chapter 17 the beginning of time. 17.1 the big bang our goals for learning: what were conditions...
TRANSCRIPT
![Page 1: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/1.jpg)
Chapter 17The Beginning of Time
![Page 2: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/2.jpg)
17.1 The Big Bang
Our goals for learning:• What were conditions like in the early
universe?• What is the history of the universe
according to the Big Bang theory?
![Page 3: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/3.jpg)
What were conditions like in the early universe?
![Page 4: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/4.jpg)
The universe must have been much hotter and denser early in time.
Estimating the Age of the Universe
![Page 5: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/5.jpg)
The early universe must have been extremely hot and dense.
![Page 6: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/6.jpg)
Photons converted into particle–antiparticle pairs and vice versa.
E = mc2
The early universe was full of particles and radiation because of its high temperature.
![Page 7: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/7.jpg)
What is the history of the universe according to the Big
Bang theory?
![Page 8: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/8.jpg)
Defining Eras of the Universe
• The earliest eras are defined by the kinds of forces present in the universe.
• Later eras are defined by the kinds of particles present in the universe.
![Page 9: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/9.jpg)
Four known forces in universe:
Strong Force Electromagnetism
Weak Force
Gravity
![Page 10: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/10.jpg)
Thought Question
Which of the four forces keeps you from sinking to the center of Earth?
A. GravityB. ElectromagnetismC. Strong ForceD. Weak Force
![Page 11: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/11.jpg)
Thought Question
Which of the four forces keeps you from sinking to the center of Earth?
A. GravityB. ElectromagnetismC. Strong ForceD. Weak Force
![Page 12: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/12.jpg)
Four known forces in universe:
Strong Force Electromagnetism
Weak Force
Gravity
Do forces unify at high temperatures?
![Page 13: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/13.jpg)
Four known forces in universe:
Strong Force Electromagnetism
Weak Force
Gravity
Do forces unify at high temperatures?
Yes!(Electroweak)
![Page 14: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/14.jpg)
Four known forces in universe:
Strong Force Electromagnetism
Weak Force
Gravity
Do forces unify at high temperatures?
Yes!(Electroweak)
Maybe (GUT)
![Page 15: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/15.jpg)
Four known forces in universe:
Strong Force Electromagnetism
Weak Force
Gravity
Do forces unify at high temperatures?
Yes!(Electroweak)
Who knows?(String Theory)
Maybe (GUT)
![Page 16: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/16.jpg)
Planck Era
Time: < 10-43 secTemp: > 1032 K
No theory of quantum gravity
All forces may have been unified
![Page 17: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/17.jpg)
GUT Era
Time: 10-43 – 10-38 secTemp: 1032 – 1029 K
GUT era began when gravity became distinct from other forces.
GUT era ended when strong force became distinct from electroweak force.
![Page 18: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/18.jpg)
Electroweak Era
Time: 10-10 – 10-10 secTemp: 1029 – 1015 K
Gravity became distinct from other forces.
Strong, weak, and electromagnetic forces may have been unified into GUT force.
![Page 19: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/19.jpg)
Particle Era
Time: 10-10 – 0.001 secTemp: 1015 – 1012 K
Amounts of matter and antimatter are nearly equal.
(Roughly one extra proton for every 109 proton–antiproton pairs!)
![Page 20: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/20.jpg)
Era of Nucleosynthesis
Time: 0.001 sec–5 minTemp: 1012–109 K
Began when matter annihilates remaining antimatter at ~ 0.001 sec.
Nuclei began to fuse.
![Page 21: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/21.jpg)
Era of Nuclei
Time: 5 min–380,000 yrsTemp: 109–3,000 K
Helium nuclei formed at age ~3 minutes.
The universe became too cool to blast helium apart.
![Page 22: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/22.jpg)
Era of Atoms
Time: 380,000 years–1 billion yearsTemp: 3,000–20 K
Atoms formed at age ~380,000 years.
Background radiation is released.
