Roger Freedman Robert Geller William Kaufmann III Universe Tenth Edition Chapter 26 Exploring the Early Universe By reading this chapter, you will learn 26 1 How the very young universe expanded enormously in a brief instant of time 26 2 How the fundamental forces of nature and the properties of empty space changed during the first second after the Big Bang 26 3 How the physics of subatomic particles affected the evolution of the early universe 26 4 As the early universe expanded and cooled, most of the matter and antimatter annihilated each other 26 5 Which chemical elements in today s universe are remnants of the primordial fireball (??? jh) 26 6 How the first stars and galaxies formed in the early universe 26 7 What steps scientists are taking in the quest toward an all encompassing theory of everything The First Three Minutes 1
Planck Epoch No Physics exists to describe the cosmos previous to this time: 10 43 seconds (unless M theory bears out) Impossibly high temperatures (10 32 K), inconceivably tiny universe (10 35 m) at the end of this brief epoch All four fundamental forces strong, weak, electromagnetic, and gravity were expressed as one. Unified by the high energy/temperature into a single force Particles, the Four Forces and the Standard Model 2
Forces Due to Particle Exchange Well, it s not momentum 3
The CERN Particle Collider 4
Discovery of the Higgs Particle Unification of the Four Forces Spontaneous Symmetry: High Energy State Rolls Downhill 5
String Theory A step towards a ToE or Supergrand Unified Theory Stems from the transition from continuum Physics to quantum Physics at the turn of the 20 th C Starting in the 80 s the notion arose that strings were a better model for the basic constituents of matter Feynman diagrams describing Standard Model interactions are too convoluted to incorporate these extra dimensions Branes are introduced to explain interactions, but they need more dimensions Dimensions 6
Other Dimensions Flatland, a Romance in Many Dimensions Edwin Abbott Abbott, 1885 A square and his wife in Flatland An introduction to greater dimensions M Theory String theory required 9+1 dimensions However, this produced 5 equally valid variations! Unacceptable! A lesser known theory, Supergravity, postulated 10+1 dimensions Merging the two ideas resolved the 5 variations However, the addition of the 11 th dimension caused the strings to weave into Membranes A theory of the trigger Multidimensional Universe or multiverse Gravity is the weakest force because it stretches between branes and is diluted Intersection of branes initiates a BB So time didn t have to begin with the BB 7
Lisa Randall Astrophysicist at Harvard Leading Brane proponent Warped Passages: Unraveling the Universe's Hidden Dimensions See also David Deutsch, Hugh Everett How the Universe Got Its Spots Jenna Levin and others propose a more topological description of cosmology than M Theory We are here 8
Inflationary Epoch As the name implies, a period of enormous expansion The Universe grew from 10 28 m to 10 16 m To put this in perspective, think of the size of a proton compared to a parsec! The Universe cooled, as any expanding system of particles would, then reheated shortly after inflation ended. The energy used to push the Universe outward was released as heat A Note About Inflation Proposed by Alan Guth of MIT in the early 1980s, Inflation does a good job of explaining the Universe as we see it today During this era the early Universe expanded faster than the speed of light Not a violation of SR since nothing is actually moving > c It solves the flatness problem, the horizon problem, and the monopole problem Flatness: why (total energy density of the universe) is so close to crit Horizon: why the CMB varies so little (isotropy) Monopoles: N or S magnetic pole w/o the other BICEP2 MAY have found Primordial B mode polarization CMB photons polarized by intense gravitational waves rapid inflation at 10 38 s, earlier than thought 9
Polarized Light Polarization of the Cosmic Microwave Background Where Inflation Comes From Current theory holds that a different value of the cosmological constant, inflation, was present during this epoch This formed an inflaton field, a type of scalar field You can think of a scalar field like gravity near the ground the higher you go the more potential for falling fast you have Invoking a scalar field is common in theoretical physics, and perfectly legal, but it doesn t make a theory true. For that, real evidence is required And from observation, the Universe is in a period of inflation now, with the current scalar field being dark energy (whatever that is) 10
