The Beginning of Time Somewhere, something incredible is waiting to be known. - Carl Sagan

The Beginning of TimeThe Beginning of Time

Somewhere, something incredible is waiting to be

known.- Carl Sagan

WHEN I heard the learn’d astronomer;

When the proofs, the figures, were ranged in columns

before me;

When I was shown the charts and the diagrams, to

add, divide, and measure them;

When I, sitting, heard the astronomer, where he

lectured with much applause in the lecture-room,

How soon, unaccountable, I became tired and sick;

Till rising and gliding out, I wander’d off by myself,

In the mystical moist night-air, and from time to time,

Look’d up in perfect silence at the stars.

WHAT DO YOU THINK?1.1. Did the universe have a Did the universe have a

beginning?beginning?

2.2. Into what is the universe Into what is the universe expanding?expanding?

3.3. Will the universe last Will the universe last forever?forever?

4.4. Are there other universes?Are there other universes?

5.5. Can we ever find out what Can we ever find out what started everything?started everything?

6.6. Should we try??Should we try??

In this chapter you will discover…In this chapter you will discover…

CosmologyCosmology, which seeks to explain how the , which seeks to explain how the universe began, how it evolves, and its fateuniverse began, how it evolves, and its fate

Um… not COSMETOLOGY…

In this chapter you will discover…In this chapter you will discover…

CosmologyCosmology, which seeks to explain how the , which seeks to explain how the universe began, how it evolves, and its fateuniverse began, how it evolves, and its fate

The best theory that we have for the evolution of The best theory that we have for the evolution of the universe—the the universe—the Big BangBig Bang

How astronomers trace the emergence of matter How astronomers trace the emergence of matter and the formation of galaxiesand the formation of galaxies

Key Essay QuestionsKey Essay Questions

How did the universe How did the universe begin?begin?

How will it end? How will it end?

How do we know? How do we know? What evidence do we What evidence do we have? have?

Facts Facts Must be explained by a scientific theory to Must be explained by a scientific theory to

be consideredbe considered

QuasarsQuasars more prevalent far away; we more prevalent far away; we don’t see them beyond ~ 13 Billion light don’t see them beyond ~ 13 Billion light years. years.



Cosmic Cosmic MicrowaveMicrowave Background Radiation Background Radiation



The Night Sky The Night Sky isis Dark Dark (Olber’s Paradox)(Olber’s Paradox)

Olber’s Paradox – Why is the Night Olber’s Paradox – Why is the Night Sky Dark?Sky Dark?

IfIf the universe contains an infinite number the universe contains an infinite number of stars, uniformly distributed in space, of stars, uniformly distributed in space,

and the universe is infinitely old, and the universe is infinitely old, thenthen::

Olber’s Paradox – Why is the Night Olber’s Paradox – Why is the Night Sky Dark?Sky Dark?

IfIf the universe contains an infinite number of stars, uniformly the universe contains an infinite number of stars, uniformly

distributed in space, and the universe is infinitely old, distributed in space, and the universe is infinitely old, thenthen::

Overall brightnessOverall brightness received in any direction from received in any direction from those stars is constant.those stars is constant.

Farther away, more space, but more stars in that Farther away, more space, but more stars in that space. space.

In every direction, eventually look at surface of a star, In every direction, eventually look at surface of a star, so…. so….

Every point in the sky should be as bright as the Every point in the sky should be as bright as the surface of a starsurface of a star. .

Olber’s ParadoxOlber’s Paradox

If…then If…then logical argument logical argument

assumptionassumption conclusionconclusion

Clearly the night sky IS darkClearly the night sky IS dark

The conclusion is false so one or more The conclusion is false so one or more assumptions must be incorrect!assumptions must be incorrect!

The universe is not infinite in size, and not The universe is not infinite in size, and not infinite in age!infinite in age!



Hubble’s LawHubble’s Law: Distant Galaxies move away from : Distant Galaxies move away from us, faster. The Universe is changing in time. us, faster. The Universe is changing in time.



