DOCSLIB.ORG

Big Bang Cosmology and the Microwave Background

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Big Bang Cosmology and the Microwave Background Figure 1. The Thermal History of the Universe The figure (adapted courtesy of Mike Big Bang Cosmology Turner) shows important epochs in the history of the universe according to stan- dard Big Bang cosmology. It also shows and the Microwave the particles of matter and radiation con- stituting the universe during each epoch. The history is laid out on logarithmic Background scales to emphasize the early part. The scales are temperature, thermal energy kT, universal scale factor a(t) (note that a(t) 5 1/(z 1 1) where z is the redshift), Salman Habib and Raymond J. Laflamme density r(t), and time. Temperature, ther- mal energy, redshift, and energy density (or the equivalent mass density) all de- crease with time, whereas the scale of the universe a(t) ; R(t)/R(t0) increases. ig Bang cosmology implies a cer- (that is, massless particles). The The temperature plotted is the tempera- Btain predictable course for the ther- physics during this time is highly spec- ture of the radiation, which until recombi- mal history of the universe. Here we ulative. It is assumed that thermal en- nation is the temperature of the baryonic review that history, emphasizing the ergies were initially at the Planck scale matter (neutrons and protons) as well. two classic pieces of evidence that sup- (1028 eV), where the exotic and poorly The formulae relating these variables are port it: the relative abundances of the understood phenomenon of quantum shown beneath the figure. They follow light elements produced by primordial gravity could have played a crucial from conservation of energy and from the nucleosynthesis and the existence, spec- role. Many particle physicists and as- assumptions that matter and radiation trum, and fantastic isotropy of the cos- trophysicists believe that a bit later, as were initially in thermal equilibrium and mic microwave background. We will the temperature cooled to 1026 kelvins, that the universe has expanded adiabati- also discuss the modifications that there was a brief period of inflation. cally since the hot Big Bang. The rela- might be caused by the presence of During the inflationary phase, the size tionship between r(t) and a(t) changes cold dark matter. of the universe grew exponentially by a depending on whether the universe is ra- Figure 1 outlines the calendar of factor of at least 1028. Less speculative diation-dominated or matter-dominated, events, or major epochs, in the history. is the prediction that at a temperature that is, on whether most of the energy in It can be divided into two main periods: around 1012 kelvins, a quark-hadron the universe is in the form of radiation the radiation-dominated period, which transition occurred, when all the quarks (photons, neutrinos, and other particles lasted for approximately ten thousand and gluons combined to form protons moving at speeds near c) or most of the years (1011 seconds), and the matter- and neutrons. The particles of cold energy is in the form of matter. The tem- dominated period from ten thousand dark matter, if they exist, would also perature and scale-factor axes are lined years after the Big Bang to the present. have been created sometime after the up with respect to each other by the ob- During the first fraction of a second inflationary phase. servation that at present (t 5 t0) the tem- after the Big Bang, the constituents of perature of the cosmic background radia- the universe undoubtedly included the The radiation-dominated era. tion is approximately 3 kelvins and that 22 particles of the standard model of parti- From about 10 second to the present, by definition a(t0) ; 1. The time and den- cle physics: leptons, quarks, and the standard Big Bang cosmology presents sity axes are lined up with the size axis gauge bosons that mediate interactions an almost universally accepted picture, by using a specific value for the Hubble among them, all moving at velocities so which is borne out by the COBE data constant and the assumption that the di- close to the velocity of light that from and other recent observations. By that mensionless density parameter V is equal the point of view of thermodynamics, time the universe consisted of particles to 1. Then one can place any event on they behaved as particles of radiation that were stable (or long-lived com- all three axes if one knows its position on 82 Los Alamos Science Number 22 1994 Big Bang Cosmology and the Microwave Background chronfig.adb 7/26/94 Cold dark matter Recombination: Quark- Primordial begins to neutral atoms form; baryon nucleo- form microwave background