Through a Glass Darkly: Dark Energy and The Fate of the Universe

1
Through a Glass Darkly Dark Energy and The
Fate of the Universe
2
A Scientific History of the Creation of the
Universe

• What was the Universe like during its earliest
  moments?
• Brief description of the key eras since the Big
  Bang
• Note Cosmology doesnt address WHY creation
  occurs

3
Earliest ideas about cosmology A story of three
(very clever) ancient Greek Astronomers
Aristarchus, Eratosthenes, Ptolemy
4
Aristarchus of Samos (c. 250 BCE) Determined
relative size of moon (w.r.t Earth), distance to
Sun
5
Lunar Eclipse Movie (Notice radius of Earth in
Shadow)
6
Moons diameter observed to be 1/3 Earths
shadow size
7
Eratosthenes (276 - 195 BC)

• Measured Circumference of the Earth (within 10
  of modern value! )
• Sun is at the zenith in the city of Syene at
  noon on the summer solstice.
• But at the same time in Alexandria, it is 7?
  from the zenith.

8
Eratostheness Method for Finding the
Circumference of the Earth
9
Claudius Ptolemy (AD 100-170)

• Almagest
• star catalogue
• instruments
• motions model of planets, Sun, Moon

His model fit the data, made accurate
predictions, but was horribly contrived!
10
Age-old problem How does one explain retrograde
motion of the wandering stars?
Movie. Click to play.
Images of Saturn and Jupiter every 2 weeks for 6
months
11
Ptolemys Geocentric Model

• Earth is at center
• Sun orbits Earth
• Planets orbit on small circles whose centers
  orbit the Earth on larger circles

12
Standard Model of the Universe c.100AD-1600AD
13
Nicholaus Copernicus (1473-1543)

• Polish canon (religious leader)
• Suggested sun-centered (heliocentric) solar
  system
• He thought Ptolemys model was contrived
• Yet he believed in circular motion!
• His model doesnt fit observations any better
  than Ptolemys geocentric model!

14
Copernicus (heliocentric) explanation of
retrograde motion
15
Johannes Kepler (1571- 1630) Finds elliptical
orbit for Mars
16
Keplers model for the Solar System A Concentric
Series of Crystalline Spheres
17
Galileos discovery (1610) of Jupiters moons
with his telescope showed that Earth was not the
center of all orbits strongly supported a
heliocentric model
18
Galileos discoveries of Venus phases with his
telescope showed that Venus must orbit the Sun
strongly supported a heliocentric model
.

• Venus is clearly smallest when it is at superior
  conjunction and largest when it is close to
  inferior conjunction.

19
Galileos observation of the phases of Venus was
the final evidence which buried the geocentric
model.
Geocentric
Heliocentric
No gibbous or full phases!
All phases are seen!
Galileo observed all phases!
20
Sir Isaac Newton (1642 1727) the greatest
physicist who ever lived
As a young faculty member at Cambridge University
(c.1665)
As Warden of the Royal Mint (1705)
Newton was knighted by Queen Anne. However, the
act was "an honor bestowed not for his
contributions to science, nor for his service at
the Mint, but for the greater glory of party
politics in the election of 1705"
21
Standard Model of the Universe c. 1650 AD
22
18th - 19th CenturyAstronomers Study of
Properties of Stars (and lots of Comets)
23
Some stars occur in vast groups Globular
Clusters and Nebulae
24
Importance of stellar spectra 1 Lines
determine what are stars made of (like
fingerprints)
25
(No Transcript)
26
Importance of stellar spectra 2 Determine speed
of stars (and galaxies)
27
The Harvard College Observatory Women Astronomers
c.1910(they systematically classified stars
based on their spectra)
28
Cosmology c.1900Only one galaxy (ours!)
29
Is the Milky Way Galaxy the Entire Universe? The
Curtis Shapley DebateSaimthsonian Institure,
Washington, DC 1920
Shapley Nebulae are nearby stars, gas,dust
30
1925 Hubble former Rhodes scholar and lawyer
determines distance to Andromeda Nebula its
another Galaxy 2 Million light-years away
Curtis wins debate!
31
Hubble expansion is measured using Doppler shift
of spectra of galaxies
32
1929 Hubble makes the most important
cosmological observation of the century Universe
is expanding!
33
Age of Universe derived from the Hubble expansion
Ho72 8 km/s
Age 1/Ho 13.6 109 yrs
34
(No Transcript)
35
Historical origins of the Big Bang model

