Exploring Cosmology: A Journey Through the Universe's Mysteries

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UNIVERSITY
ASTRONOMY
 
Professor Don Figer
Cosmology
 
1
Announcements
 
Final: Wednesday, April 29
th
, 10:45 am to 1:15 pm
I will be in Adobe Connect room
You can also text at 5855984731
2
Aims and outline for this lecture
 
describe the big bang theory and its predictions
describe cosmological observations
speculate on fate of the Universe
3
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WHAT IS COSMOLOGY?
 
Definition of Cosmology
 
Cosmology is the study of the Universe. More precisely it is
the study of causes and effects related to the largest
structures in the Universe.
formation of matter/energy (from subatomic particles)
distribution of matter/energy (into galaxies)
evolution of matter/energy (from subatomic particles to
heavy elements in stars)
The word cosmology comes from the Greek words “kosmo”
(world) and “logia” (study of).
Motivating questions include:
Was there a beginning to the Universe?
Will there be an end to the Universe?
Why does matter exist?
5
Elements of Cosmology
 
spatial extent
finite (with edges)
finite (unbounded)
infinite
our location
Earth at center
Sun at center
solar system near
center
solar system far
from center
no center
 
history
both finite
(creation, future
destruction)
both infinite
(no beginning, no
end)
finite past, infinite
future
motion
static
expanding
cyclic
6
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HISTORY OF
COSMOLOGY
 
 
Aristotle’s Cosmology
 
8
History of Cosmology to Newton
 
Ptolemy thought that the Earth was the center of Universe
that orbited around it.
Copernicus thought that the Sun was center of the Universe.
Newton proposed that celestial bodies obeyed the law of
gravitation, just as do bodies on Earth.
 
9
Newtonian Cosmology
 
Newton’s 
Philosophiae Naturalis Principia Mathematica
,
1687
Newtonian gravity, F = GMm/r
2
, and second law, F = ma
Approximate size of solar system (Cassini, 1672)
from parallax of Mars
Finite speed of light (Ole R
ømer, 1676)
from timing of Jupiter’s moons
Did not have distances to stars
Did not know about galaxies
10
 
It’s Full of Stars
 
11
 
Should the Night Sky be Dark?
 
12
Olbers’ Paradox
 
Heinrich Olbers wrote a
paper in 1826 asking why
the night sky is dark.
An infinite number of stars
should produce an
infinitely bright night (and
day!) sky.
The resolution comes from
the fact that there aren’t
an infinite number of stars
that we can see and that
some of the starlight is
redshifted.
This is one of the earliest
cosmological observations.
13
History of Cosmology to Shapley
 
Einstein extended Newton’s idea by proposing that all laws of
nature are the same everywhere. This means that the speed
of light is constant.
de Sitter, Schwarzschild, Eddington, and Friedmann
introduced an expanding/accelerating Universe with matter in
it.
Shapley thought the Universe consisted only of just the Milky
Way, but Curtis disagreed (and was right).
 
14
History of Cosmology to Now
 
Lemaitre proposed the Big Bang Theory (but not the TV show,
thus severely limiting his royalties/residuals).
Hubble discovered his redshift-distance law.
Penzias and Wilson discovered background radiation leftover
from the Big Bang, but thought it was bird poop at first.
It was not poop, so they won a Nobel Prize!
COBE measured the background radiation – another Nobel
Prize!
Schmidt, Riess, and Perlmutter detected that the expansion of
the Universe is increasing – another Noble Prize!
15
 
Penzias and Wilson
 
16
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COSMIC MICROWAVE
BACKGROUND
 
CMB
 
The Cosmic Microwave Background (CMB) is background
radiation observed from all directions in the sky.
Penzias and Wilson found it in 1965.
The radiation is fit by a black body with T=2.725 K.
The average energy of a CMB photon is ~meV and the peak
wavelength is ~1 mm.
18
Recombination
19
 
At one point in the early Universe, the temperature was high
enough so that all the hydrogen was ionized.
This means that the Universe was flooded with free electrons.
Free electrons scatter photons, so the photons were
constantly being redirected.
The effect of this is that the Universe was opaque.
At a certain temperature (~3,000 K), the electrons and
protons recombined.
Thus, the Universe became transparent.
Last Scattering
 
