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Cosmology IV: The Early Universe Lecture 30 Announcement Prelim #3 on Wednesday, Nov. 14 In class: 11:15am - 12:05pm (Uris Auditorium) Will emphasize lectures 22-31 (Galactic Center to Habitability of Worlds) Closed notes and closed book Lec 30: The Early Universe 2 Lecture Topics Problems with the Big Bang The Early Universe Theory of everything Inflation Pair-production Nucleosynthesis Pillars of the Big Bang The Multiverse The Anthropic Principle What grade does Cosmology get? Lec 30: The Early Universe 3 Problems with Big Bang The Big Bang described thus far is very successful in may aspects. However, there are two major problems that need to be addressed The Horizon problem Why is the CMB so uniform? The Flatness problem Why are we so close to Wk = 0 (a flat universe)? Lec 30: The Early Universe 4 What is a Horizon? Our horizon (in a Cosmological sense) is the maximum distance we can see out to in the Universe. More generally, for any point in the Universe, the horizon is the maximum distance from which light could have reached that point, within the age of the Universe. Nothing outside your horizon can have any effect on you, because it has never been in causal contact. Lec 30: The Early Universe 5 The Horizon Problem Looking at one part of the sky and looking in the opposite direction radio telescopes see the same CMB temperature to 1 part in 100,000 Suppose the Universe is 14 billion years old, then the two directions are separated by 28 billion lightyears 28 billion lightyears Lec 30: The Early Universe Earth 6 The Horizon Problem Looking at one part of the sky and looking in the opposite direction radio telescopes see the same CMB temperature to 1 part in 100,000 Suppose the Universe is 14 billion years old, then the two directions are separated by 28 billion lightyears Thus they should not be “causally connected” That is, they don’t know about each other The two regions should not have the same temperature In the past the situation is even worse. 100,000 years after the Big Bang the separation would be 10 million lightyears Lec 30: The Early Universe 7 The Flatness problem Measurements of the curvature of the Universe indicate it is almost exactly flat. However, both the average density and critical density change with time. In the past, right after the BIG BANG if the average density was slightly larger or smaller we would have a very obviously closed or open Universe. At the beginning of the Big Bang the density would have to be very close to the critical value (1 part in 1060!). Lec 30: The Early Universe 8 Epochs of the Universe From the Big Bang until now, the universe can be viewed as proceeding through different “epochs” (time periods). Distinguishing characteristics of epochs Each succeeding epoch is cooler and less dense. Different “forces” and/or “particles” may dominate! Lec 30: The Early Universe 9 Present 1015 102 105 107 10-5 1012 10-15 1017 10-25 1022 10-35 1027 Epochs GUT Planck 1032 T (K) t (sec) 10-45 GUT = E-M, Weak, & Strong forces unified All four forces unified (Quantum Gravity) 1010 1 10-10 10-30 10-50 10-30 10-10 1 1010 Radius (cm) Lec 30: The Early Universe 11 Theory of Everything Unite gravity with the other fundamental forces. Merging of gravity with quantum mechanics and other forces. We don’t have a theory yet but the most promising ones involves “string theory” and “higher dimensions” String Theory suggests there are 11 dimensions (10 spatial + 1 time). Lec 30: The Early Universe 12 Present 1015 102 105 107 10-5 1012 10-15 1017 10-25 1022 Epochs “Heavy particles in equilibrium with the radiation field (Pair Production) Hadron t (sec) 10-45 1027 Inflation GUT GUT = E-M, Weak, & Strong forces unified Planck 1032 T (K) 10-35 All four forces unified (Quantum Gravity) 1010 1 10-10 10-30 10-50 10-30 10-10 1 1010 Radius (cm) Lec 30: The Early Universe 13 Inflation (Part I) At 10-35 sec after the Big Bang the Universe cooled to 1027 K! This caused a “phase transition” Like ice changing into water The strong force split from the other forces releasing tremendous amounts of energy The Universe expanded by a factor of 1050 in 10-33 sec! Lec 30: The Early Universe 14 Inflation (Part II) This rapid expansion phase is called inflation. Universe causally connected before inflation CMB will be the same in all directions afterward Solves Horizon Problem! Universe becomes flat Because of stretching of space Space will now be flat due to inflation Solves Flatness Problem! Lec 30: The Early Universe 15 Present 1015 102 105 107 10-5 1012 10-15 1017 Epochs Lepton 10-25 Electron, muons, etc. in equilibrium (Pair Production for low mass particles) “Heavy particles in equilibrium with the radiation field (Pair Production) 1022 Hadron t (sec) 10-45 1027 Inflation GUT GUT = E-M, Weak, & Strong forces unified Planck 1032 T (K) 10-35 All four forces unified (Quantum Gravity) 1010 1 10-10 10-30 10-50 10-30 10-10 1 1010 Radius (cm) Lec 30: The Early Universe 16 What is Anti-Matter? A particle and its anti-particle have the same mass but opposite charge. Many antiparticles can be created in laboratories. Positrons (anti-electrons) are used routinely in medicine to imagine internal organs using Positron Emission Tomography (PET). Lec 30: The Early Universe 17 Pair Production Particle-antiparticle annihilation occurs when matter and anti-matter destroy each other in a burst of g-rays. The reverse is called pair production: 2 g particle + anti-particle Pair production happens spontaneously, and depends upon the temperature. Higher T more energetic photons more massive particles produced Lec 30: The Early Universe 18 Pair production (cont’d) In the early universe temperatures were high enough for pair production to take place. There was a “sea” of photons, particles and anti-particles. The “threshold” temperatures are: Temperature Particles Pairs T ~ 1013 K proton, anti-proton T ~ 6109 K electron, positron T < 109 K no pair production Lec 30: The Early Universe 19 Pair Production (cont’d) Above these threshold temperatures, particles and anti-particles will exist in equilibrium (as many created as destroyed). As the universe expands and the “plasma” cools, we expect particles and anti-particles to annihilate one another leaving just photons. This didn’t happen! We are here. This is because there are asymmetries between matter and anti-matter. Still not fully understood Lec 30: The Early Universe 20 Present 1015 102 105 107 10-5 1012 10-15 1017 Epochs Formation of light elements Nuclear Lepton 10-25 Electron, muons, etc. in equilibrium (Pair Production for low mass particles) “Heavy particles in equilibrium with the radiation field (Pair Production) 1022 Hadron t (sec) 10-45 1027 Inflation GUT GUT = E-M, Weak, & Strong forces unified Planck 1032 T (K) 10-35 All four forces unified (Quantum Gravity) 1010 1 10-10 10-30 10-50 10-30 10-10 1 1010 Radius (cm) Lec 30: The Early Universe 21 Fraction of total mass in the universe Big Bang Nucleosynthesis Predictions 10-1 4He Observations 10-5 3He 7Li 10-9 Deuterium Expected from CMB 10-12 10-32 10-31 10-30 10-29 10-28 Present density of baryons (g/cm3) Lec 30: The Early Universe 22 Present Dark Energy Dominated Stellar Epochs Galactic First Galaxies 1015 102 Matter Dominated 105 107 Atomic Atoms form, matter photon decoupling Nuclear Formation of light elements Lepton 10-5 1012 10-15 1017 10-35 t (sec) 10-45 1022 1027 Inflation “Heavy particles in equilibrium with the radiation field (Pair Production) Hadron GUT GUT = E-M, Weak, & Strong forces unified Planck 1032 T (K) 10-25 Radiation Dominated Electron, muons, etc. in equilibrium (Pair Production for low mass particles) All four forces unified (Quantum Gravity) 1010 1 10-10 10-30 10-50 10-30 10-10 1 1010 Radius (cm) Lec 30: The Early Universe 23 In-Class Question What were two problems with the Big Bang theory? a) Horizon and Bigness b) Flatness and Expansion c) Expansion and Bigness d) Horizon and Flatness e) There were no problems Lec 30: The Early Universe 25 In-Class Question What were two problems with the Big Bang theory? a) Horizon and Bigness b) Flatness and Expansion Sky is more uniform than it should be (not c) Expansion and Bigness causally connected) d) Horizon and Flatness We are very near a e) There were no problems flat universe (W ~ 1) What is the answer to these problems? a) Cosmic string theory b) Inflation c) Accelerating Universe d) All of the above e) None of the above Lec 30: The Early Universe 26 In-Class Question What were two problems with the Big Bang theory? a) Horizon and Bigness b) Flatness and Expansion Sky is more uniform than it should be (not c) Expansion and Bigness causally connected) d) Horizon and Flatness We are very near a e) There were no problems flat universe (W ~ 1) What is the answer to these problems? a) Cosmic string theory Expansion of space due to “phase transition” in b) Inflation the early universe. c) Accelerating Universe d) All of the above e) None of the above Lec 30: The Early Universe 27 Pillars of the Big Bang Hubble Expansion Universe expanding in all directions (necessary but not sufficient) Cosmic Background Radiation probes T ~ 1 eV, t ~ 105 years Light Element Abundances probes T ~ 1 MeV, t ~ 10 mins Lec 30: The Early Universe 29 These two agree!!! But how did it all begin? Quantum gravity emergence: Universe derives from quantum fluctuations The seeds of galaxies cannot be infinitely close together Multiverse: Maybe we are one of many universes continuously being created As above or intersection of higher dimensional spaces Laws of physics may be different in each universe See Michal Turner article in Sep 2009 Scientific American The Multiverse Our observable Universe extends out to a distance of about 42 billion light-years. Our cosmic horizon, which represents how far light has been able to travel since the big bang (as well as how much the universe has expanded in size since then). Assuming that space does not just stop there and may well be infinitely big Cosmologists make educated guesses as to what the rest of it looks like. Us 42 billion light-years Observable Universe See Scientific American - Aug. 2011 article by George Ellis Level 1 Multiverse: Plausible: Our volume of space is a representative sample of the whole. Distant alien beings see different volumes‚ but all of these look basically alike but we can’t see each other. Level 2 Multiverse: Questionable Sufficiently far away, things look quite different from what we see. The laws of physics would differ from bubble to bubble, leading to an almost inconceivable variety of outcomes. The Anthropic Principle Philosophical position, rather than hard science. (Not universally agreed on.) Essential it states “we are here, so the Universe must have formed in such a way as to allow life”. Can have powerful reasoning implications. Lec 30: The Early Universe 34 The Anthropic Principle If any of a number of fundamental constants were altered just slightly, the Universe wouldn’t be capable of sustaining life. It may seem that the Universe is very well suited to us, but if it wasn’t then there wouldn’t be anyone around to ask the question, why is the Universe the way it is? Lec 30: The Early Universe 35 Theory Report Card From James Peebles (noted cosmologist), Sci. Am, Jan. 2001 Lec 30: The Early Universe 36