90%90% of the Universe is of the Universe is HydrogenHydrogen, 10% is Helium, 10% is Helium



QuasarsQuasars more prevalent far away; we don’t see them more prevalent far away; we don’t see them beyond ~ 13 Billion light years. beyond ~ 13 Billion light years.

Cosmic Microwave Background RadiationCosmic Microwave Background Radiation The Night Sky is Dark The Night Sky is Dark (Olber’s Paradox)(Olber’s Paradox) Hubble’s Law:Hubble’s Law: Distant Galaxies move away from us, Distant Galaxies move away from us,

faster. The Universe is changing in time.faster. The Universe is changing in time. 90%90% of the Universe is of the Universe is HydrogenHydrogen, 10% is Helium, 10% is Helium

Penzias & Wilson’s Horn Antenna used to discover

CMBR

WMAP satellite (2001)

Boomerang Balloon-Lofted Probe above Antarctica (1998 & 2003)

What is the Cosmic Microwave What is the Cosmic Microwave Background?Background?

Relic “heat” energy from Big BangRelic “heat” energy from Big Bang

ReleasedReleased ~ 1/2 million years after Bang ~ 1/2 million years after Bang


BeforeBefore ~ ½ million years, universe was a ~ ½ million years, universe was a “sea” of high energy particles & photons“sea” of high energy particles & photons

AfterAfter, universe cools, allowing neutral matter , universe cools, allowing neutral matter to formto form


Radiation then is visible through spaceRadiation then is visible through space

RedshiftedRedshifted as universe expands as universe expands



The Night Sky is Dark The Night Sky is Dark (Olber’s Paradox)(Olber’s Paradox) Hubble’s Law:Hubble’s Law: Distant Galaxies move away from us, Distant Galaxies move away from us,

faster. The Universe is changing in time.faster. The Universe is changing in time. 90%90% of the Universe is of the Universe is HydrogenHydrogen, 10% is Helium, 10% is Helium Cosmic Microwave Background RadiationCosmic Microwave Background Radiation QuasarsQuasars more prevalent far away; we don’t see them more prevalent far away; we don’t see them

beyond ~ 13 Billion light years. beyond ~ 13 Billion light years.

AssumptionsAssumptions

Physics:Physics: The laws we know of around us work The laws we know of around us work everywhere in the same way.everywhere in the same way.

Isotropy: Isotropy: The Universe looks the same as it appears to The Universe looks the same as it appears to us – everywhereus – everywhere

Homogeneity: Homogeneity: The Universe is made of the same stuff The Universe is made of the same stuff we see around us - everywherewe see around us - everywhere

Facts + Assumptions Facts + Assumptions TheoryTheory

The Big Bang TheoryThe Big Bang Theory

The universe The universe startedstarted ~ 14 Billion years ago ~ 14 Billion years ago

All All energyenergy, incredibly hot and dense , incredibly hot and dense

Expands incredibly fast (Expands incredibly fast (inflationinflation))

Matter (protons, electrons, neutrons) created Matter (protons, electrons, neutrons) created from energy (E = mcfrom energy (E = mc22))

Facts + Assumptions Facts + Assumptions TheoryTheory

The Big Bang TheoryThe Big Bang Theory

Some protons (Hydrogen) fuse to create HeliumSome protons (Hydrogen) fuse to create Helium

Universe cools and expandsUniverse cools and expands

Eventually, neutral atoms form…Eventually, neutral atoms form…

““RecombinationRecombination” era is when CBR can be seen” era is when CBR can be seen

A Big Bang Timeline…

A A ScientificScientific Story… Story…

What would the universe have been like in What would the universe have been like in the first few …the first few …billionthsbillionths of of billionthsbillionths of a second? of a second?SecondsSeconds??Three Minutes?Three Minutes?

Why did the universe expand so quickly?Why did the universe expand so quickly?When did galaxies form?When did galaxies form?Why did galaxies form?Why did galaxies form?

