Big Bang, Black Holes, No Math Early Times & Fate of The Universe Topic 2: Particle Physics 1 Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback

Big Bang, Black Holes, No Math

Early Times & Fate of The Universe Topic 2: Particle Physics

1

Big Bang, Black Holes, No MathASTR/PHYS 109

Dr. David TobackLecture 26



2

Was Due for Today – L26• Reading:

– Unit 6 (was due already)• Pre-Lecture Reading Questions:

– Unit 6: Stage 2• End-of-Chapter Quizzes:

– Chapter 18• Papers:

– Paper 3 Revision (if desired): Stage 2

– Paper 4: Stage 1 due Monday– Honors: Monday at 11:55PM on

eCampus



3

Unit 6

Going back in time and going forward in time

Before the first millionth of a second

and the Fate of the Universe



4

Outline of Unit 6

1.Possible Fates of the Universe, Dark Matter and Dark Energy

2.Particle Physics, Dark Matter and the Very Early Universe

3.Inflation

Today



5

Overview of Today’s Lecture

1. Fundamental particles and interactions

2. What does Particle Physics have to tell us about the Universe before the first millionth of a second?

3. Could the Dark Matter be due to a new type of Particle? Supersymmetry?



6

How Physicists Think About This

•What are the Fundamental Particles of Nature?

•What are the Forces of Nature that keep composite particles together and/or forces them to decay?

Can we use this knowledge to help understand the Universe?



7

Start by listing the particles and

interactions we’ve already

discussed, then list the others we haven’t discussed



The Known Fundamental Particles

6 Types of Quarks• Up, Down, Strange, Charm,

Bottom and Top6 Types of “electrons” • Electron, Muon, Tau, and a

Neutrino for each4 Types of Force Carriers• W, Z, gluon and photon• Graviton is the 5th?Also the recently discovered

Higgs Boson which is an oddball that helps give the other mass



Feynman Diagram of Electromagnitism

•A diagram of how the particles “talk” to each other

•These two are attracted

Time

Hydrogen Atom

e-P

P e-

+

-



10

Quarks and the Strong Force

• Protons and Neutrons made of quarks

• The strong force holds the quarks together inside the nucleon

• The force mediator is the “gluon”– Quarks “talk”

to each other via gluons



11

Gravity

• The mass of an object attracts it to all other objects

• Call this a Gravitational interaction– Haven’t

observed the “particle” of gravity interactions yet

– Give it a name anyway: “Graviton”



12

Interaction: The Weak Force

•Responsible for radioactivity, the decay of atomic nuclei

•The Particles that “mediate” this interaction are known as the W and Z particles

•These particles were predicted in the late 1960’s and discovered in the 80’s –Einstein didn’t know about them



13

The Weak Force

A W can decay into an electron and a neutrino

e

W

A Down Quark can “change” into an up quark by “emiting”

a W

u

d

W

Lives 10-24

Seconds



14

Neutron Proton + W Proton + Electron + Neutrino

Neutron Decay

Neutron

Proton

Electron

Neutrino

Up Quark

Down Quark

Down Quark

W

Up Quark



15

Proton + Electron Neutron + Neutrino

Creating Neutron Stars

Proton Neutron

Electron

Neutrino

(leaves the

star)

Up Quark

Down Quark

Up Quark

W

Down Quark



16

Electron+Positron Z muon + antimuon

Other “Weak Force” Interactions

e+

Z

e-

+

-

Can create lots of different types of

particles this way in collisions

Electron+Positron Z quark + antiquark quar

k

Antiquark



17

Composite ParticlesProtons and Neutrons

Other Examples: Quark and Anti-Quark PairA Pion and a Kaon

Composite particles of quarks are called “Hadrons”



18

Most of these other composite particles decay after a very short time (~10-24 seconds)

Pion Photon + Photon

Particle Decay

Pion

Up Quark

Photon

Photon

Anti-Up Quark



19

Lots of Others in the Particle Physics “Zoo”

Lots more than are listed

here…Most are VERY

short livedSome are very

heavy



20

Particle Physics and the Early Universe

•If a particle CAN exist and CAN be produced in high energy collisions it WILL (eventually) be produced

•Early Universe High Energy collisions Lots of different kinds of particles in the early Universe



21

Particle

Anti-ParticlePhoton

To understand what really happened in the early Universe requires knowing what all the

particles are that can be created and how they interact

Each Particle Can be Part of the Story



Other Fundamental Particles?

