1. Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr
Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 16

2. Was Due Today – L16 Reading: (BBBHNM Unit 3)
Pre-Lecture Reading Questions (PLRQ)
Unit 3, Stage 2: Due before class this coming Wednesday
End-of-Chapter Quizzes:
Chapter 10
Papers:
Paper 1 Revision (if desired), Stage 2: Due before class this coming Wednesday
Check on regrades to before submitting
Turn in to both CPR and turnitin on eCampus even if the text is the same (that way we know that it’s the same)
Paper 2, Stage 2: Due before class this coming Wednesday
Make sure you have submitted to both CPR and turnitin on eCampus

3. Overview
Finished: The Exploding Universe
This Time: Expansion of Space-Time and General Relativity
After That: Photons and Hydrogen in the Universe

4. General Relativity and Expanding Space-Time
Outline
General Relativity and Expanding Space-Time
Expanding Space and Red-Shifts

5. Recapping the Data
Galaxies are moving away from us, faster if they are further away AND we see this to be true in ALL DIRECTIONS
Simple-but-wrong explanation: We are the center of an explosion!

6. Not consistent with other data Need a better explanation!
Is this right?
Only consistent with this data if we’re at the center of the Universe and not moving
Not consistent with other data
Need a better explanation!

7. General Relativity to the Rescue
Space-time can change
E.g. Mass causes it to curve and stretch
What if space-time is expanding?

8. Balloon Analogy
Our Universe doesn’t have any over all curvature, but thinking of Space-Time like the SURFACE of a balloon is something you can try at home
Surface of a balloon is a two dimensional example/analogy
There is no inside, space IS just the surface
As space-time expands, the distance between any two spots increases, but there is no spot ON THE SURFACE that is the center of the expansion

9. Expanding Space

10. Another Example of Expanding Space

11. The Expanding Universe
It’s not just galaxies moving through space
Space is expanding, carrying the galaxies along!

12. Galaxies Moving in Space
Space is like a river carrying boats along
Line is like the speed of the river
Stuff above the line
Galaxies that are moving “away” from us in space
Stuff below the line
Galaxies moving “towards” us

13. Velocity?
How does this explain why things are moving FASTER the further away they are?

14. Expanding Space Analogy:
Analogy:
A loaf of raisin bread where the dough is rising and expanding, taking the raisins with it

15. More on Expanding Space-Time and Raisin Bread
Distance

16. Expanding Space-Time and Red-shifts

17. Photons in Expanding Space-Time
Since space is so empty, light from 10 billion years ago can reach us just fine
What happens to photons as they travel in the Universe?
The wavelength gets stretched as space expands  The wavelength gets longer

18. What do photons look like in Expanding Space-Time?
A distant galaxy emits a short wavelength photon towards our galaxy billions of years ago
The Grid shows space

19. Space-Time Expands
The expansion of space-time stretches the photon to longer wavelengths as it travels
The Grid is bigger now

20. Space-Time Expands More
The farther the photon has traveled, the more it is stretched
Still bigger

21. How We Observe It
When the photon arrives at our galaxy we see it with a larger wavelength
The bigger the distance the more red-shifted it has become!
Even bigger as time goes by

22. Red Shifts in an Expanding Universe

23. Galaxies Moving in Space again
Red-shift due to expanding space
Stuff above the line
Additional red-shift due to galaxies moving away from us through space
Stuff below the line
Slightly less red-shift for galaxies moving “towards” us through space

24. Expanding Space-Time Explains all the data (and more in next Chapter)
Note: Implies that the Universe looks the same to “everyone” in the Universe “everywhere”
Said better: Everyone would observe all the distant galaxies moving away from them the same we do here on Earth
Call this the Cosmological Principle

25. No Center of the Universe?
I’m the center of expansion! Everyone moves away from me!
Nowhere on the surface can be called the center
No “center” of the Universe
Or can consider “Everywhere” to be the “center” of expansion
Yes… As we’ve always known, Aggieland IS the center of the Universe
There may well be no “Before” the Big Bang
General Relativity says space and time come into existence together
No! I’m the center of expansion! Everyone moves away from me!