Inflation transition synthesis structure decouples Radiation 25 20 15 10 5 temperature 10 10 10 10 10 1 (kelvins) 24 21 18 15 12 9 6 3 -3 10 eV 10 eV 10 eV 10 eV 10 eV 10 eV 10 eV 10 eV 1eV 10 eV Thermal energy Kinetic energy High-energy Nuclear binding Atomic binding of a sprinter cosmic rays energy energy Scale factor 10-25 10-20 10-15 10-10 10-5 1 a(t) 1065 1049 1033 1017 10 10-15 10-30 Density ρ(t) (g/cm3) Nuclear Water Air 1 atom/cm3 matter 1 103 106 109 Years 10-36 10-30 10-24 10-18 10-12 10-6 1 106 1012 1018 Seconds Galaxy forms NOW Solar system forms Constituents of the Universe Neutrino background νe νµ ντ νν Leptons ( e -)( µ -)( τ -) e ± 2 kelvins and quarks u c t + + 3 + 3 ++ 3 n, p H ,D , H , He H, D, He, ( d )( s )( h ) 4 ++ 7 ++ 4 7 Baryons He , Li + He, Li Gluons Gauge Light nuclei Neutral atoms bosons ± W , Z Photon-to-baryon ratio ~ 3 × 109 THE BIG BANG Microwave background Photons γ 3 kelvins Radiation-Dominated Matter-Dominated Era Era a(t ) ∝ t 1/2 a(t ) ∝ t 2/3 ρ(t ) ∝ (a(t ))-4 ∝ t -2 ρ(t ) ∝ (a(t ))-3 ∝ t -2 T ∝ (a(t ))-1 ∝ 1 + z T ∝ (a(t ))-1 ∝ 1 + z one axis (usually temperature, sometimes redshift). Note that the scale-factor axis does not show the expansion due to inflation. In the lower portion of the figure, the line for neutrinos (and antineutrinos) turns into a wiggly line to indicate that at that time the neu- trinos decoupled from matter and photons and subsequently expanded freely. The decoupling occurred when the universe became cool enough and dilute enough that neutrinos no longer interacted significantly with matter, at a temperature around 1010 kelvins. Similarly, at a temperature of about 3000 kelvins, the line for photons turns into a wiggly line to indicate their decoupling from mat- ter due to recombination, the combining of the electrons with the positively charged nuclei to form neutral atoms. The subsequent free expansion of photons produced the cosmic microwave background radiation now observed. Number 22 1994 Los Alamos Science 83 Big Bang Cosmology and the Microwave Background pared to the age of the universe then): proportionally, the radiation continued baryons that were neutrons, a fraction electrons, neutrinos, protons and neu- to have a black-body spectrum, or that decreased with time as neutrons trons, and photons, as well as the yet- Planck distribution, a fact that explains were converted to protons through the unidentified constituents of dark matter. why the black-body spectrum of the weak interactions. Calculations predict Unstable particles such as mu and tau cosmic background radiation is not a that the number of neutrons at the time leptons, mesons, and the gauge bosons surprise. However, the temperature of of primordial nucleosynthesis is approx- of the weak force had disappeared the radiation, which is proportional to imately 12 percent of the total number through decay to stable particles. Fig- the average energy per quantum or in- of baryons and that almost all those ure 1 outlines the changes through versely proportional to the average neutrons ended up in helium-4 nuclei, time of the constituents of matter. wavelength, decreased inversely with the most tightly bound of the light- At about t 5 1022 second, the uni- the scale factor, T ~ (a(t))21, or in pro- element nuclei. In other words, Big verse was a “primeval fireball” consist- portion to the redshift (T ~z). The en- Bang cosmology predicts that the cos- ing of baryonic matter and radiation in ergy density of the radiation therefore mic abundance by weight, or mass frac- thermal equilibrium (and perhaps dark decreased due to both the stretching of tion, of helium-4 nuclei relative to hy- matter). Moreover, most of the energy the wavelengths of the quanta and the drogen nuclei (protons) is about 24 was in the form of radiation. That fol- dilution of their number density; thus percent, in agreement with observation. 24 lows from simply extrapolating the pre- wrradiation decreased rapidly, as (a(t)) . The second determinant of relative sent density of matter and radiation Equation 3 in the caption of Figure 3 abundances produced by primordial nu- back through the presumed adiabatic in the main text is solved to relate the cleosynthesis is the ratio of the number expansion of the universe. The energy scale factor to time. In particular, when of photons to the number of baryons (or density therefore obeyed the formula radiation was the major contributor to equivalently the photon entropy per for black-body radiation, that is, for ra- the energy density, a(t) increased as baryon). That ratio does not change diation in thermal equilibrium with a t1/2, and so the temperature of the uni- with time and therefore, as we will see totally absorbing body.
