1. Universe Tenth Edition Chapter 26 Exploring the Early Universe Roger Freedman Robert Geller William Kaufmann III

3. 26-1 How the very young universe expanded enormously in a brief instant of time 26-2 How the fundamental forces of nature and the properties of empty space changed during the first second after the Big Bang 26-3 How the physics of subatomic particles affected the evolution of the early universe 26-4 As the early universe expanded and cooled, most of the matter and antimatter annihilated each other 26-5 Which chemical elements in today ’ s universe are remnants of the primordial fireball 26-6 How the first stars and galaxies formed in the early universe 26-7 What steps scientists are taking in the quest toward an all encompassing “ theory of everything ” By reading this chapter, you will learn

4. The Isotropy Problem

5. The Observable Universe With and Without Inflation

7. Inflation Solves the Flatness Problem

9. Polarized Light

10. Polarization of the Cosmic Microwave Background

11. The Four Forces and the Standard Model

19. Forces Due to Particle Exchange

20. Spontaneous Symmetry Breaking of Water

21. The CERN Particle Collider

23. Discovery of the Higgs Particle

24. Unification of the Four Forces

26. Inflation: Transitioning from the False Vacuum to the True Vacuum

28. Virtual Pairs

30. Pair Production and Annihilation

31. Inflation: From Virtual to Real Particles

33. Nucleosynthesis In the Early Universe

34. The Growth of Density Fluctuations

38. A Globular Cluster

39. A Timeline of Light in the Universe

40. A Cold Dark Matter Simulation with Dark Energy

41. “Bottom Up” Galaxy Formation: Simulation

42. “Bottom Up” Galaxy Formation: Observation

47. A Galaxy Under Construction

48. Using Simulations to Constrain the Matter Density of the Universe

50. The History of the Universe

54. Hidden Dimensions of Space

56. Key Ideas Cosmic Inflation: A brief period of rapid expansion, called inflation, is thought to have occurred immediately after the Big Bang. During a tiny fraction of a second, the universe expanded to a size many times larger than it would have reached through its normal expansion rate. Inflation explains why the universe is nearly flat and the 2.725-K microwave background is almost perfectly isotropic.

57. Key Ideas The Four Forces and Their Unification: Four basic forces— gravity, electromagnetism, the strong force, and the weak force— explain all the interactions observed in the universe. The Standard Model accurately describes all the known particles in nature and their observed interactions (except for gravity). The weak force and electromagnetic force became unified into a single force called the electroweak force at higher energies than those typically found in today’s universe. This unification has been observed in high-energy particle accelerators. Grand unified theories (GUTs) are attempts to explain three of the forces (strong force, weak force, and electromagnetic force) in terms of a single force. This has not been observed, and particle accelerators fall far short of having the energy to directly probe the high energy where this unification is predicted to occur.

58. Key Ideas A supergrand unified theory would explain all four forces (including gravity) at extremely high energies as a single force act- ing similarly on all the particles in nature. String theory attempts to make this unification, and it would describe the quantum nature of gravity. Supergrand unification is hypothesized to occur before the Planck time (t = 10 −43 seconds after the Big Bang). Spontaneous Symmetry Breaking: As the universe expands and cools, the unified forces break into separate forces. Starting around the Planck time, gravity became a distinct force through a sponta- neous symmetry breaking. During a second spontaneous symmetry breaking, the strong nuclear force became a distinct force. A final spontaneous symmetry breaking separated the electromagnetic force from the weak nuclear force; from that moment on, the uni- verse behaved as it does today.

59. Key Ideas Particles and Antiparticles: Heisenberg ’ s uncertainty principle states that the amount of uncertainty in the mass of a subatomic particle increases as it is observed for shorter and shorter time periods. Because of the uncertainty principle, particle-antiparticle pairs can spontaneously form and disappear within a fraction of a second. These pairs, whose presence can be detected only indirectly, are called virtual pairs. The collision of two high-energy photons can produced a real particle- antiparticle pair. In this process, called pair production, the photons disappear, and their energy is transformed into the masses of the particle-antiparticle pair. In the process of annihilation, a colliding particle-antiparticle pair disappears and two high-energy photons appear.

60. Key Ideas The Origin of Matter: Just after the inflationary epoch, the universe was filled with particles and antiparticles formed from numerous high-energy photons. The particles also annihilated to produce a state of thermal equilibrium between the particles and the photons. As the universe expanded, its temperature decreased. When the temperature fell below the threshold temperature required to produce each kind of particle, annihilation of that kind of particle began to dominate over production. Matter is much more prevalent than antimatter in the present day universe, because particles and antiparticles were not created or maintained in exactly equal numbers. What caused this initial asymmetry is not known.

61. Key Ideas Nucleosynthesis: Helium could not have been produced until the cosmological redshift eliminated most of the high-energy photons. These photons created a deuterium bottleneck by breaking down deuterons before they could combine further to form helium. Density Fluctuations and the Origin of Stars and Galaxies: The large-scale structure of the universe arose from primordial density fluctuations. The first stars were much more massive and luminous than stars in the present-day universe. The material that they ejected into space seeded the cosmos for all later generations of stars.

62. Key Ideas Galaxies are generally located on the surfaces of roughly spherical voids. Models based on dark energy and cold dark matter give good agreement with details of this large-scale structure. The Frontier of Knowledge: The search for a theory that unifies gravity with the other fundamental forces suggests that the universe actually has 11 dimensions (ten of space and one of time), seven of which are folded on themselves so that we cannot see them. The fundamental objects in our universe may be very small strings, rather than pointlike particles.