26. How big IS the Universe?
We can’t really know how big the Universe is, since all we can see is back a certain distance in TIME Could be infinite We talk about the Visible Universe

27. Next… Move to more evidence we live in an expanding space-time by looking at photons and hydrogen in the Universe

28. Lecture on Chapter 11 now complete

29. For Next Time– L15 Reading: (BBBHNM Unit 3)
Pre-Lecture Reading Questions (PLRQ)
Unit 3, Stage 2: Due before class Wednesday after spring break
End-of-Chapter Quizzes:
If we finished Chapter 11 then end-of-chapter quiz 11 (else just up to Chapter 10)
Papers:
Paper 1 Revision (if desired), Stage 2: Due before class Wednesday after spring break
Check on regrades to before submitting
Turn in to both CPR and turnitin on eCampus even if the text is the same (that way we know that it’s the same)
Paper 2, Stage 2: Due before class Wednesday after spring break
Make sure you have submitted to both CPR and turnitin on eCampus

30. For Next Time– L16 Reading: (BBBHNM Unit 3)
Pre-Lecture Reading Questions (PLRQ)
Unit 3, Stage 2: Due before class Wednesday
End-of-Chapter Quizzes:
If we finished Chapter 11 then end-of-chapter quiz 11 (else just up to Chapter 10)
Papers:
Paper 1 Revision (if desired), Stage 2: Due before class Wednesday
Check on regrades to before submitting
Turn in to both CPR and turnitin on eCampus even if the text is the same (that way we know that it’s the same)
Paper 2, Stage 2: Due before class Wednesday
Make sure you have submitted to both CPR and turnitin on eCampus

31. Full set of Readings So Far
Required:
BBBHNM: Chaps. 1-12
Recommended:
TFTM: Chaps. 1-3
BHOT: Chaps. 1-7, 9 and 11 ( )
SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-to-page 153)
TOE: Chaps. 1 & 2

32. End of Lecture

33. Clicker Question
True or False: Once a bunch of atoms are in thermal equilibrium, the energy of an individual atom doesn’t change
True
False

34. Clicker Question
True or False: If I have a bunch of electrons, positrons and photons in thermal equilibrium, we will never have another positron annihilate with an electron and raise the number of photons
True
False

35. Clicker Question
Why can electrons, positrons, and photons be in thermal equilibrium with each other, even if they are creating and annihilating one another?
They can be the same temperature
They are in thermal contact
Can only become in thermal equilibrium when interactions cease
A and B

36. Clicker Question
On a cold winter morning, which is a lower temperature, a metal sign pole or a wooden bench?
The metal pole
The wooden bench
They are the same temperature
They are at absolute zero

37. Clicker Question
Two stars in the Milky Way have the same temperature. Are they in thermal equilibrium with each other?
Yes No

38. Clicker Question
Let’s say you were the person observing the galaxies, but each other person in the room were a galaxy. Which person in the room is moving away from you most quickly?
Back left
Back right
Front left
Front right

39. Clicker Question
Which of the following is the best ranking for the speeds (from fastest to slowest) at which galaxies A, C, and D would be moving away from an observer in galaxy B?
A > C > D
D > A > C
C > D > A
D > C > A C A B E
Early Universe
Universe Some Time Later D

40. Clicker Question For the most distant galaxies, which is true?
Most of the red-shift of their spectral lines is because they are moving very fast through space
Most of the red-shift of their spectral lines is because space is expanding

41. Clicker Question
Let's say I have two galaxies in space and they are exactly stationary relative to each other. What will happen next?
Since they are so massive that they will attract each other by gravity and start moving towards each other.
Since space-time is expanding, the distance between them will grow as space-time expands so they will start moving away from each other.
It depends on the overall distance between them.

42. Clicker Question
Are the Earth and Sun moving away from each other since space-time is expanding?
Yes. It is just a matter of time before the Earth will leave the Sun's orbit.
Yes, but the gravitational attraction between the two keeps them at the same distance
No, because the Sun is big enough to prevent space-time from expanding locally
No, because the only thing that matters is that the Earth is attracted to the Sun

43. Clicker Question If space-time is expanding, is our galaxy expanding?
Yes. Everything in the universe is moving away from everything else.
No. It isn't expanding because the gravitational attraction of masses pulls the galaxy back together again

44. Clicker Question If space-time is expanding, are atoms expanding?
Yes. Everything in the universe is moving away from everything else.
No, they aren't expanding because the electric charge attraction and quantum mechanics keep the atoms the same size in space

