Download Lecture 39: Early Universe Test 3 overview 11/21

Cosmology
• Origin, early history, and fate of the Universe
• Does the Universe have a beginning? An end? What physics
processes “caused” the Universe to be what it is? Are other
universes possible? Would they look like ours (have the
same physics)?
• Olber’s Paradox: sky dark at night  Universe is finite in
time and/or space
• Cosmological Principle - the Universe appears the same
from any location - Isotropic
- no center, no edge
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Beginning of Universe
• Called the “Big Bang” but not normal explosion
moving outward into existing 3D space
• “explosion” occurred everywhere at same time
and expanding universe “creates” its own space
as it expands “outward”
• Einstein predicted in 1915 General Theory of
relativity (though he initially thought it was a
mistake)
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Expanding Universe
Dark energy 
acceleration
Dark matter 
slowing
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Expanding Universe – if finite in size
Time 1
Red = void =
nothingness (hard
to picture). Space
just gets bigger
with time
Time 2
Time 3
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Expanding Universe
• No edge, no center to Universe
• Consider balloon. 2D surface in 3D space. All
points moving away from each other with v = Ad.
All points are the same: no edge or center
• Universe is 3D surface on a 4D manifold
(wormholes “burrow” through this) with v=Hd
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Expanding Universe
• As Universe expands it cools
• Physical processes at any time depend on:
-Temperature
-Nature of forces and particles
• Current Temperature is 3 degrees K
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Temperature vs Time
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Cosmic Microwave Background
• Temperature > 3000 degrees Universe opaque  atoms
ionized - free H, He nuclei plus free electrons
• T<3000 atoms form  transparent Universe -400,000 to 1,000,000 years after Big Bang
• Burst of light everywhere - now observed as 3 degree
microwave background -- (1964: Bell Labs)
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Recombination – Occurs at ~400,000 years
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Microwave Background
• When emitted at time = 400,000 years
Temp = 3000 degrees
wavelength = 1 micron (visible)
• Same photons observed now. Universe has
expanded/stretched by about 1000 (all directions)
Temp = 3 degrees
wavelength = 1 mm (microwave)
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Cosmic Microwave Background
COBE satellite
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Cosmic Microwave Background
photons permeate Universe
fluctuations in
“temperature” 
granularity in early
Universe (fossil record)
 galaxy formation from
primordial clumps of
matter/energy
Blue=colder
South Pole Telescope (Donna Kubik’s talk) looking
at details of this “cosmic” radiation
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History of Universe
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Creation of
Matter
early Universe hot
enough to make
particleantiparticle pairs.
Example
photon  proton  antiproton
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after 0.000001
seconds, too cool
to make protons
and antiprotons
neutrons and
antineutrons
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Matter – Antimatter Asymmetry
• early universe: very hot, makes matter-antimatter
• For some reason matter becomes more
abundant in the early stages of Universe
1000000001 matter for 1000000000 antimatter
• Antimatter completely annihilated
• Hence we're left only with matter today:
t0
antimatter
matter
(0.25 protons, ~109 photons, ~108 neutrinos+antineutrinos)/m3
• Fossil record
• Do not (yet) understand
t  t1
antimatter
matter
t  today
antimatter
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matter
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Creation of Light Nuclei
• During first few minutes have about the same number of protons and
neutrons and can have the following reactions
p + n  pn (deuterium) + gamma
pn + n  pnn (tritium) + gamma
pn + p  ppn (Helium-3) + gamma
pn + pn  Helium-4 + gamma
pnn + pn  He-4 + n
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Creation of Light Nuclei
Protons and neutrons combine to make Helium: first
10 minutes
Relative number of protons and neutrons depends on:
- neutron being a little heavier than the proton
- neutron decays with 15 minute lifetime
- how quickly Helium is made
• We end up with #n/#p = 14% or 2 neutrons for every 14 protons
• Almost all the neutrons are in He giving about 75% H and 25% He
after first 3 minutes (and still mostly today)
• fraction of H, He, H2, He3, Li are “fossil” record from this time. Tell
temperature of Universe at t=1 minute
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Evidence for Big Bang
• galaxies all moving away from us (Hubble Law)
• cosmic microwave background at 3 degrees K
• relative amount of Hydrogen to Helium (plus other
light elements) seen throughout the Universe
 moment of Creation about 13-14 billion years ago
But somehow 40% of Americans don’t
“believe” in this as it is “against” their
religious views. Which seems to deny the
wonder of the Universe that was created!!
(I don’t get it)
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Unsolved Mysteries: Include
•
•
•
•
Dark Matter
earlier lecture
Dark Energy
earlier lecture
Domination of Matter
this lecture
Why the strength of the forces and the masses of
particles seem to be “just right”  multiple
universes - Multiverse??
• Weakness of Gravity  Extra Dimensions??
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Forces and Particles  Multiverse?
 the 4 forces and the particles (electrons, protons, etc)
are “just right” for the formation of intelligent life
EXAMPLES
 if gravity were stronger then stars’ lifetimes would be
shorter
 if the neutron mass were lighter then the proton mass
then normal Hydrogen would be unstable and rare 
let’s look at this in greater detail
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How Many Universes are There?
Answer: 1 or infinite
What if?? many different universes exist
 each forms its own space
 each has own starting conditions and
possibly different physics
Our Universe: proton stable, Hydrogen  Life
Other Universe: proton decays, Hydrogen rare  No life
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Neutrons and Protons
• Neutron’s mass is slightly more than proton’s
mass
•  neutrons decay, lifetime of 15 minutes
• If flip n and p mass then protons decay
m p  938.3 MeV / c
2
n  p  e  e