Load more

Recommended publications
  • The Particle Zoo
    219 8 The Particle Zoo 8.1 Introduction Around 1960 the situation in particle physics was very confusing. Elementary particlesa such as the photon, electron, muon and neutrino were known, but in addition many more particles were being discovered and almost any experiment added more to the list. The main property that these new particles had in common was that they were strongly interacting, meaning that they would interact strongly with protons and neutrons. In this they were different from photons, electrons, muons and neutrinos. A muon may actually traverse a nucleus without disturbing it, and a neutrino, being electrically neutral, may go through huge amounts of matter without any interaction. In other words, in some vague way these new particles seemed to belong to the same group of by Dr. Horst Wahl on 08/28/12. For personal use only. particles as the proton and neutron. In those days proton and neutron were mysterious as well, they seemed to be complicated compound states. At some point a classification scheme for all these particles including proton and neutron was introduced, and once that was done the situation clarified considerably. In that Facts And Mysteries In Elementary Particle Physics Downloaded from www.worldscientific.com era theoretical particle physics was dominated by Gell-Mann, who contributed enormously to that process of systematization and clarification. The result of this massive amount of experimental and theoretical work was the introduction of quarks, and the understanding that all those ‘new’ particles as well as the proton aWe call a particle elementary if we do not know of a further substructure.
    [Show full text]
  • AST 541 Lecture Notes: Classical Cosmology Sep, 2018
    ClassicalCosmology | 1 AST 541 Lecture Notes: Classical Cosmology Sep, 2018 In the next two weeks, we will cover the basic classic cosmology. The material is covered in Longair Chap 5 - 8. We will start with discussions on the first basic assumptions of cosmology, that our universe obeys cosmological principles and is expanding. We will introduce the R-W metric, which describes how to measure distance in cosmology, and from there discuss the meaning of measurements in cosmology, such as redshift, size, distance, look-back time, etc. Then we will introduce the second basic assumption in cosmology, that the gravity in the universe is described by Einstein's GR. We will not discuss GR in any detail in this class. Instead, we will use a simple analogy to introduce the basic dynamical equation in cosmology, the Friedmann equations. We will look at the solutions of Friedmann equations, which will lead us to the definition of our basic cosmological parameters, the density parameters, Hubble constant, etc., and how are they related to each other. Finally, we will spend sometime discussing the measurements of these cosmological param- eters, how to arrive at our current so-called concordance cosmology, which is described as being geometrically flat, with low matter density and a dominant cosmological parameter term that gives the universe an acceleration in its expansion. These next few lectures are the foundations of our class. You might have learned some of it in your undergraduate astronomy class; now we are dealing with it in more detail and more rigorously. 1 Cosmological Principles The crucial principles guiding cosmology theory are homogeneity and expansion.
    [Show full text]
  • 1 Lecture 26
    PHYS 445 Lecture 26 - Black-body radiation I 26 - 1 Lecture 26 - Black-body radiation I What's Important: · number density · energy density Text: Reif In our previous discussion of photons, we established that the mean number of photons with energy i is 1 n = (26.1) i eß i - 1 Here, the questions that we want to address about photons are: · what is their number density · what is their energy density · what is their pressure? Number density n Eq. (26.1) is written in the language of discrete states. The first thing we need to do is replace the sum by an integral over photon momentum states: 3 S i ® ò d p Of course, it isn't quite this simple because the density-of-states issue that we introduced before: for every spin state there is one phase space state for every h 3, so the proper replacement more like 3 3 3 S i ® (1/h ) ò d p ò d r The units now work: the left hand side is a number, and so is the right hand side. But this expression ignores spin - it just deals with the states in phase space. For every photon momentum, there are two ways of arranging its polarization (i.e., the orientation of its electric or magnetic field vectors): where the photon momentum vector is perpendicular to the plane. Thus, we have 3 3 3 S i ® (2/h ) ò d p ò d r. (26.2) Assuming that our system is spatially uniform, the position integral can be replaced by the volume ò d 3r = V.