• Georges LeMaitre, a Belgian priest and
  mathematician, proposed (1920s) that the
  expansion of the universe can be traced to an
  exceedingly dense primeval atom
• when the whole universe exploded in fireworks
  of unimaginable beauty and with a big noise
• Einstein, after listening to a lecture by
  LeMaitre said This is the most beautiful and
  satisfactory explanation of creation to which I
  have ever listened. 
• LeMaitre used the term Cosmic Egg. Now known as
  the Big Bang theory

36
The Hubble expansion implies that the Universe
emerged single highly dense state The Big Bang.

• LeMaitre (1902s) first proposed a Cosmic Egg
  cosmology
• In the 1940s, based on Hubbles Law, George Gamow
  proposed the universe began in a colossal
  explosion.
• In the 1950s, the term BIG BANG was coined by an
  unconvinced Sir Fred Hoyle.
• Sci Fi fans Sir Fred Hoyle (Astronomer Royal of
  England) wrote an excellent science fiction
  novel The Black Cloud
• In the 1990s, there was an international
  competition to rename the BIG BANG with a more
  appropriate name, but no new name was selected.

37
The farther we look into space, the farther back
in time we are seeing
Note that there is a farthest distance (particle
horizon) corresponding to VHubble c. Regions
farther away cannot be seen!
38
Most distant object a galaxy ever seen (formed
500 Million yr after big bang 13.4 Billion yr
ago!
39
Galaxies first formed about 500-1000 million yrs
after Big Bang
brown color represents neutral Hydrogen
Movie. Click to play.
40
(No Transcript)
41
1965 Second most astonishing cosmological in
history Discovery of Cosmic Background Radiation
(CBR)

• In 1965 radio astronomers Penzias and Wilson
  accidentally discovered The microwave radiation
  that fills all space is evidence of a hot Big
  Bang.
• They were trying to measure the radio noise of
  the galactic halo, but found (an annoying) weak
  excess isotropic noise
• The signal was consistent with a radiation from
  a thermal source at 3 K.
• A paper had just been written (but not yet
  published) predicting exactly this radio noise
  from the big bang.
• Penzias Wilson won the Nobel Prize for this
  discovery in 1978

42
The CBR Spectrum and Maps

• Since 1965 many observations have confirmed the
  CBR and measured its spectrum
• The satellites COBE (1990) and WMAP (2003) have
  made detailed maps of the CBR.
• These observation show
• The spectrum is exactly thermal with T 2.73K
• It is isotropic
• There are very small irregularities in the
  brightness across the sky

43
Decoupling Era Matter and radiation no longer
interact if temperature is cooler than 3,000 K
Hot (Tgtgt 3,000? K)
Cool (T lt 3,000? K)
At an age 300,000 years, the universe was
finally cool enough from its initial primordial
fireball that electrons and protons could combine
to form atoms (era of recombination).
44
The microwave sky map shows large-scale Doppler
shifts .
You are looking at the remnant radiation of the
ashes of the Big Bang glowing 300,00 years
after creation
45
1980s Discovery of Dark Matter
46
Dark Matter in Galaxy Clusters causes
Gravitational Lensing (requires 5x- 10x more mass
than all known matter)
47
Curvature of Space-time (Universe)

• General Relativity local space-time is curved
  (positively) by presence of masses
• What about OVERALL curvature of Universe (not
  near any masses)?
• The geometry of the universe depends on the
  combined average mass density of all forms of
  matter and energy. The three possibilities are
• ZERO CURVATURE Two parallel beams of light
  never intersect the universe is flat.
• POSITIVE CURVATURE Two initially parallel beams
  of light gradually converge the universe is
  spherical and is closed.
• NEGATIVE CURVATURE Two initially parallel beams
  of light gradually diverge the universe is
  hyperbolic and is open.
• In principle, we can measure (e.g. using long
  laser beams in a triangle, but not practical)

48
Curvature of space-time
49
1998 The universe appears to be filled with dark
energy.

• Our observations suggest that the universe is
  flat.
• This conflicts somewhat with our observation that
  all known radiation, matter, and dark matter only
  account for 30 of the total density of the
  universe.
• There must be an additional source somewhere
  dark energy.

50
Supernovae of type Ia all have (nearly) the same
peak luminosity can be used to measure distance!
51
Evidence for Dark Energy (negative pressure of
the vacuum) comes from observations of distant
exploding stars (supernovae)
52
Observations of distant supernovae indicate that
we live in an accelerating universe.
53
What causes this cosmic acceleration?
Key idea The vacuum isnt empty It has (a lot
of) enrgy and negative pressure (causes
acceleration)
54
(No Transcript)
55
History of Cosmic Expansion
Current Observations
56
Future SNAP telescope (can detect much fainter
Supernovae). Possible launch 2012
57
(No Transcript)
58
Another cosmological standard model.