Evidence for the Big Bang Topic 2: Expanding Space-Time Big Bang, Black Holes, No Math 1 Big Bang,...

Evidence for the Big BangTopic 2: Expanding Space-Time

Big Bang, Black Holes, No Math

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ASTR/PHYS 109

Dr. David TobackLecture 16



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Was Due Today – L16• Reading:

– (BBBHNM Unit 3)• Pre-Lecture Reading Questions:

– PLRQ Unit 3 Revision (if desired), Stage 1 due Wednesday before class

• End-of-Chapter Quizzes:– 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 Wednesday before class• (Text needs to be in turnitin on eCampus)

• Honors Paper:– Stage 1 must be approved explicitly– Stage 2 due Monday March 30



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Overview

•Finished: The Exploding Universe

•This Time: Expansion of Space-Time and General Relativity

•After That: Photons and Hydrogen in the Universe



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Outline

•General Relativity and Expanding Space-Time•Expanding Space and Red-Shifts



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Recapping the DataGalaxies are moving

away from us, faster if they are further away AND moving the SAME WAY same way in ALL DIRECTIONS

Simple-but-wrong explanation: We are the center of an

explosion!



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Is this right?

Only consistent this data if we’re at the center of

the Universe and not moving

Not consistent with other dataNeed a better explanation!



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General Relativity to the Rescue

•Space-time can change–E.g. Mass causes it to curve and stretch

•What if space-time is expanding?



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Expanding Space

Analogy:

A loaf of raisin bread where the dough is rising and expanding, taking the raisins with it



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Another Example of Expanding Space



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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–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



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Expanding Space

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/originredshifts2.swf



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The Expanding Universe

It’s not just galaxies moving through space

Space is expanding, carrying the galaxies along!



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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



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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



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More on Expanding Space-Time and Raisin Bread

Distance

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/RaisinBread.swf



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Expanding Space-Time

and Red-shifts



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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



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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



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Space-Time Expands

The expansion of space-time stretches the photon to longer wavelengths as it travels

The Grid is bigger now



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Space-Time Expands More

The farther the photon has traveled, the more it is stretched

Still bigger



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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



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Red Shifts in an Expanding Universe

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/originredshifts1.swf



Expanding Space-Time

•Explains all the data (and more in next Chapter)

•Note: Implies that the Universe look the same to “everyone” in the Universe “everywhere”

•Call this the Cosmological Principle

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No Center of the Universe?

• 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 is no “Before” the Big Bang– Space and time come

into existence together

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I’m the center of

expansion! Everyone

moves away from

me!

No! I’m the center

of expansion

! Everyone

moves away

from me!



How big IS the Universe?

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We can’t really know how big the Universe is, since all we can see is back a certain distance in TIME

Could be infiniteWe talk about the Visible Universe



Next… Move to more evidence we live in

an expanding space-time by looking at

photons and hydrogen in the

Universe 26



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For Next Time– L16• Reading:


– PLRQ Unit 3 Revision (if desired), Stage 1 due Wednesday before class

• 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 Wednesday before class• (Text needs to be in turnitin on eCampus)

• Honors Paper:– Stage 1 must be approved explicitly– Stage 2 due Monday March 30



Full set of Readings So Far•Required:–BBBHNM: Chaps. 1-12

•Recommended:–TFTM: Chaps. 1-3–BHOT: Chaps. 1-7, 9 and 11 (117-122)–SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-to-page 153) –TOE: Chaps. 1 & 2

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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?

a)Back leftb)Back rightc)Front leftd)Front right 30



Clicker QuestionWhich 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)A > C > Db)D > A > Cc)C > D > Ad)D > C > A

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Clicker QuestionAre the Earth and Sun moving away from

each other since space-time is expanding?

a)Yes. It is just a matter of time before the Earth will leave the Sun's orbit.

b)Yes, but the gravitational attraction between the two keeps them at the same distance

c)No, because the Sun is big enough to prevent space-time from expanding locally

d)No, because the only thing that matters is that the Earth is attracted to the Sun

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Clicker QuestionLet's say I have two galaxies in space

and they are exactly stationary relative to each other. What will happen next?

a)Since they are so massive that they will attract each other by gravity and start moving towards each other.

b)Since space-time is expanding, the distance between them will grow as space-time expands so they will start moving away from each other.

