Chapter 17 The Beginning of Time

Running the Expansion Backward Temperature of the Universe from the Big Bang to the present (10 10 years ~ 3 x seconds)

A Scientific History of the Universe The Big Bang Theory –The scientific theory of the universe’s earliest moments. –It presumes that all we see today, from the Earth out to the cosmic horizon, began as a tiny, hot and dense collection of radiation and matter. –It describes how expansion and cooling has led to the present universe of stars and galaxies. –It explains some current observational facts.

Eras of the Universe

Conditions of the Earlier Universe It was so hot, that photons (light energy) could transform into matter, and vice - versa, according to Einstein’s equation: E=mc 2 where E = energy m = mass c = speed of light. Antimatter is common

Electron-positron Creation And Annihilation Reactions

The First Instant – Planck Era Occurs within the first seconds. ?????- current theories fail to explain what might have been happening during this era. A theory that links quantum mechanics and general relativity is required, but does not yet exist…perhaps someday in the future, we will have such a theory.

The GUT (Grand Unified Theories) Era Occurs after seconds and lasts to seconds. Today, the universe is governed by four forces that we know of: 1.Gravity. 2.Electromagnetism. 3.Strong nuclear force. 4.Weak nuclear force. The number of forces governing the universe were fewer during the GUT era. GUT explains the merger of the four forces into only two forces. electromagnetism+weak force  electroweak force. electroweak force + strong nuclear force  GUT force

The Four forces are distinct at low temperatures but may merge at very high temperatures

At the end of the GUT era… Strong nuclear forces become distinct This released an enormous amount of energy which caused a sudden and dramatic expansion called Inflation

Electroweak Era Occurs from seconds to seconds. (after the GUT era) Intense radiation filled all of space, creating particle/antiparticle pairs. These newly formed particles would transform back into energy through particle annihilation. The universe continues to expand and cool.

Electromagnetic and weak forces become distinct. Two particles predicted to exist then were the W and Z bosons. These particles exist at temperatures ~ K. In 1983, the particle accelerator at CERN produced energies equivalent to K., and they discovered the W and Z particles. At the end of the electroweak era…

The particle era Occurs from seconds to seconds. Spontaneous creation and annihilation of particles continues. Electrons Neutrinos Quarks – building blocks of protons and neutrons. Antimatter is common

The era of nucleosynthesis Occurs from seconds to 3 minutes. After matter annihilates antimatter near the end of the electroweak era, protons, neutrons, electrons and neutrinos survive. By this time, antimatter is rare.

Era of Nuclei Occurs after 3 minutes and continues to 500,000 years after the Big Bang. By fusion, hydrogen nuclei have formed into helium nuclei. Most of the matter in the universe is in a state of plasma made up of hydrogen and helium nuclei + electrons.

Era of Atoms Occurs after 500,000 years to 1 billion years after the Big Bang. The universe consists of a mixture of neutral atoms and plasma. Protogalactic clouds form At the end of this era, the first galaxies and stars have formed.

Era of Galaxies Occurs after 1 billion years to present day after the Big Bang. Galaxies, galactic clusters and stars have formed. New galaxies and stars continue to form out of atoms, molecules and plasma.

Evidence for the Big Bang The Big Bang Model has gained widespread acceptance in the scientific community for two main reasons: 1.Cosmic Microwave Background Radiation: The Big Bang model predicts that the radiation produced at the end of the era of nuclei should still be present today. The discovery of the cosmic microwave background verified this. 2.Observations of actual helium content of the universe closely match the amount predicted by the Big Bang model.

Photons released after the era of nuclei make up the cosmic microwave background

Spectrum of the Cosmic Microwave Background - COBE Mission data. Data points Theoretically calculated curve

All-Sky map shows slight temperature differences in the cosmic microwave background

GUT theory and Inflation – possible explanation for the following problems Where does the structure come from? –Density enhancements would be required for galaxy formation to occur. Why is the large scale universe so smooth? –Big Bang Theory cannot yet explain why distant reaches of the universe look so similar. Why is the density almost critical? –Density of matter is ~ (20-100)% of critical density. Big Bang Theory does not say anything about what the density should be.

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