The CMB photons that we
now see were last
scattered at the time of
recombination.
This corresponds to a
redshift of 1,100.
According to the most
accepted model, the
Universe was about
400,000 years old at this
time.
20
 
CMB Cooling
 
21
 
COBE Map
 
22
 
WMAP vs. COBE
 
23
 
Planck vs. WMAP
 
24
 
Acoustic Oscillations
 
25
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EXPANSION OF THE
UNIVERSE AND THE BIG
BANG THEORY
 
 
The Universe is Expanding
 
27
 
Center of the Universe
 
28
 
Galactic Redshifts
 
29
 
Hubble’s Plot
 
30
 
Hubble’s Plot – Bigger Scale
 
31
Hubble’s Law
32
 
Hubble estimated distances to galaxies in his sample
(underestimating them considerably) and saw that the
velocities were proportional to the distances.
Hubble’s law is the relationship between distance and
redshift for a galaxy.
Recall that redshift is z=

0
=v/c.
The law is cz=H
0
d=v, where c is the speed of light, H
0
 is
“Hubble’s constant,” and d is the distance to the galaxy.
H
0
 is ~70 +/-5 km/s/Mpc.
(There appears to be a discrepancy between estimates for the
Hubble Constant from two different methods.)
 
How Long Ago Were Galaxies Touching?
 
33
Big Bang
34
 
This calculation is the basis for a “big bang” theory.
That is, by projecting the expansion backward, we can
imagine that there was a time when all matter was in a dense
state.
We call the quantity, 1/H
0
 the “Hubble time.”
It is the approximate age of the Universe.
undefined
 
BIG BANG
NUCLEOSYNTHESIS
 
Big Bang Nucleosynthesis
 
The Universe was so hot around the time of the Big Bang that
atomic nuclei did not exist.
Matter existing as a sea of protons and neutrons.
This matter built up light elements as it cooled (allowing
protons and neutrons to recombine).
The standard model predicts that the Big Bang produced 75%
H and 24% He and very little of anything else.
Those ratios are generally observed, representing a great
success for the Big Bang standard model.
36
 
BBN Reactions
 
37
 
BBN Nuclei
 
38
 
Abundance Observations
 
39
 
You Are Big Bang and Stars
 
40
undefined
 
ACCELERATION OF THE
UNIVERSE
 
Acceleration
42
 
The universe is expanding at a higher rate with time.
This effect was discovered during 1998, by two independent
projects, the Supernova Cosmology Project and the High-Z
Supernova Search Team.
Both teams used distant Type Ia supernovae to measure the
acceleration.
The technique measures brightness and z for each supernova.
Assuming that Type Ia are the same everywhere (“standard
candle”), then the distance modulus should simply be a function
of distance. If z is only a function of distance, then the relation
between m-M and z should be linear.
Unexpectedly, the relation is not linear.
Confirmatory evidence has been found in baryon acoustic
oscillations, and in analyses of the clustering of galaxies.
The accelerated expansion of the universe is thought to have
begun since the universe entered its dark-energy-dominated era
roughly 5 billion years ago.
Dark Energy
 
“Dark Energy” is the name
given to the “thing” that is
causing the Universe to
accelerate.
Einstein originally included
it in his equations, but set
it to zero, presuming that
such a thing could not
exist.
Dark energy makes up the
majority of the energy in
the Universe.
It is generally labelled as
capital “lambda, “
.”
Perlmutter, Riess, Schmidt
win Nobel Prize.
43
 
Standard Candle vs. z
 
44
 
SNe Observations
 
45
 
SNe Observation Predications
 
46
undefined
 
HISTORY OF THE
UNIVERSE
 
 
History Graphic
 
48
 
Galaxies in Early Universe
 
49
undefined
 
FATE OF UNIVERSE
 
The End of Days
 
The Universe will continue to expand forever or it will stop
expanding at some point and collapse on itself (the “Big
Crunch”).
It is similar to what you might expect for a ball thrown up in
the air. Either it has enough energy to overcome gravity and fly
away forever, or it doesn’t, in which case it falls back down.
If the Universe has more mass than some “critical” value,
then it will collapse back onto itself.
51
Components
52
Omega Fractions
53
 
Omega Fractions
 
We have only directly
seen 5% of the whole
Universe!
 
