Lecture Notes: The Beginning of the Universe and the Role of Fundamental Forces

Introduction

• Big Bang: Occurred 13.8 billion years ago.
• Fundamental question in science: How and why the universe began.
• Challenges the boundaries of theory, experiment, physics, and philosophy.

Concepts of Space-Time

• Stephen Hawking's view: Nothing before the universe began.
• Space-Time Geometry: Time began with the universe; prior conditions are as meaningless as searching north of the North Pole.

Theories of the Beginning

• Inflation: Split-second exponential expansion after the Big Bang.
• Multiverse Theory: Eternal inflation producing bubble universes.
• Big Bounce Theory: Universe in cycles of expansion and contraction.
• Scale Variance: Roger Penrose's concept of universal equivalency at different scales.
• String Theory: Universe as a result of dimensional collisions; 11-dimensional space.

Current Understanding

• Universe’s origins remain a mystery with various hypotheses.

Exploration Beyond the Universe

• Proxima Centauri: Closest star, 4.24 light-years away.
• Milky Way: Contains around 100,000 million stars.

The Hottest Place in the Universe

• Large Hadron Collider (LHC): Produced temperatures of 5.5 trillion degrees Celsius by smashing lead atoms.

Fundamental Forces and Planck's Contribution

• Planck Temperature: 1.4 x 10^32 Kelvin, the highest possible temperature.
• Quantum Mechanics and General Relativity: Incompatibility during the Planck era.
• Quantum Gravity Theories:
  • Gravitons: Hypothetical particles that convey gravity.
  • Loop Quantum Gravity: Space-time is pixelated.
  • String Theory: Involves 10 or 11 dimensions.

Early Universe and Fundamental Forces

• Electro-Weak Force: Unification of weak nuclear force and electromagnetism at high energies.
• Grand Unification: Strong force unites with electro-weak force at high temperatures.

Problems with the Standard Big Bang

• Horizon Problem: Uniform temperature across the universe.
• Flatness Problem: Universe appears flat on a large scale.
• Magnetic Monopoles: Lack of detection in the universe.

Inflation Theory

• Alan Guth's Inflation: Universe expanded exponentially, solving the homogeneity and flatness problems.
• Observable Universe: 93 billion light years across, possibly small part of a larger cosmos.

Particle Physics and Higgs Boson

• Higgs Field: Gives particles mass; confirmed by LHC in 2012.

Fundamental Particles

• Quarks and Leptons: 12 fundamental particles.
• Standard Model: Includes matter and force carrier particles.

Matter vs. Antimatter

• Imbalance between matter and antimatter leads to the existence of the universe.
• Right-handed Neutrinos: Hypothetical particles that could explain the imbalance.

Neutrinos

• IceCube Neutrino Observatory: Studies neutrinos using Antarctic ice.
• Neutrino's Role: Provides insights into the early universe, potentially detectable through cosmic neutrino background.

Primordial Black Holes

• Stephen Hawking's Theory: Black holes formed from density fluctuations in early universe.
• LISA Telescope: Future mission to detect gravitational waves from these primordial black holes.

Big Bang Nucleosynthesis

• Formation of Light Elements: Hydrogen, Helium, and Lithium formed within the first few minutes.

Dark Matter and Dark Energy

• Dark Matter: Accounts for missing mass; possibly MACHOs or WIMPs.
• Dark Energy: Accounts for accelerated expansion of the universe; possibly vacuum energy or quintessence.

Conclusion

• Universe composition: 68% Dark Energy, 27% Dark Matter, 5% Normal Matter.
• Ongoing research and discovery continue to shape our understanding of the cosmos.