Astrofísica para Todos

This book is a gentle introduction for all those wishing to learn about modern views of the cosmos. Our universe originated in a great explosion – the big bang. For nearly a century cosmologists have studied the aftermath of this explosion: how the universe expanded and cooled down, and how galaxies were gradually assembled by gravity. The nature of the bang itself has come into focus only relatively recently. It is the subject of the theory of cosmic inflation, which was developed in the last few decades and has led to a radically new global view of the universe.

Students and other interested readers will find here a non-technical but conceptually rigorous account of modern cosmological ideas – describing what we know, and how we know it. One of the book’s central themes is the scientific quest to find answers to the ultimate cosmic questions: Is the universe finite or infinite? Has it existed forever? If not, when and how did it come into being? Will it ever end?

The book is based on the undergraduate course taught by Alex Vilenkin at Tufts University. It assumes no prior knowledge of physics or mathematics beyond elementary high school math. The necessary physics background is introduced as it is required. Each chapter includes a list of questions and exercises of varying degree of difficulty.

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Summary

Part I Te Big Bang and the Observable Universe
1 A Historical Overview
1.1 The Big Cosmic Questions
1.2 Origins of Scientifc Cosmology
1.3 Cosmology Today
2 Newton’s Universe
2.1 Newton’s Laws of Motion
2.2 Newtonian Gravity
2.3 Acceleration of Free Fall
2.4 Circular Motion and Planetary Orbits
2.5 Energy Conservation and Escape Velocity
2.6 Newtonian Cosmology
2.7 Olbers’ Paradox
3 Special Relativity
3.1 The Principle of Relativity
3.2 The Speed of Light and Electromagnetism
3.3 Einstein’s Postulates
3.4 Simultaneity
3.5 Time Dilation
3.6 Length Contraction
3.6.1 Speeding Muons
3.7 E = mc2
3.8 From Space and Time to Spacetime
3.9 Causality in Spacetime
4 The Fabric of Space and Time
4.1 The Astonishing Hypothesis
4.2 The Geometry of Space
4.2.1 Euclidean Geometry
4.2.2 Non-Euclidean Geometry
4.3 Curved Space
4.3.1 The Curvature of Surfaces
4.3.2 The Curvature of Three-Dimensional Space
4.4 The General Theory of Relativity
4.5 Predictions and Tests of General Relativity
4.5.1 Light Defection and Gravitational Lensing
4.5.2 Gravitational Time Dilation
4.5.3 Black Holes
4.5.4 Gravitational Waves
5 An Expanding Universe
5.1 Einstein’s Static Universe
5.2 Problems with a Static Universe
5.3 Friedmann’s Expanding Universe
6 Observational Cosmology
6.1 Fingerprints of the Elements
6.2 Measuring Velocities
6.3 Measuring Distances
6.4 The Birth of Extragalactic Astronomy
7 Hubble’s Law and the Expanding Universe
7.1 An Expanding Universe
7.2 A Beginning of the Universe?
7.3 The Steady State Theory
7.4 The Scale Factor
7.5 Cosmological Redshift
7.6 The Age of the Universe
7.7 The Hubble Distance and the Cosmic Horizon
7.8 Not Everything is Expanding
8 The Fate of the Universe
8.1 The Critical Density
8.2 The Density Parameter
9 Dark Matter and Dark Energy
9.1 The Average Mass Density of the Universe and Dark Matter
9.2 Dark Energy
9.3 The Fate of the Universe—Again
10 The Quantum World
10.1 Quantum Discreteness
10.2 Quantum Indeterminism
10.3 The Wave Function
10.4 Many Worlds Interpretation
11 The Hot Big Bang
11.1 Following the Expansion Backwards in Time
11.2 Thermal Radiation
11.3 The Hot Big Bang Model
11.4 Discovering the Primeval Fireball
11.5 Images of the Baby Universe
11.6 CMB Today and at Earlier Epochs
11.7 The Three Cosmic Eras
12 Structure Formation
12.1 Cosmic Structure
