Through a Glass Darkly:
Dark Energy and The Fate of the
Universe
2 July 2016
CLAS Saturday Scholar Lecture
1
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 doesn’t
address WHY creation
occurs
2 July 2016
CLAS Saturday Scholar Lecture
2
Earliest ideas about
cosmology:
A story of three (very clever)
ancient Greek Astronomers :
Aristarchus,
Eratosthenes,
Ptolemy
2 July 2016
CLAS Saturday Scholar Lecture
3
Aristarchus of Samos (c. 250 BCE)
Determined relative size of moon (w.r.t
Earth), distance to Sun
2 July 2016
CLAS Saturday Scholar Lecture
4
Lunar Eclipse Movie
(Notice radius of Earth in Shadow)
2 July 2016
CLAS Saturday Scholar Lecture
5
Moon’s diameter
observed to be ~
1/3 Earth’s
shadow size
2 July 2016
CLAS Saturday Scholar Lecture
6
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.
2 July 2016
CLAS Saturday Scholar Lecture
7
Eratosthenes’s Method for Finding the
Circumference of the Earth
2 July 2016
CLAS Saturday Scholar Lecture
8
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!
2 July 2016
CLAS Saturday Scholar Lecture
9
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
2 July 2016
CLAS Saturday
Lecture
10
for Scholar
6 months
Ptolemy’s Geocentric Model
•Earth is at center
•Sun orbits Earth
•Planets orbit on small
circles whose centers
orbit the Earth on
larger circles
2 July 2016
CLAS Saturday Scholar Lecture
11
“Standard Model”
of the Universe
c.100AD-1600AD
2 July 2016
CLAS Saturday Scholar Lecture
12
Nicholaus Copernicus
(1473-1543)
• Polish canon (religious leader)
• Suggested sun-centered
(heliocentric) solar system
• He thought Ptolemy’s model was
contrived
• Yet he believed in circular motion!
• His model doesn’t fit observations
any better than Ptolemy’s
geocentric model!
2 July 2016
CLAS Saturday Scholar Lecture
13
Copernicus’
(heliocentric)
explanation of
retrograde
motion
2 July 2016
CLAS Saturday Scholar Lecture
14
Johannes Kepler (1571- 1630)
Finds elliptical orbit for Mars
Horoscope written by
Kepler found last year at
UCSC library
Kepler’s Boss:
Tycho Brahe
2 July 2016
CLAS Saturday Scholar Lecture
15
Kepler’s model for the
Solar System: A
Concentric Series of
Crystalline Spheres
2 July 2016
CLAS Saturday Scholar Lecture
16
Galileo’s discovery (1610) of Jupiter’s moons
with his telescope showed that Earth was not
the center of all orbits strongly supported a
heliocentric model
2 July 2016
CLAS Saturday Scholar Lecture
17
Galileo’s 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 18
CLAS Saturday Scholar Lecture
and largest when it is close to inferior conjunction.
2 July 2016
Galileo’s observation of the phases of Venus was the
final evidence which buried the geocentric model.
Geocentric
No gibbous or full phases!
2 July 2016
Heliocentric
All phases are seen!
GalileoCLASobserved
all phases!
Saturday Scholar Lecture
19
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"
2 July 2016
CLAS Saturday Scholar Lecture
20
“Standard Model” of the Universe
c. 1650 AD
2 July 2016
CLAS Saturday Scholar Lecture
21
18th - 19th Century:
Astronomers Study of Properties of
Stars (and lots of Comets)
2 July 2016
CLAS Saturday Scholar Lecture
22
Some stars occur in vast groups:
Globular Clusters and Nebulae
2 July 2016
CLAS Saturday Scholar Lecture
23
Importance of stellar spectra 1: :
Lines determine what are stars
made of (like fingerprints)
2 July 2016
CLAS Saturday Scholar Lecture
24
2 July 2016
CLAS Saturday Scholar Lecture
25
Importance of stellar spectra 2:
Determine speed of stars (and galaxies)
2 July 2016
CLAS Saturday Scholar Lecture
26
The Harvard College Observatory Women
Astronomers c.1910
(they systematically classified stars based
on their spectra)
I’m the boss
2 July 2016
CLAS Saturday Scholar Lecture
27
Cosmology c.1900:
Only one galaxy (ours!)
Home
2 July 2016
CLAS Saturday Scholar Lecture
28
Is the Milky Way Galaxy the Entire Universe?
