THEORIES OF THE UNIVERSE

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

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

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

Date: Scientists: Johanes Kepler, Tycho Brahe Theory Description: 1 st Law-planets move in an elliptical orbit around the Sun 2 nd Law-the closer a planet to the Sun, the faster it moves 3 rd 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

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

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

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

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

Date: 1980 Scientists: Alan Guth Theory Description: Explains some limitations of the Big Bang theory. Right after the Big Bang [ 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

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.