1. Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr
Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 10, 11 & 12

2. Was Due for Today – L10 Reading: (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
Let us know if you have been misgraded
Unit 1 Revision: New grades posted soon.
Unit 2 Revision (if desired): Stage 2
End-of-Chapter Quizzes:
Chapter 6
Paper 1:
Stage 1 due Monday before class
Can submit a draft for feedback on eCampus if you like
MUST submit to turnitin on eCampus

3. Was Due for Today – L11 Reading: (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
Let us know if you have been misgraded
Unit 1 Revision: Grades posted soon (still doing regrades)
Unit 2 Revision (if desired): Stage 2
End-of-Chapter Quizzes:
Chapter 6
Paper 1:
Stage 1 due Monday before class
MUST submit to turnitin on eCampus
Honors Paper:
Stage 0 due today

4. Was Due for Today – L12 Reading: (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
Let us know if you have been misgraded
Unit 1 Revision: Grades posted
sent about how to pass if you haven’t passed already
End-of-Chapter Quizzes:
Chapter 6
Paper 1:
Stage 1 in CPR and turnitin on eCampus
Honors Paper:
Stage 1 due March 11th

5. 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 Dark Matter
Will be due 1 week after we finish Chapter 6

6. Papers in CPR/Schedule
Schedule is Like PLRQ since it is in CPR:
Each Paper has 4 (or 6) Steps:
Mentioned after we start the chapter (just did that)
Assigned after we finish the chapter
Submit text 1 week later (Stage 1)
Calibrations/Reviews/Self-Assessment due the week after that (Stage 2)
Revision (optional): Stage 1 due one week later
If you did a Stage 1, Calibrations/Reviews/Self-Assessment due one week after that

7. Style of the Paper
Explain it to someone who isn’t taking the class (no jargon)
~600 words (This is the equivalent of both side of a sheet of paper, double spaced)
No citations! Use your own words
Text should be professional. You are “trusted guide” not a “buddy” or “comedian”

8. Paper Format Must follow expected Format Usually 5 paragraphs. Needs:
Introduction paragraph
1 paragraph per piece of evidence (3 total?)
Conclusion paragraph that ties it together

9. Help Available for Stage I
Submit a draft for feedback from the TA
Submit on eCampus in “Rough Drafts (Optional)”
Drafts due Friday at midnight
If you submit late, we can try to give feedback but we can’t guarantee it
We also recommend going to the writing center

10. Biggest reason people don’t do well
Read ALL the instructions on CPR
See the FAQ on papers
Don’t forget to submit to turnitin.com

11. Best Guess Schedule Paper 1: Text due 10/1 (Ch 6)
Honors Stage 0 (not in CPR): Due 10/6

12. So Far Topics Light and Doppler Shifts  Done
Gravity, General Relativity and Dark Matter Done
Atomic Physics and Quantum Mechanics  Now
Nuclear Physics and Chemistry
Temperature and Thermal Equilibrium

13. Where We Are Going Next
In Chapter 3 we learned a little about how the stuff of the Universe is put together
Big things are made from LOTS of small things
Small things: The Fundamental Building Blocks of Nature
What is the “stuff” in atoms?

14. The Largest Stuff Most of the light we see from space comes from stars
What are stars made of?
Stars are lots of atoms interacting
The ways they interact creates light we can see
Can study the distant stars by looking at the light from them
Can study atoms here on Earth. Are they the same?

15. How do Atoms work? ElectroMagnetism (electric charge)
What holds electrons and protons together
Quantum Mechanics
The funny way atoms form
Electrons in orbits
Atoms absorbing and emitting photons (light)
Chapter 7

16. Different Types of Atoms
Chapter 8
The Strong Force
Keeps protons and neutrons together in the atomic nucleus
Different types of nuclei  different types of atoms
Different atoms  Different light…
Nuclear Physics and Chemistry
Studying the Stars using their light
Spectral lines of the atoms
Atomic “fingerprints”
The light we see from the stars