The Curtis –Shapley Debate
Saimthsonian Institure, Washington, DC 1920
2 July 2016
Curtis: Nebulae
are are
Shapley:
Nebulae
entire ‘Island Universes
nearby stars, gas,dust
(other
galaxies)
CLAS Saturday
Scholar Lecture
29
1925: Hubble [former Rhodes scholar and
lawyer] determines distance to Andromeda
‘Nebula’ : it’s another Galaxy 2 Million lightyears away – Curtis wins debate!
2 July 2016
CLAS Saturday Scholar Lecture
30
Hubble expansion is measured using
Doppler shift of spectra of galaxies
2 July 2016
CLAS Saturday Scholar Lecture
31
1929: Hubble makes the most
important cosmological observation of
the century: Universe is expanding!
2 July 2016
CLAS Saturday Scholar Lecture
32
Age of Universe derived from the
Hubble expansion
Ho=72 ± 8 km/s
2 July 2016
At t=0 The
Universe has
radius = 0
(Big Bang!)
9 yrs
Age = 1/H
=
13.6
·
10
o
CLAS Saturday
Scholar Lecture
33
2 July 2016
CLAS Saturday Scholar Lecture
34
Historical origins of the Big Bang model
•
Georges LeMaitre, a Belgian priest and
mathematician, proposed (1920’s) 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
2 July 2016
CLAS Saturday Scholar Lecture
35
The Hubble expansion implies that the Universe
emerged single highly dense state: The Big Bang.
•
LeMaitre (1902’s) first proposed a
‘Cosmic Egg’ cosmology
•
In the 1940s, based on Hubble’s 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.
2 July 2016
CLAS Saturday Scholar Lecture
36
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
be seen! CLAS Saturday Scholar Lecture
2 July cannot
2016
37
Most distant object [a galaxy] ever seen (formed
~500 Million yr after big bang – 13.4 Billion yr ago!
2 July 2016
CLAS Saturday Scholar Lecture
38
Galaxies first formed about 500-1000 million
yrs after Big Bang
brown color represents neutral Hydrogen
Movie. Click to play.
2 July 2016
CLAS Saturday Scholar Lecture
39
2 July 2016
CLAS Saturday Scholar Lecture
40
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
2 July 2016
CLAS Saturday Scholar Lecture
41
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= 2.73°K
– It is isotropic
– There are [very small]
irregularities in the brightness
across the sky
2 July 2016
CLAS Saturday Scholar Lecture
42
Decoupling Era
Matter and radiation no longer interact if temperature is
cooler than ~3,000 K
Hot (T>> 3,000 K)
Cool (T < 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).
2 July 2016
CLAS Saturday Scholar Lecture
43
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
2 July 2016
CLAS Saturday Scholar Lecture
44
years after creation
1980’s: Discovery of Dark Matter
2 July 2016
CLAS Saturday Scholar Lecture
45
Dark Matter in Galaxy Clusters
causes Gravitational Lensing
(requires 5x- 10x more mass
than all known matter)
2 July 2016
CLAS Saturday Scholar Lecture
46
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
in a triangle, butCLAS
not Saturday
practical)
2 Julybeams
2016
Scholar Lecture
47
Curvature of space-time
2 July 2016
CLAS Saturday Scholar Lecture
48
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.
2 July 2016
CLAS Saturday Scholar Lecture
49
Supernovae of type Ia all have (nearly) the
same peak luminosity: can be used to measure
distance!
2 July 2016
CLAS Saturday Scholar Lecture
50
Evidence for Dark Energy (negative pressure of the
vacuum) comes from observations of distant exploding stars
(supernovae)
2 July 2016
CLAS Saturday Scholar Lecture
51
Observations of distant supernovae indicate that
we live in an accelerating universe.
2 July 2016
CLAS Saturday Scholar Lecture
52
What causes
this cosmic
acceleration?
Key idea: The
vacuum isn’t empty:
It has (a lot of)
enrgy and negative
pressure (causes
acceleration)
2 July 2016
CLAS Saturday Scholar Lecture
53
2 July 2016
CLAS Saturday Scholar Lecture
54
History of Cosmic Expansion
Current
Observations
2 July 2016
CLAS Saturday Scholar Lecture
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Future: SNAP telescope (can detect much
fainter Supernovae). Possible launch 2012
2 July 2016
CLAS Saturday Scholar Lecture
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2 July 2016
CLAS Saturday Scholar Lecture
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Another cosmological ‘standard model’….
2 July 2016
CLAS Saturday Scholar Lecture
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