Conditions in the Early UniverseConditions in the Early Universe

Most Most distant quasars & galaxies distant quasars & galaxies observed from time when Universe was ~ 1 billion years observed from time when Universe was ~ 1 billion years old.old.

Cosmic microwave backgroundCosmic microwave background is earliest light available (~400,000 years after Big Bang) is earliest light available (~400,000 years after Big Bang)

HowHow to know conditions at to know conditions at beginning of timebeginning of time? ?

Conditions in the Early UniverseConditions in the Early Universe

Know forces, conditions & Know forces, conditions & expansion rate of Universe expansion rate of Universe today.today.

Run expansion backwards, Run expansion backwards, model early universe!model early universe!

Today: FOUR forces seen in natureToday: FOUR forces seen in nature

Gravity (longest distance, weakest force)Gravity (longest distance, weakest force)

Running the film backwards….


Gravity (longest distance, weakest force)Gravity (longest distance, weakest force)Electromagnetic (light!)Electromagnetic (light!)



Gravity (longest distance, weakest force)Gravity (longest distance, weakest force)Electromagnetic (light!)Electromagnetic (light!)Weak (radioactive decay, neutron decay)Weak (radioactive decay, neutron decay)



Gravity (longest distance, weakest force)Gravity (longest distance, weakest force)Electromagnetic (light!)Electromagnetic (light!)Weak (radioactive decay, neutron decay)Weak (radioactive decay, neutron decay)Strong (“nuclear glue force”)Strong (“nuclear glue force”)


Today: Today: SuccessfullySuccessfully created tests conditions created tests conditions in lab to in lab to linklink Electromagnetic, Weak, Strong Electromagnetic, Weak, Strong forcesforces

““The Grand Unified Theory”The Grand Unified Theory”

We hypothesize that We hypothesize that allall four natural forces four natural forces were unifiedwere unified during during VERYVERY early universe early universe


Planck Era (t < 10Planck Era (t < 10–43–43 sec) sec)

(small details about) The Big Bang

““Planck Era” (t < 10Planck Era” (t < 10–43–43 sec) sec)

We are as yet unable to link…We are as yet unable to link…quantum mechanics & general relativityquantum mechanics & general relativity

We are still trying to describe what happened in We are still trying to describe what happened in this era with the LHC!this era with the LHC!


GUT Era (10GUT Era (10–43–43 < t < 10 < t < 10–38–38 sec) sec)

The Universe contained The Universe contained twotwo natural natural forces:forces:

• GravityGravity• Grand Unified Theory (GUT) forceGrand Unified Theory (GUT) force

electromagnetic + strong + weak forces unifiedelectromagnetic + strong + weak forces unified


GUT Era (10GUT Era (10–43–43 < t < 10 < t < 10–38–38 sec) sec)

Lasted until Universe was Lasted until Universe was 1010–38–38 sec old. sec old.• ““cooled” to 10cooled” to 102929 K K

• strong forcestrong force emerges separate and distinct emerges separate and distinct from electro-weak forcefrom electro-weak force

• energy released by this caused a sudden and energy released by this caused a sudden and dramatic dramatic inflationinflation of the size of the Universe of the size of the Universe


Electroweak EraElectroweak Era


Electroweak Era (10Electroweak Era (10–38–38 < t < 10 < t < 10–10–10 sec) sec)

Universe contained three natural forces: Universe contained three natural forces: gravity, strong, & gravity, strong, & electroweakelectroweak

Lasted until Universe was Lasted until Universe was 1010–10–10 sec old. sec old.• Now “cooled” to 10Now “cooled” to 101515 K K• electromagnetic & weak forces separatedelectromagnetic & weak forces separated


Electroweak Era (10Electroweak Era (10–38–38 < t < 10 < t < 10–10–10 sec) sec)

Experimentally verified in 1983!Experimentally verified in 1983!

• Discovery of W & Z bosonsDiscovery of W & Z bosons

• Electroweak particles predicted to exist above Electroweak particles predicted to exist above 10101515 K K


And then something happens…And then something happens…

From this high-energy state, galaxies and From this high-energy state, galaxies and stars must eventually formstars must eventually form

What triggers galaxy formation?What triggers galaxy formation?