17. Overview of the story Big things are made from LOTS of small things
Small things: The Fundamental Building Blocks of Nature
What is the “stuff” in atoms
ElectroMagnetism (electric charge)
What holds electrons and protons together
Quantum Mechanics
Why atoms form the way they do
Electron in orbits
Atoms absorbing and emitting photons (light)
The Strong Force
Keeps protons and neutrons together
Different types of nuclei  different types of atoms
Different atoms  Different light…
Nuclear Physics and Chemistry Different TYPES of Atoms
Studying the Stars using their light
Spectral lines of the atoms
Atomic “fingerprints”
The light we see from the stars
This
Lecture
Next
Lecture

18. The Fundamental Building Blocks
Our best understanding:
The very BIG stuff is made up of LOTS of very small stuff
Need to understand:
What are the fundamental building blocks of nature
How it’s all held together
How they “create” the light we see

19. Early evidence for the Atomic Model
Experiment
(1910’s):
Shoot atoms at a “target”
Theory: 1?
Bag stuffed with cotton 2?
Bag stuffed with cotton and a few small rocks
The experiment gives results like #2!
The positive charge in an atom and most of its mass is concentrated in a tiny, very dense center: The Nucleus

20. The Building Blocks of Nature
In the 19-teens and 20’s experiments determined:
Atoms are made of a nucleus surrounded by electrons
Many types of nuclei
Only one kind of electron

21. Nuclear Physics
Many years later (using many of the same methods):
Nucleus is composed of neutrons and protons
Number of protons and neutrons in the nucleus determines the atom type

22. The Fundamental Building Blocks of Nature
Electrons
Neutrons
Protons
Neutrons and Protons are really made of quarks
Discovered in the 1970’s
We’ll talk more about this in the next chapter
Talked about this in Chapter 3
More in Chapter 8

23. Putting Them Together
How do we put these fundamental building blocks together to form atoms?

24. Overview of the story This Lecture Next Lecture
Big things are made from LOTS of small things
Small things: The Fundamental Building Blocks of Nature
What is the “stuff” in atoms
ElectroMagnetism (electric charge)
What holds electrons and protons together
Quantum Mechanics
Why atoms form the way they do
Electron in orbits
Atoms absorbing and emitting photons (light)
The Strong Force
Keeping protons and neutrons together
Different kinds of nuclei
Nuclear Physics and Chemistry  different atoms
Spectral lines of the atoms
Atomic “fingerprints”
The light we see from the stars
This
Lecture
Next
Lecture

25. ElectroMagnetism
You probably already know that protons and electrons have “electric” charges
Positive charge and negative charge attract each other
Call this ElectroMagnetism + -

26. Weirdness…
You probably never thought about it this way but in many ways the way things with electric charge attract is the same as in gravity + -

27. Gravity vs. ElectroMagnetism
Every object in the universe attracts every other object in the universe
The bigger the mass, the bigger the attraction
The further the distance between the objects, the smaller the attraction
ElectroMagnetism
Every charged object in the universe “attracts” every other charged object in the universe
The bigger the charge, the bigger the attraction
The further the distance between the objects, the smaller the attraction
Physics 201
Physics 218
Physics 202
Physics 208

28. What’s different? Gravity: All objects attract no matter what
(As far as we know…)
ElectroMagnetism:
Ignores neutral particles

29. Other Differences ElectroMagnetism is MUCH stronger than gravity
If I have two electrons, the electric force between them is so powerful that it is 1042 times stronger than gravity
Can “ignore” gravity inside atoms

30. Aside ElectroMagnetism is MUCH weaker than the Strong Force
For two quarks inside a proton the Strong Force is ~100 times stronger than the EM force
Can almost “ignore” EM inside protons

31. Atomic Physics How do we make up atoms?
Start with a simple (partially wrong) atomic model
Positive Nucleus attracts the negatively charged electrons and keeps them in “orbit”
Then move to the weird world of Quantum Mechanics

32. The simplest atom: Hydrogen
A Hydrogen Atom
The simplest atom: Hydrogen
One electron and one proton
(Partially wrong)
Figure not to scale - +
| |
~10-15 m
| ~10-10 m |