mn  939.6 MeV / c 2
me  0.5 MeV / c 2
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Snowflakes
each snowflake is unique do to the slight
variations in the conditions when they formed
•
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Anthropic Principle and Multiverse
• intelligent life in our universe depends on
having the physics “just right”. Why?
 anthropic principle holds that with an
infinite number of universes, there is a nonzero probability that one is “just right”
 That’s ours where the masses of the
neutron, proton and electron, and the
strengths of the forces are “just right”
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Goldilocks and the Three Bears
This universe has the
matter-antimatter
variation too small
This universe has the proton
mass too large
This universe has
the strong
nuclear force too
strong
This
universe has
the electron
mass too
small
This universe
has the weak
nuclear force
too weak
Our Universe is
just right
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How Many Dimensions are There?
Answer:
“Common Sense” = 3
Physics Theories = 9 or 10
Need to explain why gravity is so weak
Fgravity
( Hydrogen )  1039
Felectric
 0.000000000000000000000000000000000000001
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Gravity + Electric Force:Geometry
• the 1/R2 is due to the area of a surface of the
sphere
• the force carriers (photon or graviton) are
spread out over this surface
mass1mass2
Fgravity  G
R2
Felectric
Area  4R2
ch arg e1ch arg e2
E
R2
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What if – Extra Dimensions
electric force (our senses) is in
“normal” 3D space
gravity in 3D and extra
dimensions
 gravity weaker in normal 3D
space
brane =
“normal” 3D
space
bulk = extra
dimensions
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Extra Dimensions -- Geometry
• normal 3D space  1/R2
• 2D
space  1/R
• 3 extra dimensions  1/R5
3D space
area=R2
2D space
“area”=2R
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PHYS 162 Conclusions
• the Universe is an extraordinary place much of which
(stars, supernovas, neutron stars) are understood by our
knowledge of physics
• But many unanswered questions
• what is dark matter and dark energy
• what is the origin of the Universe
•Are there Extra Dimensions or an infinite number of
Universes
•How probable is the development of intelligent life
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Test 3 Overview
• 33 multiple choice. Scantron, bring pencil
• Formation of planets. temperature of solar nebula, and how it
varies with distance  type of planet formed. Heavy elements
freeze out first. Extrasolar planets detected in a number of ways
(motion of stars, planet eclipsing star, directly). Planetary
atmospheres: high temp and/or low surface gravity prevent the
planet from holding on to light gases like hydrogen.
• Life in the Universe. Need star to be long-lived and not in binary
system. Need planet to be the right distance from its star.
Communicate with ET by radio with Drake equation giving
estimate of number of possible civilizations in Milky Way.
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Galaxies. Ellipticals:little rotation, little gas/dust or active star formation
Spiral: rotation/gas/dust and active star formation, and irregulars active
star formation but indistinct shape. Galaxies are moving away from us
with v=Hd v=velocity, d=distance, and H=Hubble constant. Milky Way
has inner nucleus, spiral arms (active star formation, halo of old stars
(early shape)
Cosmology. Hubble law  Universe is expanding, gives universe’s age,
depends on Hubble “constant” changes with time. Closed universe has
gravity slowing the expansion so it starts to contract. Open universe
expands forever. Early universe was very hot and when matter was
created. First electrons, protons and neutrons, then protons and neutrons
give hydrogen and helium nuclei minutes after the Big Bang. 400,000
years later atoms form, Universe became transparent, and light appeared,
seen as the cosmic microwave blackbody radiation temperature of 3
degrees K.
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Measuring Distances – summary
• Type Ia supernovas (white dwarves which hit the Chandrashekar
limit) are best for distant objects as always about the same absolute
luminosity
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Extra Slides
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Isotropic Universe
• the Universe appears the same from any location on any large scale
- no center, no edge  size is unknown infinite vs finite
- same number of galaxies, same types, in any large “box”
• A civilization on a planet 12 BLY away sees exactly what we do –
expanding Universe and same Hubble law
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Microwave Background
• Universe has expanded/stretched by 1000 
“Cosmological Redshift” (different then redshift
due to Doppler effect)
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Exploring Very Early Times
• “Fossil” evidence available to astronomy are remnants
from the first few minutes and later after the Big Bang
• For earlier times  use physics
• Particle accelerators can briefly reproduce the
Temperature of early times. The highest energy
machine is equivalent to about 1 picosecond
(.000000000001) after the universe began
• Understood earlier by extrapolation. Going back to the
moment of Creation needs a complete knowledge of
gravity and a more complete understanding of time
itself
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Hydrogen

Simplest atom – just
one electron and one
proton
 “heavy” hydrogen or
deuterium adds one
neutron to the nucleus
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Neutrons and Protons
• Neutron’s mass is slightly more than proton’s
mass
•  neutrons decay, lifetime of 15 minutes
m p  938.3 MeV / c
2
n  p  e  e

mn  939.6 MeV / c 2
me  0.5 MeV / c 2
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What if Multiverse
• many (infinite??) universes in a multiverse
•not really “next” to each other. “nothingness” separates
•no communication between universes
two artist conceptions – mostly meaningless
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Hydrogen  Life
 Hydrogen bonding allows complicated molecules
to form and readily change forms
 amino acids, proteins, RNA, DNA etc
 “pure” Carbon is biologically inert; need
hydrocarbons, water, ammonia for biology
 CH2 CH4
H2O
NH3
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