The Cosmic Microwave Background and Quantum Physics Ruth Durrer Universit´ e de Gen` eve D´ epartment de Physique Th´ eorique et Center for Astroparticle Physics MITP Workshop Quantum Vacuum and Gravitation Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 1 / 26
Contenu Introduction 1 Fluctuations in the CMB 2 Why inflation 3 Evidence for Λ 4 Conclusions 5 Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 2 / 26
Introduction The cosmological initial fluctuations most probably stem from quantum fluctuations generated during inflation. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 3 / 26
Introduction The cosmological initial fluctuations most probably stem from quantum fluctuations generated during inflation. What are the strongest indications that this is so? Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 3 / 26
Introduction The cosmological initial fluctuations most probably stem from quantum fluctuations generated during inflation. What are the strongest indications that this is so? CMB parameter estimation favors a composition of the Universe with close to 70% quantum vacuum energy. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 3 / 26
Introduction The cosmological initial fluctuations most probably stem from quantum fluctuations generated during inflation. What are the strongest indications that this is so? CMB parameter estimation favors a composition of the Universe with close to 70% quantum vacuum energy. How sure are we? Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 3 / 26
Introduction Accidental discovery of the CMB by Arno Penzias and Robert Wilson 50 years ago (Nobel Prize 1978) Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 4 / 26
Introduction Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 5 / 26
Introduction Gamov has predicted the existence of the CMB already in 1948. Here with Alpher and Hermann. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 6 / 26
The cosmic microwave background (CMB) The Universe is expanding. In the past it was much denser and hotter. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 7 / 26
The cosmic microwave background (CMB) The Universe is expanding. In the past it was much denser and hotter. At T > 3000K hydrogen was ionised and the ’cosmic plasma’ of protons, electrons and photons was strongly coupled by Thomson scattering and in thermal equilibrium. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 7 / 26
The cosmic microwave background (CMB) The Universe is expanding. In the past it was much denser and hotter. At T > 3000K hydrogen was ionised and the ’cosmic plasma’ of protons, electrons and photons was strongly coupled by Thomson scattering and in thermal equilibrium. At T ≃ 3000K protons and electrons combined to neutral hydrogen. The photons became free and their distribution evolved simply by redshifting of the photon energies to a thermal distribution with T 0 = 2 . 7255 ± 0 . 0006K today. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 7 / 26
The cosmic microwave background (CMB) The Universe is expanding. In the past it was much denser and hotter. At T > 3000K hydrogen was ionised and the ’cosmic plasma’ of protons, electrons and photons was strongly coupled by Thomson scattering and in thermal equilibrium. At T ≃ 3000K protons and electrons combined to neutral hydrogen. The photons became free and their distribution evolved simply by redshifting of the photon energies to a thermal distribution with T 0 = 2 . 7255 ± 0 . 0006K today. This corresponds to about 400 photons per cm 3 with typical energy of E γ = kT 0 ≃ 2 . 3 × 10 − 4 eV ≃ 150GHz ( λ ≃ 0 . 2cm). This is the observed CMB. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 7 / 26
The cosmic microwave background (CMB) The Universe is expanding. In the past it was much denser and hotter. At T > 3000K hydrogen was ionised and the ’cosmic plasma’ of protons, electrons and photons was strongly coupled by Thomson scattering and in thermal equilibrium. At T ≃ 3000K protons and electrons combined to neutral hydrogen. The photons became free and their distribution evolved simply by redshifting of the photon energies to a thermal distribution with T 0 = 2 . 7255 ± 0 . 0006K today. This corresponds to about 400 photons per cm 3 with typical energy of E γ = kT 0 ≃ 2 . 3 × 10 − 4 eV ≃ 150GHz ( λ ≃ 0 . 2cm). This is the observed CMB. At T > 9300K ≃ 0 . 8eV the Universe was ’radiation dominated’, i.e. its energy density was dominated by the contribution from these photons (and 3 species of relativistic neutrinos which made up about 35%). Hence initial fluctuations in the energy density of the Universe should be imprinted as fluctuations in the CMB temperature. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 7 / 26
The frequency spectrum of the CMB Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 8 / 26
CMB fluctuations and structure formation We assume that structures in the Universe (galaxies, clusters, filaments and voids) formed by gravitational instability from small initial fluctuations. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 9 / 26
CMB fluctuations and structure formation We assume that structures in the Universe (galaxies, clusters, filaments and voids) formed by gravitational instability from small initial fluctuations. Due to the expansion of the Universe the fluctuations grow only very slowly and statistical initial fluctuations are far too small. Initial fluctuations of the order of 10 − 5 are needed. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 9 / 26
CMB fluctuations and structure formation We assume that structures in the Universe (galaxies, clusters, filaments and voids) formed by gravitational instability from small initial fluctuations. Due to the expansion of the Universe the fluctuations grow only very slowly and statistical initial fluctuations are far too small. Initial fluctuations of the order of 10 − 5 are needed. A inflationary phase can generate them. As we have seen in the previous talk, during inflation quantum fluctuations of the metric and of the scalar field are amplified by their coupling to the time dependent background metric. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 9 / 26
CMB fluctuations and structure formation We assume that structures in the Universe (galaxies, clusters, filaments and voids) formed by gravitational instability from small initial fluctuations. Due to the expansion of the Universe the fluctuations grow only very slowly and statistical initial fluctuations are far too small. Initial fluctuations of the order of 10 − 5 are needed. A inflationary phase can generate them. As we have seen in the previous talk, during inflation quantum fluctuations of the metric and of the scalar field are amplified by their coupling to the time dependent background metric. These fluctuations get ’squeezed’ and after inflation they become classical fluctuations of the energy density and of the metric. They are also present as coherent fluctuations in the CMB. Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 9 / 26
CMB fluctuations and structure formation We assume that structures in the Universe (galaxies, clusters, filaments and voids) formed by gravitational instability from small initial fluctuations. Due to the expansion of the Universe the fluctuations grow only very slowly and statistical initial fluctuations are far too small. Initial fluctuations of the order of 10 − 5 are needed. A inflationary phase can generate them. As we have seen in the previous talk, during inflation quantum fluctuations of the metric and of the scalar field are amplified by their coupling to the time dependent background metric. These fluctuations get ’squeezed’ and after inflation they become classical fluctuations of the energy density and of the metric. They are also present as coherent fluctuations in the CMB. Immediately after its discovery, astrophysicists began to search for fluctuations in the CMB. The found them in 1992 with the COBE satellite (Nobel Prize 2006). Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 9 / 26
Fluctuations in the CMB T 0 = 2 . 7255 K ∆ T ( n ) = � ℓ m a ℓ m Y ℓ m ( n ) C ℓ = �| a ℓ m | 2 � , D ℓ = ℓ ( ℓ + 1 ) C ℓ / ( 2 π ) 6000 5000 4000 [ µ K 2 ] 3000 D TT From the Planck Collaboration � 2000 Planck Results XIII (2015) 1000 arXiv:1502.01589 0 600 60 300 30 ∆ D TT � 0 0 -30 -300 -60 -600 2 10 30 500 1000 1500 2000 2500 � Ruth Durrer (Universit´ e de Gen` eve, DPT & CAP) CMB Mainz, June 2015 10 / 26
Recommend
More recommend
