1. Discovering the Universe Eighth Edition Discovering the Universe Eighth Edition Neil F. Comins William J. Kaufmann III CHAPTER 18 Cosmology Cosmology

2. WHAT DO YOU THINK? 1. What is the universe? 2. Did the universe have a beginning? 3. Into what is the universe expanding? 4. How strong is gravity compared to the other forces in nature? 5. Will the universe last forever?

3. What is the Universe? The universe consists of all matter, energy, and space-time that we can ever detect or that will ever be able to affect us. The universe consists of all matter, energy, and space-time that we can ever detect or that will ever be able to affect us. Cosmology is the study of the large –scale structure and evolution of the universe. Cosmology is the study of the large –scale structure and evolution of the universe.

4. How did the Universe Begin? The best theory scientists can come up with is the Big Bang. The best theory scientists can come up with is the Big Bang. All matter and energy existed in an infinitely dense area All matter and energy existed in an infinitely dense area In the first moments of the universe (~13.7 billion years ago) matter and energy expanded explosively in an event called the Big Bang In the first moments of the universe (~13.7 billion years ago) matter and energy expanded explosively in an event called the Big Bang

5. Evidence for the Big Bang Cosmic Microwave Background Radiation Cosmic Microwave Background Radiation -Remnants of the energy from the big bang cause space to have a temperature of ~2.73 K. -This background radiation was predicted by calculations before it was discovered in the 1960’s

6. Bell Labs Horn Antenna This Bell Laboratories horn antenna at Holmdel, New Jersey, was used by Arno Penzias (right) and Robert Wilson in 1965 to detect the cosmic microwave background.

7. Evidence for the Big Bang: Cosmological Redshift Supports that the universe is expanding !

8. Evidence for the Big Bang Hubble’s Law allows us to estimate the age of the universe Hubble’s Law allows us to estimate the age of the universe (assuming the universe has been expanding at a constant rate) 1/H 0 = 1/71 km/s/Mpc = 13.7 billion years 1/H 0 = 1/71 km/s/Mpc = 13.7 billion years

9. Unification of the Four Forces

10. Cosmic Timeline This figure shows our current thinking about the evolution of star and galaxy formation in the universe.

11. Evolutionary Timeline of the Universe This figure shows that star formation started quickly and has been tapering off ever since.

12. Observable Universe

13. Fate of the Universe Models Models 1. Closed Universe – the universe will eventually slow down and collapse again. 1. Closed Universe – the universe will eventually slow down and collapse again. 2. Open Universe – the universe will keep expanding forever 2. Open Universe – the universe will keep expanding forever

14. Fate of the Universe Scientists believe some kind of dark energy is causing the universe to accelerate outward. Scientists believe some kind of dark energy is causing the universe to accelerate outward. This suggests the universe will continue to expand forever. This suggests the universe will continue to expand forever. Current evidence suggest we live in an open universe. Current evidence suggest we live in an open universe.

15. http://hubblesite.org/hubble_discoveries/dark_energy/

16. Summary of Key Ideas

17. The Big Bang Astronomers believe that the universe began as an exceedingly dense cosmic singularity that expanded explosively in an event called the Big Bang. The Hubble law describes the ongoing expansion of the universe and the rate at which superclusters of galaxies move apart. Astronomers believe that the universe began as an exceedingly dense cosmic singularity that expanded explosively in an event called the Big Bang. The Hubble law describes the ongoing expansion of the universe and the rate at which superclusters of galaxies move apart. The observable universe extends about 13.7 billion light- years in every direction from Earth to what is called the cosmic light horizon. We cannot see any objects that may exist beyond the cosmic light horizon because light from these objects has not had enough time to reach us. The observable universe extends about 13.7 billion light- years in every direction from Earth to what is called the cosmic light horizon. We cannot see any objects that may exist beyond the cosmic light horizon because light from these objects has not had enough time to reach us.

18. The Big Bang According to the theory of inflation, early in its existence, the universe expanded super rapidly for a short period, spreading matter that was originally near our location throughout a volume of the universe so large that we cannot yet observe much of it. The observable universe today is thus a growing volume of space containing matter and radiation that was in close contact with our matter and radiation during the first instant after the Big Bang. This explains the isotropic and homogeneous appearance of the universe. According to the theory of inflation, early in its existence, the universe expanded super rapidly for a short period, spreading matter that was originally near our location throughout a volume of the universe so large that we cannot yet observe much of it. The observable universe today is thus a growing volume of space containing matter and radiation that was in close contact with our matter and radiation during the first instant after the Big Bang. This explains the isotropic and homogeneous appearance of the universe.

