A chronology of our changing views of the cosmos

340 BC	Aristotle, On the Heavens
1st century AD	Ptolemy: maps of the earth and the heavens for "picturing the world."
1514	Nicholas Copernicus: the sun is the center of the planets.
1609	Kepler & Galileo
1687	Newton, Principia Mathematica Naturalis Causae
1783	John Mitchell the gravitational field (forces) of a massive star might stop light from escaping
1823	Heinrich Olbers' paradox: : "why doesn't the night sky look uniformly bright?"
1915	General Theory of Relativity, Albert Einstein (static universe and a cosmological constant) gravity affects light-quantum particles
1922	Alexander Friedmann, expanding universe is deduced from General Theory of Relativity
1924	other galaxies discovered by Edwin Hubble
1928	Chandrasekahr limit proposed on stellar masses predicts existence of white dwarf stars
1929	Edwin Hubble discovers star's luminosity based on Doppler shift appear in the red end of the spectrum and thus confirms expanding universe
1939	Robert Oppenheimer explains what occurs when massive stars implode: a region in space-time is created from which nothing may ever escape.
1951	Roman Catholic Church explains the Big Bang Theory is in accord with scripture
1965	Penzias & Wilson, Bell Labs, universal microwave radiation
1965	Roger Penrose theorizes that "a singularity" exists in a collapsed star of sufficient mass: later called a "black hole."
1969	The term black hole is coined by John Wheeler to explain the collapse of massive stars
1971	Hawking shows how some radiation may escape a black hole
1981	Vatican conference on cosmology and the big bang theory.

What is origins of our current concepts of the material universe?

Hawking's observations:

"Radiation from black holes was the first example of a prediction that depended on both great theories of this century, general relativity and quantum mechanics."

"This means that the laws of physics need not breakdown at the origin of the universe. The state of the universe and its contents, like ourselves, are completely determined by the laws of physics, up to the limit set by the uncertainty principle. So much for free will."

"Our own sun contains about 2 percent of these heavier elements because it is a second or third generation star. It was formed some five thousand million years ago out of a cloud of rotating gas containing the debris of earlier supernovas."

103

"...a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the Earth."

"So long as the universe had a beginning that was a singularity, one could suppose that it was created by an outside agency. But if the universe is really completely self contained, having no boundary or edge, it would be neither created nor destroyed. It would simply be. What place then, for a creator?"

126

"it is forbidden by the second law of thermodynamics. This says that disorder or entropy always increases with time. In other words, it is Murphy's Law – things get worse."

"The increase of disorder or entropy with time is one example of what is called an arrow of time, something that gives direction to time and distinguishes the past from the future."

Three varieties of the arrows of time:

Thermodynamic, increasing entropy.

Psychological, we recall the past but not the future.

Cosmological, universal expansion rather than contraction.

131

"...If we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall be able to take part in the discussion of why the universe exists. If we find the answer to that, it would be the ultimate triumph of human reason. For then we would know the mind of God."

166-67

Ian Tattersall | Richard Feynman | Jacob Bronowski | Stephen Hawking | Ernst Mayr

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