A History of the Universe Astronomy 315 Professor Lee Carkner Lecture 2 “There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarrely inexplicable. There is another theory which states that this has already happened”. --Douglas Adams, “The Hitchhikers Guide to the Galaxy”

Our Place in the Universe  Before we look at the history of the universe, we will look at our place in it   We now realize that we occupy no unique or special place in the universe   After Nicolaus Copernicus who theorized that the sun, and not the Earth, was the center of the solar system  So where are we?

The Earth

The Solar System

The Solar Neighborhood

The Milky Way

The Andromeda Galaxy

The Virgo Cluster

Where Do We Fit In?  We can think about our position in the universe in terms of scale  We live on a planet (Earth)   Star is in a galaxy (Milky Way)    Supercluster is in a (the?) universe  Each “step up” is a huge increase in size

The Big Bang  The best model for the beginning of the universe is the hot big bang model  Key points:     Why do we believe this? 

About the Big Bang  We can see the expansion of the universe and the glow of the early hot universe   The universe has a beginning but no center or edge   The universe is not really like any macroscopic object we are familiar with

The First Three Minutes  What was the early universe like?    Almost impossible to simulate the very early universe  What do we know?   Universe consists of photons and subatomic particles (like quarks)

Inflation    After the inflationary era all four forces separate and the universe cools to the point where protons, neutrons and electrons form

Recombination  The early universe is dominated by photons (particles of light) but after about 1 million years the universe cools to the point where atoms form    The lack of collisions allowed the matter to be influenced by gravity

Formation of Structure  After about 1 billion years the universe is a big ball of atoms and photons   Why?   This is why we have matter organized into stars, galaxies and clusters of galaxies, instead of a big uniform cloud of stuff

Fluctuations in the Radiation from the Big Bang

Structure of the Universe  On the largest scale the universe is full of superclusters of galaxies   The clusters are full of galaxies   Stars are the basic building blocks of the universe

Large Scale Structure

The Hubble Deep Field

The Early Stars  The first stars were made out of hydrogen and helium, the two simplest elements   Nuclear reactions inside the stars produced heavier elements   Most of the universe (80%) is still hydrogen, however

Stellar Products  The next generation of stars had small amounts of these heavier elements in them   When any star dies it leaves behind a burned out core   Collectively known as compact objects

Composition of the Universe  Lots of galaxies in clusters and superclusters  Galaxies made up of:   

Summary  The universe began with a hot big bang  Universe cooled and formed atoms   Stars process the original light elements into heavier ones 

The Future  The universe had a beginning, will it have an end?  Will the universe expand forever?   Will the stars burn up all available fuel? 

Next Time  Read Chapter 2  Question of the Day:  How does the fact that we are standing on a giant ball affect the way we see the universe?  Meet in Planetarium on Friday!