physics we need topic 5: temperature and equilibrium big bang, black holes, no math 1 big bang,...

Physics We NeedTopic 5: Temperature and

Equilibrium

Big Bang, Black Holes, No Math

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ASTR/PHYS 109Dr. David TobackLecture 13 & 14


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Was due Today – L14• Reading:

– BBBHNM Unit 3• Pre-Lecture Reading Questions:

– Let us know if you were misgraded– Unit 3, Stage 1

• End-of-Chapter Quizzes:– Chapter 8

• Papers: – Paper 1, Stage 2– Paper 2, Stage 1:

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

• Honors Paper:– Stage 1 due March 11th


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Where we are…Topics1. Light and Doppler Shifts Done2. Gravity, General Relativity and

Dark MatterDone3. Atomic Physics and Quantum

Mechanics Done4. Nuclear Physics and Chemistry

Done5. Temperature and Thermal

Equilibrium This Time


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Looking at the Lights in the Sky

What we know about the universe comes from multiple places

So far:•Learned about the light coming from the stars

•The evidence that stars are made of atoms


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Other Stuff Out There…

•We don’t just look at the stars…

•We can learn a lot from looking at light in other ways too…–Talk about this today…


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The World in a JarAs we’ll see, in many

ways when we look at the stuff in the sky (other than the stars) it looks like we’re sitting in a giant jar of stuff, like atoms

What does it look like to sit inside a jar of atoms?

Why should you care?


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Start Simple: Atoms in a Jar•Since we can see how atoms

interact in a jar on Earth we can predict what would happen on Universe sizes

•Next: learn what it’s like to be inside a jar filled with atoms

•Gas (bunch of atoms) is well described by its Temperature and will eventually come into Thermal Equilibrium– Describe both these ideas next


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Overview of Today’s Material

1. Temperature: Photons and Atoms

2. Thermal Equilibrium3. Moving in a Gas4. Different types of

Equilibrium5. What we can, and can’t,

learn from a system in Thermal Equilibrium


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Temperature

What do we mean when we use the word temperature?


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TemperatureHow do we typically “think”

about Temperature?•When we’re outside and we

“feel” cold, the thermometer reads a small number

•When we’re outside and we “feel” hot, the thermometer reads a large number

What is the thermometer measuring?


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“Feeling” Cold•What is hitting you when you are outside? 1.Photons2.Atoms

Can think of temperature as the energy of the particles hitting you


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Temperature of AtomsSame number, and type, of atoms in

both

Low Energy:Cold Gas

High Energy: Hot Gas


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Temperature of Atoms and Photons

• Even if a room is completely dark we can still feel warm because atoms hit our skin– High energy atoms

high temperature– Low energy atoms

low temperature• Our skin is a lousy

thermometer Feels “cooler” in the shade because we absorb fewer photons


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Thermal Equilibrium

Lets say I’m hanging out in a room and part of the room is hot and part of the room is cold

Eventually the air mixes and the room has the same temperature everywhere

Same as putting ice in a cooler full of water Eventually it will get cold


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What’s really happening?

Look at the atomic level• You have high energy atoms and

low energy atoms• What happens to high energy

atoms when they collide with low energy atoms?


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Atomic Perspective

•High energy atom’s perspective: I collide with a low energy atom and “transfer” some of my energy

•Low energy atom’s perspective: I collide with a high energy atom and “take” some of its energy


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What happens in a room with lots of atoms after lots of collisions?