•Are there other fundamental particles out there we haven’t discovered yet?

•How would we know?•Any reason to believe there might be?

22



23

Some fun evidence that Dark Matter is Made of

Particles

Colliding Clusters of Galaxies



24

Look at Colliding Clusters of Galaxies

Atoms

Dark Matter

Atoms

Dark Matter

Atoms in the Galaxies interact and slow down as they pass through each other

Dark Matter doesn’t interact much so it isn’t slowed down much



25

Colliding Galaxy Clusters

Atoms and Dark Matter

Atoms andDark Matter

The atom part and the Dark Matter part of Galaxies interact differently as they pass through each other

Atoms Atoms

Dark Matter Dark Matter



26

Colliding Galaxy Clusters

Atoms and Dark Matter

Atoms andDark Matter

Atoms Atoms

Dark Matter Dark Matter

Light from a Galaxy

GalaxyGalaxy Galaxy



27

Evidence for This in Nature?Colliding Clusters of Galaxies

Blue is the part from lensing only“Fast Dark Matter”

Red part from observing the light“Slow Atoms”



28http://bigbang.physics.tamu.edu/Figures/StolenAnimations/bullett_anim_lg.mpg



29

What IS Dark Matter?We don’t know…

Still working on it…Next we’ll tell you about an exciting possibility we’ve been working on



Matter and Mediators

•All the (fundamental) matter particles act in similar ways–Electrons, quarks, muons etc.

•All the mediators act in ways that are different from matter particles, but in ways that are similar to each other–Photons and gluons etc.



Why are the Matter Particles and Mediators

Different?We don’t know… But we

have some interesting ideas…

Supersymmetry



String Theory (and other particle physics theories) predict that they may be related in ways we just haven’t “discovered” yet

Idea: Since each particle has an anti-particle partner, maybe each matter particle has a mediator partner, and every mediator particle has a matter partner

Maybe they are more similar than we think?



33

Call this “Symmetry” in nature Supersymmetry

•Essentially, Supersymmetry predicts that each particle has a “super” partner

•Electron Supersymmetric Electron–S-electron or Selectron–Put a ~ on top of it–Quark Squark etc.–W Wino etc.

e~



34

The Supersymmetric “Zoo”



35

More on Supersymmetry

A property of Supersymmetry particles is that we think the number of “superpartners” in an interaction is “conserved”– Almost like electric charge

•Always even or odd number of SUSY particles on both sides

– Each diagram must conserve charge and “Superparticle number”



36

Conservation of Charge and “Superpartner” Number

Electric Charge Conserved

e-

e-

Superpartner number

conserved

e-

e~

~



37

So What?

•If Superpartner number is conserved the lightest supersymmetric particle can’t decay would last forever–Same reason electrons and protons don’t decay… Nothing they can decay into

•If it’s neutral then this could be Dark Matter!



38

Dark Matter = Supersymmetric Particles?

SupersymmetricParticles created

in the early Universe?Still here today?



39

Exciting Possibility

If this theory is correct:1. We understand the

relationship between matter and mediators (and other important particle physics issues) AND

2. Have solved one of the most important problems in Astronomy and Cosmology

No evidence yet…



40

Dark Matter = Fundamental Particles?

Dark MatterParticles created

in the early Universe?Still here today?



41Dar

k M

atte

r Par

ticle

Proton Proton

Ok… Its more complicated than this since Dark Matter Particles

don’t easily interact with detectors…

A “smoking gun” would be producing them in collision experiments at the LHC at

CERN

Dark M

atter P

articleDetector



An Aerial View of the LHC

CMS

ATLAS

27 km in Circumference!

One of the largest and the most complex scientific instrument ever conceived &

built by humankind

pp

Collides high energy protons

Two huge detectors

Lake LemanGeneva Airport



Accelerate protons to REALLY high energies, then bash them togetherProduce Dark Matter so we can “Discover” it



44

Final Thoughts on Particle Physics

• Why does nature have so many different particles?

