The 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.
2.
3.
4.
5.
6.
Did the universe have a
beginning?
Into what is the universe
expanding?
Will the universe last
forever?
Are there other universes?
Can we ever find out what
started everything?
Should we try??
In this chapter you will discover…

Cosmology, which seeks to explain how the
universe began, how it evolves, and its fate
Um… not COSMETOLOGY…
In this chapter you will discover…

Cosmology, which seeks to explain how the
universe began, how it evolves, and its fate

The best theory that we have for the evolution of
the universe—the Big Bang

How astronomers trace the emergence of matter
and the formation of galaxies
Key Essay Questions

How did the universe
begin?

How will it end?

How do we know?
What evidence do we
have?
Facts
Must be explained by a scientific theory to
be considered





The Night Sky is Dark
Hubble’s Law
90% of the Universe is Hydrogen
Cosmic Microwave Background Radiation
Quasars
Facts
Must be explained by a scientific theory to
be considered

The Night Sky is Dark (Olber’s Paradox)
Olber’s Paradox – Why is the Night
Sky Dark?
 If the universe contains an infinite number
of stars, uniformly distributed in space,
and the universe is infinitely old, :
 Then the sky SHOULD be as bright as a
star, in every direction!
Olber’s Paradox
If…then logical argument
assumption  conclusion
Clearly the night sky IS dark
 The conclusion is false so one or more
assumptions must be incorrect!
 The universe is not infinite in size, and not
infinite in age!

Olber’s Paradox – Why is the Night
Sky Dark?

If the universe contains an infinite number of stars, uniformly
distributed in space, and the universe is infinitely old, then:




Overall brightness received in any direction from
those stars is constant.
Farther away, more space, but more stars in that
space.
In every direction, eventually look at surface of a star,
so….
Every point in the sky should be as bright as the
surface of a star.
Facts
Must be explained by a scientific theory to
be considered

90% of the Universe is Hydrogen, 10% is Helium
Facts
Must be explained by a scientific theory to
be considered

Hubble’s Law: Distant Galaxies move away from
us, faster. The Universe is changing in time.
Facts
Must be explained by a scientific theory to
be considered

Quasars more prevalent far away; we
don’t see them beyond ~ 13 Billion light
years.
Facts
Must be explained by a scientific theory to
be considered

Cosmic Microwave Background Radiation
Penzias & Wilson’s Horn
Antenna used to discover
CMBR
WMAP satellite (2001)
Boomerang Balloon-Lofted Probe
above Antarctica (1998 & 2003)
Facts
Must be explained by a scientific theory to
be considered





The Night Sky is Dark (Olber’s Paradox)
90% of the Universe is Hydrogen, 10% is Helium
Hubble’s Law: Distant Galaxies move away from us,
faster. The Universe is changing in time.
Quasars more prevalent far away; we don’t see them
beyond ~ 13 Billion light years.
Cosmic Microwave Background Radiation
Assumptions

Physics: The laws we know of around us work
everywhere in the same way.

Isotropy: The Universe looks the same as it appears to
us – everywhere

Homogeneity: The Universe is made of the same stuff
we see around us - everywhere
Facts + Assumptions Theory

The Big Bang Theory

The universe started ~ 14 Billion years ago

All energy, incredibly hot and dense

Expands incredibly fast (inflation)

Matter (protons, electrons, neutrons) created
from energy (E = mc2)
Facts + Assumptions Theory

The Big Bang Theory

Some protons (Hydrogen) fuse to create Helium

Universe cools and expands

Eventually, neutral atoms form…

“Recombination” era is when CBR can be seen
What is the Cosmic Microwave
Background?

Relic “heat” energy from Big Bang

Released ~ 1/2 million years after Bang
What is the Cosmic Microwave
Background?

Before ~ ½ million years, universe was a
“sea” of high energy particles & photons

After, universe cools, allowing neutral matter
to form
What is the Cosmic Microwave
Background?

Radiation then is visible through space

Redshifted as universe expands
A Big Bang Timeline…
A Scientific Story…

What was universe like in the first few …
billionths of billionths of a second?
 Seconds?
 Three Minutes?


Why did the universe expand so quickly?
(YouTube video!)

When did galaxies form? WHY?
Conditions in the Early Universe

Most distant quasars & galaxies observed from
time when Universe was ~ 1 billion years old.

Cosmic microwave background is earliest light
available (~400,000 years after Big Bang)

How to know conditions at beginning of time?
Conditions in the Early Universe

Know forces, conditions &
expansion rate of Universe
today.

Run expansion backwards,
model early universe!
Running the film backwards….

Today: FOUR forces seen in nature

Gravity (longest distance, weakest force)
Running the film backwards….

Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)
 Electromagnetic (light!)

Running the film backwards….

Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)
 Electromagnetic (light!)
 Weak (radioactive decay, neutron decay)

Running the film backwards….

Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)
 Electromagnetic (light!)
 Weak (radioactive decay, neutron decay)
 Strong (“nuclear glue force”)

Running the film backwards….