54
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HOMEWORK
 
No Homework
 
There is no homework associated with this lecture.
The following questions/problems are potential ones for the
final.
Calculate the Hubble Constant from the Slide titled, “Hubble’s
Plot – Bigger Scale.” (Answer: 15,000 km/s divided by 200
Mpc = 75 km/s/Mpc)
Which component of the Universe currently represents the
greatest/least energy density? (greatest: dark energy, least:
radiation)
What is the source of the following in the Universe?
hydrogen (answer: big bang nucleosynthesis)
oxygen (answer: stellar nucleosynthesis)
iron (answer: supernovae)
 
56
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Delve into the fascinating field of cosmology with Professor Don Figer as he unravels the big bang theory, cosmological observations, and ponders the fate of the Universe. Learn about the origins of cosmology, its elements, history from Aristotle to Newton, and the evolution of our understanding of the cosmos. Join the discussion on the study of the Universe's largest structures, its formation, distribution, and evolution, and ponder existential questions about the Universe's beginning and end.


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  1. UNIVERSITY ASTRONOMY Professor Don Figer Cosmology 1

  2. Announcements Final: Wednesday, April 29th, 10:45 am to 1:15 pm I will be in Adobe Connect room You can also text at 5855984731 2

  3. Aims and outline for this lecture describe the big bang theory and its predictions describe cosmological observations speculate on fate of the Universe 3

  4. WHAT IS COSMOLOGY?

  5. Definition of Cosmology Cosmology is the study of the Universe. More precisely it is the study of causes and effects related to the largest structures in the Universe. formation of matter/energy (from subatomic particles) distribution of matter/energy (into galaxies) evolution of matter/energy (from subatomic particles to heavy elements in stars) The word cosmology comes from the Greek words kosmo (world) and logia (study of). Motivating questions include: Was there a beginning to the Universe? Will there be an end to the Universe? Why does matter exist? 5

  6. Elements of Cosmology spatial extent finite (with edges) finite (unbounded) infinite history both finite (creation, future destruction) both infinite (no beginning, no end) finite past, infinite future our location Earth at center Sun at center solar system near center solar system far from center no center motion static expanding cyclic 6

  7. HISTORY OF COSMOLOGY

  8. Aristotles Cosmology 8

  9. History of Cosmology to Newton Ptolemy thought that the Earth was the center of Universe that orbited around it. Copernicus thought that the Sun was center of the Universe. Newton proposed that celestial bodies obeyed the law of gravitation, just as do bodies on Earth. 9

  10. Newtonian Cosmology Newton s Philosophiae Naturalis Principia Mathematica, 1687 Newtonian gravity, F = GMm/r2, and second law, F = ma Approximate size of solar system (Cassini, 1672) from parallax of Mars Finite speed of light (Ole R mer, 1676) from timing of Jupiter s moons Did not have distances to stars Did not know about galaxies 10

  11. Its Full of Stars 11

  12. Should the Night Sky be Dark? 12

  13. Olbers Paradox Heinrich Olbers wrote a paper in 1826 asking why the night sky is dark. An infinite number of stars should produce an infinitely bright night (and day!) sky. The resolution comes from the fact that there aren t an infinite number of stars that we can see and that some of the starlight is redshifted. This is one of the earliest cosmological observations. 13

  14. History of Cosmology to Shapley Einstein extended Newton s idea by proposing that all laws of nature are the same everywhere. This means that the speed of light is constant. de Sitter, Schwarzschild, Eddington, and Friedmann introduced an expanding/accelerating Universe with matter in it. Shapley thought the Universe consisted only of just the Milky Way, but Curtis disagreed (and was right). 14

  15. History of Cosmology to Now Lemaitre proposed the Big Bang Theory (but not the TV show, thus severely limiting his royalties/residuals). Hubble discovered his redshift-distance law. Penzias and Wilson discovered background radiation leftover from the Big Bang, but thought it was bird poop at first. It was not poop, so they won a Nobel Prize! COBE measured the background radiation another Nobel Prize! Schmidt, Riess, and Perlmutter detected that the expansion of the Universe is increasing another Noble Prize! 15