• Why are some so much heavier than the others?– Protons are 2000 times heavier than

electrons– Top quarks are 175 times heavier than

protons• How do we know we aren’t missing any?• Could the “fundamental” particles actually be

composite?• Other Forces?Not only are these important fundamental

questions, but they are important in cosmology since what particles CAN exist in nature determines what happens in the Very Early Universe



45

For Next Time – L27• Reading & Pre-Lecture Reading Questions:

– None• End-of-Chapter Quizzes:

– If we finished Chapter 19, then Chapter 19 (if not, then just Chapter 18)

• Papers:– Paper 4: Stage 1 due Monday, Stage 2 the

following Monday– Honors: Monday at 11:55PM on eCampus

• Notes: – Monday is the last day of class– All EOC quizzes will be due Monday May 11th at

11:55PM. You cannot pass the course without doing all of them

– Make sure you have turned in all papers (including Revisions) into turnitin. You will lose points if you don’t.

– Won’t start calculating grades until the 11th



46



Clicker Question

If there really is dark energy, what is the ultimate fate of our universe?

a)Big crunchb)Expand forever, but slowing down

c)Expand forever, but speeding up

Early Times & Fate of the

Universe Topic 1:

Possibilities

47



Clicker Question

48

What does dark energy do to the photons in the universe?

a)Makes them more energetic by adding energy to the universe

b)Stretches them by stretching space-space time making them more energetic

c)Stretches them by stretching space-space time making them less energetic



Clicker Question

Dark energy is forcing the universe to accelerate. What is accelerating?

A) The galaxies moving through space

B) The expansion of space-time

C) Only the dark matterEarly Times

& Fate of the Universe Topic 1:

Possibilities

49



Clicker Question

What is happening to the density of the universe over time?

a)Increasesb)Decreasesc)Stays the same


Universe Topic 1:

Possibilities

50



Clicker Question


Universe Topic 1:

Possibilities

51

If space-time is expanding, why aren't atoms expanding?

a)They areb)Because the electric charge

attraction and quantum mechanics keep the atoms the same size in space

c)Both are true, but A is a more important effect than B

d)Both are true, but B is more true that A.



Clicker Question


Universe Topic 1:

Possibilities

52

What does dark energy do to the temperature in the universe?

a)Raises it by adding energy to the universe

b)Lowers it by stretching space-time

c)Dark Energy doesn’t affect Temperature



Clicker Question

What will happen to galaxies 100 billion years in the future?

a)They'll stay the way they are now because dark matter will keep them together

b)They'll slowly get ripped apart because dark energy will expand the universe so quickly it will overcome the attraction of gravity


Universe Topic 1:

Possibilities

53


Early Times & Fate of The Universe Topic 2: Particle Physics Early Times

& Fate of the Universe Topic 1:

Possibilities

End of the Semester – L13• All Reading Questions are now due• If we finished Chapter 18, then Chapter 18 due before

class next time (else just 17)• All chapters due by Tues Dec 4th at midnight

• Next time: Last day of class• Need to finish all the end of Chapter quizzes as well as

AMS 2– That’s the end of semester evaluation– Need to finish this before you can finish all the end of

chapter quizzes– If they are not complete, you will get an Incomplete for

the course• Will not do the 5th paper, but will allow a paper 4

revision with a short time scale– Text due Monday Dec 3rd

– Rest due by Dec 7th54



Prep for Next Time – P26

55

• Reading– Reading the rest of BBBHNM

• Reading questions– Chapter 18, 19,20 and 22 (can do in

installments)• End-of-Chapter Quizzes

– If we finished this lecture, do Chapter 18, 19 and 22 (else just 17)

• Papers– Paper 1, 2 or 3: Misgraded? Let us know– Paper 3 revision: Was due Monday,

Reviews due next Monday– Paper 4: Was due today (same format as

last two papers), Reviews due next Wednesday



Was due today – L13

•All Reading and Reading Questions are now due

•End of Chapter quizzes•Chapter 18 was due today

•Paper 4 calibrations, reviews and self-assessment was due before class today 56



Full set of Readings So Far•Required:

–BBBHNM: Chaps. 1-22•Recommended:

–TFTM: Chaps. 1-5–BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-137), 12

–SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6-8 (up-to-page 164)

–TOE: Chaps. 1-3–Seeds (Cosmology in the 21st Century)



