Download Development of the Modern “World View”

Development of the Modern “World View”
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Prior to 1610, the “universe” consisted of the Sun, Moon, 5 planets, and the
background of stars. World models were based on the patterns and motions
of just these objects.
The First Revolution in Our World View:
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In 1543 the Polish cleric Nicholas Copernicus (1473-1543) proposed a
heliocentric model for the Universe — in which Earth and the other planets
orbited the Sun.
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The Copernican Revolution involved more than just a model of planetary
motion; conceptually it replaced the Earth as the immobile center of the
Universe. As such, it conflicted with religious doctrine of the day.
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The heliocentric model was simple and elegant, replacing the complex
geocentric model, which, with the accumulation of centuries of data on
planetary positions, had grown increasingly complex.
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Copernicus did not promote his model, and his ideas were considered little
more than philosophical concepts until observational evidence supporting
the heliocentric model was discovered, more than 70 years after his death.
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Invention of the telescope in 1610 opened up an entire new universe, and
helped cement the first revolution in our worldview, the overthrow of the
geocentric model and acceptance of the heliocentric model.
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The heliocentric model was adopted by the middle of the 17th century, amidst
the turmoil of the Renaissance, when the new worlds opened up by the
technology of telescopes and new theoretical information (an explanation of
orbits provided by Kepler) became known.
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Galileo Galilei provided this new information by “inventing” the telescope in
1610, which opened up new worlds to humanity. In addition to revealing that
the planets were in fact worlds of their own, his observations revealed:
 The Milky Way (MW) consisted of countless stars, millions more than
previously known.
 Stars could be double or multiple, slowly orbiting each other.
 Great star clusters, swirling gas clouds, and mysterious “spiral nebulae”
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The countless stars revealed by the telescope were understood to be
luminous objects like the Sun, only at vast distances. The Universe was
much larger than previously understood.
The Next 300 Years:
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For about 300 years (~1610 to ~1920), the heliocentric model kept the Sun
and its family of planets at the center of the Universe.
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During this three hundred year period, as telescope technology improved,
astronomers cataloged the double stars, star clusters, and nebulae, and
debated the nature of the nebulae.
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Invention of photography in the mid-19th century finally permitted accurate,
repeatable records of celestial objects to be compiled.
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The rise of astrophysics, the study of the physical properties of celestial
objects, not just their positions on the sky, led to new insight into the
operating principles of the universe.
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The nature of the spiral nebulae and the true structure of the Milky Way
became increasingly controversial subjects.
The Second Revolution:
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A second revolution in our understanding of the universe occurred from
1910 – 1930, when new technology again led to new observational
discoveries, at the same time that a theoretical revolution occurred in physics.
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New large telescopes were constructed using curved mirrors, allowing fainter
stars to be detected and photographed.
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By mapping the positions and motions of globular star clusters, great
systems of stars, which orbit the Milky Way, astronomers realized that the
solar system was NOT located at the center of the Milky Way, but about
24,000 light years out from the center.
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Using the 100-inch telescope at Mt Wilson, Edwin Hubble determined that
the Andromeda spiral nebula was a separate galaxy, not a component of
the Milky Way.
Astronomers realized that the Milky Way was a galaxy, an “island universe”
of stars, gas, and dust. The spiral nebulae were recognized as other island
universes, stretching to enormous distances.
From observations of their spectra, astronomers discovered that almost all
galaxies were moving away from the Milky Way.
Albert Einstein revolutionized understanding of forces and gravity, with his
theories of special (1905) and general (1915) relativity.
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This new cosmology implied:
 The universe was vastly larger than previously conceived.
 The universe was expanding, as could have been predicted by Einstein
(but wasn’t).
 The Milky Way was one of perhaps a 100 billion galaxies, stretching as
far as could be seen.
 The universe had an origin in time; the moment when the expansion
began.