INTRODUCTION  TO  COSMOLOGY

KNOWLEDGE  EXCHANGE  SEMINAR

Paola Andreani

15  May  2017

The  meaning  of  time

FROM  THESE LECTURES

• You won’t get:• a full picture of the so-called standard model of Cosmology• A course in Cosmology

• You will get:• An overview of the major problems in Observational Cosmology• A flavour of one of the major discussion in Physics about the meaning of time

• PART ONE: INTRODUCTION TO COSMOLOGY

PLANCK  IMAGE  OF  THE  SKY  

Planck  2013

The  CMB  dipole

the  barycentre  of  the  Solar  system  is  mo𝑣𝑖𝑛𝑔  𝑎𝑡  𝑎  𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦  𝑜𝑓  371  ±1 km/s  towards(l,b)  =  (264.14±0.15  ,  48.28±0.15)  

𝚤 = 1 ΔT  =  3.372  ±  0.014  mK

COBE  2001

THE  CMB AS  A  COSMOLOGICAL  PROBE

Planck  2013

Komatsu  2014

HOW  A  PERFECT  BBIS  CREATED?

Komatsu,  2014

recombination

decoupling

H  and  4He  are  formed  +  traces  of  D,  T,  3He,  6Li,  7Li,  7Be

HISTORY  OF  THE  UNIVERSE

𝜌M =   EF GHI(K)⁄IH

N

𝜌R =  EP GHI(K)⁄IH

Q

𝜌Λ (a)=  𝜌Λ  (𝑎0)

Rich,  2010

HISTORY  OF  THE  UNIVERSE

𝜌M =   EF GHI(K)⁄IH

N

𝜌R =  EP GHI(K)⁄IH

Q

𝜌Λ (a)=  𝜌Λ  (𝑎0)

Rich,  2010

THE  CMB AS  A  COSMOLOGICAL  PROBE

Planck  2013

Planck  2015

C(𝜃)=(1/4𝜋)  ∑ 2ℓ𝓁 + 1 𝐶ℓ𝓁𝑃ℓ𝓁(cos  θ)��

ℓ𝓁~180°/𝜃

r(t)  =  a(t)  x à kphysical (t)  =  kcomoving /  a(t)𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒  𝑓𝑙𝑢𝑐𝑡𝑢𝑎𝑡𝑖𝑜𝑛𝑠

Planck  2013

THE  FRIEDMANN’S EQUATIONSTime  evolution  of  the  scale  factor  a(t)  is  determined  by  2  coupled  equations  

Friedmann equation

where

equation  of  state(pressure  as  a  function  of  energy  density

where  :for  non-­‐relativistic  matter  𝑝~0Relativistic  p  rad =𝜌rad/3Dark  energy  w=  pde/  𝜌de

In  a  ΛCDM  universe  the  Friedmann equation  becomes

and  Ω𝑇 =  Ω𝑅 +  Ω𝑀 +  ΩΛ

THE  ‘STANDARD’  RULER:SOUND  HORIZON  AT  RECOMBINATION

Time  development  of  an  initial  adiabatic  over-­‐density  in  a  Universe  with  CDM,  𝜈, 𝛾,  b

all  components  together  

recombination

Baryon-­‐photon  plasma  propagates  at  the  speed  of  sound

CDM  and  baryons  attracted  into  the  potential  wellformed  by  the  CDM  at  the  origin

a0 xs =  (153.3   ± 2)Mpc

Rich,  2010

THE  HORIZON  PROBLEM

Casual  connection  amongregions  which  could  never  have  exchanged  a  signal,  How?

THE  FLATNESS  PROBLEM

ΩI =  Eq r stuN(v v⁄̇ )x

ΩI =  Eq rEy

I=T,R,M,Λ

THE  MONOPOLE  PROBLEM

Rajantie,  2016

The  monopole  flux  F  ≈  nv/(4π)n =  #  densityv =  velocity  ~  c  (for  Mmonopole ~  1011 GeV/c2)  accelerating  in  galactic  magnetic  fields

THE  MONOPOLE  PROBLEM

Rajantie,  2016

The  monopole  flux  F  ≈  nv/(4π)n =  #  densityv =  velocity  ~  c  (for  Mmonopole ~  1011 GeV/c2)  accelerating  in  galactic  magnetic  fields

• NO  evidence  for  Dirac  Monoples from  accelerator  searches,  etc• NO  evidence  for  Grand  Unified    Monopoles  at  level  of  Astrophysics    bounds  (~  10-­‐15  cm-­‐2sr-­‐1s-­‐

1)• The  resulting  extended  Parker  bound  is  so  stringent  that  it  excludes  all  monopoles  at  cosmic  

densities  predicted  by  traditional  Big  Bang  theory  • Since  2010  the  ATLAS  experiment  at  the  LHC  has  sought  magnetic  monopoles  in  the  debris  of  8  

TeV proton–proton  collisions  by  looking  for  highly  charged  particles  captured  in  an  electromagnetic  calorimeter• The  monopole  flux  F  ≈  nv/(4π)• where  v  is  the  typical  monopole  velocity  ~  the  speed  of  light  for  monopoles  of  mass  1011

GeV/c2  or    less  accelerating  in  galactic  magnetic  fields• n  is  the  number  density  of  monopoles  

QUANTUM  FLUCTUATIONS produced  before/during  inflation  responsible  for  the  density  fluctuationsseen  in  the  cmb

From  microscopic  to  macroscopic  scales:  become  observables

QUANTUM  FLUCTUATIONS produced  before/during  inflation  responsible  for  the  density  fluctuationsseen  in  the  cmbFrom  microscopic  to  macroscopic  scales:  become  observables

• Small  quantum  fluctuations  of  all  physical  fields  everywhere

• similar  to  waves  in  the  vacuum,  which  appear  and  then  rapidly  oscillate,  move  and  disappear.  