33. Is the world this simple?
This is a nice simple model
Why does the electron stay in “orbit”?
Simple (partially wrong) answer: There is a “Force” that keeps it in orbit just like Gravity keeps the Earth orbiting the Sun

34. Problem
ElectroMagnitism says electrons slow down when they move in circles
Observe this for electrons moving in big circles
Should be true for electrons in small circles (atoms) also
 Spiral down until they hit the nucleus and we’d have nothing: No atoms!
Would take ~10 picoseconds (10-11s)

35. Another Problem
Stars can be in orbit any distance from the center of the galaxy
Depends only on their speed
Electrons should, depending on their speed, be able to be almost anywhere near the nucleus (like a planet or a comet)
Don’t observe this… Only specific distances from the nucleus

36. Overview of the story This Lecture Next Lecture
Big things are made from LOTS of small things
Small things: The Fundamental Building Blocks of Nature
What is the “stuff” in atoms
ElectroMagnetism (electric charge)
What holds electrons and protons together
Quantum Mechanics
Why atoms form the way they do
Electron in orbits
Atoms absorbing and emitting photons (light)
Different TYPES of Atoms
The Strong Force
Keeping protons and neutrons together (atomic nuclei)
Nuclear Physics and Chemistry
Different atoms  Different light…
Studying the Stars using their light
Spectral lines of the atoms
Atomic “fingerprints”
The light we see from the stars
This
Lecture
Next
Lecture

37. Quantum Mechanics
How do we explain these weird features that we observe about Atoms?
Quantum Mechanics!
LOTS we COULD say about QM, but since we could spend years on this we’ll focus only on the most important points you need

38. Quantum Mechanics Two big issues:
All particles can be described both as particles AND waves
Saw this for photons
True for electrons (and protons etc.) also!
In atoms: Electrons can ONLY be in one of the available energy states, and at certain distances from the nucleus
Keep atoms from collapsing! (Good!)
“Quantizes” the interactions with light i.e. only some energy photons interact with atoms

39. Energy of Electron Waves
Small energy electron have large wavelengths
Small wavelength electrons have large energy

40. Only Orbits with Specific Wavelengths Work
The electron “wave” has to go all the way around
Can have one peak/trough, two peaks/troughs, three peaks/troughts etc…
A quantized number
The Quantum in Quantum Mechanics

41. Only Orbits with Specific Wavelengths Work
Lower Energy and closer to the nucleus
Higher Energy and further away from the nucleus

42. Energy and Distance from The Nucleus
Higher Energy and further away from the nucleus
Lower Energy and closer to the nucleus
Only these levels are allowed!

43. How Photons Interact with an Atom
To understand better how photons interact with the stuff in an atom, “how we’ll SEE atoms”, we need to say a bit more about Energy and about Quantum Mechanics
Lots of different ways they can interact… start with the simple interactions

44. Simple: Photon-Atom Collision
Before: Start with a high energy photon and a low energy atom
After: Lower energy photon, higher energy atom (like two billiard balls colliding)
Same TOTAL energy before and after collision
Conservation of Energy

45. Clicker Question
After a collision with a stationary atom, the energy of a photon is
Higher
Lower
Same

46. Clicker Question
After a collision with a stationary atom, the speed of a photon is
Higher
Lower
Same

47. Clicker Question
After a collision with a stationary atom, the wavelength of a photon is
Longer
Shorter
Same

48. Atom-Photon Perspective
Photon’s perspective: I collide with a low energy atom and “transfer” some of my energy
Atom’s perspective: I collide with a high energy photon and “take” some of its energy

49. Quantum Mechanics and EM
In General Relativity we found that it is better to describe the “force” of gravity as the curvature of space-time
How do we “better” describe ElectroMagnetism, especially with Quantum Mechanics?
Electric fields
Answer: In ElectroMagnetism “Force” is essentially all about the “emission” and “absorption” of photons by charged particles like electrons and protons

