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The Life of the Universe From Beginning to End • Early Universe is extremely hot and dense • All 4 forces were merged • As Universe cooled, forces became unique • Energy of photons high enough to create matter and vice versa • GUT – strong and electroweak forces united • SuSy – GUT and Gravity united The Big Bang Theory • The early Universe was exceedingly hot and dense • Big Bang theory explains how the early Universe cooled and evolved into the Universe we observe today • Relies on Theoretical and Observational data Planck Era • t < 10-43 s • T > 1032 K • Current physics is unable to understand times before the Planck era – Need to unite physics of large scales (general relativity) with physics of small scales (quantum mechanics) GUT Era • 10-43 s < t < 10-38 s • 1029 K < T < 1032 K • Supersymmetry force splits into GUT force and gravity Electroweak Era • 10-38 s < t < 10-10 s • 1015 K < T < 1029 K • GUT force splits into strong and electroweak forces – Huge release of energy Inflation • Inflation expands Universe at exponential rate Particle Era • 10-10 s < t < 10-3 s • 1012 K < T < 1015 K • Electroweak splits into weak force and electromagnetism – All four forces distinct • T too low for spontaneous conversion of photons to particles • Photons became quarks, which merge into protons and neutrons Era of Nucleosynthesis • 0.001 s < t < 5 min • 109 K < T < 1012 K • Fusion begins – T still so high that most He nuclei will break apart again • Expansion reduces density so fusion ceases despite T being so high • 75% H, 25% He, trace others Era of Nuclei • 5 min < t < 380,000 years • 3000 K < T < 109 K • Photons still hot enough to ionize, so electrons and nuclei stay separated • Photons cannot travel far because they are scattered by electrons Era of Atoms • 380,000 yrs < t < ~109 yrs • T < 3,000 K • T drops low enough for atoms to form • With electrons bound to nuclei, photons can travel long distances – Cosmic Microwave Background Era of Galaxies • t > 109 years • Universe filled with nearly homogeneous distribution of matter and dark matter after era of atoms • Slightly overdense regions collapse to form first stars and galaxies • Gravity dominates on large scales A Few Questions • Where did the large scale structure come from? • Why is the Universe so uniform? • Why is the density of the Universe so close to the critical density? Inflation • Separation of strong force from GUT force would release enormous amount of energy • Energy would cause the Universe to expand by factor of 1030 in 10-36 sec Inflation and Structure • Huge expansion would make tiny quantum fluctuations in density large ripples • A ripple the size of a nucleus would become the size of our solar system • Creates density enhancements that give rise to the structure we observe today Inflation and Uniformity • No reason why things so far away should be similar • Things close by should be • Inflation takes things that were very close together and spreads them out a lot – Universe was all close together, so everything was uniform, then inflation spread it out Inflation and Density • Density implies curvature of spacetime – Think general relativity – Critical density has flat geometry • If Universe started somewhat curved, inflation would make it seem much flatter Evidence for the Big Bang The Cosmic Microwave Background The CMB • Line – a theoretically calculated thermal radiation spectrum based on the Big Bang Theory • Dots – Observed data • They match! The Fate of the Universe Two Things to Consider • Expansion of the Universe • Gravity – makes things collapse • Critical density – the density required to balance gravitational attraction and expansion • Dark energy – a repulsive force opposite of gravity An Accelerating Universe • SN Ia data show that we most likely live in an accelerating universe • Acceleration is driven by some force that is not well-understood – Dark energy The Big Rip The End