c)It depends on the overall distance between them. 33



Clicker QuestionIf space-time is expanding, is our galaxy

expanding?a)Yes. Everything in the universe is

moving away from everything else. b)No. It isn't expanding because the

gravitational attraction of masses pulls the galaxy back together again

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Clicker Question

If space-time is expanding, are atoms expanding?

a)Yes. Everything in the universe is moving away from everything else.

b)No, they aren't expanding because the electric charge attraction and quantum mechanics keep the atoms the same size in space

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Clicker QuestionFor the most distant

galaxies, which is true?

a)Most of the red-shift of their spectral lines is because they are moving very fast through space

b)Most of the red-shift of their spectral lines is because space is expanding 36



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For Next Time– L15• Reading:


– 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• (Text needs to be in turnitin on eCampus)

• Honors Paper:– Stage 1 due tonight before midnight



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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



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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



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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



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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



Prep for Next Time – P14

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• 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



Prep for Next Time – P15

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• 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



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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



Frequently Asked Question Page

• I have created a new webpage on the main course page

• http://faculty.physics.tamu.edu/toback/109/109FAQ.shtml

• 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 emailing

– If it’s there, I’ll probably point you there in the first place

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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

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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



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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?



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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?



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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



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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…



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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



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???

•Do we REALLY believe we’re the center of the Universe AND not moving?

•A better explanation?



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Is there really no center of the

Universe?



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Where we are

Full reading so far:•BBBHNM: Chaps. 1-11•TFTM: Chaps. 1-3•BHOT: Chaps. 1-7, 9 and 11

(117-122)•SHU: Chaps. 1-3, 4(77-86),

5(95-104), 6, 7 (up-to-page 153)

•TOE: Chaps. 1 & 2



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

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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

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For Next Time• Finished:

– The Exploding Universe– Expansion of Space-Time and General

Relativity• Next Time:

– Chapter 12: Cosmic Background RadiationFull reading so far:• BBBHNM: Chaps. 1-12• TFTM: Chaps. 1-3• BHOT: Chaps. 1-7, 9 and 11 (117-122)• SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-

to-page 153) • TOE: Chaps. 1 & 2Lecture prep: Turn in on eLearning

Two questions from the Chapter 12 you want to know the answer to



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Consistent with what we observe!

We’re at the CENTER and NOT MOVING: Red Shifted Light



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If We’re at the Center

Equal amounts of stuff on each side

Consistent with what we observe!

Fast Stuff

Slow Stuff

Medium

Speed



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Not what we observe!

Another possibility: We’re at the center and MOVING

Not really blue shifted, just less-red

shifted



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If We’re not at the Center

Lots of stuff on this sideNot much stuff on this side

Not what we observe!

Fast Stuff

Slow Stuff

Medium

Speed



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Consistent with the Data?

•Red shifts are the same in all directionsThe Universe looks the same in all directions

•Consistent with assumption



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Writing Assignments1. Short Assignment 1 was due today

before the beginning of Class• Any revisions will be due 1 week

after it is returned2. Short Assignment 2 is posted

• Currently Due Tuesday Oct 27th which is one week after we finish Chapter 12

3. 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 dueNeed to start Unit 3 eLearning stuff



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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



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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?



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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…



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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



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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



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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…



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The Cosmological PrincipleWe 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



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Cosmological Principle and Hubble’s law

•Red shifts are the same in all directionsThe 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



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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



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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



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Cosmology and General Relativity

According to the theory of general relativity, gravity is

caused bythe 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.



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•This is a test…



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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

What it looks like when I’m stationary



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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)



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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



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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.



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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.



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The Expanding Universe (2)

You have the same impression from any other

galaxy as well

This does not mean that we are at the center of the universe!



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•This is some text



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



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The Questions…



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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.



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The Expanding UniverseOn large scales, galaxies are moving apart,

with velocity proportional to distanceIt’s not galaxies moving through

space, Space is expanding, carrying the galaxies along!



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•More text



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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 95



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•Need stuff on Curvature?



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Shape and Geometry of the Universe

Back to our 2-dimensional analogy:

Measure curvature of its space!

Closed surface

Flat surface

Open surface(positive

curvature)

(zero curvature)

(negative curvature)

How can a 2-D creature investigate the geometry of the sphere?



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Evidence for the Big Bang Topic 2: Expanding Space-Time Big Bang, Black Holes, No Math 1 Big Bang,...

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