50. Quantum Mechanics – Force Carriers
Think of the force between electrically charged things as being caused by the exchange of “virtual” photons
The force, or interaction, is “carried” by particles

51. Example with Two Electrons
First electron emits a “force-carrying” particle (a photon)
Causes a recoil of the first electron
You shoot a gun and lurch back
The other electron “catches” it and gets “banged”
Your friend gets hit with the bullet and falls backward
Net result: The two particles move differently, “as if” there were a force between them

52. Visualizing Our Analogy
1: Two electrons hanging out
2: electron on the right “emits” a photon and “recoils” - -
3: Photon bangs into the left electron and bumps it
Both now move apart: Same sign charges “repel” each other

53. A Proton and Electron 1: A proton and an electron hanging out
2: Proton on the right “emits” a photon and “recoils” - +
3: Photon bangs into the electron
Doesn’t transfer Momentum
Transfers information on how to move
Opposite signs attract
For those of you who know a little bit, this is how “electric fields” work

54. More Interactions
Can also get electrons and protons interacting with REAL photons
Photons we can see, as opposed to ones that are emitted then absorbed never to be seen outside the interaction
Real photons can be emitted or absorbed

55. Electron and Photon Interacting
Electron can “absorb” a photon
 Electron becomes more energetic -

56. Electron Emitting a Photon
Electron can “emit” a photon
 Electron becomes less energetic -

57. A Simple way of drawing things: Feynman Diagrams
Electron can “absorb” a photon  becomes more energetic
Electron can “emit” a photon  becomes less energetic e e e e g g

58. Feynman Diagram for an Atom
A diagram of how the particles “talk” to each other
These two are attracted
Hydrogen Atom P P g e- e-

59. Photon and Atom
If a photon with the right energy hits an atom and is absorbed, the electron can “jump” to an “excited state”

60. Excited Atom Emits a Photon
If an atom is in an excited state, it’s just a matter of time before it emits a photon with exactly the energy between the two states

61. Other ways of drawing the same thing
An electron can move into a more energetic orbit when it absorbs a real photon with exactly the right energy
The photon is absorbed, and the electron goes into an excited state
A high energy atom can “emit” a photon and go into a lower energy state

62. A Proton bumps into an atom and excites it
Atom in a Higher Energy State
Atom in Lowest Energy State
Proton

63. An Excited Atom Emits a Photon
Atom in Lowest State
Atom in a high Energy State
Photon with a specific energy

64. Absorbing and Emitting a Photon

65. Lots of Different Energy States

66. Photons and Atoms Photons can interact with Atoms in three ways
Very low energy photon: Because the electron in the atoms can only have quantized states around the nucleus VERY low energy photons will be ignored, or bump the path of the atom
Ignoring is a kind of interaction
If an atom encounters a photon with the “right energy” photon it can get “excited” and go into a higher energy state. Photon is absorbed and is gone forever
If a REALLY energetic photon comes along it can completely knock an electron out of orbit from a nucleus

67. Putting it All Together
A cartoon of an atom and a photon
Note: The electron being completely out of the atom is a perfectly good “energy state”

68. Atomic Transitions
Any photon that hits the atom with the right energy will be absorbed
Absorbs only special colors

69. How is this helpful? Atomic Fingerprinting
Can look at light from a light bulb
 all colors observed
Look at light from a light bulb with Hydrogen gas in the way
Only special colors will be absorbed!
Atomic Fingerprinting

70. Outline for Unit 2: Physics We Need
Light and Doppler Shifts Done
Gravity, General Relativity and Dark Matter Done
Atomic Physics and Quantum Mechanics Done
Nuclear Physics and Chemistry  Next
Temperature and Thermal Equilibrium

71. Prep For Next Time – L10 Reading: (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
Let us know if you have been misgraded
Unit 1 Revision: New grades posted soon.
Unit 2 Revision (if desired): Stage 2
End-of-Chapter Quizzes:
If we finished Chapter 7 then End-of-Chapter Quiz 7a & 7b (else, just through Chapter 6)
Paper 1:
Stage 1 due Monday before class
Can submit a draft for feedback on eCampus if you like by FRIDAY
MUST submit to turnitin on eCampus