The higher energy atoms will slowly become lower energy atoms

The lower energy atoms will become higher energy atoms

Eventually we get lots of medium energy atoms


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Thermal Equilibrium

•Eventually all the atoms will (roughly) have the same energy–Said better: The same temperature

•We call this Thermal Equilibrium


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A Bigger Example With More Than Two Balls

• Think of a perfect pool table (no friction to slow down the balls) with a cue ball and a rack of balls at the other end; all are stationary– We then shoot the cue ball at

the rack (we break)• Right after we shoot, but before

the cue hits the rack, we’re are NOT in equilibrium– One ball is VERY energetic and

the others have no kinetic energy


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After the Cue Ball Hits the Rack

•After the cue ball strikes the rack, the cue ball has smaller energy and all the other balls have some energy– As the balls bounce off each

other they will, eventually, all have roughly the same energy

•Actually more complicated, but it turns out we can predict the distribution of energies

– Call this Thermal Equilibrium


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Pool Table ExampleCue ball after it hits the rack

All balls have roughly the same energy Call This THERMAL

EQUILIBRIUM


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Silly Pool Table Example

NOT THERMAL EQUILIBRIUM


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Next consider some things that

don’t typically happen to jars in

the real world


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Moving in a Gas

•What if the jar is moving?

•What if the jar is stationary, and I (as the observer) am moving inside it?–These are equivalent by relativity


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An Observer Inside a Gas in Thermal Equilibrium

What does it look like “in here”?

1.Equal number from all directions

2.Same “temperature” in all directions


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What if I, or the Jar, is Moving?

What does it look like “in here”?

1.Equal number from all directions

2.DIFFERENT “temperature” in different directions

BlueShifted

RedShifted


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Fish “Temperature”

•The fish have the same “temperature” in both cases– Just “looks” different

•Can tell I’m in a bunch of fish that are at Thermal Equilibrium

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Bottom Line

I can tell that I am located in a gas in thermal equilibrium if:

1. The temperature is the same in all directions OR

2. The temperature looks as if either me or the gas is moving in a single direction

A gas in Thermal Equilibrium is well described by its Temperature


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Other Types of Thermal Equilibrium?

There are other types of Thermal Equilibrium

•Different types of gas can mix and come into thermal equilibrium

•Atoms (or particles) can interact and come into thermal equilibrium


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Example 1: Two Gases Mixing

• Let’s say I have two different gases with different temperatures on opposite sides of a jar– High Mass atoms and Low Mass

Atoms• Before: Not in thermal equilibrium,

doesn’t LOOK like equilibrium– Different temperatures on each side– If I weren’t at the center, it would

look different than if I were at the center

• During: The atoms “mix” and come to thermal equilibrium

• After: We’re in thermal equilibrium equal temperatures everywhere


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Two Gases Mixing

Low Mass Atoms High Mass Atoms

http://bigbang.physics.tamu.edu/Figures/StolenAnimations/HeatTransferred.avi


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Other Examples

•Different types of atoms can “mix” and come into thermal equilibrium with each other

•Hydrogen and oxygen can mix and turn into water in thermal equilibrium


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Electrons and Photons

•An electron and an anti-electron can collide and turn into two photons

•Two photons can collide and turn into an electron and an anti-electron–If they have enough energy


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Photons and “Electrons”

2 Photons can turn into 2 “Electrons”

2 “Electrons” can turn into 2 Photons

+ -

-+


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Electron and Photons• If we have lots of electrons

they will interact and create more photons

• If there are lots of high energy photons they will interact and create more electrons

•Eventually both the number of electrons and photons, as well as the energy, comes into Thermal Equilibrium


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Positron

ElectronPhoton

Electrons, positrons, and

photons in equilibrium

between production and

annihilation

Visualize: Electrons and Photons


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Always end up the same way

•If I start with ONLY high energy electrons and positrons, eventually I’ll end up with electrons, positrons and photons in thermal equilibrium

•If I start with ONLY high energy photons, eventually I’ll end up with electrons, positrons and photons in thermal equilibrium


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Lots of Types of Thermal Equilibrium

• Given enough time (and things not changing) all places in the room will come to have the same temperature i.e., be in thermal equilibrium

• Depending on what the particles are (electrons, photons, atoms etc.) they can turn into different types of particle bring the number of objects AND energy into Thermal Equilibrium also

• If we know how it all starts, we can always figure out how it will end


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What Thermal Equilibrium Can, and Can’t, Tell Us

• Lots of different ways of starting out will come to the same thermal equilibrium

