Chapter 26: The Early Universe

Homework

Reading Preparation
- Study Guide/Reading Notes
Key Formulae to Know
WebLecture
Study Activity
Chat Preparation Activities
Chapter Quiz
Lab Work

Reading Preparation

Reading: Astronomy, Chapter 26: The Early Universe

Study Guide

Section 1: The universe exhibits isotropy, uniform radiation from stars and cosmic background radiation in all directions. It could not have evolved to form galaxies if its average mass density been even slightly less than critical density, and it would have been so tightly packed with matter that it would have collapsed if its density had been even slightly greater than the critical density. Astronomers conclude that the actual density of the early universe was very close to critical density, and that a rapid inflation accounts for isotropic cosmic background radiation, while scattering from cold matter accounts for its polarization.
Section 2: The inflationary model is used to explain the origins of the four fundamental forces (gravity, electromagnetic force, the strong nuclear force, the weak nuclear force). The tandard model of elementary particles is used to explain all subatomic particles as combinations of quarks, leptons, bosons, and the Higgs particle. Each force is associated with a field-generating particle. Below energies of 100 GeV, particles behave differently, leading to symmetry "breaking" and different force responses. Physicists and astronomers have yet to succeed in explaining how all four forces could have combined as a single force, or the exact conditions under which they separated.
Section 3: The Heisenberg uncertainty principle describes our inability to determine position and momentum (or energy and time over which energy is measured) with perfect accuracy. Within the time limit, it is possible for particles and their antiparticles to spontaneously appear and annihilate one another. These virtual pairs cannot be observed, but while they exist, they create electrical fields which do affect stable particles. Scientists speculate that during the inflationary period, virtual pairs were separated so quickly that they could not annihilate one another, and continued to exist as real particles and antiparticles.
Section 4: Expansion made collisions less frequent, and the temperature of the universe fell to the point where quarks could stick together in stable protons and neutrons. While pair production and annihilation continued to the point that most matter and antimatter disappeard, the process was not symmetrical, and more matter than antimatter survived.
Section 5: Neutron decay released neutrinos, which became part of the background radiation. Neutron and proton collisions built deuterium nuclei, and subsequent collisions built helium nuclei.
Section 6: Because these processes were not entirely uniform, matter was distributed with density fluctuations that led to the formation of galaxies and stars through gravitational collapse. Concentrations of matter (where the density was greater than the surroundings) over a large enough volume would initiate collapse that would continue to draw matter in. These fluctuations had to exceed the Jeans length, or the distributions would even out without collapsing further. Where they were large enough, extremely large (and therefore shortlived) population III stars with no heavy elements would form. Explosions of these stars would not leave core material behind to form black holes or neutron stars. To account for all the matter indicated by gravitaitonal forces, we have to assume the existence of both hot dark matter (light particles traveling at high speeds) and cold dark matter (more massive particles traveling at slower speeds). Computer models using different energies and distributions of hot and cold dark matter have been studied to determine whether any produce the observed large-scale distribution of matter.
Section 7: One attempt to explain matter and energy distribution in the universe is string theory, which involves multiple dimensions (up to 11) manipulated to produce the unification of forces. The theory explains matter as folds in space, crumpled in some cases so tightly as to appear as particles and vibrating like strings on a guitar to produce different interactions, which we interpret as different particles.

Key Equations

Heisenberg Uncertainty Principle (energy)	$Δ E * Δ t = \frac{h}{2 π}$	ΔE: Uncertainty in Energy Δt: Uncertainty in time h: Planck's Constant
Heisenberg Uncertainty Principle (mass)	$Δ m * Δ t = \frac{h}{2 π c^{2}}$	Δm: Uncertainty in mass Δt: Uncertainty in time h: Planck's Constant c: speed of light
Particle decay	$\begin{array}{l} n \to p + e - + \overset{⇀}{ν} \\ p + e - \to n + ν \\ p + n \to {}^{2}H + γ \end{array}$	n: neutron p: proton e-: electron ν neutrino; ν: antineutrino
Jeans length for density fluctuation	$L_{J} = \sqrt{\frac{π kT}{mG ρ_{m}}}$	L_J: Jeans length (minimum) k: Boltzmann constant T: Temperature (K) m: mass of a single particle of gass G: Gravitational constant ρ_m: density of matter

Web Lecture

Read the following weblecture before chat: Origins of the Universe

Study Activity

View the Smithsonian Illustris Project movie (this is an mp4 file that has to download to play). It begins at about 0.4 billion years after the Bang, when matter has taken atomic form, and follows the development of concentrations of matter as they form galaxies and collide. How is matter structured?

View the Sloan Digital Sky Survey Flight through the Universe, which uses plotted locations for about 400 000 galaxies.

View the Large Scale Simulation which used computer simulations of matter organization, then compared the results to actual galaxy distributions.

UNL Tools Exercises

ClassAction: Cosmology
- Under Outlines, Check out the Fate of the Universe, Hubble's Law, Dark Matter and Dark Energy.

Chapter Quiz

Required: Complete the Mastery exercise with a passing score of 85% or better.
Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!

Lab Work

Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.

Lab instructions: Curvature of Space

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Astronomy

Chapter 26 Homework