45. For Next Time– L15 Reading: (BBBHNM Unit 3)
Pre-Lecture Reading Questions:
Let us know if you were misgraded
End-of-Chapter Quizzes:
If we finished Chapter 11 then end-of-chapter quiz 11 (else just up to Chapter 10)
Papers:
Paper 1 Revision (if desired), Stage 1 due Wednesday before class
(Text needs to be in turnitin on eCampus)
Paper 2, Stage 2 due before class Monday
Honors Paper:
Stage 1 due tonight before midnight

46. Prep for next time – L17 Reading: BBBHNM: 13
Pre-Lecture Reading Questions:
Chapter 13
End of Chapter Quizzes:
Chapter 11 (if we finished 11, if not, just 10)
Papers:
Paper 0 Revision: Was due before class. Let us know if you think you were mis-graded
Paper 1: Still working on re-grades.
Paper 1 Revision: If you want to do a revision, due Wednesday before class.
Paper 2: Calibrations/Reviews are due Wednesday before class
Honors Paper: Stage 0 approval required

47. Velocity?
How does this explain why things are moving FASTER the further away they are?
As the radius of the balloon increases, the farther apart the spots on the balloon, the faster they will be moving apart

48. Prep for Today (Is now due) – L15
Reading:
BBBHNM 12
Reading questions:
Chapter 12
End-of-Chapter Quizzes:
Chapter 10
Paper Stuff
Paper 2: CPR Calibrations and reviews due today

49. Was due before Class – L17 Reading: BBBHNM: 12
Pre-Lecture Reading Questions:
Chapter 12
End of Chapter Quizzes:
Chapter 10
Papers:
Paper 0 Revision: Was due before class. Let us know if you think you were mis-graded
Paper 1: Still working on re-grades.
Paper 1 Revision: If you want to do a revision, due Wednesday before class.
Paper 2: Calibrations/Reviews are due Wednesday before class
Honors Paper: Stage 0 approval required

50. Prep For Next Time – L7
Note: May change depending on how far we get in lecture
Reading:
BBBHNM: All reading through Chapter 13
Reading Questions:
All reading questions through 13
eLearning Quizzes:
If we finished Chapter 11 then end-of-chapter quiz 11 (else just through Chapter 10)
Papers:
Paper 2 calibrations and reviews due before class on Tuesday

51. Prep for Next Time – P14 Reading: BBBHNM 12 Reading questions:
Chapter 12
End-of-Chapter Quizzes:
If we finished Chapter 11 then end-of-chapter quiz 11 (else just 10)
Papers:
Text was due Yesterday at 5:45PM
Calibrations/Reviews due Monday March 19

52. Prep for Next Time – P15 Reading: BBBHNM 12 Reading questions:
Chapter 12
End-of-Chapter Quizzes:
If we finished Chapter 11 then end-of-chapter quiz 11 (else just 10)
Paper Stuff
Paper 2: CPR Calibrations and reviews due today

53. Prep for Today (Is now due) – L14
Reading:
BBBHNM 11
Reading questions:
Chapter 11
End-of-Chapter Quizzes:
Chapter 9
Paper Stuff
Paper 1 Revision: CPR due Fri 6PM
Paper 2 Submission: Wed 4PM in CPR

54. Frequently Asked Question Page
I have created a new webpage on the main course page
I’ve tried to take all the questions I keep getting and put answers to them there
Please read it and send fixes, comments, questions and requests for additions
In the future, you might check there if you have a question about the course before ing
If it’s there, I’ll probably point you there in the first place

55. Paper 2 Revisions Will allow Paper 2 revisions
I was REALLY pleased by some of the great papers
Then again, some really weren’t good
If you are not going to submit a good paper, then we aren’t going to give you a chance to revise
If you aren’t doing well with calibrations, we expect you to ask for help

56. Final Note
General Relativity doesn’t really explain WHY this expansion occurs, but expanding space is perfectly allowed
Thus, the expansion could occur since its only SPACE that is expanding

57. Our Best Understanding
Thus, either we believe we’re at the center of an explosion or take seriously the idea that we’re part of an expanding Space-Time
More evidence that we’re part of an expanding space-time?

58. What if we Think about it Differently
Maybe it just “looks” like we’re at the center of the Universe and not moving
Could this be true?
Could be, but what’s the reason it looks like we’re at the center?

