Lectures on History of Science – Lecture 22: Wonders beyond sky – the development of cosmology in modern times

Summary

The quote, “space extending to all directions is called Yu(宇), time stretching from the past to the present is called Zhou(宙)”, in the philosophical treatise Shizi back to Warring States Period reflects the insightful exploration of this planet we live and the stars we look up at. Human beings has being gradually discovering our position in the universe by forming cosmological hypothesis from Huntian(浑天, spherical sky) in ancient China and Aristotelian/Ptolemaic earth-centered universe in ancient Greece, to Copernican/Brunonian sun-centered modal during the Renaissance ,then to the epoch-marking Curtis-Shapley Debate in the early 20th century. And the first milestone of modern-time cosmology was marked with the observation of Hubble Expansion and the moving away of galaxies, which eventually solved the Great Debate. Since 16^th century, Galilean and Newtonian space-time model and Newton’s gravity theory has dominated the mainstream of physics for 3 centuries and witnessed a clearer understanding of light and light spped. Finally, Michelson-Morley experiment revealed interference properties of light and diminished the concept of “ether”. It verifies the constancy of light speed and lays a critical foundation for the creation and wide acceptance of relative space-time model and the relativity of gravity. The theory of relativity acts as the framework of modern-time cosmology. Concepts involving a variety of natural science subjects keep coming out such as the Hot Big Bang Cosmology, Inflation Theory, dark matter and dark energy, seemingly independent but implicitly interrelated.