58

Prep For Next Time – L12• Note: May change depending on how far we

get in lecture• Reading:

–BBBHNM: All reading through Chapter 20• Reading Questions:

–All reading questions through 20• eLearning Quizzes:

–If we finished Chapter 18 then end-of-chapter quiz 18 (else just through Chapter 17)

• Papers:–Text of Paper 4 assignment due Wednesday at 11:55PM

–Calibrations, Reviews and Self-assessment due before class on Monday



59

Prep For Next Time – L13• Note: May change depending on how far we

get in lecture• Reading:

–BBBHNM: All reading through Chapter 20• Reading Questions:

–All reading questions through 20• eLearning Quizzes:

–If we finished Chapter 18 then end-of-chapter quiz 18 (else just through Chapter 17)

• Papers:–Rest of Paper 4 assignment due before class on Tuesday



End of the Semester – L27• Last day of class• Will not cover Chapter 21

– All Reading Questions are now due• Need to finish all the end of Chapter

quizzes (except Chapter 21) as well as AMS 2– AMS is the end of semester evaluation– All due by end of the day on

Wednesday– If they are not complete, you will get

an I• Will not do the last paper, but will allow

a paper 4 revision– Monday May 7th, and 10th

60



61

Outline of Unit 6

1.Possible Fates of the Universe

2.Dark Matter3.Particle Physics4.Inflation5.Dark Energy

Today



Prep for Next Time – P25

62

• Reading– BBBHNM 22

• Reading questions– Chapter 22

• End-of-Chapter Quizzes– If we finished Chapter 20 then end-of-

chapter quiz 20 (else just 19) • Papers

– Paper 1, 2 or 3: Misgraded? Let us know– Paper 3 revision: Due tonight at Midnight– Paper 4: Due tonight at Midnight



63

Course Evaluations

This semester course evaluations will be done online

"Department of Physics On-Line Course Evaluation System“

http://evaluation.tamu.edu/

Please, take a few minutes to fill these out. I really appreciate it!



64

For Next TimeNext Lectures– Inflation (Chapter 21)– Dark Energy (Chapter 22)Full reading for Unit 6:• BBBHNM: Chaps. 18-22• SHU: 8 (159-164)• BHOT: 11 (122-137), 12• Seeds (Cosmology in the 21st Century, Web Handout)Full reading through Unit 6:• BBBHNM: Chaps. 1-22• TFTM: Chaps. 1-5• BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-137), 12• SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6-8 (up-to-page

164) • TOE: Chaps. 1-3• Seeds (Cosmology in the 21st Century)Lecture prep: Turn in on eLearning

Two questions from Chapter 21 you want to know the answer to



65

Course Evaluations

This semester two separate course evaluations will be done online

1."Department of Physics On-Line Course Evaluation System“

http://evaluation.tamu.edu/2.SLATE Award Evaluations

http://pica.tamu.edu Please, take a few minutes to fill

these out. I really appreciate it!



Papers• Paper 1 is done• Paper 2 grades are on eLearning

– All grades fixed, revision paper grades posted

• Paper 3 is done: • Paper 4:

– Calibrations were due today before class

– Let us know if you see problems– Let us know if you want to resubmit

66



Paper 5

• We have decided to just to take the 3 highest paper grades from papers 2-5– Thus, paper 5 is optional– For papers 2-4 we will only count

the higher of the original or the revised version

– If you want to do paper 5 it is due on the last day of class. The calibrations are due one week later

67



Other Stuff• Elearning:

– Unit 5 has Unit 6 questions (sigh…)

– 5 and 6 will both be due last day of class

• Schedule from here on out– Mon Apr 26: Ch 20 &21 (paper 4

CPR due)– Wed Apr 28: Ch 21 & 22– Mon May 3: Ch 22 (last day of

class, paper 5 due)68



•Interested in learning more next semester?

•Take Astronomy 111

69



70

The Story

Last Time:•Lots of Evidence for Dark

Matter–Don’t know what it is

This Time: The Early Universe and Particle Physics–Fundamental and Composite Particles

–New idea: Could Supersymmetry explains Dark Matter?



71

Other Composite Particles?

Protons and Neutrons are composite particles

Can we put the fundamental particles together in different ways to create other

particles?