59. The Cosmological Principle
At any given time the Universe ought to look the same to observers in all typical galaxies and in whatever directions they look
In other words, the universe should look the same no matter where you look at it from
There IS no center

60. Advantage of this way of thinking
No longer need to live in a special place in the Universe
If this idea is true, then the Universe looks essentially the same for ANY OTHER OBSERVER any where else in the Universe
Can’t check this…

61. No center or edge of the Universe?
2-dimensional analogy:
Ant that can only walk on the surface of a sphere:
Surface is finite, but has no edge
For a creature living on the sphere, having no sense of the third dimension, there’s no center (on the sphere!): All points are equal
Alternative: Any point on the surface can be defined as the center of a coordinate system

62. ???
Do we REALLY believe we’re the center of the Universe AND not moving?
A better explanation?

63. Is there really no center of the Universe?

64. Where we are Full reading so far: BBBHNM: Chaps. 1-11 TFTM: Chaps. 1-3
BHOT: Chaps. 1-7, 9 and 11 ( )
SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-to-page 153)
TOE: Chaps. 1 & 2

65. Paper 1 Stuff Done with grades Graded unfairly? Let us know!
Passing score: Need ALL of the following
Text score: more than 21 points (70%)
Calibrations: more than 15 points
Reviews: more than 15 points
Overall score: more than 70 points
Revision CPR
Updated assignment requirements and rubric
Text submission due date has passed
Do full CPR grading
Grading due Wednesday at noon

66. Paper 2 and Other Stuff Paper 2: Submissions were due Friday at noon
CPR grading due Friday at Noon
Elearning:
Unit 3 in progress
Paper 3:
Due 1 week after we finish Chapter 12 66

67. For Next Time Finished: The Exploding Universe
Expansion of Space-Time and General Relativity
Next Time:
Chapter 12: Cosmic Background Radiation
Full reading so far:
BBBHNM: Chaps. 1-12
TFTM: Chaps. 1-3
BHOT: Chaps. 1-7, 9 and 11 ( )
SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-to-page 153)
TOE: Chaps. 1 & 2
Lecture prep: Turn in on eLearning
Two questions from the Chapter 12 you want to know the answer to

68. We’re at the CENTER and NOT MOVING: Red Shifted Light
Consistent with what we observe!

69. Equal amounts of stuff on each side Consistent with what we observe!
If We’re at the Center
Equal amounts of stuff on each side
Slow Stuff
Medium
Speed
Fast Stuff
Consistent with what we observe!

70. Another possibility: We’re at the center and MOVING
Not really blue shifted, just less-red shifted
Not what we observe!

71. If We’re not at the Center
Lots of stuff on this side
Not much stuff on this side
Medium
Speed
Slow Stuff
Fast Stuff
Not what we observe!

72. Consistent with the Data?
Red shifts are the same in all directions
The Universe looks the same in all directions
Consistent with assumption

73. Writing Assignments
Short Assignment 1 was due today before the beginning of Class
Any revisions will be due 1 week after it is returned
Short Assignment 2 is posted
Currently Due Tuesday Oct 27th which is one week after we finish Chapter 12
Research Paper is posted
Stage 0 due Thurs Oct 29th
Stage 1 due Thurs Nov 5th
Final paper due the last day of class, Tuesday Dec 8th
Unit 2 eLearning stuff now due
Need to start Unit 3 eLearning stuff

74. Truth?
This is science, can’t PROVE this assumption to be true
We haven’t been able to go to any really distant places to check it yet
May never be able to fully check it

75. A Hypothesis
Make a hypothesis: The Universe looks the same to ALL OBSERVERS
If this were true, what would the implications be?
Could this explain what we see?
Can we test this some other way?

76. Everywhere?
Need to be careful not to overstate this point…
It’s not exactly the same, but basically the same
Start with some examples to tell better what we mean…

77. The Forest and the Trees
If the trees in the forest are uniformly distributed, nearby trees may give the appearance of bunching
The universe might not appear uniform right around where we are looking
But, on LARGE SCALES our view appears identical in whichever direction we look

78. From Awhile ago…
From the Front Steps of the NY museum you can’t see the structure
From up high you can clearly see the streets of New York form a grid

79. What matters is the Scale
If we look at distant galaxies, there seems to be more or less the same number of them in every direction, provided we view it on a large scale compared to the distance between galaxies
Have to ignore the distances on small scales
Need to be clear… we’re talking about REALLY Big scales (like 100 million light years)
Remembering that we’re talking about BIG sizes, let’s move forward…