  16. Penzias and Wilson 16

  17. COSMIC MICROWAVE BACKGROUND

  18. CMB The Cosmic Microwave Background (CMB) is background radiation observed from all directions in the sky. Penzias and Wilson found it in 1965. The radiation is fit by a black body with T=2.725 K. The average energy of a CMB photon is ~meV and the peak wavelength is ~1 mm. 18

  19. Recombination At one point in the early Universe, the temperature was high enough so that all the hydrogen was ionized. This means that the Universe was flooded with free electrons. Free electrons scatter photons, so the photons were constantly being redirected. The effect of this is that the Universe was opaque. At a certain temperature (~3,000 K), the electrons and protons recombined. Thus, the Universe became transparent. 19

  20. Last Scattering The CMB photons that we now see were last scattered at the time of recombination. This corresponds to a redshift of 1,100. According to the most accepted model, the Universe was about 400,000 years old at this time. 20

  21. CMB Cooling 21

  22. COBE Map 22

  23. WMAP vs. COBE 23

  24. Planck vs. WMAP 24

  25. Acoustic Oscillations 25

  26. EXPANSION OF THE UNIVERSE AND THE BIG BANG THEORY

  27. The Universe is Expanding 27

  28. Center of the Universe 28

  29. Galactic Redshifts 29

  30. Hubbles Plot 30

  31. Hubbles Plot Bigger Scale 31

  32. Hubbles Law Hubble estimated distances to galaxies in his sample (underestimating them considerably) and saw that the velocities were proportional to the distances. Hubble s law is the relationship between distance and redshift for a galaxy. Recall that redshift is z= 0=v/c. The law is cz=H0d=v, where c is the speed of light, H0 is Hubble s constant, and d is the distance to the galaxy. H0 is ~70 +/-5 km/s/Mpc. (There appears to be a discrepancy between estimates for the Hubble Constant from two different methods.) 32

  33. How Long Ago Were Galaxies Touching? 33

  34. Big Bang This calculation is the basis for a big bang theory. That is, by projecting the expansion backward, we can imagine that there was a time when all matter was in a dense state. We call the quantity, 1/H0the Hubble time. It is the approximate age of the Universe. 34

  35. BIG BANG NUCLEOSYNTHESIS

  36. Big Bang Nucleosynthesis The Universe was so hot around the time of the Big Bang that atomic nuclei did not exist. Matter existing as a sea of protons and neutrons. This matter built up light elements as it cooled (allowing protons and neutrons to recombine). The standard model predicts that the Big Bang produced 75% H and 24% He and very little of anything else. Those ratios are generally observed, representing a great success for the Big Bang standard model. 36

  37. BBN Reactions 37

  38. BBN Nuclei 38

  39. Abundance Observations 39

  40. You Are Big Bang and Stars 40

  41. ACCELERATION OF THE UNIVERSE

  42. Acceleration The universe is expanding at a higher rate with time. This effect was discovered during 1998, by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team. Both teams used distant Type Ia supernovae to measure the acceleration. The technique measures brightness and z for each supernova. Assuming that Type Ia are the same everywhere ( standard candle ), then the distance modulus should simply be a function of distance. If z is only a function of distance, then the relation between m-M and z should be linear. Unexpectedly, the relation is not linear. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies. The accelerated expansion of the universe is thought to have begun since the universe entered its dark-energy-dominated era roughly 5 billion years ago. 42

  43. Dark Energy Dark Energy is the name given to the thing that is causing the Universe to accelerate. Einstein originally included it in his equations, but set it to zero, presuming that such a thing could not exist. Dark energy makes up the majority of the energy in the Universe. It is generally labelled as capital lambda, . Perlmutter, Riess, Schmidt win Nobel Prize. 43

  44. Standard Candle vs. z 44

  45. SNe Observations 45

  46. SNe Observation Predications 46

  47. HISTORY OF THE UNIVERSE

  48. History Graphic 48

  49. Galaxies in Early Universe 49

  50. FATE OF UNIVERSE

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