Yes…



72

Outline of Today’s Lecture

•What are the fundamental particles and their interactions?

•Particles, anti-particles and composite particles in the Early Universe

•Supersymmetry, if correct, may provide a Dark Matter candidate



Bosons


6 Types of Quarks• Up, Down, Strange,

Charm, Bottom and Top6 Types of “electrons” • Electron, Muon, Tau,

and a Neutrino for each4 Types of Force Carriers• W, Z, gluon and photon• Graviton is the 5th? Fermio

nsSome are very heavy, some are

very light



74

Next we move on to the particles and

interactions we haven’t talked much about yet…

Are there more Fermions or Bosons in

Nature?



75

More fundamental particles?

• In the 1930’s Paul Dirac realized that for every particle in nature an anti-particle must exist–Since an electron exists we must be able to create anti-electrons

–Same with quarks and anti-quarks

•Doubled the particle spectrum



7676

Writing Assignments

Short Assignments 1, 2 & 3Re-do’s are still possible. Want to revise again? Talk to me

eLearning:Unit 5 past dueNeed to be working on Unit 6



7777

Last Paper

Due last day of class1. If you did the Black Hole

paper your paper is posted now, on Dark Matter

2. If you did not do the Black Hole paper you must turn in a Research Paper

Turn in at eLearning like usual



78

Schedule from Here on Out•Tuesday: Dec 1st Chapter 20

–The rest of the reading is now due–Be working on eLearning Unit 6 stuff–Last content for last paper

•Thursday: Dec 3rd Chapter 21•Tuesday: Dec 8th Chapter 22

–Paper due at midnight•Thursday Dec 10th, No classes, Reading period

•Tuesday 15th: Finals week, no final –Paper revisions due



79

Problem with answers

• If all these particles existed in the early Universe, why aren’t all these particles still around today?

• Most types of particles have short lifetimes and would have decayed away

• Particles with a long lifetime are still around– Protons– Electrons– Photons etc.



80

An Interaction: ElectroMagnetism

Positive charge and negative charge attract each other

+

-

For example, an electron and a

positron



81

Quantum Mechanics and EM

Electron “absorbs” a

photon

e

e

Electron “emits” a

photon

e

e



82

Feynman Diagram of Electromagnitism

•A diagram of how the particles “talk” to each other

•These two are attracted

Time

Hydrogen Atom

e-P

P e-



83

A Hydrogen Atom

The simplest atom: Hydrogen

One electron and one proton

+

-

| ~10-10 m |

| |

~10-15 m



84

Particles: Quarks

•Each nucleon is made of 3 quarks

•Composed of two different types of quark

•Called “up” quarks and “down” quarks

•Each quark has fractional charge



85

Interaction: Strong Force

• The strong force holds the quarks together inside the nucleon

• The force mediator is the “gluon”– Quarks “talk”

to each other via gluons



86

Schedule from Here on Out•Wed April 22nd: 24th lecture

–The rest of the reading is now due–Stage 1 Research Topic Proposal must be approved

–WebCT Unit 6 stuff•Mon April 27th: 25th lecture•Wed April 29th: 26th lecture•Mon May 4th: Class cancelled

–Research paper due at midnight after class

•Wed May 6th: No classes, Reading period•Mon May 8th: Finals week, no final

–Paper revisions due



87

A Theory

•Particle Physicists have been working on to answer these questions for many years

•Current best Theory that answers some of them (unproven)

Supersymmetry



88

Any Experimental evidence for Supersymetric Particles? Not yet… A “smoking gun”

would be producing them in collision experiments at Fermilab or the LHC at CERN



89

High Energy Collisions

Dark M

atter P

article

Dar

k M

atte

r Pa

rticle

Detector

Proton Proton

Ok… Its more complicated than this

since Dark Matter Particles don’t easily

interact with detectors…



90

Notes:

• Now done with Early Times and the Fate of the Universe

• Next up: Big objects and Black Holes– Galaxy formation– Star formation– Black Holes

• If there is time at the end of the semester– Inflation– Dark Energy



91

Paper 1 Results•In general the papers were good•Typical problems include:

– Introduction doesn’t outline the paper OR the reasons why we believe

– Focused too much on explaining the jargon (Doppler effect) instead of the story (galaxies all moving away from us indicates an explosion)