The Observable Universe With and Without Inflation How Inflation Fixes Flatness The Flatness problem: the ratio of the current energy density ( ) of the Universe to the critical density is 1 Doesn t seem like much, but when you allow for expansion and run the clock backwards, the ratio differs from 1 (perfectly flat) by one part in 10 60! Inflation fixes this by essentially flattening all the bumps in the Universe, much like inflating a balloon smoothes out all the wrinkles is currently very close to zero; 0 means flat Inflation Solves the Flatness Problem 11
Horizons: The Isotropy Problem Think of a horizon as the furthest distance than can be seen for which there is time for light to travel If an event happens in one region that would affect another region, then there must be sufficient time for the effect to travel that distance Re: a light cone! Light Cones A way to plot space and time It tells you how much information you can have at a certain time, limited by the speed of light The x y plane represents space and the z axis represents time Now is 0, past is, future is + Not far in the past (white arrow) only nearby events can be known Events that happened long ago (gold arrow) can be known even if they were far away The Isotropy Problem 12
Run the clock backwards. It turns out that, given the short time scales involved, there was insufficient time for energy to travel from one region to another, a necessary condition for a near uniform temperature Planck But why was there variation? High temperatures imply uniformity Heisenberg s Uncertainty Principle prohibits absolute uniformity, because that means there d be no limit on detail in data Therefore, in a quanta sized early universe there must be Quantum Fluctuations Particle Epoch Quarks cool and form more massive particles Two up and one down = p + Two down and one up = N Interactions abound m N > m p so more p + than N Heavy decays to lighter 6p + for 1N Too hot for nuclei to form Universe has cooled to 10 9 K by end of era The Freeze Out ; baryons cease to perish in the high temperature As for electrons 13
Virtual Pairs: more Heisenberg Pair Production and Annihilation Inflation: From Virtual to Real Particles 14
Nucleosynthesis Era Universe cools to 3000K 1s < 3 min Atoms form (ionized): N half life ~ 15 minutes By 3 minutes, 14p for 2N Some neutrons had decayed into protons, so p + :N, 6:1 becomes 7:1 2p + + 2N = He So out of 16 nucleons, 1 He for 12 H Hydrogen, including deuterium (75% by mass) Helium (25% by mass) Lithium (10 9 < He) Nucleosynthesis In the Early Universe Atom Epoch 3 min < t < 380,000 years Universe cools enough for electrons to attach to atoms Down to 18 K by end of era Universe becomes transparent, photons free to travel The Last Scattering CMB starts now ½ of 1% of radio noise is CMB 15
The Growth of Density Fluctuations, the outgrowth of Quantum Fluctuations Dark Matter/Energy Horizons and Flatness are interrelated The geometry of the Universe is determined by the amount of dark energy Left: the scale of the CMB fluctuations in the WMAP picture indicate curvature Open if the fluctuations < 1 / o 2 Flat if ~1 o, closed if > 1 o Ultimately determines the fate of the Universe If the Universe is flat, the angle is 1 o If it is curved inward (closed) the angle is > 1 o If it is curved outward (open) the angle is < 1 o 16
These values (the ones I suggested last PPT you DON T memorize) can affect the accuracy of our lookback time calculations Using Simulations to Constrain the Matter Density of the Universe A Cold Dark Matter Simulation with Dark Energy Stelliferous Era From about 380,000 years after the Big Bang until now Galaxies at about 1 billion A.B.B Average temp = 3K The era of stars, galaxies, and us Top down vs. bottom up Did massive clouds of gas form first, generating the stars (top down) or did stars form first, collecting into galaxies (bottom up)? Probably a combination Where gas was dense enough, stars formed first Where gas was rarefied, dark galaxies formed, later yielding stars Era will continue until the year 100 trillion A.B.B Youngest object ever imaged @ 800MYr A.B.B 17
The First Stars Bottom Up Galaxy Formation: Observation Bottom Up Galaxy Formation: Simulation 18
A Galaxy Under Construction The Universe at 2 Gyr Old A Timeline of Light in the Universe 19
The History of the Universe Your text was published before the BICEP evidence was in. Alan Guth may get the Nobel Prize for this if polarization is confirmed The Future: The most likely* outcome will be the open Universe AKA The Big R.I.P. The actual density of the Universe is less than the critical density / c ~ 1 *Actually too small to ever measure accurately for proper prediction The Universe will expand forever Three Foreseeable Epochs (after the Stelliferous Era): The Time of Degeneracy: 10 14 years The Time of Black Holes: 10 32 years The Time of Photons: 10 100 years 20