• So what? Since this is true we can’t learn a lot about what happened BEFORE it went into equilibrium– Single cue ball hit a rack of

balls?– Two balls hit the rack at the

same time? • Can’t tell the difference looking at

much later times…


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Different Initial ConditionsMuch later in time (after we’re in thermal

equilibrium) can’t tell if the system started in

Funny Way Usual Way


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A Universe in Thermal Equilibrium

• We will see evidence that the Universe appears to have the same temperature everywhere– Was in Thermal Equilibrium at

some point in its history• Tells us a lot about the Universe

and how it evolved (and will evolve)

• Can’t tell us about what happened BEFORE it came into Thermal Equilibrium– For example: Was there actually

a Big Bang? Something else?


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The Plan… Finished:1. Light and Doppler Shifts2. Gravity, General Relativity and

Dark Matter3. Atomic Physics and Quantum

Mechanics4. Nuclear Physics and Chemistry5. Temperature and Thermal

EquilibriumNext time:• Starting Unit 3• Using the “Physics We Need” to

teach us about the EVIDENCE for the Big Bang


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Prep for Next Time – L13• Reading:


– Unit 3, Stage 1 due Monday before class• End-of-Chapter Quizzes:

– If we finished Chapter 9 then end-of-chapter quiz 9 (else just up to Chapter 8)

• Papers: – Paper 1, Stage 2:

• Due Monday before class – Paper 2, Stage 1:

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



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Prep for Next Time – L14• Reading:


– Unit 3, Stage 2 due Wednesday before class• End-of-Chapter Quizzes:


• Papers: – Paper 1 Revision, Stage 1

• Due Wed after Spring Break, but Stage 2 will be Mon March 30

– Paper 2, Stage 1:• Due before class on Wednesday• (Text needs to be in turnitin on eCampus)



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Full set of Readings So Far•Required:

–BBBHNM: Chaps. 1-10•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 & 249


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Clicker QuestionTwo mystery galaxies (on the right) only have a single spectral line in the visible spectrum as shown below.

If the above galaxy is stationary, which way is the below galaxy moving?a)Towards usb)Away from usc)It is also stationaryd)Not enough information


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Clicker Question

A star is observed with the following light pattern. Which way is it moving? a)Towards us, slow speedb)Away from us, slow speedc)Towards us, high speedd)Away from us, high speede)Stationary


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Clicker Question

Which best describes the two galaxies below? a)Both are moving towards us, but the left one is moving faster than the one on the rightb)Both are moving towards us, but the right one is moving faster than the one on the leftc)Both are moving away from us, but the left one is moving faster than the one on the rightd)Both are moving away from us, but the right one is moving faster than the one on the left


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Clicker Question

True or False: Two stars at the same temperature in the Milky Way are in thermal equilibrium

a)Yesb)No

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Clicker Question

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

a)Trueb)False

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Clicker Question

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

a)Trueb)False

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Clicker Question

Why can electrons, positrons, and photons be in thermal equilibrium with each other, even if they are creating and annihilating one another?

a)They can be the same temperature

b)They are in thermal contactc)Can only become in thermal

equilibrium when interactions cease

d)A and B

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Clicker Question

On a cold winter morning, which is a lower temperature, a metal sign pole or a wooden bench?

a)The metal poleb)The wooden benchc)They are the same temperatured)They are at absolute zero

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Was due today – L7• Reading:

–BBBHNM: All reading through Chapter 11• Reading Questions:

–All reading questions through 11• eLearning Quizzes:

–All quizzes through Chapter 8• Papers:

–Calibrations and grading you didn’t pass Paper 1, were due before class

–Text submission of Paper 2 was due in CPR and turnitin.com before class


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Was Due Today– L14• Reading:

– BBBHNM: All reading through Chapter 9• Pre-Lecture Reading Questions:

– Through Chapter 9• End of Chapter Quizzes:

– Chapter 8• Papers:

