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Lecture 2: History of Cosmology


... the currently observable universe started in and expanded from a very hot, dense ... 1916: German astrophysicist Karl Schwarzschild proposed black holes ... – PowerPoint PPT presentation

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Title: Lecture 2: History of Cosmology

Lecture 2 History of Cosmology
  • Aug 23, 2007

Plan for Todays lecture
  • Scientific thinking and scientific method
  • When Cosmology became Science from ancient
    Greeks to the Renaissance
  • Movie History of Hubble Space Telescope
  • History of Modern Cosmology from Newtons
    Gravity to the Big Bang

Let the Journey Begin
  • We especially need imagination in science. It
    is not all mathematics, nor all logic, but is
    somewhat beauty and poetry.

Maria Mitchell (1818 1889) Astronomer and first
woman elected to American Academy of Arts
The most incomprehensive thing about the Universe
is that it is comprehensible. -- Albert Einstein
In the Beginning
  • Modern cosmology is scientific
  • Based on detailed observations and complicated
  • But the quest of the origin and fate of the
    universe lasted as long as the human civilization
  • The earliest cosmological models are based on
    human experience, and are strongly influenced by
    culture, mythology and religion
  • But what makes Cosmology a Science?

Scientific Thinking
  • It is a natural part of human behavior.
  • We draw conclusions based on our experiences.
  • Progress is made through trial and error.

The Scientific Method
  • Question
  • Hypothesis
  • a tentative explanation
  • Prediction
  • Test
  • Result
  • confirm, reject, or modify

Hallmarks of Good Science
  • Science seeks explanations for observed phenomena
    that rely solely on natural causes.
  • Science progresses through the creation and
    testing of models of nature that explain the
    observations as simply as possible.
  • Occams Razor
  • A scientific model must make testable predictions
    that could force us to revise or abandon the

-- a model which survives repeated testing
Scientific Theory Can be WRONG!
  • In fact, the very nature of scientific theory is
    that it has to be testable, I.e., it has to be,
    in principle, falsifiable
  • Scientific theory first tries to explain existing
  • Then seeks to make testable prediction and seeks
    to reach its limitation in application
  • Then either the hypothesis can be improved, or it
    has to be abandoned
  • All theories has its limitation, to put it in
    another way, all theories was, or will be WRONG!
  • But at each step, we are getting closer to the
  • So, do you believe in the Big Bang???

Do I believe in Big Bang ??
  • Yes the currently observable universe started
    in and expanded from a very hot, dense state and
    it is still expanding the big bang theory has
    passed all the tests we have so far
  • No the Big Bang theory can only take us to the
    limit where current physics theory (relativity
    and quantum theory) can be applied it is not the
    end of the story, and will be improved upon
  • Irrelevant the Big Bang theory explains well
    the physical universe but it has little to do
    with belief or faith, and it provides no direct
    answer to your more personal universe
    spiritual, religious, ethical etc.

Ancient Greeks First Cosmologists
  • Greeks built first cosmological models based on
    reasoning and observations
  • They used these models to explain, and to predict
    planetary motions
  • Most of Greek models are Geocentric, but even
    Heliocentric models (e.g. Aristarchus) was
    proposed (2000 years ahead of his time)
  • In Greek Cosmology, we see the close relation
    between science and philosophy

Plato (428 - 348 BC)
  • All natural motion is circular
  • Reason is more important than observation

Claudius Ptolemy (AD 100-170)
  • star catalogue
  • instruments
  • motions model of planets, Sun, Moon

His model fit the data, made accurate
predictions, but was horribly contrived!
Ptolemys Geocentric Model
  • Earth is at center
  • Sun orbits Earth
  • Planets orbit on small circles whose centers
    orbit the Earth on larger circles
  • the small circles are called epicycles

Nicolaus Copernicus (1473-1543)
  • He thought Polemys model was contrived
  • Yet he believed in circular motion
  • De Revolutionibus Orbium Coelestium

Copernicus Heliocentric Model
  • Sun is at center
  • Earth orbits like any other planet
  • Inferior planet orbits are smaller
  • Explained the available observations better than
    Polemys model

Johannes Kepler (1571-1630)
  • Greatest theorist of his day
  • a mystic
  • forces made the planets move
  • Keplers three laws (assignment learn Keplers
    laws at masteringastronomy.com)

Galileo Galilei (1564-1642)
  • First man to point a telescope at the sky
  • wanted to connect physics on earth with the
  • Galileo discovered that Jupiter had four moons of
    its own.
  • Jupiter was the center of its own system.
  • Heavenly bodies existed which did not orbit the
  • Dialogue Concerning the Two Chief World Systems

