1	Chapter 17 The Beginning of Time Chapter Outline Running the Expansion Backward A Scientific History of the Universe Evidence for the Big Bang Inflation Did the Big Bang Really Happen?
2	Temperature of the Early Universe Expansion of spacetime initiated 12-16 billion years (4-5 x 10¹⁸ s) ago Cosmic microwave background radiation (CMBR) is a remnant from 400,000 years after initiation of expansion As spacetime expanded universe became less dense and the temperature declined steadily to the 3^o K observed today for the CMBR Knowing the history of the expansion within the 400,000 years of the initiation is important to understanding why the universe is the way it is
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4	Particle Creation and Annihilation Very early universe filled with high-energy photons (gamma-rays) Over time these high-energy photons are replaced with large numbers of low-energy photons Interaction of two gamma-ray photons possessing greater energy (E = mc²) than the masses of protons, neutrons, or electrons can create particle/antiparticle (or matter/antimatter) pairs Conversely, when matter/antimatter pairs interact they annihilate and create two gamma-ray photons Expansion separates created pairs so they do not annihilate each other
5	Planck Era (<10^-43 s) Quantum mechanics Has been a very successful theory for subatomic scale Is an incomplete theory in that it does not apply to large masses and large scales General relativity (gravity) Has been a very successful theory for large scale motion and structure of spacetime Is an incomplete theory in that it does not apply to subatomic scale phenomena Quantum gravity Would be applicable to times less than 10^-43 s when scale of the universe is subatomic scale No such theory exists today
6	GUT Era (10^-43-10^-38 s) Shortly after initiation of expansion of spacetime, a series of events should have taken place All four forces in nature - gravity, electromagnetic, and strong and weak nuclear forces – should have been unified into single force at time of Big Bang As temperature declined in very early universe, gravity separated first and then the strong force leaving the electroweak force Inflation – sudden dramatic expansion of space in 10^-36 s associated with separation of strong force
7	Why Does Any Matter Remain? Expansion of space stops pair production (photon energy declining) and pair annihilation continues increasing photons at expense of particles If equal amounts of matter and antimatter existed, there would be no matter But there is matter, so there must be an asymmetry in favor of matter over antimatter Neutrinos and antineutrinos could be produced because they have small masses Neutrinos/antineutrinos increased at expense of other particles producing co-existing “neutrino world”
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10	Cosmic Microwave Background Radiation 1965, Arno Penzias and Robert Wilson obtain first definitive evidence for cosmic microwave background radiation.
11	Transition to Era of Atoms
12	Helium Synthesis
13	Standard Big Bang Has Problems Flatness problem Observational tests suggest that universe astonishingly close to flat marginally-open Friedmann universe or the least probable one. Homogeneity problem CMBR coming from 15 x 10⁹ light years in one direction being incredibly like that coming from 15 billion light years in any other direction.
14	Inflationary Epoch 1981 1980s, Alan Guth proposed inflationary epoch could account for flatness and homogeneity problems. Epoch begins 10^-35 s and lasts 10^-24 s Extremely small portion of universe ballooned outward in all directions at speeds greater than speed of light Expands 10⁵⁰ times to become visible universe of today Inflated portion pushed other material far beyond its boundaries
15	Inflation – Stretching of Spacetime Ripples
16	Flatness Problem
17	How Does the Inflationary Epoch Help the Problems Homogeneity problem - because inflated portion so small, its properties such as temperature extremely homogeneous accounting for homogeneity of observable universe Flatness problem - because observable universe is tiny fraction of entire universe, it appears very flat
18	CMBR Temperature Variations
19	380,000 Year Old Universe
20	An Improved Look at 380,000 Year Old Universe (WMAP) H = present speed of universe’s expansion = 71 km/s/Mpc W_m = present density of matter (baryonic and dark) divided by value necessary to make universe flat = 0.27 W_L = present density of dark energy = 0.73 t₀ = 13.7 billion years t_dec = 379,000 years
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22	The Big Picture Predicting conditions in the early universe is straightforward; the real questions is how matter and energy behave under such extreme conditions. Our current understanding of physics allows us to reconstruct the conditions that prevailed in the universe all the way back to the first 10^-10 s. Our understanding is less certain back to 10^-38 s. Beyond 10^-43 s, we encounter the present limits of physical theory (quantum gravity). Although it may sound strange to talk about the universe during its first fraction of a second, our ideas about the Big Bang rest on a solid foundation of observational, experimental, and theoretical evidence. We cannot say with absolute certainty that the Big Bang really happened, but no other model ever proposed has so successfully explained how our universe came to be as it is.