12.2 Assembling Structure
12.3 Watching Cosmic Structures Evolve
12.4 Primordial Density Fluctuations
12.5 Supermassive Black Holes and Active Galaxies
13 Element Abundances
13.1 Why Alchemists Did Not Succeed
13.2 Big Bang Nucleosynthesis
13.3 Stellar Nucleosynthesis
13.4 Planetary System Formation
13.5 Life in the Universe
14 The Very Early Universe
14.1 Particle Physics and the Big Bang
14.2 The Standard Model of Particle Physics
14.2.1 The Particles
14.2.2 The Forces
14.3 Symmetry Breaking
14.4 The Early Universe Timeline
14.5 Physics Beyond the Standard Model
14.5.1 Unifying the Fundamental Forces
14.6 Vacuum Defects
14.6.1 Domain Walls
14.6.2 Cosmic Strings
14.6.3 Magnetic Monopoles
14.7 Baryogenesis
Part II Beyond the Big Bang
15 Problems with the Big Bang
15.1 The Flatness Problem: Why is the Geometry of the Universe Flat?
15.2 The Horizon Problem: Why is the Universe so Homogeneous?
15.3 The Structure Problem: What is the Origin of Small Density Fluctuations?
15.4 The Monopole Problem: Where Are They?
16 The Theory of Cosmic Infation
16.1 Solving the Flatness and Horizon Problems
16.2 Cosmic Infation
16.2.1 The False Vacuum
16.2.2 Exponential Expansion
16.3 Solving the Problems of the Big Bang
16.3.1 The Flatness Problem
16.3.2 The Horizon Problem
16.3.3 The Structure Formation Problem
16.3.4 The Monopole Problem
16.3.5 The Expansion and High Temperature of the Universe
16.4 Vacuum Decay
16.4.1 Boiling of the Vacuum
16.4.2 Graceful Exit Problem
16.4.3 Slow Roll Infation
16.5 Origin of Small Density Fluctuations
16.6 More About Infation
16.6.1 Communication in the Infating Universe
16.6.2 Energy Conservation
17 Testing Infation: Predictions and Observations
17.1 Flatness
17.2 Density Fluctuations
17.3 Gravitational Waves
17.4 Open Questions
18 Eternal Infation
18.1 Volume Growth and Decay
18.2 Random Walk of the Infaton Field
18.3 Eternal Infation via Bubble Nucleation
18.4 Bubble Spacetimes
18.5 Cosmic Clones
18.6 The Multiverse
18.7 Testing the Multiverse
18.7.1 Bubble Collisions
18.7.2 Black Holes from the Multiverse
19 String Theory and the Multiverse
19.1 What Is String Theory?
19.2 Extra Dimensions
19.3 The Energy Landscape
19.4 String Theory Multiverse
19.5 The Fate of Our Universe Revisited
20 Anthropic Selection
20.1 The Fine Tuning of the Constants of Nature
20.1.1 Neutron Mass
20.1.2 Strength of the Weak Interaction
20.1.3 Strength of Gravity
20.1.4 The Magnitude of Density Perturbations
20.2 The Cosmological Constant Problem
20.2.1 The Dynamic Quantum Vacuum
20.2.2 Fine-Tuned for Life?
20.3 The Anthropic Principle
20.4 Pros and Cons of Anthropic Explanations
21 The Principle of Mediocrity
21.1 The Bell Curve
21.2 The Principle of Mediocrity
21.3 Obtaining the Distribution by Counting Observers
21.4 Predicting the Cosmological Constant
21.4.1 Rough Estimate
21.4.2 The Distribution
21.5 The Measure Problem
21.6 The Doomsday Argument and the Future of Our Civilization
21.6.1 Large and Small Civilizations
21.6.2 Beating the Odds
22 Did the Universe Have a Beginning?
22.1 A Universe that Always Existed?
22.2 The BGV Theorem
22.2.1 Where Does This Leave Us?
22.2.2 A Proof of God?
23 Creation of Universes from Nothing
23.1 The Universe as a Quantum Fluctuation
23.2 Quantum Tunneling from “Nothing”
23.2.1 Euclidean Time
23.3 The Multiverse of Quantum Cosmology
23.4 The Meaning of “Nothing”
24 The Big Picture
24.1 The Observable Universe
24.1.1 What Do We Know?
24.1.2 Cosmic Infation
24.2 The Multiverse
24.2.1 Bubble Universes
24.2.2 Other Disconnected Spacetimes
24.2.3 Levels of the Multiverse
24.2.4 The Mathematical Multiverse and Ockham’s Razor
24.3 Answers to the “Big Questions”
24.4 Our Place in the Universe

Autores: Delia Perlov, Alex Vilenkin