Forces and Fate

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Forces and Fate

Introduction to Expansion

The universe’s expansion challenges our understanding of how and why it occurs. Observations often lead to revisiting “well-understood” phenomena, exposing gaps in knowledge.

The Four Fundamental Forces

  1. Gravity
  • Weakest force but governs the cosmos due to its range and universal influence.
  1. Electromagnetism
  • Governs charged particles, combining electricity and magnetism.
  • Unified in the 1800s for simplicity and elegance, showing how electricity and magnetism are manifestations of the same force.
  1. Strong Nuclear Force
  • Binds protons and neutrons in atomic nuclei, overcoming the electromagnetic repulsion of like charges.
  1. Weak Nuclear Force
  • Responsible for radioactive decay; unified with electromagnetism into the electroweak force, showcasing deeper connections in physics.

Gravity: The Weak Yet Dominant Force

Characteristics

  • Gravity is the weakest fundamental force, yet it governs the universe due to its infinite range and cumulative effects.
  • Always attractive, acting on all objects with mass.

Laws by Isaac Newton

  • Newton’s Laws:
  • Gravity’s force is proportional to the product of two masses and inversely proportional to the square of their distance.
  • Explained planetary motion using ellipses and the inverse square law.

Curvature of Space-Time

Newton vs. Einstein

  • Newton: Space is flat, static, and gravity is a force of attraction.
  • Einstein: Mass curves space-time, and this curvature dictates the motion of objects.

Key Observations

  • Deflection of Light: Einstein predicted that light bends in the presence of massive objects, confirmed during a solar eclipse.
  • Black Holes: Extreme curvature of space-time prevents even light from escaping.

Cosmological Geometry and Curvature

Measuring Curvature

  • Space can have:
  • Flat Geometry: Triangle angles sum to 180°.
  • Positive Curvature: Angles sum to more than 180°, like on a sphere.
  • Negative Curvature: Angles sum to less than 180°, like on a saddle.

Tools for Measurement

  • Parallax: Measuring angles between stars at different times of year to calculate spatial curvature.
  • Cosmic Microwave Background (CMB): Acts as a standard ruler to determine universal curvature.

Relativity and the Fate of the Universe

Einstein’s General Relativity

  • Unified time and space into space-time.
  • Demonstrated that mass and energy influence the curvature of the cosmos.

The Future of the Universe

  • The density of mass-energy determines whether the universe:
  1. Expands forever.
  2. Contracts into a “big crunch.”
  3. Coasts infinitely.

Conclusion

The interplay of forces, mass, and curvature defines the universe’s structure and fate. Through relativity, we understand that gravity is not merely a force but the curvature of space-time itself. The ultimate destiny of the cosmos hinges on measuring mass-energy and understanding its influence on space and time.

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