    [Show full text]
  • Theoretical and Experimental Aspects of the Higgs Mechanism in the Standard Model and Beyond Alessandra Edda Baas University of Massachusetts Amherst
    University of Massachusetts Amherst ScholarWorks@UMass Amherst Masters Theses 1911 - February 2014 2010 Theoretical and Experimental Aspects of the Higgs Mechanism in the Standard Model and Beyond Alessandra Edda Baas University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/theses Part of the Physics Commons Baas, Alessandra Edda, "Theoretical and Experimental Aspects of the Higgs Mechanism in the Standard Model and Beyond" (2010). Masters Theses 1911 - February 2014. 503. Retrieved from https://scholarworks.umass.edu/theses/503 This thesis is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Masters Theses 1911 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. THEORETICAL AND EXPERIMENTAL ASPECTS OF THE HIGGS MECHANISM IN THE STANDARD MODEL AND BEYOND A Thesis Presented by ALESSANDRA EDDA BAAS Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE September 2010 Department of Physics © Copyright by Alessandra Edda Baas 2010 All Rights Reserved THEORETICAL AND EXPERIMENTAL ASPECTS OF THE HIGGS MECHANISM IN THE STANDARD MODEL AND BEYOND A Thesis Presented by ALESSANDRA EDDA BAAS Approved as to style and content by: Eugene Golowich, Chair Benjamin Brau, Member Donald Candela, Department Chair Department of Physics To my loving parents. ACKNOWLEDGMENTS Writing a Thesis is never possible without the help of many people. The greatest gratitude goes to my supervisor, Prof. Eugene Golowich who gave my the opportunity of working with him this year.
    [Show full text]
  • Fine-Tuning, Complexity, and Life in the Multiverse*
    Fine-Tuning, Complexity, and Life in the Multiverse* Mario Livio Dept. of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154, USA E-mail: [email protected] and Martin J. Rees Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK E-mail: [email protected] Abstract The physical processes that determine the properties of our everyday world, and of the wider cosmos, are determined by some key numbers: the ‘constants’ of micro-physics and the parameters that describe the expanding universe in which we have emerged. We identify various steps in the emergence of stars, planets and life that are dependent on these fundamental numbers, and explore how these steps might have been changed — or completely prevented — if the numbers were different. We then outline some cosmological models where physical reality is vastly more extensive than the ‘universe’ that astronomers observe (perhaps even involving many ‘big bangs’) — which could perhaps encompass domains governed by different physics. Although the concept of a multiverse is still speculative, we argue that attempts to determine whether it exists constitute a genuinely scientific endeavor. If we indeed inhabit a multiverse, then we may have to accept that there can be no explanation other than anthropic reasoning for some features our world. _______________________ *Chapter for the book Consolidation of Fine Tuning 1 Introduction At their fundamental level, phenomena in our universe can be described by certain laws—the so-called “laws of nature” — and by the values of some three dozen parameters (e.g., [1]). Those parameters specify such physical quantities as the coupling constants of the weak and strong interactions in the Standard Model of particle physics, and the dark energy density, the baryon mass per photon, and the spatial curvature in cosmology.
