Big Bang Theory Evidence to Know for Cosmology

The Big Bang Theory explains how our universe began and evolved. Key evidence includes cosmic microwave background radiation, the expansion of galaxies, and the abundance of light elements. These findings help us understand the universe's structure and its ongoing changes.

1. Cosmic Microwave Background Radiation

   • The CMB is the afterglow radiation from the Big Bang, filling the universe uniformly.
   • It provides a snapshot of the universe when it was just 380,000 years old, revealing its temperature and density fluctuations.
   • The uniformity and slight anisotropies in the CMB support the theory of cosmic inflation and the hot Big Bang model.

2. Expansion of the Universe (Hubble's Law)

   • Hubble's Law states that galaxies are moving away from us, with their speed proportional to their distance.
   • This observation implies that the universe is expanding, supporting the Big Bang Theory.
   • The rate of expansion is quantified by the Hubble constant, which helps estimate the age of the universe.

3. Abundance of Light Elements (Primordial Nucleosynthesis)

   • The Big Bang produced light elements like hydrogen, helium, and lithium in specific ratios.
   • Observations of these abundances match predictions from nucleosynthesis models, confirming the Big Bang Theory.
   • The relative amounts of these elements provide insights into the conditions of the early universe.

4. Large-Scale Structure of the Universe

   • The distribution of galaxies and galaxy clusters forms a web-like structure, influenced by gravitational forces.
   • This large-scale structure aligns with predictions from the Big Bang and cosmic inflation theories.
   • Understanding this structure helps explain the evolution of the universe over billions of years.

5. Olbers' Paradox

   • Olbers' Paradox questions why the night sky is dark if the universe is infinite and filled with stars.
   • The resolution lies in the finite age of the universe and the expansion, which limits the observable universe.
   • This paradox supports the Big Bang Theory by indicating that the universe has a beginning and is not static.

6. Redshift of Distant Galaxies

   • Light from distant galaxies is redshifted, indicating they are moving away from us due to the universe's expansion.
   • The degree of redshift correlates with distance, providing evidence for an expanding universe.
   • This phenomenon supports the Big Bang Theory by showing that the universe was once much smaller and denser.

7. Cosmic Inflation Theory

   • Cosmic inflation proposes a rapid expansion of the universe in the first moments after the Big Bang.
   • This theory explains the uniformity of the CMB and the large-scale structure of the universe.
   • Inflation helps resolve several cosmological problems, such as the flatness and horizon problems.

8. Baryon Acoustic Oscillations

   • Baryon acoustic oscillations are regular, periodic fluctuations in the density of visible baryonic matter.
   • These oscillations provide a "standard ruler" for measuring cosmic distances and understanding the universe's expansion.
   • They are a key piece of evidence for the Big Bang and the evolution of the universe.

9. Gravitational Waves

   • Gravitational waves are ripples in spacetime caused by accelerating massive objects, such as merging black holes.
   • Their detection provides insights into the dynamics of the universe and supports general relativity.
   • Gravitational waves can offer information about the early universe and events that occurred shortly after the Big Bang.

10. Dark Matter and Dark Energy

    • Dark matter is an unseen substance that makes up about 27% of the universe, influencing its structure and formation.
    • Dark energy is a mysterious force driving the accelerated expansion of the universe, constituting about 68% of it.
    • Both dark matter and dark energy are essential for understanding the universe's composition and evolution post-Big Bang.