– No interconnetion of the topics– Writing was weak. Seek help at the

Writing center!•If you aren’t happy with your grade you have 1 week to turn it back in



92

Best Papers

The best papers all had the same structure 5 paragraphs

1. Intro (Tell WHAT question you are answering and OUTLINE the 3 reasons)

2. Reason 1 (Galaxies moving away)3. Reason 2 (Expansion of space

time)4. Reason 3 (CBR)5. Summary and tie it all together



93

Feynman Diagrams

If a particle and its anti-particle meet they can annihilate and turn into pure energy which

turn into something else



94

Electron

PositronPhoton

Electrons, positrons, and photons can

annihilate and pair-produce

Occurs frequently in the Early

Universe

Need to take this into account in our understanding

Electrons and Photons



95

A Little History First

• The 1930’s -50’s scientists started discovering more “fundamental particles” coming from the Heavens and in high energy collision experiments

• “Who ordered that?” – I.I. Rabi

Cosmic Ray

Bangs into a detector

which “draws”

the particle trajectories



96

Collide High Energy Particles to Create New Particles

New Particle

New

Par

ticl

e

Detector

Electron Anti-Electron



97

Learn some History From Chemistry?

•Atoms are not fundamental particles

•Each is just a different way of putting together combinations of protons neutrons and electrons

•Are the “new” particles “composite?”



98

Particles: Building Blocks of Nature

Many of the particles we’ve discussed so far are composite

•Atoms = nucleus + electrons

•Nuclei = neutrons + protons

•Nucleons = a group of quarks



99

Quiz

What is the primary topic of today’s lecture and WHY are we talking about it?

Don’t forget to include your name and today’s date



100

For Next Time

•Inflation in the Early Universe

•More on the story on Dark Matter and the new evidence for Dark Energy



101

Any Evidence for This Theory?

Lots of indirect evidence, but nothing solid

The “smoking gun” would be observing Supersymmetric particles!1. Collision experiments at

Fermilab and the LHC at CERN2. Dark Matter “interaction”

detectors here on earthPeople at Texas A&M are leaders in

both searches!



102

Are these Forces all “the same?”

•It turns out that electromagnetism and the weak force are really understood to be a single force called the “electroweak” force…

•Haven’t been able to make a successful unification with gravity or the strong force… still working on it…



103

•The reading for this is SHU 6 and BHOT 11



104

BHOT 11 cont…

•Force particles can be “grouped” into four categories.

•We don’t know if this is really 1 interaction, or 4 separate things (kinda like lots of different atoms, but it turns out that all atoms are really just different combinations of protons and neutrons and electrons)



105

•If the force-carrying particle is heavy it will be difficult to produce and exchange them over long distance so the forces will only a short range

•On the other hand if the force carrying particles have no mass then their “range” is infinite



106

•“What’s the matter in the Universe”



107



108



109

Particle

Anti-ParticlePhoton

Particle pairs can always produce photon pairsIf the photons are energetic enough they can interact and a produce a heavy pair, but those

can decay alsoVERY early times Lots of different Stuff in the

Soup

Each Particle Can be Part of the Soup



110

Why do nucleons stick together?

•If what holds the atom together is the opposite charge of the protons and the electrons… Why don’t the same sign charges of the protons “blow the nucleus apart?”



111



112

dddd uu

uuuudd

uuuudd

dddd uu

uuuudd

dddd uu dddd uu dddd uudddd uu

uuuudd uuuudd

uuuudd

p n



113



114

Outline

•SHU 6? Probably not•BHOT 11•TCSQ: 1-?



115

BHOT 11

• Theories of Everything• Unification of physics• Forces of nature• Changing the electric charge would

change the balance of electromagnetic and gravitational pressures exerted in stars as they burned

• If changed only a small amount then life wouldn’t exist



116

•Why is the electric charge the way it is?

•We don’t know… what a unified theory of everything that tells us WHY it should be the value it is…

•What a theory that has BOTH gravity and Quantum Mechanics



117

BHOT 11 cont…

• Quantum mechanics governs the interactions between the elementary particles (as previously discussed)

• They govern the interactions between electrons and the nucleus and give us atoms.

