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The Going Gets Weird. What came before inflation?. 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 10 18 GeV , gravity becomes as strong as other forces:

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slide1

The Going Gets Weird

What came before inflation?

  • 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 1018GeV, 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
slide2

History of the Universe

EventkBT or TTime

Planck Era 1018GeV 10-43 s

Inflation begins 31015GeV 10-38 s

Inflation ends, baryons created, Grand Un. 31015GeV 10-36 s

Supersymmetry Scale, Dark matter created 500 GeV 10-12 s

Electroweak Scale 50 GeV 10-10 s

Quark Confinement 150 MeV 1.410-5 s

Neutrinos Decouple 1 MeV 0.4 s

Neutron/Proton freezeout 0.7 MeV 1.5 s

Electron/Positron Annihilation 170 keV 30 s

Primordial Nucleosynthesis 80 keV 200 s

Matter/Radiation Equality 0.76 eV 57 kyr

Recombination 0.26 eV 380 kyr

First structure formation 30 K 500 Myr

Now 2.725 K 13.75 Gyr

slide3

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
slide4

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 apparentlydifferent laws of physics
slide5

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
slide6

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 10120 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
slide7

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 possibleshould be considered
  • Smallness of vacuum energy density may besimply because we need it to exist
  • Some other physical constants may similarly beinevitably “fine tuned” for life
slide8

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
slide9

History – what should I know?

EventkBT or TTime

Planck Era 1018GeV 10-43 s

Inflation begins 31015GeV 10-38 s

Inflation ends, baryons created, Grand Un. 31015GeV 10-36 s

Supersymmetry Scale, Dark matter created 500 GeV 10-12 s

Electroweak Scale 50 GeV 10-10 s

Quark Confinement 150 MeV 1.410-5 s

Neutrinos Decouple 1 MeV 0.4 s

Neutron/Proton freezeout 0.7 MeV 1.5 s

Electron/Positron Annihilation 170 keV 30 s

Primordial Nucleosynthesis 80 keV 200 s

Matter/Radiation Equality 0.76 eV 57 kyr

Recombination 0.26 eV 380 kyr

First structure formation 30 K 500 Myr

Now 2.725 K 13.75 Gyr

Events and Order

Just Below 1 MeV

Just Below 1 eV

slide10

Equations

  • Hubble’s Law:
  • Expansion of everything:
  • Scaling of density:
  • Radiation:
  • Friedmann Equation:
  • Omega:
  • Time-Temperature Relations

Crude approximation:

Include when mc2 < 3kBT

Exclude when mc2 > 3kBT

  • Dens.Curv.Name
  • < 1 k = -1 Open
  • = 1 k = 0 Flat
  • > 1 k = +1 Closed
  • Collision rate:
slide11

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?
    • (1H), 4He, 2H, 3He, 6Li, 7Li
    • 3H and 7Be 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!