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Lecture 1:Our Evolving View of the

Universe

Dr. Michael Burton

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History of Science & Astronomy: The Greeks

• 550BC Pythagoras: Natural phenomena described by mathematics.

• 300BC Aristotle: Universe governed by physical laws.

• (Aristarchus proposed heliocentric model.)

• 200AD Ptolemy: Geocentric cosmology.Epicycles and Deferents, as explained in the

Almagest

History of Science & Astronomy: The Renaissance

• 1543 Nicolaus Copernicus: Heliocentric cosmology in De Revolutionibus (circles).

• 1573 Tycho Brahe: De stella nova in Cassiopeia - precise observations.

• 1619 Johannes Kepler: Three (empirical) laws of planetary motion (ellipses).

• 1610 Galileo Galilei: Telescope shows an imperfect, non-geocentric universe.– Dialogue on the Two New Sciences

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History of Science & Astronomy: Physics

• 1687 Isaac Newton: Principia: Physical laws to explain the observations.– Laws of Motion and Gravity allow predictions.

• 1905 Albert Einstein: Special and General theories of Relativity explain nature of light and gravity.

• ???? You ???? Quantum Gravity and a Unified Field theory for Forces of Nature.

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Scientific Method & Astronomy

• The universe is comprehensible.

• Scientific method is a procedure for formulating theories, which can be tested by experiment to build models to describe phenomena in the universe.

• Observations of the heavens have led to the discovery of some fundamental laws of nature.

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Key Ideas

• The heliocentric theory simplified the explanation of planetary motions compared to geocentric theory.

• In it the Earth is but one of several planets orbiting the Sun

• Ellipses describe the paths of planets around the Sun more accurately than circles do.

• The invention of the telescope lead to new discoveries about the universe around us.

• Newton based his explanation of the universe on three assumptions called the Laws of Motion.

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Key Ideas

• Together with the law of gravity, they explained Kepler’s empirical laws with great accuracy.

• Einstein’s theories of relativity accounted for small discrepancies in Newton’s Laws which were only apparent through careful observation.

• The theory of relativity, which explains the universe on the largest scales, is incomplete and has yet to be reconciled with quantum theory, which explains it on the smallest scales.