80. The Cosmological Principle
We make the following fundamental assumptions:
1) Homogeneity: On the largest scales, the local universe has the same physical properties throughout the universe
Every region has the same physical properties (mass density, expansion rate, etc.)
2) Isotropy: On the largest scales, the local universe looks the same in any direction that one observes
You should see the same large-scale structure in any direction
3) Universality: The laws of physics are the same everywhere in the universe

81. Cosmological Principle and Hubble’s law
Red shifts are the same in all directions
The Universe looks the same in all directions
Consistent with assumption
Helps reassure astronomers that we are really looking at some appreciable part of the universe and not just some local region

82. Could it be true?
Simple geometry shows that if the universe looks identical in whichever direction WE look then this would be true if we were observing the universe from anywhere else
Certainly is self-consistent

83. Before we Begin
1st Short Writing Assignment Handed out today
Posted on the Webpages
Research Paper Assignment Handed out today
Also posted on the Webpages

84. Cosmology and General Relativity
According to the theory of general relativity, gravity is caused by
the curvature of space-time.
The effects of gravity on the largest cosmological scales should be related to the curvature of space-time!
The curvature of space-time, in turn, is determined by the distribution of mass and energy in the universe.
Space-time tells matter how to move;
matter tells space-time how to curve.

85. This is a test…

86. Two Objects Moving Away from Me
What it looks like when I’m stationary (or in my reference frame)

87. Two Objects Moving Away From Me
What it looks like when I’m moving relative to the objects

88. Same Thing: My Reference Frame
What it looks like when I’m stationary

89. BHOT 6: Curved Space Einstein’s theory of general relativity.
Gravity is not a force like other forces, but rather the weird consequence that space time is not flat
Space-time is curved or “warped” by the distribution of mass and energy in it. Bodies, such as the earth or an apple, are not made to move on curved orbits from the “force of gravity” rather they move in curved orbits because they follow the nearest thing to a straight path in curved space. (the shortest distance between two points)

90. BHOT 6 cont… Picture on page 39 of BHOT.
In GR, bodies always fallow a geodesic in four dimensional space time.
Example from SHU 4: “Imagine a heavy object such as a cannonball), representing the sun being placed in the middle of a tau rubber sheet which represents space-time. The weight of the ball will make it sink into the rubber sheet, creating a cone shaped dent all around it – rather reminiscent of the surface of swirling water rushing down a plug hole” Picture on page 81

91. TFTM 3 cont… Photons as waves and as particles...
Light "waves" are actually LOTS of photons all moving together. However, in reality they are separate particles (Feynman diagram?) and each photon interacts with an atom individually. Again a diagram?
What happens to photons as they travel in the universe? Now? Then?
Now: Space is so empty that light from 10 billion years ago can reach us just fine.

93. SHU 4 cont…
Say something about the cosmological constant? It’s a cute story, but so what for now…
Cute story about how Einstein blew him off… then came Hubble.
Church liked the idea, encouraged him (funded him!) to pursue it.
With Hubble’s data could predict, roughly, that the “moment of creation” was about 15 billion years ago.

94. The Expanding Universe (2)
This does not mean that we are at the center of the universe!
You have the same impression from any other galaxy as well

95. This is some text

96. We’re not at a special place in the universe every galaxy is moving apart at a relative speed proportional to their separation

97. The Questions…

98. Could it be true?
Freidmann: Two assumptions
1) The universe looks identical in whichever direction we look
2) This would be true if we were observing the universe from anywhere else.
Predicted Hubble’s stuff (1929) in 1922.

99. The Expanding Universe
On large scales, galaxies are moving apart, with velocity proportional to distance
It’s not galaxies moving through space, Space is expanding, carrying the galaxies along!

102. More text

104. No center of the Universe?
Consider an Ant walking around “the universe”
Nowhere on the surface can be called the center
No “center” of the Universe
Everywhere can be considered the center
There is no “Before” the Big Bang
Space and time come into existence together

105. Need stuff on Curvature?

106. Shape and Geometry of the Universe
Back to our 2-dimensional analogy:
How can a 2-D creature investigate the geometry of the sphere?
Measure curvature of its space!
Flat surface
(zero curvature)
Closed surface
Open surface
(positive curvature)
(negative curvature)