– Paper 0: Grades were posted in eCampus. Let you know if you were misgraded

– Paper 0 Revision (if necessary – See eCampus score, not CPR Score): Open now, Text due Monday before class. All Calibrations/Reviews following Monday

– Paper 1: Changed due date, Calibrations/Reviews due this coming Tuesday at 11:55PM

– Paper 2: Changed due date, Text due Wednesday before class


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Was Due Today– L15• Reading:



– Chapter 8• Papers:

– Paper 0: Grades were posted in eCampus. Let us you know if you think you were misgraded. Currently done with all regrade requests

– Paper 0 Revision (if you didn’t pass the first time – See eCampus score, not CPR Score): Text was before class. All Calibrations/Reviews next Monday

– Paper 1: Calibrations/Reviews due Tomorrow (Tuesday) at 11:55PM

– Paper 2: Text due Wednesday before class


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Paper 2 Organization Stuff• I have extended the due date until Tuesday

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

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

– 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 at the

same time• Calibrations will be due right after Spring

Break

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Prep for Today (Is due now) – L12

•Reading: – BBBHNM 9

•Reading questions: – Chapter 9 or the recommended

reading•End-of-Chapter Quizzes:

– Chapter 7 & 8•Papers:

– Calibrations for Paper 1, if needed

– Text of Paper 2 due next week


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Prep for Today (Is due now) – L13

•Reading: – BBBHNM 10

•Reading questions: – Chapter 10 or the recommended

reading•End-of-Chapter Quizzes:

– Chapter 8•Paper 2:

– Text due Tuesday at 5:45PM– Calibrations/Reviews due Monday

March 19


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Paper 2: The Assignment• Abbreviated Description: What is the

evidence that Stars are made of Atoms? • Explain it to someone who isn’t taking

the class (no jargon)• Format:

– Introduction paragraph– ~1 paragraph per piece of evidence– Conclusion paragraph that ties it

together– http://faculty.physics.tamu.edu/toback/109/

WritingAssignments/samplepaper.shtml 65


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Prep for Next Time – L12•Reading:

– BBBHNM 10– Lots of fun recommended Reading also on

next slide•Reading questions:

– Chapter 10 or the recommended reading•End-of-Chapter Quizzes:

– If we finished Chapter 9, end-of-chapter quiz due before next class (else just 8)

•Papers:– If you did a Paper 1 Revision, Calibration

due Monday– Paper 2 due Tuesday on CPR and

turnitin.com


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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 12• Reading Questions:

–All reading questions through 12• eLearning Quizzes:

–If we finished Chapter 9 then end-of-chapter quiz 9 (else just through Chapter 8)

• Papers:–Paper 2 text feedback (if desired) due Monday March 11th for guaranteed feedback.

–Due Tuesday March 19th in CPR and turnitin.


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Prep For Next Time – L14• Note: May change depending on how far we get in

lecture• Reading:




• Papers:– Paper 0: Grades were posted in eCampus. Let us

know if you were misgraded. – Paper 0 Revision (if necessary – See eCampus score,

not CPR Score): Open now, Text due Monday before class. All Calibrations/Reviews following Monday

– Paper 1: Changed due date, Calibrations/Reviews due this coming Tuesday at 11:55PM

– Paper 2: Changed due date, Text due Wednesday before class


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Prep For Next Time – L15• Note: May change depending on how far we get in

lecture• Reading:

– BBBHNM: All reading through Chapter 10 (already assigned)

• Pre-Lecture Reading Questions:– Through Chapter 10 (already assigned)

• End of Chapter Quizzes:– Chapter 9

• Papers:– Paper 0: Grades were posted in eCampus. Let us

you know if you think you were misgraded. Currently done with all regrade requests

– Paper 0 Revision (if you didn’t pass the first time – See eCampus score, not CPR Score): Text was before class. All Calibrations/Reviews next Monday

– Paper 1: Calibrations/Reviews due Tomorrow (Tuesday) at 11:55PM

– Paper 2: Text due Wednesday before class

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