19. A Brief History of Spacetime, Matter, Energy, and Everything Four basic forces—gravity, electromagnetism, the strong nuclear force, and the weak nuclear force— explain the interactions observed in the universe. Four basic forces—gravity, electromagnetism, the strong nuclear force, and the weak nuclear force— explain the interactions observed in the universe. According to current theory, all four forces were identical just after the Big Bang. At the end of the Planck time (about 10 -43 s after the Big Bang), gravity became a separate force. A short time later, the strong nuclear force became a distinct force. A final separation created the electromagnetic force and the weak nuclear force. According to current theory, all four forces were identical just after the Big Bang. At the end of the Planck time (about 10 -43 s after the Big Bang), gravity became a separate force. A short time later, the strong nuclear force became a distinct force. A final separation created the electromagnetic force and the weak nuclear force. Before the Planck time, the universe was so dense that known laws of physics do not describe the behavior of spacetime, matter, and energy. Before the Planck time, the universe was so dense that known laws of physics do not describe the behavior of spacetime, matter, and energy.

20. A Brief History of Spacetime, Matter, Energy, and Everything In its first 30,000 years, the universe was radiation dominated, during which time photons prevented matter from forming clumps. Then it was matter-dominated, during which time superclusters and smaller clumps of matter formed. Today it is dark-energy-dominated. Dark energy of some sort supplies a repulsive gravitational force that causes superclusters to accelerate away from each other. In its first 30,000 years, the universe was radiation dominated, during which time photons prevented matter from forming clumps. Then it was matter-dominated, during which time superclusters and smaller clumps of matter formed. Today it is dark-energy-dominated. Dark energy of some sort supplies a repulsive gravitational force that causes superclusters to accelerate away from each other. Astronomers think that during the first 379,000 years of the universe, matter and energy formed an opaque plasma, called the primordial fireball. Cosmic microwave background radiation is the greatly redshifted remnant of the universe as it existed about 379,000 years after the Big Bang. Astronomers think that during the first 379,000 years of the universe, matter and energy formed an opaque plasma, called the primordial fireball. Cosmic microwave background radiation is the greatly redshifted remnant of the universe as it existed about 379,000 years after the Big Bang.

21. A Brief History of Spacetime, Matter, Energy, and Everything By 379,000 years after the Big Bang, spacetime expansion caused the temperature of the universe to fall below 3000 K, enabling protons and electrons to combine to form hydrogen atoms. This event is called the era of recombination. The universe became transparent during the era of recombination, meaning that the microwave background radiation contains the oldest photons in the universe. By 379,000 years after the Big Bang, spacetime expansion caused the temperature of the universe to fall below 3000 K, enabling protons and electrons to combine to form hydrogen atoms. This event is called the era of recombination. The universe became transparent during the era of recombination, meaning that the microwave background radiation contains the oldest photons in the universe.

22. A Brief History of Spacetime, Matter, Energy, and Everything Clusters of galaxies and individual galaxies formed from pieces of enormous hydrogen and helium clouds, each of which became a separate supercluster of galaxies. Clusters of galaxies and individual galaxies formed from pieces of enormous hydrogen and helium clouds, each of which became a separate supercluster of galaxies. All of the superclusters and some of the clusters of galaxies within each supercluster are moving away from one another. All of the superclusters and some of the clusters of galaxies within each supercluster are moving away from one another. During the matter-dominated era, structure formed in the universe. As the universe goes farther into the dark energy-dominated era, the large-scale structure of superclusters of galaxies will fade away. During the matter-dominated era, structure formed in the universe. As the universe goes farther into the dark energy-dominated era, the large-scale structure of superclusters of galaxies will fade away.

23. The Fate of the Universe The average density of matter and dark energy in the universe determines the curvature of space and the ultimate fate of the universe. The average density of matter and dark energy in the universe determines the curvature of space and the ultimate fate of the universe. Observations show that the universe is flat and that the cosmic microwave background is almost perfectly isotropic, resulting from a brief period of very rapid expansion (the inflationary epoch) in the very early universe. Observations show that the universe is flat and that the cosmic microwave background is almost perfectly isotropic, resulting from a brief period of very rapid expansion (the inflationary epoch) in the very early universe. The universe is accelerating outward and it will expand forever. The universe is accelerating outward and it will expand forever.