• They govern the interactions between the protons and neutrons and give us nuclei

• They govern the interactions between quarks to give us protons and neutrons



118

BHOT 11 cont…• Picture on page 119• The force, or interaction, is “carried” by

particles• Example: Let’s say we have two

electrons (same charge). The way they interact is that the electron emits a force-carrying particle

• This causes a recoil of the first electrons (kinda like shooting a gun)

• The other electron “catches” it and gets banged (kinda like if you got hit with the bullet)

• The net result is that two particles move differently and “as if” there were a force between them



119

BHOT 11 cont…

• This example is the “force” of repulsion of two same charge objects

• It turns out each force is transmitted by its own distinctive type of force carrying particle

• This force depends on the type of particle doing the “force carrying”

• own the forces will be long-range



120

BHOT 11 cont…

•The force carrying particles exchanged between matter particles are said to be “virtual” because, unlike real particles, they cannot be directly detected by a particle detector

•We know they exist because they do have a measurable affect: they give rise to the force between matter particles



121

TCSQ 1&2

•Not much to say in chapter 1•The Standard Model of Particle

physics•Does this go in section 2?•Figure 2.6, page 17.•Protons determine the

chemical nature of the atom•Not going to do the history

here…



122

TCSQ 2 cont…

•E=mc2

•The timeline of particle discoveries? Fig 2.15, page 31

•Anti-particles?•Where does this stuff go?•Matter-anti-matter puzzle.•The particle zoo, page 35, Fig

2.18.



123

TCSQ 2 cont…

•Sect 2.8, quarks•Sect 2.8, quark pictures and the atom, Fig 2.19, page 38.

•Can just know about the quarks and leptons, need to understand how they interact

•This is the stuff about forces.



124

The Answer

The same strong force keeps the nucleons together



125

Forming Protons

Quark

Quark

ProtonNuclear Reaction

Quark

qqq Proton



126

BHOT 11 cont…

•First force: Gravity•Universal•Everything feel gravity and

how strong the force between particles is depends on their mass or energy

•Picture of Earth around sun and light getting bent… Page 77 and page 43.



127

BHOT 11 cont…

• Gravity continued… We think of gravity being caused by the exchange of virtual gravitons (not yet confirmed).

• Gravity is the weakest of the forces by a lot

• Two important things to know:– It acts even at long distances– It is (as far as we know) always

attractive



128

•So what, if objects are really far away we might never notice gravity, but if they are really HEAVY then the attraction can be big

•Earth going around the sun•Others tend to cancel out



129

BHOT 11 cont…

• Force 2: Electromagnetic force• Most people know about this also,

it is what causes the interactions between electrically charge particles that we know and love

• Electrons and protons• Electrons and quarks• Ignores electrically neutral

particles such as neutrons and neutrinos



130

BHOT 11 cont…

• It is MUCH stronger than gravity

• If I have two electrons the electric force between them is so strong that it is 1042 times stronger than gravity

•However, we have two types of charge, Positive and negative + and –

•This is special because opposite sign attract and same sign repel



131

BHOT 11 cont…

• So what? Most objects we know and love (the earth, us etc.) have VERY equal numbers of protons and neutrons (i.e., objects made of atoms/molecules and they are all electrically neutral or they would attract more charge to make them so)

• Bottom line: all the forces from all these charges tend to cancel each other out and there is very little force left over.



132

BHOT 11 cont…

•However, on the size of atoms and molecules electric charge becomes REALLY important

• Its what holds the electrons moving around the nucleus (the protons)

•We think of the force between electrically charged things as being caused by the exchange of virtual photons

•Cool Feynman diagram here…



133

BHOT 11 cont…

• Force 4: Strong force• This is MUCH stronger than all the

other forces• Its what holds the quarks together

inside the proton and the neutron• Question: If the electrons are held

near an nucleus because they have opposite charge from the nucleus (or the protons in the nucleus), why don’t all the protons (which have the same charge) all scatter apart?



134

BHOT 11 cont…

•The answer is the strong force

•It is SO STRONG that it provides more force to keep the protons together than the electric force has to push them apart

•Note for the amused: This is why we need neutrons



135

•You have to have the extra “strong” particles around to keep it all together.