Today: Successfully created tests
conditions in lab to link Electromagnetic,
Weak, Strong forces


“The Grand Unified Theory”
We hypothesize that all four natural forces
were unified during VERY early universe
(small details about)
The Big Bang
Planck Era (t < 10
–43
sec)
(small details about)
The Big Bang
“Planck Era” (t < 10
–43
sec)

We are as yet unable to link…
quantum mechanics & general relativity

We are still trying to describe what happened in
this era with the LHC!
(small details about)
The Big Bang
–43
GUT Era (10

–38
< t < 10
sec)
The Universe contained two natural
forces:
•
•
Gravity
Grand Unified Theory (GUT) force
electromagnetic + strong + weak forces unified
(small details about)
The Big Bang
–43
GUT Era (10

–38
< t < 10
–38
Lasted until Universe was 10
29
sec)
sec old.
•
“cooled” to 10
•
strong force emerges separate and distinct
from electro-weak force
•
energy released by this caused a sudden and
dramatic inflation of the size of the Universe
K
(small details about)
The Big Bang
Electroweak Era
(small details about)
The Big Bang
–38
Electroweak Era (10


–10
< t < 10
sec)
Universe contained three natural forces:
gravity, strong, & electroweak
–10
Lasted until Universe was 10
•
•
15
sec old.
Now “cooled” to 10 K
electromagnetic & weak forces separated
(small details about)
The Big Bang
–38
Electroweak Era (10

–10
< t < 10
sec)
Experimentally verified in 1983!
•
Discovery of W & Z bosons
•
Electroweak particles predicted to exist above
15
10 K
And then something happens…

From this high-energy state, galaxies and
stars must eventually form

What triggers galaxy formation?

Why bubbles and voids?
And now something else is
happening…

What is dark matter??

Why doesn’t the universe slow down as
much as it should be?

What is dark energy?
What is Dark Matter?
•
Recall rotation curve of
Milky Way Galaxy.
•
Hydrogen beyond our Sun
orbit faster than predicted
by Kepler’s Law
•
Most of Galaxy’s light
from stars closer to center
What is Dark Matter?

Two possible explanations:
•
We do not understand gravity
(on galaxy-size+ scales)
•
Higher velocities of Hydrogen
gas caused by gravitational
attraction of unseen
matter…called dark matter
What is Dark Matter?

IF we trust our theory of gravity...

there may be 10 times more dark than
luminous matter in our Galaxy

luminous matter is confined to the disk

dark matter is found in the halo and far
beyond the luminous disk
And still more Dark Matter!

In other galaxies, we “see” same phenomena


Rotation Curves of Spirals
In clusters of galaxies, too
Measuring Motions of galaxies
 Measuring “Temperature” of gas
 Gravitational Lensing

Velocities in Clusters of Galaxies
•
Pioneered by Fritz Zwicky in
1930’s

Zwicky found clusters had to
be MUCH more massive!.
•
his proposals of dark matter
were met with skepticism
Gravitational Lensing
•
Theory of Relativity
states that massive
objects distort
spacetime.
•
Massive cluster bends path of light (like a lens)
•
Blue arcs are lensed images of galaxy behind cluster
Agreement between methods
•
Cluster masses measured by all three
independent methods agree:
•
Most galaxy clusters contain greater than
100 times more mass than accounted for by
light of stars within them!
•
Galaxy clusters contain far more mass in
dark matter than in stars
A problem on the horizon?
Dark Energy ?!?#%

If the universe is really larger than it
should be…
Something must be making it expand…
 Energy must be present
 But we can’t see its source:

Dark Energy!
https://www.youtube.com/watch?v=3FZv4U5YbNc
Why is Dark Energy Important?

Consider ultimate fate of the universe…
Option 1: Universe continues to expand,
slows, stops, recollapses….
 (The big “crunch”)

Why is Dark Energy Important?

Consider ultimate fate of the universe…

Option 2: Universe
continues to expand,
accelerating faster
and faster

(The big “stretch”)
The Geometry of Space

Space (and Time!) can take the shape of

Volume reaches a maximum size, then
recollapses, or

Infinitely expanding volume, accelerating over
time, or…

Volume that gets bigger, but slows down to
eventual stop (in an infinite amount of time)
The Geometry of Space

Space (and Time!) can take the shape of

Volume reaches a maximum size, then
recollapses (CLOSED)

An infinitely expanding volume, accelerating
over time (OPEN)

A volume that gets bigger, but slows down to
eventual stop in an infinite amount of time
(FLAT)
Evidence for an Accelerating
Universe?
Four Models for the Future of the
Universe




Recollapsing Universe: the expansion will
someday halt and reverse
Critical Universe: will not collapse, but will
expand more slowly with time
Coasting Universe: will expand forever with
little slowdown
Accelerating Universe: the expansion will
accelerate with time (currently “favored”)
The critical density!

How can we tell what the future holds?

The amount of mass in the volume of space
controls gravitational force’s impact

Estimating “critical density” is key!
The Critical Density
•
IF gravitational attraction between galaxies
can overcome the expansion of the Universe
in localized regions.
•
how strong must gravity be to stop the entire
Universe from expanding?
•
it depends on the total mass density of the
Universe
The Critical Density
•
if mass < critical density, the Universe will
expand forever
•
if mass > critical density, the Universe will
stop expanding and then contract

The value of Ho tells us the current kinetic
energy of the Universe AND indicates the
critical density is 10–29 g / cm3
The Critical Density
•
BUT all the luminous matter that we observe
accounts for < 1% of critical density
•
And for dark matter to stop Universal
expansion, even more would be required…

This line of research suggests the Universe
will expand forever!
Key Terms
Big Bang
closed universe
confinement
cosmic light horizon
cosmic microwave background
cosmological constant
cosmological redshift
cosmology
dark ages
dark energy
decoupling
era of recombination
expanding universe
Grand Unified Theory (GUT)
homogeneity
horizon problem
inflation
inflationary epoch
isotropy
isotropy problem
matter-dominated universe
open universe
pair production
Planck time
primordial fireball
primordial nucleosynthesis
quark
quintessence
radiation-dominated universe
strong nuclear force
superstring theories
Theories of Everything
universe
weak nuclear force