72. Prep For Next Time – L11 Reading: (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
Let us know if you have been misgraded
Will post Unit 1 Revision grades soon
End-of-Chapter Quizzes:
If we finished Chapter 7 then End-of-Chapter Quiz 7a & 7b (else, just through Chapter 6)
Paper 1:
Stage 1 due Monday before class
MUST submit to turnitin on eCampus
Honors Paper:
Stage 0 due today
Stage 1 due March 11

73. Full set of Readings So Far
Required:
BBBHNM: Chap 1-8
Recommended:
BHOT: Chap. 1-6, 9 and 11 ( )
SHU: Chap. 1-3, 6 and 7 (up-to page 153)
TOE: Chap. 1

74. End of Lecture

75. Clicker Question
What would happen to the Einstein ring around a galaxy who's Dark Matter suddenly wasn't there?
Nothing
It would get smaller
It would get bigger
It would disappear
None of the above

76. Clicker Question
What would happen if you were shot by a gun that fires "dark matter” bullets which have the same size and mass as a regular bullet?
Your molecules would significantly spread out from an expansion of space-time
A black hole would form inside you
Objects behind you would be gravitationally lensed
Your body would barely notice
You would die like you would if you got shot with any kind of bullet

77. Clicker Question Why is dark matter "dark“?
Because it is closely linked to dark energy
Because it has no mass
Because it is made of black holes
Because it doesn’t interact with light

78. Clicker Question As far as we know, Dark Matter exists:
Everywhere in the universe
Only near black holes
Mostly in or around galaxies
It doesn't exist
We don't know where it exists

79. Clicker Question
A man shoots a red photon straight up into the air next to a very tall building. The photon rises in the air. Which statements are true:
The photon slows down as it rises, the same way a rock would
The photon loses energy, the same way a rock would
The photon gets blue-shifted

80. Clicker Question
Instead of throwing a rock into the air, a man shoots a red photon straight up into the air next to a very tall building. The following question are about the photon when it reaches the top of the building. Which of the following statements are true
Question 1: Speed
The speed of the photon stays the same
The speed of the photon slows down like a rock would
Question 2: Energy
The energy of the photon stays the same
The energy of the photon gets lower (like the kinetic energy would for a rock)
The energy of the photon gets larger (since it is getting closer to outer space)
Question 3: Color
The color of the photon stays the same
The color of the photon is red-shifted (gets a longer wavelength)
The color of the photon is blue-shifted (gets a shorter wavelength)

81. Clicker Question
A hydrogen atom is hit by a photon and the electron absorbs the photon and moves to an excited state. Later, a photon with the exact same energy is emitted from the atom, and the electron moves back to its original state.
Is this the same photon as before?
Yes, it was inside the electron
Yes, it was bouncing around inside the atom
No, the electron destroyed the original photon and created the new photon
No, the nucleus destroyed the original photon and created the new photon

82. Paper 1 Stuff Paper 1 is Pass/Fail Grade now posted on eLearning
May change as we do re-grades
Reasons you might have failed:
Overall grade was low
Calibrations were low
Self-assessment was low
Didn’t turn in on time
Need an extension? Tell me IN ADVANCE
Will assess late penalties for late papers
You need a passing grade to pass the course

83. Paper 1 Stuff Continued Check if you are grading fairly:
Count the number of no’s in your Rubric. 5 no’s? Can’t be a “great paper” and receive a 9.
Were you misgraded?
Send us an ASAP and we’ll look
Need to revise to get a passing grade?
CPR Revision now open
Same procedure, but grading will emphasize your paper
Text due Monday before class
Calibration the following Monday
Need help? Send us an
Paper 2: due 1 week after we finish Chapter 8

84. More Quantum Weirdness
Electron can “absorb” a photon  becomes more energetic
Electron can “emit” a photon  becomes less energetic g e e e g e