    [Show full text]
  • Large Scale Structure Signals of Neutrino Decay
    Large Scale Structure Signals of Neutrino Decay Peizhi Du University of Maryland Phenomenology 2019 University of Pittsburgh based on the work with Zackaria Chacko, Abhish Dev, Vivian Poulin, Yuhsin Tsai (to appear) Motivation SM neutrinos: We have detected neutrinos 50 years ago Least known particles in the SM 1 Motivation SM neutrinos: We have detected neutrinos 50 years ago Least known particles in the SM What we don’t know: • Origin of mass • Majorana or Dirac • Mass ordering • Total mass 1 Motivation SM neutrinos: We have detected neutrinos 50 years ago Least known particles in the SM What we don’t know: • Origin of mass • Majorana or Dirac • Mass ordering D1 • Total mass ⌫ • Lifetime …… D2 1 Motivation SM neutrinos: We have detected neutrinos 50 years ago Least known particles in the SM What we don’t know: • Origin of mass • Majorana or Dirac probe them in cosmology • Mass ordering D1 • Total mass ⌫ • Lifetime …… D2 1 Why cosmology? Best constraints on (m⌫ , ⌧⌫ ) CMB LSS Planck SDSS Huge number of neutrinos Neutrinos are non-relativistic Cosmological time/length 2 Why cosmology? Best constraints on (m⌫ , ⌧⌫ ) Near future is exciting! CMB LSS CMB LSS Planck SDSS CMB-S4 Euclid Huge number of neutrinos Passing the threshold: Neutrinos are non-relativistic σ( m⌫ ) . 0.02 eV < 0.06 eV “Guaranteed”X evidence for ( m , ⌧ ) Cosmological time/length ⌫ ⌫ or new physics 2 Massive neutrinos in structure formation δ ⇢ /⇢ cdm ⌘ cdm cdm 1 ∆t H− ⇠ Dark matter/baryon 3 Massive neutrinos in structure formation δ ⇢ /⇢ cdm ⌘ cdm cdm 1 ∆t H− ⇠ Dark matter/baryon
    [Show full text]
  • Cosmology Slides
    Inhomogeneous cosmologies George Ellis, University of Cape Town 27th Texas Symposium on Relativistic Astrophyiscs Dallas, Texas Thursday 12th December 9h00-9h45 • The universe is inhomogeneous on all scales except the largest • This conclusion has often been resisted by theorists who have said it could not be so (e.g. walls and large scale motions) • Most of the universe is almost empty space, punctuated by very small very high density objects (e.g. solar system) • Very non-linear: / = 1030 in this room. Models in cosmology • Static: Einstein (1917), de Sitter (1917) • Spatially homogeneous and isotropic, evolving: - Friedmann (1922), Lemaitre (1927), Robertson-Walker, Tolman, Guth • Spatially homogeneous anisotropic (Bianchi/ Kantowski-Sachs) models: - Gödel, Schücking, Thorne, Misner, Collins and Hawking,Wainwright, … • Perturbed FLRW: Lifschitz, Hawking, Sachs and Wolfe, Peebles, Bardeen, Ellis and Bruni: structure formation (linear), CMB anisotropies, lensing Spherically symmetric inhomogeneous: • LTB: Lemaître, Tolman, Bondi, Silk, Krasinski, Celerier , Bolejko,…, • Szekeres (no symmetries): Sussman, Hellaby, Ishak, … • Swiss cheese: Einstein and Strauss, Schücking, Kantowski, Dyer,… • Lindquist and Wheeler: Perreira, Clifton, … • Black holes: Schwarzschild, Kerr The key observational point is that we can only observe on the past light cone (Hoyle, Schücking, Sachs) See the diagrams of our past light cone by Mark Whittle (Virginia) 5 Expand the spatial distances to see the causal structure: light cones at ±45o. Observable Geo Data Start of universe Particle Horizon (Rindler) Spacelike singularity (Penrose). 6 The cosmological principle The CP is the foundational assumption that the Universe obeys a cosmological law: It is necessarily spatially homogeneous and isotropic (Milne 1935, Bondi 1960) Thus a priori: geometry is Robertson-Walker Weaker form: the Copernican Principle: We do not live in a special place (Weinberg 1973).
