The Birth and Evolution of Our Universe: From the Big Bang to Present Day

Expert reviewed • 22 November 2024 • 7 minute read

Introduction

The Big Bang theory represents our best understanding of how the universe began and evolved. This model, supported by extensive observational evidence, describes the universe's journey from an incredibly dense, hot state to its current form over approximately 13.7 billion years.

The Early Universe

The First Moments

The universe began from a singularity - a point of infinite density and temperature. The sequence of events that followed occurred in remarkably quick succession:

  • Formation of Fundamental Forces (t<10−43t < 10^{-43} seconds)

    • The four fundamental forces (gravitational, electromagnetic, strong nuclear, and weak nuclear) separated from their unified state
    • First, gravity separated at 103210^{32} K
    • The strong nuclear force separated from the electroweak force at 102710^{27} K

  • Cosmic Inflation (10−4310^{-43} to 10−3510^{-35} seconds)

    • The universe expanded exponentially, increasing in size by a factor of 102510^{25}
    • This rapid expansion prevented gravitational collapse
    • Temperature decreased significantly during this period

Matter Formation

  • Particle-Antiparticle Creation (10−3510^{-35} to 10−610^{-6} seconds)

    • Energy converted into matter and antimatter
    • Quarks and leptons formed with their antiparticles
    • Continuous annihilation produced gamma radiation

  • Baryogenesis (10−610^{-6} to 1 second)

    • Slight asymmetry favored matter over antimatter
    • Quarks combined to form protons and neutrons
    • The universe continued cooling

The Formation of Elements

Big Bang Nucleosynthesis (First 3 Minutes)

The first elements formed through nuclear fusion as the universe cooled:

  • Protons and neutrons combined to form:
    • Deuterium (2H^2\text{H})
    • Tritium (3H^3\text{H})
    • Helium-4 (4He^4\text{He})

The process can be represented by these nuclear equations:

p+n→D+γ\text{p} + \text{n} \rightarrow \text{D} + \gamma D+n→T+γ\text{D} + \text{n} \rightarrow \text{T} + \gamma T+p→4He+γ\text{T} + \text{p} \rightarrow {^4He} + \gamma

Recombination Era (380,000 Years)

When the universe cooled to approximately 3,000 K:

  • Electrons combined with nuclei to form neutral atoms
  • Photons decoupled from matter
  • The universe became transparent to radiation

Evidence for the Big Bang

1. Hubble's Discovery of Universal Expansion

Edwin Hubble made two crucial observations:

  • Galaxies show redshifted spectra, indicating recession
  • A linear relationship exists between galactic distance and recession velocity

Hubble's Law is expressed as:

v=H0Dv = H_0D

Where:

  • vv is the recession velocity
  • H0H_0 is Hubble's constant
  • DD is the distance to the galaxy

2. Cosmic Microwave Background Radiation (CMBR)

  • Discovered accidentally by Penzias and Wilson
  • Represents the afterglow of the Big Bang
  • Has a temperature of 2.7 K
  • Peak wavelength matches theoretical predictions:
λpeak=2.898×10−3T meters\lambda_{peak} = \frac{2.898 \times 10^{-3}}{T} \text{ meters}

3. Primordial Element Abundances

The current universe contains:

  • 73-75% Hydrogen
  • 23-26% Helium
  • ~2% heavier elements

These ratios match Big Bang nucleosynthesis predictions perfectly.

Modern Discoveries: Accelerating Expansion

Recent observations of Type Ia supernovae reveal:

  • The universe's expansion is accelerating
  • This contradicts expectations from gravity alone
  • Suggests the existence of dark energy

Return to Module *: From the Universe to the Atom