•The strong force is really only between quarks and the force carrying particle is known as the creatively named “gluon”



136

Neutron Proton + Electron + Neutrino

Neutron Decay

Neutron

ProtonDecay

Electron

Neutrino



137

The Feynman Diagrams

e

e

W

d

u



138


•Why do we need so many different particles?

•Why are some so much heavier than the others?

•How do we know we aren’t missing any?

The Standard Model of particle physics has been enormously successful

But:



139

This is a test



140

More stuff

•This is a test



141

Quantum Mechanics – Force Carriers

•Why?•We now 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



142

Example with Two Protons

• First proton emits a “force-carrying” particle

• Causes a recoil of the first proton– You shoot a gung and lurch back

• The other proton “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



143

Diagram

+ +

2: Proton on the right “emits” a photon and “recoils”

3: Photon bangs into the left proton and bumps it

Both now move apart: Same sign charges “repel” each

other

1: Two Protons hanging out



144

A Proton and Electron

- +

2: Proton on the right “emits” a photon and “recoils”

3: Photon bangs into the electronDoesn’t transfer Momentum

Transfers information on how to move

Like signs attract

1: A proton and an electron hanging out



145



146

Photons and Electrons

Photons can turn into Electron pairs

Electron pairs turn into Photons

+ -

-+



147

Anti-Matter Stuff• When matter and anti-matter meet they

annihilate and disappear in a burst of energy

• How could all the matter in the universe exist and be easily detectible if theoretically there should be just as much antimatter around?

• Either the matter and antimatter should have annihilated each other, or we ought to be able to detect as much antimatter in the universe, which we clearly do not.

• Evidence for anti-electrons (positrons) in 1932



148

SHU 6??? Not here…

• This is where the discussion starts about anti-matter. Why is there more matter in the universe than anti-matter? This is still and open question.

• At the moment we believe (think? Speculate) that at VERY high energies (very early time) (threshold energies for protons is about 1013 degrees K quarks can interact and produce slightly more quarks than anti-quarks (sphalerons).



149

• This takes CP violation to cause it not to go the other way at the same rate

• Eventually all the quarks become protons and neutrons (via decay) and eventually the neutrons decay to protons and electrons, thus what we see is proton, neutron, and electron (photon and neutrino) because only those are stable

• Its about evolution and decay



150



151

Put them together in other ways

•This is some text



152

This is a test



153

Turns out there are other Particles

•This is some text



154

Very Early Universe is Still Very Complicated

•There are lots of other elementary particles we haven’t talked about yet and they have a big impact

•One example is a Muon which is (for our purposes) just a heavier version of an electron–More on them later



155

Electron

PositronGamma-ray photonElectron pairs can

always produce photon pairs

If the photons are energetic enough they can interact and create

electron pairs

electron and photon Soup

Photons and Electrons at 6 Billion Degrees



156

Photons and Muons

At very high energies photons can also turn into

Muon pairs

Muon pairs can turn into Photons

+ -

-+



157

Muon

Anti-MuonGamma-ray photon

Muon pairs can always produce

photon pairsIf the photons are energetic enough

they can interact and create muon pairs muon and photon

Soup

Muons Are Part of the Soup



158

•Conserved Quantities



159

•What about lepton number? •Can’t tell because of the

neutrinos? Probably conserved, but no evidence

•Charge is also probably conserved

•No evidence either way that lepton number isn’t conserved

•What about baryon number?



160

Very Early Universe is Very Complicated

What particles exists determine what’s going on in the Very Early Universe

Problem: We don’t know if we have

discovered all the fundamental particles yet

• Good reasons to believe there are new ones out that we just haven’t found yet– Need bigger accelerators and/or

Other tools– More on this later also



161

TCSQ 2 cont…

• Unanswered questions in particle physics

• Why do three versions exist of each type of quark and lepton of a given electric charge?

• Can the values of the masses of these particles be understood?



162

•Are there other particle types that are too massive to have been discovered so far?

•Are the quarks and leptons structure-less?

•Are there other forces yet to be discovered?



163

BHOT 11 cont…

•Really want to talk about problems of incorporating gravity?

•Useful stuff stops at page 122…

Documents

Big Bang, Black Holes, No Math Early Times & Fate of The Universe Topic 2: Particle Physics 1 Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback