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THEORIES OF THE UNIVERSE
FLAT EARTH THEORY
FLAT EARTH THEORY
• Date: Ancient Times
• Scientists: Babylonians, Egyptians
• Theory Description: The world is a flat disk, not a
sphere
• Evidence: None. As early as the 4 th century BC,
scientists and philosophers, such as Aristotle,
realized that the Earth was a sphere
PTOLEMY UNIVERSE
PTOLEMY UNIVERSE
• Date: approximately 145 AD
• Scientists: Claudius Ptolemy
• Theory Description: Earth is the center of the
universe. Everything revolves around Earth.
• Evidence: Ptolemy used math and observations
to say that earth didn’t move. Copernicus
disputed theory based on his observations.
COPERNICUS UNIVERSE
COPERNICUS UNIVERSE
• Date: 1514
• Scientists: Nicolaus Copernicus
• Theory Description: The Sun, not Earth, is the center of the
universe (Heliocentric). The Sun does not move. Earth and the
planets revolve around it.
• Evidence: Observed planets movements. Sometimes Mars
moves forward, sometimes backwards and sometimes it slowed
down. Revolving around the Sun, not Earth was the only way to
explain this. Also, Newton’s Laws of Motion-when 2 objects orbit
each other, the light mass moves more than the heavier
KEPLER UNIVERSE
KEPLER UNIVERSE
• Date: 1609-1619
• Scientists: Johanes Kepler, Tycho Brahe
• Theory Description:
• 1st Law-planets move in an elliptical orbit around the Sun
• 2nd Law-the closer a planet to the Sun, the faster it moves
• 3rd Law-the precise relation between the distance of a planet
from the Sun and how fast it completes an orbit
• Evidence: Brahe measured planet positions every day for years.
Kepler found that Mars movement matched an elliptical, not
circular orbit
FRIEDMANN UNIVERSE
FRIEDMANN UNIVERSE
• Date: 1922
• Scientists: Alexander Friedmann
• Theory Description: Universe begins with a Big Bang and
continues expanding for billions of years (the stage we’re in
now). The gravitational attraction of all this matter causes the
expansion to stop, and universe starts to collapse (Big Crunch).
The universe becomes cold and dark.
• Evidence: Hubble formulated the law describing the expansion
(1929) from observing distant galaxies.
OSCILLATING UNIVERSE
OSCILLATING UNIVERSE
• Date: 1920’s
• Scientists: Richard Tolman
• Theory Description: Combination of Big Bang and Big Crunch
theories. This is not the end of the universe, but signals
beginning of another cycle: expansion followed by impulsion, or
an oscillation universe.
• Evidence: CMB radiation supports the continued expansion of
Big Bang and the universe ending in either Big Freeze or Heat
Death. However, recent evidence shows universe is not closed
and will expand forever
BIG BANG THEORY
BIG BANG THEORY
• Date: 1927
• Scientists: Edwin Hubble, Albert Einstein
• Theory Description: based on observations that other galaxies
are moving away from ours as if propelled by an explosion
• Evidence:
• 1-universe had a beginning
• 2-Hubble’s Law-galaxies appear to be moving from us
• 3-Cosmic Microwave Background (CMB) Radiation was
discovered in 1965 and proved universe had a very hot origin
STEADY STATE UNIVERSE
STEADY STATE UNIVERSE
• Date: 1948
• Scientists: Hermann Bondi, Thomas Gold, Fred Hoyle
•
Theory Description: Perfect Cosmological Principle-the
universe looks the same from every spot and at every time
[applies only to the universe if seen from al far distance-planets,
stars and galaxies are different from the space between them]
There is no beginning and no end to the universe.
• Evidence: Disproved when quasars discovered in distant areas
of galaxy showing the ancient universe is not the same as the
younger galaxy near it. CMB radiation, left over from the Big
Bang start discovered in 1965.
ANTHROPIC UNIVERSE
• No picture exists because the “Perfect
World” only exists if we can see it.
ANTHROPIC UNIVERSE
• Date: Late 1960’s
• Scientists: Brandon Carter
• Theory Description: We live in a universe set up to allow our
existence If this universe were set up any other way, we would
not exist and bot be able to make observations. We live in a
superset of universes classed multiverse.
• Evidence: Certain physical constants are fine-tuned to allow life
to exist. If the universe expanded slightly faster then matter
would have spread out too quickly to collect in objects. If the
universe expanded slower, it would have collapsed already.
INFLATIONARY UNIVERSE
INFLATIONARY UNIVERSE
• Date: 1980
• Scientists: Alan Guth
• Theory Description: Explains some limitations of the Big Bang theory. Right
after the Big Bang [10 -35 seconds or 100 billion trillion trillion of a second] the
universe expanded extremely quickly. It then slowed down to the rate of
expansion show today. This explained problems with Big Bang theory.
• Evidence: Explains major problems with the Big Bang Theory such as why
the temperature of the background radiation remains constant over the
universe. GUT-Grand Unified Theories-unites gravity, electromagnetism, and
the weak and strong forces into one. After the universe cooled, these forces
separated.
NO BOUNDARY UNIVERSE
NO BOUNDARY UNIVERSE
• Date: 1983
• Scientists: Stephen Hawking, Jim Hartle
• Theory Description: Universe has no boundaries and imaginary
time. [Imagine an inflating balloon. A galaxy on the surface of
the balloon would move away in 1 direction and eventually end
up where it started].
• Evidence: Richard Feynman’s proposed that a particle does not
have one history in space-time but instead follows every
possible path to reach its current state.

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