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Announcements •The last Dark Sky Night is tonight. Set-up will start at 7:30pm. Cancellation notice, if needed, will be posted immediately after class. If it is cancelled we will try again Thursday night •Don’t forget about your project. Presentations will be Monday May 1 at 3:20pm. A written paper is also due at the same time. Exam 4 is after the presentations The Early Universe What was the universe like before the CBR? How about before nucleosynthesis? How far back can we go if we can’t see anything farther than this? Matter density decreases differently than energy density This term is due to the decrease in energy from the expansion of space Thus, there must have been a time when energy dominated over matter Solving the Friedmann equation for an energy dominated universe Energy decreases as 1/R4 so R(t1 ) E (t) E (t 1 ) R(t ) 4 But energy density is proportional to T4 so R(t1 ) T (t ) T (t1 ) R(t ) At the extremely high density of the early universe, the density term dominates the Friedmann equation 2 R 8 G kc 2 2 H 3 3 R R 2 Putting it all together gives a simple relationship between time and size R (t ) t During the energy dominated era, the universe expands as the square root of time So the farther back in time we go, the higher the density gets and the hotter it gets What was a universe dominated by energy like? Virtual particles of all types of elementary particles were popping in and out of existence everywhere If only particleantiparticle pairs are produced there would not be any matter in the universe There must have been particle production processes that did not conserve baryon number So to understand the early universe we must understand high-energy particle physics At the elementary particle level we talk about particle fields Some fields are easy to picture The photon is the exchange particle for the electromagnetic field One of the important things in particle physics is symmetry Spontaneous Symmetry Breaking is like a phase transition Before the Planck time (10-43 seconds) we know nothing ? Some theories say that space-time is so warped during this time that space and time can no longer be separated so that the very concept of “before this time” is meaningless During the Planck Epoch Quantum Gravity Rules Eventually gravity “freezes out” and we enter The Unified Epoch Only two fields govern everything: The Unified Field and gravity. We don’t understand what gravity is like at this time but we are starting to understand GUT’s. In the Unified Era there are only two forces Quantum Gravity Current theories are called looped quantum gravity GUT’s are Grand Unified Theories which unify the electromagnetic, weak and strong nuclear forces GUT’s deal with elementary particles The strong nuclear, electromagnetic and weak nuclear forces are united in a single Grand Unified Theory Baryogenesis occurs during the Unified Epoch More particles than antiparticles are created by symmetry breaking processes which are not well understood. We know they must have occurred, though, because our universe only contains matter and not much antimatter. Because of baryogenesis, protons must decay One mechanism is the proton decays into a positron (e+) and a pion (0) which quickly decays into a pair of gamma rays. Another is the creation of a mini charged black hole. The Unified Epoch is when Inflation occurred The universe expanded at tremendously superluminal speeds during Inflation 1m 1050 m 35 m 26 10 3 . 33 10 c s 35 37 10 s 10 s During Inflation, the temperature actually rose! After Inflation, the strong nuclear force “freezes out” and the universe enters the Quark Epoch The universe is now a quark-gluon plasma. The quarks were created in the Unified Era and move around almost unbound during the Quark Era