85. Prep For Next Time – L9 Reading: (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
Let us know if you have been misgraded
Unit 1 Revision: New grades posted soon.
Unit 2 Revision (if desired): Stage 2
End-of-Chapter Quizzes:
Chapter 6
Paper 1:
Stage 1 due Monday before class
Can submit a draft for feedback on eCampus if you like
MUST submit to turnitin on eCampus

86. Summary: Atoms vs. Planets
Quantum Mechanical effects only the very small (atoms)
Electron orbits around a nucleus: Quantized “radii”
Planets around the Sun: Not Quantized (too big)

87. Aside: Actually true for the Earth also
Aside: Actually true for the Earth also. However, it would take 1024 years (a Quadrillion years, or a yotta-year) to spiral down into the Sun. That’s a billion times the lifetime of the universe

88. Atomic Transitions
What happens if a photon doesn’t have the exact right energy to excite an atom it meets?
Passes the atom unabsorbed
Note… knocking the electron completely out of the atom is a perfectly good “excited state”
Wrong energy

89. Special Photon Energies
Atoms only “absorb” or “emit” Special wavelength photons
Can only go from one state to another
Only specific colors absorbed
Only photons with specific energy can come out

90. Analogy
Think about Asteroids (or other space junk) banging into the Earth
Small piece of junk: Not much happens
Big asteroid: Wipes out the dinosaurs
REALLY BIG Asteroid: Knocks the Earth out of orbit and off into space (this would be bad)

91. Aside
Smaller:
As far as we know all protons (and neutrons) are identical
Each particle has an anti-particle
More on this stuff later
Bigger:
How atoms combine to form molecules and how molecules interact is really chemistry
Won’t spend too much time on this

92. Other Questions
What are stars made of?
What can we learn from looking at them?
How do we know?
Need to know about the stuff out there and how it interacts to create the light we see on Earth

93. Big Picture: Looking at the Heavens
What we know about the universe comes from multiple places
Already earned about the light coming from the heavens
Need to know more about WHAT PRODUCES the light we observe

94. Only Orbits with Specific Wavelengths Work
The electron “wave” has to go all the way around
Can “wave” once, twice, three times etc…
A quantized number

95. Only Orbits with Specific Wavelengths Work
Lower Energy and closer to the nucleus
Higher Energy and further away from the nucleus

96. Paper Stuff Paper 1 now in progress
The calibration and review portions are due by Wed Feb 24th, BEFORE class
Paper 2 will be due 1 week after we finish Chapter 8
Tentatively, due March 8th

97. What’s the evidence for all this?
What Do we Need to Know?
When we look at the heavens, we want an answer to the question “what IS all that stuff made of?”
Going Further: What is all the stuff that the “stuff” is made of?
What’s the evidence for all this?

98. In-Class Writing Assignment
Write down, during the course of lecture,
Two questions you want to know the answer to

99. Papers for the Course There will be three papers for the course
Due dates are posted there
Paper 1 will be assigned after we start Chapter 9, due one week after we finish Chapter 9

100. In Class Quiz
Answer the following question:
Tell why the subject of “light” is SO IMPORTANT that we spent an entire on it
Make sure to include what we learned that was so important (AND WHY!!)

101. Does this make sense?
Most objects we know and love (the Earth, us etc.) have LOTS of electrons and protons
If EM is so much stronger than Gravity why don’t we feel it?
Why doesn’t the Earth feel the electric charge of the electrons and protons in the Sun?

102. EM vs. Gravity
Answer: Equal numbers of protons and electrons
Each atom/molecule is exactly electrically neutral or they would attract more charge to make them so

103. Bottom line: Accelerating charges emit photons, and accelerating masses emit gravity “waves.” Can’t explain atoms in your body that “live for years”

104. Like charges repel each other Opposite charges attract each other
What’s different?
Gravity:
All objects attract no matter what
(As far as we know…)
ElectroMagnetism:
Ignores neutral particles
Like charges repel each other
Opposite charges attract each other

105. Only Orbits with Specific Wavelengths Work

107. This is some text