Why bubbles and voids?Why bubbles and voids?

And now something else is And now something else is happening…happening…

What is What is dark matterdark matter????

Why doesn’t the universe slow down as Why doesn’t the universe slow down as much as it should be?much as it should be?

What is What is dark energydark energy??

What isWhat is Dark Dark Matter?Matter?

• Recall rotation curve of Recall rotation curve of Milky Way Galaxy.Milky Way Galaxy.

• Hydrogen beyond our Sun Hydrogen beyond our Sun orbit faster than predicted orbit faster than predicted by Kepler’s Lawby Kepler’s Law

• Most of Galaxy’s light Most of Galaxy’s light from stars closer to centerfrom stars closer to center

What is Dark Matter?What is Dark Matter?

Two possible explanations:Two possible explanations:

• We do not understand gravity We do not understand gravity (on galaxy-size+ scales)(on galaxy-size+ scales)

• Higher velocities of Hydrogen Higher velocities of Hydrogen gas caused by gravitational gas caused by gravitational attraction of unseen matter…attraction of unseen matter…called called dark matterdark matter

What is Dark Matter?What is Dark Matter?

IF we trust our theory of gravity...IF we trust our theory of gravity... there may be 10 times more dark than there may be 10 times more dark than

luminous matter in our Galaxyluminous matter in our Galaxy

luminous matter is confined to the diskluminous matter is confined to the disk

dark matter is found in the halo and far dark matter is found in the halo and far beyond the luminous diskbeyond the luminous disk

And still And still moremore Dark Matter! Dark Matter!

In other galaxies, we “see” same phenomenaIn other galaxies, we “see” same phenomenaRotation Curves of SpiralsRotation Curves of Spirals

In clusters of galaxies, tooIn clusters of galaxies, tooMeasuring Motions of galaxiesMeasuring Motions of galaxiesMeasuring “Temperature” of gasMeasuring “Temperature” of gasGravitational LensingGravitational Lensing

Velocities in Clusters of GalaxiesVelocities in Clusters of Galaxies

• Pioneered by Fritz Zwicky in Pioneered by Fritz Zwicky in 1930’s1930’s

Zwicky found clusters had to Zwicky found clusters had to be MUCH more massive!.be MUCH more massive!.• his proposals of dark matter his proposals of dark matter

were met with skepticismwere met with skepticism

Gravitational LensingGravitational Lensing

• Theory of Relativity Theory of Relativity states that massive states that massive objects distort objects distort spacetime.spacetime.

• Massive cluster bends path of light Massive cluster bends path of light (like a lens)(like a lens)

• Blue arcs are lensedBlue arcs are lensed images of galaxy images of galaxy behindbehind cluster cluster

Agreement between methodsAgreement between methods

• Cluster masses measured by all three Cluster masses measured by all three independent methods agree:independent methods agree:

• Most galaxy clusters contain greater than Most galaxy clusters contain greater than 100 times more mass than accounted for by 100 times more mass than accounted for by light of stars within them!light of stars within them!

• Galaxy clusters contain far more mass in Galaxy clusters contain far more mass in dark matter dark matter than in starsthan in stars

A problem on the horizon?

Dark Dark EnergyEnergy ?!?#% ?!?#%

If the universe is really larger than it If the universe is really larger than it should be…should be…Something must be making it expand…Something must be making it expand…Energy must be present Energy must be present But we can’t see its source:But we can’t see its source:

Dark Energy! https://www.youtube.com/watch?v=3FZv4U5YbNc

Why is Dark Energy Important?Why is Dark Energy Important?

Consider Consider ultimate fate ultimate fate of the universe…of the universe…

Option 1: Universe continues to expand, Option 1: Universe continues to expand, slows, stops, recollapses…. slows, stops, recollapses….

(The big “crunch”)(The big “crunch”)

Why is Dark Energy Important?Why is Dark Energy Important?