• Inflation  stretched  them,  together  with  stretching  the  universe.  

• When  the  wavelength  of  the  fluctuations  became  sufficiently  large,  they  stop  moving  and  oscillating,  and  do  not  disappear.  They  look  like  frozen  waves.

• When  expansion  of  the  universe  continues,  new  quantum  fluctuations  become  stretched,  stop  oscillation  and  freeze  on  top  of  the  previously  frozen  fluctuations.

• This  process  continues,  and  eventually  the  universe  becomes  populated  by  inhomogeneous  scalar  field.  Its  energy  takes  different  values  in  different  parts  of  the  universe.  These  inhomogeneities are  responsible  for  the  formation  of  galaxies.

• Fluctuations  may  be  scalar  (density)  and  tensor  (Quantum  fluctuations  also  generate  ripples  in  spacetime,  i.e.,  gravitational  waves,  by  the  same  mechanism.  Primordial  gravitational  waves  generate  temperature  anisotropy  in  CMB.

FROM  GWS  TO  CMB  ANISOTROPIES  

FROM  GWS  TO  CMB  ANISOTROPIES  

THE  CMB AS  A  COSMOLOGICAL  PROBE

• Cyclic  Universe:  not  only  BHs  but  the  entire  Universe  rebirth:  Cosmological  Constant  goes  to  0  and  then  strong  negative  causing  a  dramatic  collapse  followed  by  a  bounce  and  a  re-­‐expansion.  The  bounce  could  be  due  to  the  effects  of  quantum  gravity.

• Only  regions  highly  uniform   (without  GWs  and  BHs)  rebounce This  gives  a  strong  prediction  about  the  primordial  universe:  it  must  have  been  highly  homogenous  no  black  and  white  holes,  no  GWs.

• These  should  be  visible  in  the  CMB  spectrum:  non-­‐Gaussianity (fluctuations  not  random  but  correlated)  and  no  GWs  associated  with  the  CMB

• Penrose’s  scenario:  fossils  of  the  past  universe  in  remnants  of  the  Big  Bang.  After  an  infinite  amount  of  time  all  particles  decay,  only  photons  are  left.  The  late  universe  is  made  of  very  cold  photons  and  other  massless  particles  which  would  constitute  the  rebirth  of  a  new  universe.  

• The  only  information  left  (not  wiped  out  by  the  eternity  spent  in  thermal  equilibrium)  is  that  associated  to  the  GWs.  Collisions  between  BHs  produce  ripples  outward  making  great  circles  in  the  sky.  Shadows  of  events  in  the  former  universe

CYCLIC  UNIVERSE(-­‐S)  ?

Gurzadyan and  Penrose,  2010simply  an  outlier  with  lowerthan  average  variance

WHAT  IS  THE  DARK  MATTER?𝜒𝜒 → 𝑋𝑋

IS  IT  A  WIMP?

𝐶ℎ𝑒𝑚𝑖𝑐𝑎𝑙  𝑓𝑟𝑒𝑒𝑧𝑒 − 𝑜𝑢𝑡Γ  𝑖𝑛𝑒𝑙𝑎𝑠𝑡𝑖𝑐   =  𝑛𝜒 < 𝜎𝜐 > ∼ 𝐻

K𝑖𝑛𝑒𝑡𝑖𝑐  𝐷𝑒𝑐𝑜𝑢𝑝𝑙𝑖𝑛𝑔  Γ  𝑒𝑙𝑎𝑠𝑡𝑖𝑐   =  𝑛𝑋 < 𝜎𝜐 >

the  evolution  depends  on  how  the  annihilation  rate  compares  with  the  expansion  rate

CAN  IT  BE  IN  FORM  OF  NEUTRINOS  ?

Expansion  rate  

Annihilation  rate  

Thermal equilibriumT > Tf

Γ >  𝑎  ̇𝑎  

Freeze-outReactions frozen

T < Tf

Γ <    𝑎  ̇𝑎  

Cooley,  2014

WIMP  direct  searches

DARK  ENERGY  ASVACUUMFLUCTUATIONS

vacuum  energy  density  associated  with  the  Planck  scale

𝜖 =  E4m/16𝜋(ℏc)3  =  10  121 GeV

E��=  10  -­‐121

Dijkgraaf,  2014

COSMOLOGICAL  DILEMMA• Dark  matter  and  dark  energy?  

• Real  ?  Or  the  modern  ‘epicycles’?

Ptolemy’s  model  :    • mathematically  beautiful  

• successful  to  predict  and  explain  observations.

• How  could  it  be  wrong?  

The  modern  sea  monsters?

END OF PART ONE

• Literature• https://www.cosmos.esa.int/web/planck/publications#Planck2015  

• Rich  J.,  Fundamentals  of  Cosmology

• Naselsky,  Novikov,  Novikov,  The  physics  of  the  Cosmic  Microwave  Background

• Lisanti,  Lectures  on  dark  matter  physics,  arXiv:1603.03797v

• Komatsu,  Lectures

• Linde,  Lectures