This book got him in trouble with the Church!
Sir Isaac Newton (1687)
  • Published The Mathematical Principles of Natural
  • Three laws of motion
  • Low of universal gravitation
  • The basic principles of modern physics
  • Newton is, arguably, the greatest scientist ever
    in human history
  • Physics
  • Calculus
  • Optics

Immanual Kant (1755)
  • Idea of Island Universe
  • Spiral Nebulae are other Milky Ways
  • Very distant and external to our Galaxy

William Hershel, 1785
  • First attempt to map out the Milky Way Galaxy
  • Beyond the solar system
  • Extend the scope of the universe by 10,000 times
  • Hershel assumed to the solar system is at the
    center of the Milky Way Galaxy

Early 20th Century Great Physics Evolution
  • 1900 German physicist Max Planck proposed that
    energy radiates in quanta ? start of quantum
  • 1905 Einsteins special relativity ? matter,
    space and mass are closely related
  • 1915 Einsteins general relativity ? gravity and
    space/time are closed linked
  • 1916 German astrophysicist Karl Schwarzschild
    proposed black holes
  • 1919 English astrophysicist Sir Arthur Eddington
    confirmed Einsteins prediction from relativity

Late 19th to Early 20th century Great Leap in
  • 1858 American astronomer Henry Draper invented
    astronomical photography
  • Early 1920th, the new generation of telescopes,
    in particular the 100 inch telescope on Mt.
    Wilson outside LA, began to survey the heavens.

1920s Birth of Modern Cosmology
  • 1920 Great Shapley vs. Curtis debate are spiral
    nebulae island universe?
  • 1925 Hubble measured the distance to Andromeda
    the extragalactic astronomy is born, the size of
    our observed universe is again increased by
  • 1922 Russian physicist Aleksander Friedmann
    discovered the expanding solution of Einsteins
    general relativity ? theoretical prediction of
    the expansion of the universe
  • 1929 Hubble discovered the expansion of the

The most importance figure of modern cosmology
The further the galaxy, The faster it is moving
away ? The universe is expanding
The Big Bang
  • 1948 Russian-American physicist George Gamow
    published the first model about the universe
    started from a hot and dense fireball ? the hot
    big bang the predicted this creation left
    behind a faint glow that suffuses the universe
    today, the cosmic microwave background

The discovery of Cosmic Microwave Background
  • Bell lab physicists Arno Penzias and Robert
    Wilson discovered CMB by chance when building
    their low-noise communication antenna. This
    confirmed the Big Bang theory. The two key pieces
    of modern cosmology expansion of the universe
    and hot big bang, are firmly established.

Recent History (1964 - now)
  • Discovery of quasar - Marteen Schmidt, 1964
  • Opened up the distant universe
  • Discovery of microwave background - Penzias and
    Wilson 1965
  • verified the big bang cosmology
  • Establishment of modern cosmology theory (1970s)
  • Zeldovich in Russian
  • Peebles in Princeton
  • Surveys of the Universe
  • 1985, Center of Astrophysics survey
  • Observational tests of cosmology theory

Recent History
  • 1970s discovery of dark matter in galaxies
  • 1980s inflation cosmology towards the Big Bang
  • 1990 Hubble Space Telescope
  • 1992 COBE satellite to map the microwave
  • 2000 discovery of dark energy and accelerating

What have we learned?
  • How did the Greeks lay the foundations for modern
  • By developing the notion of models and putting
    emphasis on the importance of having models agree
    with observed reality.
  • What was the Ptolemaic model?
  • Ptolemys synthesis of earlier Greek ideas about
    the geocentric universe, which was a
    sophisticated model that allowed prediction of
    planetary positions.

What have we learned?
  • Briefly describe the roles of Copernicus, Kepler,
    and Galileo.
  • Copernicus created a Sun-centered model of the
    solar system designed to replace the Ptolemaic
    model, but it was no more accurate because he
    still used perfect circles. Kepler refined the
    model by introducing orbits with the correct
    characteristics. Galileos experiments and
    telescopic observations overcame remaining
    objections to the Copernican idea of the Earth is
    a planet orbiting the Sun.
  • What is a theory in science?
  • A model that explains a wide variety of
    observations in terms of just a few general
    principles, which has survived numerous tests to
    verify its predictions and explanations.

History of Modern Cosmology
  • Two most important discoveries of modern
  • Hubbles Law
  • Observations of Microwave Background
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