Consider Consider ultimate fate ultimate fate of the universe…of the universe…

Option 2: Universe Option 2: Universe continues to expand, continues to expand, accelerating faster accelerating faster and fasterand faster

(The big “stretch”)(The big “stretch”)

The The GeometryGeometry of Space of Space Space (and Time!) can take the shape ofSpace (and Time!) can take the shape of

Volume reaches a maximum size, then recollapses, Volume reaches a maximum size, then recollapses, oror

Infinitely expanding volume, accelerating over time, Infinitely expanding volume, accelerating over time, or…or…

Volume that gets bigger, but slows down to Volume that gets bigger, but slows down to eventual stop (in an infinite amount of time)eventual stop (in an infinite amount of time)

The The GeometryGeometry of Space of Space Space (and Time!) can take the shape ofSpace (and Time!) can take the shape of

Volume reaches a maximum size, then Volume reaches a maximum size, then recollapses recollapses (CLOSED)(CLOSED)

An infinitely expanding volume, accelerating over An infinitely expanding volume, accelerating over time time (OPEN)(OPEN)

A volume that gets bigger, but slows down to A volume that gets bigger, but slows down to eventual stop in an infinite amount of time eventual stop in an infinite amount of time (FLAT)(FLAT)

Evidence for an Accelerating Evidence for an Accelerating Universe?Universe?

Four Models for the Future of the Four Models for the Future of the UniverseUniverse

RecollapsingRecollapsing Universe Universe: the expansion will someday halt and reverse: the expansion will someday halt and reverse CriticalCritical Universe Universe: will not collapse, but will expand more slowly with time: will not collapse, but will expand more slowly with time CoastingCoasting Universe Universe: will expand forever with little slowdown: will expand forever with little slowdown AcceleratingAccelerating Universe Universe: the expansion will accelerate with time (currently : the expansion will accelerate with time (currently

“favored”)“favored”)

The critical density!The critical density!

How can we tell what the future holds?How can we tell what the future holds?

The amount of mass in the volume of space The amount of mass in the volume of space controls gravitational force’s impactcontrols gravitational force’s impact

Estimating “critical density” is key!Estimating “critical density” is key!

The Critical DensityThe Critical Density

• IF gravitational attraction between galaxies IF gravitational attraction between galaxies can overcome the expansion of the Universe can overcome the expansion of the Universe in localized regions.in localized regions.• how strong must gravity be to stop the how strong must gravity be to stop the entireentire

Universe from expanding?Universe from expanding?

• it depends on the total mass it depends on the total mass densitydensity of the of the UniverseUniverse


• if if mass < critical densitymass < critical density, the Universe will , the Universe will expand foreverexpand forever

• if if mass > critical densitymass > critical density, the Universe will , the Universe will stop expanding and then contractstop expanding and then contract

The value of HThe value of Hoo tells us the current kinetic tells us the current kinetic

energy of the Universe AND indicates the energy of the Universe AND indicates the critical density is 10critical density is 10–29–29 g / cm g / cm33


• BUT all the luminous matter that we observe BUT all the luminous matter that we observe accounts for < 1% of critical densityaccounts for < 1% of critical density

• And for dark matter to stop Universal And for dark matter to stop Universal expansion, even more would be required…expansion, even more would be required…

This line of research suggests the Universe This line of research suggests the Universe will expand forever!will expand forever!

Key TermsKey TermsBig Bangclosed universeconfinementcosmic light horizoncosmic microwave backgroundcosmological constantcosmological redshiftcosmologydark agesdark energydecouplingera of recombinationexpanding universeGrand Unified Theory (GUT)homogeneityhorizon probleminflationinflationary epoch

isotropyisotropy problemmatter-dominated universeopen universepair productionPlanck timeprimordial fireballprimordial nucleosynthesisquarkquintessenceradiation-dominated universestrong nuclear forcesuperstring theoriesTheories of Everythinguniverseweak nuclear force

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The Beginning of Time Somewhere, something incredible is waiting to be known. - Carl Sagan