    [Show full text]
  • A Study of John Leslie's Infinite Minds, a Philosophical Cosmology
    Document généré le 1 oct. 2021 09:18 Laval théologique et philosophique Infinite Minds, Determinism & Evil A Study of John Leslie’s Infinite Minds, A Philosophical Cosmology Leslie Armour La question de Dieu Volume 58, numéro 3, octobre 2002 URI : https://id.erudit.org/iderudit/000634ar DOI : https://doi.org/10.7202/000634ar Aller au sommaire du numéro Éditeur(s) Faculté de philosophie, Université Laval Faculté de théologie et de sciences religieuses, Université Laval ISSN 0023-9054 (imprimé) 1703-8804 (numérique) Découvrir la revue Citer cette note Armour, L. (2002). Infinite Minds, Determinism & Evil: A Study of John Leslie’s Infinite Minds, A Philosophical Cosmology. Laval théologique et philosophique, 58(3), 597–603. https://doi.org/10.7202/000634ar Tous droits réservés © Laval théologique et philosophique, Université Laval, Ce document est protégé par la loi sur le droit d’auteur. L’utilisation des 2002 services d’Érudit (y compris la reproduction) est assujettie à sa politique d’utilisation que vous pouvez consulter en ligne. https://apropos.erudit.org/fr/usagers/politique-dutilisation/ Cet article est diffusé et préservé par Érudit. Érudit est un consortium interuniversitaire sans but lucratif composé de l’Université de Montréal, l’Université Laval et l’Université du Québec à Montréal. Il a pour mission la promotion et la valorisation de la recherche. https://www.erudit.org/fr/ Laval théologique et philosophique, 58, 3 (octobre 2002) : 597-603 ◆ note critique INFINITE MINDS, DETERMINISM & EVIL A STUDY OF JOHN LESLIE’S INFINITE MINDS, A PHILOSOPHICAL COSMOLOGY * Leslie Armour The Dominican College of Philosophy and Theology Ottawa ohn Leslie’s Infinite Minds is a refreshingly daring book.
    [Show full text]
  • Science and Religion in the Face of the Environmental Crisis
    Roger S. Gottlieb, ed., The Oxford Handbook of Religion and Ecology. New York and Oxford: Oxford University Press, 2006. Pages 376-397. CHAPTER 17 .................................................................................................. SCIENCE AND RELIGION IN THE FACE OF THE ENVIRONMENTAL CRISIS ..................................................................................................... HOLMES ROLSTON III BOTH science and religion are challenged by the environmental crisis, both to reevaluate the natural world and to reevaluate their dialogue with each other. Both are thrown into researching fundamental theory and practice in the face of an upheaval unprecedented in human history, indeed in planetary history. Life on Earth is in jeopardy owing to the behavior of one species, the only species that is either scientific or religious, the only species claiming privilege as the "wise spe- cies," Homo sapiens. Nature and the human relation to nature must be evaluated within cultures, classically by their religions, currently also by the sciences so eminent in Western culture. Ample numbers of theologians and ethicists have become persuaded that religion needs to pay more attention to ecology, and many ecologists recognize religious dimensions to caring for nature and to addressing the ecological crisis. Somewhat ironically, just when humans, with their increasing industry and technology, seemed further and further from nature, having more knowledge about natural processes and more power to manage them, just when humans were more and more rebuilding their environments, thinking perhaps to escape nature, the natural world has emerged as a focus of concern. Nature remains the milieu of 376 SCIENCE AND RELIGION 377 culture—so both science and religion have discovered. In a currently popular vocabulary, humans need to get themselves "naturalized." Using another meta- phor, nature is the "womb" of culture, but a womb that humans never entirely leave.
