08 - The Origin and Fate of the Universe

Описание: This chapter explores the origin and fate of the universe, beginning with the hot big bang model. The universe began infinitely hot and cooled as it expanded. One second after the big bang at 10 billion degrees, the universe contained photons, electrons, neutrinos, and their antiparticles plus some protons and neutrons. At 100 seconds and 1 billion degrees, nuclear fusion began producing helium and other light elements. George Gamow and Ralph Alpher in 1948 predicted the cosmic microwave background radiation, confirmed by Penzias and Wilson in 1965. After 300,000 years, electrons combined with nuclei to form atoms. Density fluctuations caused denser regions to collapse into galaxies and stars. Massive stars fused heavier elements and exploded as supernovas, distributing heavy elements for next-generation stars like our sun. Earth formed from these elements, and life evolved.

However, the hot big bang model left key questions unanswered: why was the early universe so hot and uniform despite insufficient time for thermal equilibrium (horizon problem), why is expansion rate so close to critical rate (flatness problem), and what caused density fluctuations? Alan Guth proposed in 1981 that inflationary expansion in the very early universe could solve these problems. Inflation causes exponential expansion that smooths irregularities and naturally produces critical expansion rate. Andrei Linde later proposed chaotic inflation where quantum fluctuations create regions that inflate without requiring phase transitions. Inflation explains the universe's large matter content because total energy is zero - positive matter energy exactly cancels negative gravitational energy.

Quantum cosmology applies Feynman's sum over histories to curved space-times using imaginary time to avoid technical difficulties. The no boundary proposal, developed by Hawking with colleagues, suggests the universe is finite in imaginary time without boundaries, like Earth's surface but with four dimensions. In imaginary time, the universe expands from a point to maximum size and contracts back with no singularities. This predicts the universe should expand uniformly, consistent with microwave background uniformity. The no boundary condition combined with uncertainty principle predicts minimum initial non-uniformities that inflation amplified into structures we observe, confirmed by COBE satellite detection in 1992 of slight microwave background variations. These density variations caused denser regions to collapse into galaxies, stars, and eventually life. If the universe is truly self-contained with no boundary, it would neither be created nor destroyed but simply be, profoundly impacting the concept of a creator's role.