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The Big Bang Necessary? – Expansion of the Universe – Origin of CMBR • 400 photons/cc • Black body temperature profile – Helium content • Universal nucleosynthesis (like a star) Basics – Universe was hotter, denser in the past A few assumptions – Universe is a closed system • Physically • Heating/cooling – adiabatic – Treat like an adiabatic fluid (easy!) Energy of the Universe E=kT Second law of Thermodynamics DE=p DV Change in energy depends on change in volume Pressure defined p = 1/3 e e=energy density – all radiation early on Energy of light ef=hf So energy density = ef/volume hf hc e V V D E e DV eDV 1 / length So the energy of the Universe goes down as the size goes up Since E=kT, the temperature goes down as it expands Energy = all energy Photons, mass (via E=mc2), velocity, gravity, etc… Zero-th Step Time <0 Anything before the BB? How could we tell? Where could we look? Time=0 What’s it like? Don’t know… Gravity + QED = Quantum Gravity = ? Haven’t figured it out yet Time=10-43 sec Time=Planck time Based on quantum physics principles Temperature = 1032 K Density = 1093 gm/cc Scale = very small Interactions between energy/matter Quantum physics (QED), gravity – separate Can use them to describe characteristics of the Universe How? Some boring math… hG 43 10 s 5 2c h DE D t 2 h 2 mc Dt 2 h 5 mp 2 . 5 10 gm 2 2c t p tp l p ct p 1.7 1033 cm Planck lengths, time, masses… Okay what does that mean? Have to define some more stuff…. Compton time – time for a mass to violate conservation of energy law This activity is known as “quantum fluctuations” Formation of particles (matter/anti-matter) out of energy, quick destruction Happens over a quantum length (Compton length) h tc 2 2mc lc ctc Schwarzschild Radius – “size” of a black hole Schwarzschild Time – time for a photon to travel across a black hole This defines the realm of “gravity” 2Gm ls 2 c ls ts c 2 types of ways to describe the Universe – Planck length, time = QED – Compton length, time = QED – Schwarzschild length, time = gravity The way these are related defines who is in charge – gravity or QED Funny feature: a Planck mass into the formula for Compton, Schwarzschild lengths = Planck length Also, all times are equal. Meaning? Planck mass = black hole that exists for Planck time! If mass>Planck mass Enter the realm of gravity (relativity), QED not important If mass<Planck mass QED important, gravity loses. This time, this mass, this realm is when there are two separate forces – gravity, GUT GUT = grand unified theory (QED laws) So what is REALLY happening? Mini-black holes can come into/out of existence Gravity brings them into being Hawking radiation destroys them Particles (non-black holes) come into/out of existence (Compton stuff) Have energy, some particles, strange things going on – still not easy to define (or understand). Time=10-35 sec During GUT – quarks, leptons identical Now the GUT breaks down into Strong nuclear force (quarks force) Electoweak force (lepton/photon force) Breaks “symmetry” of the Universe “Freezing out” of forces – loss of freedom Release of energy (vacuum energy) Inflation starts Quarks form (along with anti-quarks) Time=10-32 sec End of Inflation After inflation, size of Universe increased by factor of 1050 Really? Expains uniformity of Universe Flatness of Universe Time=10-12 sec Another symmetry breaking Electroweak force breaks down into electromagnetic force weak nuclear force Leptons/anti-leptons form Universe full of energy (photons), quarks, leptons Time=10-10 sec Quarks win over anti-quarks Another symmetry breaking! Protons/neutrons can form Interactions between all sorts of things Not what happens today Neutrinos forced into interactions e p e n e p e n Time=10-5 sec End of neutrino interactions Universe too cool (10 billion K) Neutrinos still out there! Where are they? Time=1-3 Minutes Nucleosynthesis Universe Temperature = Stellar interior Protons, Neutrons combine to make – H2, H3 (Deuterium, Tritium) – He3, He4 – Li6, Li7, Be7 End composition: 75% p+ (H), 25% He4 (~0.01% - the rest) Gravity starts to become noticeable Time = 1 year Energy and Matter starting to diverge Cooling down at their own rates Energy (photons) – cooled by the expansion Matter – temperature determined by photons, fewer interactions Time=380,000 years Era of Decoupling Energy + Matter intertwined before now After this, they go their separate ways Energy of photons too low to interact effectively Universe becomes “transparent” to radiation Matter (gravity) controls Universe Time <1 billion years Galaxy Formation/Cluster formation? Proto-galaxy formation? Something is starting to happen…. This would be the epoch of the largest observable redshifts Might have missed a previous step (or two) Time = Now You’re looking at this. End of story (for now)