    [Show full text]
  • Inflation Without Quantum Gravity
    Inflation without quantum gravity Tommi Markkanen, Syksy R¨as¨anen and Pyry Wahlman University of Helsinki, Department of Physics and Helsinki Institute of Physics P.O. Box 64, FIN-00014 University of Helsinki, Finland E-mail: tommi dot markkanen at helsinki dot fi, syksy dot rasanen at iki dot fi, pyry dot wahlman at helsinki dot fi Abstract. It is sometimes argued that observation of tensor modes from inflation would provide the first evidence for quantum gravity. However, in the usual inflationary formalism, also the scalar modes involve quantised metric perturbations. We consider the issue in a semiclassical setup in which only matter is quantised, and spacetime is classical. We assume that the state collapses on a spacelike hypersurface, and find that the spectrum of scalar perturbations depends on the hypersurface. For reasonable choices, we can recover the usual inflationary predictions for scalar perturbations in minimally coupled single-field models. In models where non-minimal coupling to gravity is important and the field value is sub-Planckian, we do not get a nearly scale-invariant spectrum of scalar perturbations. As gravitational waves are only produced at second order, the tensor-to-scalar ratio is negligible. We conclude that detection of inflationary gravitational waves would indeed be needed to have observational evidence of quantisation of gravity. arXiv:1407.4691v2 [astro-ph.CO] 4 May 2015 Contents 1 Introduction 1 2 Semiclassical inflation 3 2.1 Action and equations of motion 3 2.2 From homogeneity and isotropy to perturbations 6 3 Matching across the collapse 7 3.1 Hypersurface of collapse 7 3.2 Inflation models 10 4 Conclusions 13 1 Introduction Inflation and the quantisation of gravity.
    [Show full text]
  • String Theory and Pre-Big Bang Cosmology
    IL NUOVO CIMENTO 38 C (2015) 160 DOI 10.1393/ncc/i2015-15160-8 Colloquia: VILASIFEST String theory and pre-big bang cosmology M. Gasperini(1)andG. Veneziano(2) (1) Dipartimento di Fisica, Universit`a di Bari - Via G. Amendola 173, 70126 Bari, Italy and INFN, Sezione di Bari - Bari, Italy (2) CERN, Theory Unit, Physics Department - CH-1211 Geneva 23, Switzerland and Coll`ege de France - 11 Place M. Berthelot, 75005 Paris, France received 11 January 2016 Summary. — In string theory, the traditional picture of a Universe that emerges from the inflation of a very small and highly curved space-time patch is a possibility, not a necessity: quite different initial conditions are possible, and not necessarily unlikely. In particular, the duality symmetries of string theory suggest scenarios in which the Universe starts inflating from an initial state characterized by very small curvature and interactions. Such a state, being gravitationally unstable, will evolve towards higher curvature and coupling, until string-size effects and loop corrections make the Universe “bounce” into a standard, decreasing-curvature regime. In such a context, the hot big bang of conventional cosmology is replaced by a “hot big bounce” in which the bouncing and heating mechanisms originate from the quan- tum production of particles in the high-curvature, large-coupling pre-bounce phase. Here we briefly summarize the main features of this inflationary scenario, proposed a quarter century ago. In its simplest version (where it represents an alternative and not a complement to standard slow-roll inflation) it can produce a viable spectrum of density perturbations, together with a tensor component characterized by a “blue” spectral index with a peak in the GHz frequency range.
    [Show full text]
  • Big Bang Blunder Bursts the Multiverse Bubble
    WORLD VIEW A personal take on events IER P P. PA P. Big Bang blunder bursts the multiverse bubble Premature hype over gravitational waves highlights gaping holes in models for the origins and evolution of the Universe, argues Paul Steinhardt. hen a team of cosmologists announced at a press world will be paying close attention. This time, acceptance will require conference in March that they had detected gravitational measurements over a range of frequencies to discriminate from fore- waves generated in the first instants after the Big Bang, the ground effects, as well as tests to rule out other sources of confusion. And Worigins of the Universe were once again major news. The reported this time, the announcements should be made after submission to jour- discovery created a worldwide sensation in the scientific community, nals and vetting by expert referees. If there must be a press conference, the media and the public at large (see Nature 507, 281–283; 2014). hopefully the scientific community and the media will demand that it According to the team at the BICEP2 South Pole telescope, the is accompanied by a complete set of documents, including details of the detection is at the 5–7 sigma level, so there is less than one chance systematic analysis and sufficient data to enable objective verification. in two million of it being a random occurrence. The results were The BICEP2 incident has also revealed a truth about inflationary the- hailed as proof of the Big Bang inflationary theory and its progeny, ory. The common view is that it is a highly predictive theory.
    [Show full text]