We don’t know, all previous history has been wiped out Assume radiation dominated era We have unified three of the forces: Strong, Electromagnetic, and Weak At about GeV, gravity becomes as strong as other forces: We need a quantum theory of gravity Weird stuff can start happening The “Planck Era” Some complicated possibilities: Entire universe might quantum tunnel from nothing Time might become meaningless Whole universe might be inflating, with only little pockets escaping to make universe What came before inflation?

History of the Universe Eventk B T or TTime Planck Era10 18 GeV s Inflation begins3  GeV s Inflation ends, baryons created, Grand Un.3  GeV s Supersymmetry Scale, Dark matter created500 GeV s Electroweak Scale50 GeV s Quark Confinement150 MeV1.4  s Neutrinos Decouple1 MeV0.4 s Neutron/Proton freezeout0.7 MeV1.5 s Electron/Positron Annihilation170 keV30 s Primordial Nucleosynthesis80 keV200 s Matter/Radiation Equality0.76 eV57 kyr Recombination0.26 eV380 kyr First structure formation30 K500 Myr Now2.725 K13.75 Gyr

Chaotic Inflation Universe may have began in inflationary era, everywhere Everything is expanding, very fast, everywhere A small pocket manages to escape and start forming a universe We’ll have to get slow roll, or something, to make it continue inflating enough This pocket grows to make observable universe Different bubbles will not collide – the universe is expanding too fast It is quite possible that there is more than one way to escape from inflation Different “universes” would have different fundamental constants

The String Landscape: Most popular theory combining gravity and quantum mechanics is string theory Many people (including me) criticize it since it has yet to produce a verifiable prediction String theory is incredibly complex No one understands it The potentials (like the graphs we have) are effectively infinite dimensional The number of minima – potential universes – is very, very large The “String Landscape” There may be many, many minima Many possible universes with apparently different laws of physics

What Remains to be Explained? Things we’ve resolved: Why the universe has the fraction of hydrogen/helium, etc. we see The nature of the cosmological background radiation How all the structure in the universe formed from initial perturbations Things we’ve got good guesses on: Where the dark matter came from Why  = 1 Why the universe is nearly uniform The likely causes of initial perturbations Why there’s more matter than anti-matter in the universe Things we don’t really know: Where the universe came from Why the vacuum energy density is so low Why the various particle physics parameters are what they are

The Smallness of the Vacuum Energy Density The vacuum energy density of the universe is just now becoming important Naïve calculation says it should be infinite Less naïve: It should be times bigger than it is What if it hadn’t been so small? If it had been 1000 times bigger, it would have dominated the universe at z = 14 Exponential growth begins at this time, all structure formation stops No globular clusters would have formed If it had been 100 times bigger, it would have dominated the universe at z = 6 No galaxies would have formed If it had been 2-3 orders of magnitude bigger, we wouldn’t be here No life would exist Other similar coincidences seem to favor the existence of life For example, resonance helps make carbon in stars

The Anthropic Principle On the boundaries of respectable science If string landscape is right (or similar ideas) there may be many “local minima” of whatever the potential is Many “bubble universes” might be formed with different physical constants, vacuum energy densities, etc. If there are enough of them, some will inevitably contain life that asks, “why is the universe the way it is?” The anthropic principle: Only universes where complex life is possible should be considered Smallness of vacuum energy density may be simply because we need it to exist Some other physical constants may similarly be inevitably “fine tuned” for life

The Final Exam Not yet written – but I’m working on it Makeup of exam – Current guess 300 points total (30% of your final total grade) 60 points: multiple choice 40 points new material 20 points old material 120 points: short essays 80 points new material 40 points old material 120 points: computation All new material

History – what should I know? Eventk B T or TTime Planck Era10 18 GeV s Inflation begins3  GeV s Inflation ends, baryons created, Grand Un.3  GeV s Supersymmetry Scale, Dark matter created500 GeV s Electroweak Scale50 GeV s Quark Confinement150 MeV1.4  s Neutrinos Decouple1 MeV0.4 s Neutron/Proton freezeout0.7 MeV1.5 s Electron/Positron Annihilation170 keV30 s Primordial Nucleosynthesis80 keV200 s Matter/Radiation Equality0.76 eV57 kyr Recombination0.26 eV380 kyr First structure formation30 K500 Myr Now2.725 K13.75 Gyr Events and Order Just Below 1 MeV Just Below 1 eV

Equations Dens.Curv.Name  < 1k = -1Open  = 1k = 0Flat  > 1k = +1Closed Crude approximation: Include when mc 2 < 3k B T Exclude when mc 2 > 3k B T Hubble’s Law: Expansion of everything: Scaling of density: Radiation: Friedmann Equation: Omega: Time-Temperature Relations Collision rate:

Some Other Things to Know Universe is always close to flat (  =1) When can you use the time formulas accurately? Actual age of universe is about 13.7 Gyr. Current temperature around 2.7 K Which elements created during nucleosynthesis? ( 1 H), 4 He, 2 H, 3 He, 6 Li, 7 Li 3 H and 7 Be created but decayed What problems does inflation seem to solve? Flatness, Horizon, Primordial fluctuations What is the relative size of each of the following components of the universe now? Ordinary matter, dark matter, dark energy, radiation Class Evaluations: Please Fill them Out Hand in to Volunteer Check off your name Never forget the wonder and majesty of the Universe!