Cosmology Cosmology in simple terms q Cosmology is

Cosmology

Cosmology in simple terms q Cosmology is the study of how the universe on the large scale: how it began, how it is now, and how it will end. q How we see the universe now: q 1. Galaxies all receding away from each other.

The Expanding Universe On large scales, galaxies are moving apart, with velocity proportional to distance. It’s not galaxies moving through space. Space is expanding, carrying the galaxies along! The galaxies themselves are not expanding!

q How we see the universe now: q 2. Cosmic Background radiation left over from some explosive event. (and it’s redshifted and cooled off because space is expanding)

The Universe Before and After Recombination of Nuclei and Electrons

The Spectrum of the Cosmic Background Radiation

q How we see the universe now: q 3. Most of the universe is Hydrogen and Helium (light elements). These light elements would have formed after protons and electrons cooled off to form simple atoms.

4. Left over neutrinos left over from some explosive event.

q How we see the universe now: 1. Galaxies all receding away from each other. 2. Cosmic Background radiation left over from some explosive event. 3. Most of the universe is Hydrogen and Helium (light elements). 4. Left over neutrinos. q Conclusion: The universe was created from one explosive event producing matter, energy, space, and time…. . this event we call The Big Bang. q From the Hubble constant, we can rewind this to determine that it occurred q ~14 billion years ago. (Oldest stars in the universe are also ~14 billion years old. ) q Note: You can’t be outside the big bang looking in…it’s spacetime being created while you’re in it. So there is no center of the universe and there is no edge of the universe…. . Like being on the surface of the balloon.

Cosmology Based on scientific observations. Cosmological principle: 1. What we see is the same everywhere in the universe. 2. The physics and math we use here is also the same everywhere in the universe.

Steady State Theory q Proposed that the universe has always been and always will be the same (it was static and unchanging) q Abandoned because we see the universe changing and we don’t see new material popping up q Abandoned because it could not explain the cosmic background radiation

A Timeline of Events

A Timeline of Events • Note: You can’t be outside the big bang looking in…it’s spacetime being created while you’re in it. • 1. 10 – 6 seconds—HOT!, 1013 K, pair production of matter and antimatter (a hot soup of energy) • 2. 1 second—cools some, 1010 K, neutrinos form • 3. 100 seconds—cools to 109 K, cool enough to form light atoms of Hydrogen&Helium • 4. 10, 000 yrs. Later—radiation era from which we see cosmic background radiation • 5. 300 million yrs. —galaxies and stars start forming

The Future of the Universe depends on • 1. Hubble’s constant— how fast galaxies are receding…how fast everything is “thrown” • 2. How dense the universe is—affects the pull of gravity of the universe in on itself. • similar to a rocket thrown away from Earth

Balls Thrown Upward from a Massive Body

The Future of Expansion Negative expands forever Flat universe… expands forever approaching a limit Closed universe eventually contracts to the “Big Crunch”

The Future of the Universe

But wait, there’s a new twist • Recent observations of Type Ia supernova indicate that • The universe is not just flying apart, but speeding up as it flies apart. ( “A Runaway universe”) • Q: So what could be accelerating the universe’s expansion? • A: Yes, this is very weird, and we don’t know why…. • We don’t know…some call this mysterious force “dark energy”, or a “cosmological constant” • It looks like the universe will keep inflating…no end in sight…. so no need to worry….

Review for test • 1. Describe our home in the Milky Way galaxy. (what does it look like? Where are we? What does it contain? ) • 2. Describe the Hubble law. (In words. In equation form. As a graph. ) • 3. Describe the Big Bang theory. (What scientific evidence supports the creation of the universe? ) • 4. How are galaxies classified? How are they similar? Different? • 5. What are the possible fates of the universe? Explain them. And, based on most recent research, how do we think the universe will end? • 6. Compare and contrast dark matter and dark energy.