![Page 23: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/23.jpg)
Era of Galaxies
Time: ~1 billion years–presentTemp: 20–3 K
The first stars and galaxies formed by ~1 billion years after the Big Bang.
![Page 24: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/24.jpg)
Primary Evidence
1. We have detected the leftover radiation from the Big Bang.
2. The Big Bang theory correctly predicts the abundance of helium and other light elements.
![Page 25: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/25.jpg)
What have we learned?• What were conditions like in the early universe?
— The early universe was so hot and so dense that radiation was constantly producing particle–antiparticle pairs and vice versa.
• What is the history of the universe according to the Big Bang theory?— As the universe cooled, particle production stopped,
leaving matter instead of antimatter.
— Fusion turned the remaining neutrons into helium.
— Radiation traveled freely after the formation of atoms.
![Page 26: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/26.jpg)
17.2 Evidence for the Big Bang
Our goals for learning:• How do we observe the radiation left over
from the Big Bang?• How do the abundances of elements support
the Big Bang theory?
![Page 27: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/27.jpg)
How do we observe the radiation left over from the Big Bang?
![Page 28: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/28.jpg)
The cosmic microwave background — the radiation left over from the Big Bang — was detected by Penzias and Wilson in 1965.
![Page 29: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/29.jpg)
Background radiation from the Big Bang has been freely streaming across the universe since atoms formed at temperature ~3,000 K: visible/IR.
Creation of the Cosmic Microwave Background
![Page 30: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/30.jpg)
Expansion of the universe has redshifted thermal radiation from that time to ~1,000 times longer wavelength: microwaves.
Background has perfect thermal radiation spectrum at temperature 2.73 K
![Page 31: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/31.jpg)
Full sky in all wavelengths
![Page 32: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/32.jpg)
WMAP gives us detailed baby pictures of structure in the universe.
![Page 33: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/33.jpg)
How do the abundances of elements support the Big Bang theory?
![Page 34: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/34.jpg)
Protons and neutrons combined to make long-lasting helium nuclei when the universe was ~3 minutes old.
![Page 35: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/35.jpg)
Big Bang theory prediction: 75% H, 25% He (by mass)
Matches observations of nearly primordial gases
![Page 36: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/36.jpg)
Abundances of other light elements agree with Big Bang model having 4.4% normal matter—more evidence for WIMPS!
![Page 37: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/37.jpg)
Thought Question
Which of these abundance patterns is an unrealistic chemical composition for a star?
A. 70% H, 28% He, 2% otherB. 95% H, 5% He, less than 0.02% otherC. 75% H, 25% He, less than 0.02% otherD. 72% H, 27% He, 1% other
![Page 38: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/38.jpg)
Thought Question
Which of these abundance patterns is an unrealistic chemical composition for a star?
A. 70% H, 28% He, 2% otherB. 95% H, 5% He, less than 0.02% otherC. 75% H, 25% He, less than 0.02% otherD. 72% H, 27% He, 1% other
![Page 39: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/39.jpg)
What have we learned?
• How do we observe the radiation left over from the Big Bang?— Radiation left over from the Big Bang is now
in the form of microwaves—the cosmic microwave background—which we can observe with a radio telescope.
• How do the abundances of elements support the Big Bang theory?— Observations of helium and other light
elements agree with the predictions for fusion in the Big Bang theory.
![Page 40: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/40.jpg)
17.3 The Big Bang and Inflation
Our goals for learning:• What aspects of the universe were
originally unexplained by the Big Bang theory?
• How does inflation explain these features of the universe?
• How can we test the idea of inflation?
![Page 41: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/41.jpg)
What aspects of the universe were originally unexplained by
the Big Bang theory?
![Page 42: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/42.jpg)
Mysteries Needing Explanation
1. Where does structure come from?
2. Why is the overall distribution of matter so uniform?
3. Why is the density of the universe so close to the critical density?
![Page 43: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/43.jpg)
Mysteries Needing Explanation
1. Where does structure come from?
2. Why is the overall distribution of matter so uniform?
3. Why is the density of the universe so close to the critical density?
An early episode of rapid inflation can solve all three mysteries!
