Transcript Slide 1
Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 7 & 8
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 1
Prep For Today (is now due) – L7
• 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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 2
Prep For Today (is now due) – L8
• 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)
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 3
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 Holes, No Math Topic 1: Light and Doppler Shifts 4
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 5
The Topics
• Some stuff we need learn a little 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
• 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 6
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?
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 7
Light
What we know about 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” Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 8
Outline for Light
1. Light is a wave… 2. …and a particle 3. Light is REALLY fast, but does have a finite speed 4. Doppler effect
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 9
Part 1: Light is a Wave
•The light we see is a “wave”, like
waves on an ocean
•Best described by it’s wavelength
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 10
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts
Water waves moving towards a wall
You are in the sky looking down at the waves as they go by Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 12
Why do we believe light is a wave?
Shine light from a laser at two small holes in a wall and see what comes out on the wall behind it The waves make patterns on the wall the same way water waves do Big Bang, Black Holes, No Math (Physics 202 & 208) 13
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 Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 14
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 15
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts Lots of photons where its bright Very few photons where its dark
White Light = Lots of Different Color Photons Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 17
Another view…
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 18
The Energy of Particles
We 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 19
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
Big Bang, Black Holes, No Math Topic 1: Light and Doppler Shifts 20
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 21
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 22
Part 3: The Speed of Light
“Not just a good idea, it’s the law!”
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 23
Light has a Finite Speed
Light has been measured to have a specific speed
–3 x 10
8
meters per second
–186,000 miles per second –1 foot per nanosecond –Really FAST –The fastest speed allowed
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 24
Maxwell’s Theory
Maxwell and others wave and calculated its expected speed
• Gave the observed
speed of light!
theories were correct
– We can now measure
incredible precision Physics 208 2.99792458 x 10 8 Big Bang, Black Holes, No Math m/s Topic 1: Light and Doppler Shifts 25
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 10
are
p
x 10
7 8
meters/second and there seconds/year
~10
16
m in a light-year
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 26
Time Machine
• The Sun is 8 light-minutes away, so we
are seeing the Sun as it was 8 minute 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 27
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?
Big Bang, Black Holes, No Math Physics 221 Physics We Need Topic 1: Light and Doppler Shifts 28
Example with Sound From a Stationary Car The sound we hear is actually a wave
–Sound waves
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 29
Now the Car is Moving
Things moving away have their waves “stretched” Things coming at us have their waves “scrunched up” Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 30
The Doppler “Effect” for Cars
Hears a Lower Pitched Sound Hears a Higher Pitched Sound A car blaring its horn and going past you will give the famous “Eeeeeeee-Yowwwwww” sound 31
What Does This Have to 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 32
Doppler Effect and Light
Red Shift
Sees light with a
larger
wavelength Galaxy moves to the right
Blue Shift
Sees light with a
smaller
wavelength Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 33
Look at Light from Galaxies
Big Bang, Black Holes, No Math
• The light from galaxies
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”
Topic 1: Light and Doppler Shifts 34
The Doppler Effect in Action
Doppler Effect
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 35
Three Observers
What does an object emitting light look like to different observers when it is 1) Not moving 2) Moving
Doppler Shift
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 36
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 37
Two Objects Moving Away from Me
What it looks like when I’m stationary (or in my reference frame)
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 38
Two Objects Moving Away From Me
What it looks like when I’m moving relative to the objects
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 39
Same Thing: My Reference Frame
Why were these three cases important?
Sorry… you’ll have to wait until we Big Bang, Black Holes, No Math 40
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
c o l o r
of the light changes 2.The speed of the light does not!
Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 41
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…) Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 42
Outline for Unit 2: Physics We Need 1. Light and Doppler Shifts
Done 2. Gravity, General Relativity and Dark Matter Mechanics Equilibrium
Next 3. Atomic Physics and Quantum 4. Nuclear Physics and Chemistry 5. Temperature and Thermal Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 43
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) Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 44
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 45
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 ever smaller -19 m) d) Undisturbed, it can go on living forever and e) They don't appear to be made of anything Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 46
Clicker Quiz
Which of the following travels the fastest?
A. Radio waves B. Gamma rays C. Red light D. Blue light E. They all move at the same speed 47
Clicker Quiz
We 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 us b) X and Y are moving away from us c) X is moving towards us and Y is moving away from us d) X is moving away from us and Y is moving towards us Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 48
Paper 0, Questions 1-5
1. 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 49
Paper 0, Questions 6-10
6. 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 50
Paper 0, Questions 11-15
11. 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.
