The Nature of the Universe and Cosmology

Introduction

• Humans historically used stories to explain the universe.
• Science and testing of ideas led to the field of cosmology.
• Understanding the universe is central to cosmology.

Early 20th Century Understanding

• The Earth was known to be very old.
  • Darwin’s theory and Lord Kelvin's calculations confirmed Earth's ancient origins.
• The universe was thought to be static; eternal and unchanging.

Challenging the Static Universe

• Vesto Slipher (1912-1917): Observed 'spiral nebulae' and found they were redshifted, moving away at high speeds.
• Georges Lemaître (1920s): Disagreed with Einstein's static universe; proposed an expanding universe.
• Alexander Friedman: Reached similar conclusions about the expanding universe.
• Edwin Hubble & Milton Humason: Measured distances to galaxies and correlated them with redshifts.
  • Farther galaxies move away faster.

Big Bang Theory

• Lemaître’s Conclusion: Universe is expanding.
• Cosmic clock running backward suggests a point where all matter was condensed.
• Conceptualized as a 'primeval atom' or 'cosmic egg.'
• Fred Hoyle: Coined the term 'Big Bang,' although skeptically.
• Universe expanded from a hot, dense state.

Evidence Supporting Big Bang

• Redshift of Distant Galaxies: All distant galaxies are moving away.
• Cosmic Microwave Background (CMB): Detected by radio astronomers in 1965.
  • Predicted remnant radiation from the Big Bang.
• Elemental Abundance: Predicted and observed ratios of elements like hydrogen and helium.
• Structure of the Universe: Aligns with Big Bang predictions.

Understanding Universe Expansion

• Expansion is not an explosion; space itself expands.
• Analogy: Expanding ruler or balloon.
• Universe has no center; every point expands away from others.
• Misconception: Big Bang was an explosion of matter in space.
• Reality: Space itself started expanding.

Determining the Age of the Universe

• Universe's age calculated to be approximately 13.82 billion years.
• Expansion rate allows calculation by running time backward.

Conclusion

• The Big Bang model is widely accepted.
• Observations continue to support the expanding universe theory.
• Understanding space and time is complex but crucial.

Production Notes

• Episode produced in association with PBS Digital Studios.
• Written by Phil Plait, edited by Blake DePastino.
• Directed by Nicholas Jenkins, audio by Michael Aranda, and visuals by Thought Cafe.