Key Ideas Cosmic Inflation: A brief period of rapid expansion, called inflation, is thought to have occurred immediately after the Big Bang. During a tiny fraction of a second, the universe expanded to a size many times larger than it would have reached through its normal expansion rate. Inflation explains why the universe is nearly flat and the 2.725 K microwave background is almost perfectly isotropic. Key Ideas The Four Forces and Their Unification: Four basic forces gravity, electromagnetism, the strong force, and the weak force explain all the interactions observed in the universe. The Standard Model accurately describes all the known particles in nature and their observed interactions (except for gravity). The weak force and electromagnetic force became unified into a single force called the electroweak force at higher energies than those typically found in today s universe. This unification has been observed in high energy particle accelerators. Grand unified theories (GUTs) are attempts to explain three of the forces (strong force, weak force, and electromagnetic force) in terms of a single force. This has not been observed, and particle accelerators fall far short of having the energy to directly probe the high energy where this unification is predicted to occur. Key Ideas A supergrand unified theory (AKA Theory of Everything) would explain all four forces (including gravity) at extremely high energies as a single force acting similarly on all the particles in nature. String theory attempts to make this unification, and it would describe the quantum nature of gravity. Supergrand unification is hypothesized to occur before the Planck time (t = 10 43 seconds after the Big Bang). Spontaneous Symmetry Breaking: As the universe expands and cools, the unified forces break into separate forces. Starting around the Planck time, gravity became a distinct force through a spontaneous symmetry breaking. During a second spontaneous symmetry breaking, the strong nuclear force became a distinct force. A final spontaneous symmetry breaking separated the electromagnetic force from the weak nuclear force; from that moment on, the uni verse behaved as it does today. 21
Key Ideas Particles and Antiparticles: Heisenberg s uncertainty principle states that the amount of uncertainty in the mass of a subatomic particle increases as it is observed for shorter and shorter time periods. Because of the uncertainty principle, particle antiparticle pairs can spontaneously form and disappear within a fraction of a second. These pairs, whose presence can be detected only indirectly, are called virtual pairs. The collision of two high energy photons can produced a real particleantiparticle pair. In this process, called pair production, the photons disappear, and their energy is transformed into the masses of the particle antiparticle pair. In the process of annihilation, a colliding particle antiparticle pair disappears and two high energy photons appear. Key Ideas The Origin of Matter: Just after the inflationary epoch, the universe was filled with particles and antiparticles formed from numerous high energy photons. The particles also annihilated to produce a state of thermal equilibrium between the particles and the photons. As the universe expanded, its temperature decreased. When the temperature fell below the threshold temperature required to produce each kind of particle, annihilation of that kind of particle began to dominate over production. Key Ideas Nucleosynthesis: Helium could not have been produced until the cosmological redshift eliminated most of the high energy photons. These photons created a deuterium bottleneck by breaking down deuterons before they could combine further to form helium. Density Fluctuations and the Origin of Stars and Galaxies:The large scale structure of the universe arose from primordial density fluctuations. The first stars were much more massive and luminous than stars in the present day universe. The material that they ejected into space seeded the cosmos for all later generations of stars. 22
Key Ideas Galaxies are generally located on the surfaces of roughly spherical voids. Models based on dark energy and cold dark matter give good agreement with details of this large scale structure. The Frontier of Knowledge:The search for a theory that unifies gravity with the other fundamental forces suggests that the universe actually has 11 dimensions (ten of space and one of time), seven of which are folded on themselves so that we cannot see them. The fundamental objects in our universe may be very small strings, rather than point like particles. 23