![Page 44: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/44.jpg)
How does inflation explain these features of the universe?
![Page 45: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/45.jpg)
Inflation can make structure by stretching tiny quantum ripples to enormous sizes.
These ripples in density then become the seeds for all structure in the universe.
![Page 46: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/46.jpg)
How can microwave temperature be nearly identical on opposite sides of the sky?
![Page 47: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/47.jpg)
Regions now on opposite sides of the sky were close together before inflation pushed them far apart.
Inflation of the Early Universe
![Page 48: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/48.jpg)
The overall geometry of the universe is closely related to total density of matter and energy.
Density = Critical
Density > Critical
Density < Critical
![Page 49: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/49.jpg)
The inflation of the universe flattens the overall geometry like the inflation of a balloon, causing overall density of matter plus energy to be very close to critical density.
![Page 50: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/50.jpg)
How can we test the idea of inflation?
![Page 51: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/51.jpg)
Patterns of structure observed by WMAP show us the “seeds” of the universe.
![Page 52: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/52.jpg)
Observed patterns of structure in the universe agree (so far) with the “seeds” that inflation would produce.
![Page 53: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/53.jpg)
“Seeds” Inferred from CMB
• Overall geometry is flat — Total mass + energy has critical density
• Ordinary matter ~4.4% of total• Total matter is ~26% of total
— Dark matter is ~22% of total— Dark energy is ~74% of total
• Age of 13.7 billion years
![Page 54: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/54.jpg)
“Seeds” Inferred from CMB
• Overall geometry is flat — Total mass + energy has critical density
• Ordinary matter ~4.4% of total• Total matter is ~26% of total
— Dark matter is ~22% of total— Dark energy is ~74% of total
• Age of 13.7 billion years
In excellent agreement with observations of present-day universe and models involving inflation and WIMPs!
![Page 55: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/55.jpg)
What have we learned?
• What aspects of the universe were originally unexplained by the Big Bang theory?— The origin of structure, the smoothness of the
universe on large scales, the nearly critical density of the universe
• How does inflation explain these features?— Structure comes from inflated quantum ripples.— Observable universe became smooth before
inflation, when it was very tiny.— Inflation flattened the curvature of space,
bringing the expansion rate into balance with the overall density of mass-energy.
![Page 56: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/56.jpg)
What have we learned?
• How can we test the idea of inflation?— We can compare the structures we see in
detailed observations of the microwave background with predictions for the “seeds” that should have been planted by inflation.
— So far, our observations of the universe agree well with models in which inflation planted the “seeds.”
![Page 57: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/57.jpg)
17.4 Observing the Big Bang for Yourself
Our goals for learning:• Why is the darkness of the night sky
evidence for the Big Bang?
![Page 58: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/58.jpg)
Why is the darkness of the night sky evidence for the Big Bang?
![Page 59: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/59.jpg)
Olbers’ Paradox
1. infinite
2. unchanging
3. everywhere the same
then stars would cover the night sky.
If the universe were
![Page 60: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/60.jpg)
Olbers’ Paradox
1. infinite
2. unchanging
3. everywhere the same
then stars would cover the night sky.
If the universe were
![Page 61: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/61.jpg)
The night sky is dark because the universe changes with time.
As we look out in space, we can look back to a time when there were no stars.
![Page 62: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/62.jpg)
The night sky is dark because the universe changes with time.
As we look out in space, we can look back to a time when there were no stars.
![Page 63: Chapter 17 The Beginning of Time. 17.1 The Big Bang Our goals for learning: What were conditions like in the early universe? What is the history of the](https://reader037.vdocuments.site/reader037/viewer/2022102906/56649ce55503460f949b3079/html5/thumbnails/63.jpg)
What have we learned?
• Why is the darkness of the night sky evidence for the Big Bang?— If the universe were eternal, unchanging, and
everywhere the same, the entire night sky would be covered with stars.
— The night sky is dark because we can see back to a time when there were no stars.