (is due now) – L6

•Reading:–BBBHNM: Chap 5

•Reading Questions:–Two questions from Chapter 5 or the recommended reading




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Prep for Today (is due now) – L7

•Reading:–BBBHNM: Chap 6

•Reading Questions:–Two questions from Chapter 6 or the recommended reading


•Paper 1–Phase I (CPR and turnitin) was due Friday

–Phase II (Calibrations) due Friday at 5:45



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• How do waves behave?

• Water waves and Sound waves

• Can “see” water waves hitting a wall and what happens to them when they hit two small openings in a wall

Big Waves Here

Small Waves Here

Waves move this way



Phase I, Phase II and Phase IIIPhase I: (Paper due 1 week after we finish

Chapter 4)• Turn in a polished draft to eLearning• 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 eLearning

Phase III: (Due one week after Phase II)• Calibrations and Reviewing due one week after

you submit

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eLearning Quizzes – L8

•You are expected to be working on the quizzes on eLearning

•You cannot pass this course without having gotten a perfect score on all of them

•You make take as many of each quiz as you like to get perfect scores without penalty

•Due before the class AFTER we finish a chapter



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In-Class Quizzes

•Turn in your two questions on the reading

•During class you will write down two more–This is a separate quiz

• If you didn’t get a grade you wanted on one of the first few reading quizzes see me about trying again



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What if we look more closely?

•What if we look at smaller and smaller “amounts” of light?

•The light we see is actually LOTS of particles all moving together

•Call these Photons

LOTS of photons

Lots of photonsA few photons



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In-Class Writing Assignment

Write down, during the course of lecture,

Two questions you want to know the

answer to



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Reading

Full reading so far:• BBBHNM: Chap 1-6• Prelude • BHOT: Chap. 1-6, 9 and 11

(117-122)• SHU: Chap. 1-3, 6, 7 (up-to-

page 153)• TOE: Chap. 1



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Before we start the next topic

•Don’t forget to take your eLearning quizzes

– Can’t pass the course without getting 100% on all of them

•Make sure your name and DATE are on EVERYTHING you turn in



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How do we answer these questions?

As previously discussed we have two avenues:

•Theory•ExperimentWhat do both have to say about Light?



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Light as a Wave



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Quiz

•What time is lecture on Wednesday?

•Where are we meeting?

–Name–Today’s date



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Before we begin

• As a special treat the class will attend a special Department of Physics colloquium on the LHC this Wednesday (Sept 17th)

• Class will start at 4PM in the teaching wing of the Engineering/Physics building, room 202 (big class room)

• Class will be over by 5PM• You will be expected to sign in

with me or Mike as your in class quiz



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Light is more than the colors we see

X-raysRadio WavesInfrared

Visiblecolor

Ultraviolet Microwaves



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In-Class Writing Assignment

Write down, during the course of lecture

Two questions you want to know the

answer to



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WebCT

• It has come to my attention that people are not finishing the quizzes in WebCT

• If they don’t get finished we will start requiring people to do them in Recitation to help enforce that they are done– You should be done with Quizzes

1-3 now– Done with Quizzes 4-6 by the

end of next week



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A Different Example

It is as if a traveling salesman were to send a letter home once a week during his travels

• While he is traveling away from home, each successive letter will have a little farther to go than the one the week before Letters will arrive a little more than a week apart

• On the way home each successive letter will have a shortest distance to travel will arrive more frequently than once a week



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Old beliefs•Light is so fast that people used to believe that it was simply instantaneous

•You can measure the speed of sound pretty easily–Listen to the alumni side at a football game. When they sing, they’re always LATE!

•Couldn’t answer the question with an experiment until 1600’s



85

Why do we believe it has a finite speed?

• Danish Astronomer Ole Christian Roemer in 1676

• Moons of Jupiter are helpful again!

• Look at the eclipses of the moons of Jupiter as it moves towards us and away from us

We can measure this really

accurately now, but that’s another

story…



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Eclipses of the Jupiter’s MoonNow you see

it!

Now you don’t!



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Measure the Time Between Eclipses

•When Jupiter is moving towards us we get shorter times between eclipses

•When Jupiter is moving away from us we get longer times between eclipses



88



89

Announcements

•Recitation tomorrow in ENPH 210

•No office hours today–Call/email if you need to meet

•WebCT Quizzez



90

Light: Wave and Particle



91



92

•Stars can be billions of light years away!

•Binary system: SHU p68•Had a way of measuring both the direction and speed of travel of every source of light in the night sky



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94



95

• However, in reality they are separate particles (feynman diagram?) and each photon interacts with an atom individually. Again a diagram?

•Individual interacting with an atom (Figure here)



96

•Question: How do we measure the distance to Jupiter?



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98

Doppler Effect and Light

Replace with P65 from SHU

• Galaxies moving towards us have shorter wavelength light•The light is more Blue, or

shifted to the Blue side of the light spectrum

•“Blue Shifted”• Galaxies moving away from

us have longer wavelength light•The light is more Red, or

shifted to the Red side of the light spectrum

•“Red Shifted”



99



100



101

•We know the Doppler effect in sound… Both volume and pitch change. Picture SHU p65



102


•Shine white light at a prism and it breaks up into its different colors

•These different colors are waves with different wavelengths



103

Light is a wave

The light we see is a “wave” and it is best described by it’s wavelength



104



105



106



107



108

•This is a test

physics we need topic 1: light and doppler shifts big bang, black holes, no math 1 big bang, black...

Documents

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introduction big

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overview of physics

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