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 51
Paper 0, Questions 16-20
16.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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 52
Prep For Next Time – L6
• Reading: – 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) Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 53
Prep For Next Time – L7
• Reading: – 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) Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 54
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 55
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 56
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 57
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 58
Prep For Next Time – L6
• Note: May change depending on how far we get in • 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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 59
Prep For Next Time – L7
• Note: May change depending on how far we get in • 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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 60
Full set of Readings So Far
•Required: –BBBHNM: Chap 1-
6
•Recommended: – BHOT: Chap. 1-
6
– SHU: Chap. 1-
3
– TOE: Chap. 1
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 61
Prep for Today (is due now) – L6
•Reading: –BBBHNM: Chap 5 •Reading Questions: –Two questions from Chapter 5
or the recommended reading
•End-of-Chapter Quizzes –Chapter 4
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 62
Prep for Today (is due now) – L7
• Reading: – BBBHNM: Chap 6 • Reading Questions: – Two questions from Chapter 6 or the
recommended reading
• End-of-Chapter Quizzes – Chapter 4 • Paper 1 – Phase I (CPR and turnitin) was due Friday – Phase II (Calibrations) due Friday at 5:45
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 63
Why do we believe light is a wave?
• How do waves
behave?
• Water waves and
Sound waves
• Can “see” water
waves hitting a wall and what when they hit wall Big Bang, Black Holes, No Math Waves move this way happens to them two small openings in a Big Waves Here Small Waves Here Physics We Need Topic 1: Light and Doppler Shifts 64
Phase I, Phase II and Phase III
Phase 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 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 eLearning Phase III: (Due one week after Phase II)
• Calibrations and Reviewing due one week after you
submit Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 65
eLearning Quizzes – L8
• You are expected to be working on • 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 66
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 67
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
Big Bang, Black Holes, No Math LOTS of photons Lots of photons Physics We Need Topic 1: Light and Doppler Shifts A few photons 68
In-Class Writing Assignment
Write down, during the course of lecture,
Two questions you want to know the answer to
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 69
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 70
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
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 71
How do we answer these questions?
As previously discussed we have two avenues:
• Theory • Experiment
What do both have to say about Light?
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 72
Light as a Wave
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 73
Quiz
• What time is lecture on
Wednesday?
• Where are we meeting? –Name –Today’s date
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 74
Before we begin
• As a special treat the class will attend
a special Department of Physics colloquium on the LHC this Wednesday (Sept 17 th )
• 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 75
Light is more than the colors we see X-rays Ultraviolet Visible
c o l o r
Microwaves Infrared Radio Waves Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 76
In-Class Writing Assignment
Write down, during the course of lecture
Two questions you want to know the answer to
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 77
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 78
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
a week
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 79
Old beliefs
•Light is so fast that people used to
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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 80
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 Big Bang, Black Holes, No Math
We can measure this really accurately now, but that’s another story…
Physics We Need Topic 1: Light and Doppler Shifts 81
Eclipses of the Jupiter’s Moon Now you see it!
Now you don’t!
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 82
Measure the Time Between Eclipses
•When Jupiter is
us we get shorter times between eclipses
•When Jupiter is
moving away from us we get longer times between eclipses Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 83
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 84
Announcements
• Recitation tomorrow in ENPH
210
• No office hours today –Call/email if you need to meet • WebCT Quizzez
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Light: Wave and Particle
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• 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 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 88
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 89
Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 90
• 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) Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 91
• Question: How do we measure
the distance to Jupiter?
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Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 93
Doppler Effect and Light
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 • “Red Shifted”
Big Bang, Black Holes, No Math Replace with P65 from SHU Physics We Need Topic 1: Light and Doppler Shifts 94
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• We know the Doppler effect in
sound… Both volume and pitch change. Picture SHU p65 Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 97
Why do we believe light is a wave?
• Shine white light
at a prism and it breaks up into its different colors
• These different
colors are waves with different wavelengths Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 98
Light is a wave
The light we see is a “wave” and it is best described by it’s wavelength Big Bang, Black Holes, No Math Physics We Need Topic 1: Light and Doppler Shifts 99
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• This is a test
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