Lesson 1: Big Bang Theory PDF

The theory states that about 13.7 billion years ago all the matter in the Universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly and it is still expanding today. Georges Lemaitre Monsignor Georges Lemaître was a Belgian Roman Catholic priest, physicist a...

The theory states that about 13.7 billion years ago all the matter in the Universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly and it is still expanding today. Georges Lemaitre Monsignor Georges Lemaître was a Belgian Roman Catholic priest, physicist and astronomer. He is usually credited with the first definitive formulation of the idea of an expanding universe and what was to become known as the Big Bang theory of the origin of the universe, which Lemaître himself called his “hypothesis of the primeval atom” or the “Cosmic Egg”. In 1927, an astronomer named George Gamow had a big idea. He said that a very long time ago, the universe started as just a single point. He said the universe stretched and expanded to get as big as it is now, and that it could keep on GEORGE GAMOW stretching. 1904-1968 Since the Big Bang, 13.7 billion years ago, the universe has passed through many different phases or epochs. Due to the extreme conditions and the violence of its very early stages, it arguably saw more activity and change during the first second than in all the billions of years since. 1.RADIATION ERA 2.MATTER ERA - Named for the dominance of radiation after the Big Bang and consists of smaller stages called Epochs namely: 1. PLANCK 2. GRAND UNIFIED 3. INFLATIONARY 4. ELECTROWEAK 5. QUARK 6. HADRON 7. LEPTON 8. NUCLEAR TEMPERATURE: 1040 KELVIN TIME AFTER BIG BANG: IMMEDIATE NO MATTER EXISTED ONLY ENERGY EXISTENCE OF SUPER FORCE (GRAVITY, STRONG NUCLEAR, WEAK, ELECTROMAGNETIC) TEMPERATURE: 1036 KELVIN TIME AFTER BIG BANG: 10-43 SECONDS *Gravity separated from superunified force. Strong, electromagnetic and weak forces were referred as “Unified Force” At the end of GUT, strong force also separated. TEMPERATURE: 1033 KELVIN TIME AFTER BIG BANG: 10-36 SECONDS UNIVERSE RAPID EXPANSION FROM A SIZE OF AN ATOM TO AN APPROXIMATE SIZE OF A GRAPEFRUIT. FORMATION OF ELECTRONS, QUARKS, ANTIQUARKS TEMPERATURE: 1020 KELVIN TIME AFTER BIG BANG: 10-32 SECONDS *Electromagnetic and weak nuclear forces separated. TEMPERATURE: 1016 KELVIN TIME AFTER BIG BANG:10-12 SECONDS * TOO HOT AND DENSE FOR SUBATOMIC PARTICLES TO MERGE. TEMPERATURE: 1010 KELVIN TIME AFTER BIG BANG: 10-6 SECONDS *COOLED DOWN ENOUGH FOR PARTICLES TO FORM LIKE PROTONS AND NEUTRONS. LEPTON EPOCH TEMPERATURE: 1012 KELVIN TIME AFTER BIG BANG: ABOUT 1 SECOND NUCLEAR EPOCH TEMPERATURE: 109 KELVIN TIME AFTER BIG BANG: ABOUT 100 SECONDS * DIFFUSION OF PROTONS AND NEUTRONS INTO NUCLEUS AND THE FORMATION OF FIRST ELEMENT “HYDROGEN”. - PRESENCE AND PREDOMINANCE OF MATTER IN SPCAE. THREE EPOCHS: 1. ATOMIC 2. GALACTIC 3. STELLAR TEMPERATURE: 3000 KELVIN TIME AFTER BIG BANG: 50000 YEARS * COOLING DOWN OF SPACE FOR THE ELECTRONS TO ATTACH WITH NUCLEI WHICH IS CALLED RECOMBINATION TIME: 200 MILLION YEARS * CLUSTERS OF ATOMS COMBINED AND BECAME THE SEEDLINGS OF GALAXIES TIME AFTER BIG BANG: 3 BILLION YEARS * FORMATION OF STARS AND ELEMENTS WITHIN IT. 1. Redshift of Galaxies The redshift of distant galaxies means that the Universe is probably expanding. If we then go back far enough in time, everything must have been squashed together into a tiny dot. The rapid eruption from this tiny dot was the Big Bang. In 1929, Edwin Hubble announced that almost all galaxies appeared to be moving away from us. In fact, he found that the universe was expanding - with all of the galaxies moving away from each other. This phenomenon was observed as a redshift of a galaxy's spectrum. This redshift appeared to be larger for faint, presumably further, galaxies. Hence, the farther a galaxy, the faster it is receding from Earth. * This principle is also known as the “HUBBLE’S LAW” 2. Microwave Background Very early in its history, the whole universe was very hot. As it expanded, this heat left behind a "glow" that fills the entire Universe. The Big Bang theory not only predicts that this glow should exist, but that it should be visible as microwaves - part of the Electromagnetic Spectrum. In 1964, two astronomers, Arno Penzias and Robert Wilson, in an attempt to detect microwaves from outer space, inadvertently discovered a noise of extraterrestrial origin. The noise did not seem to emanate from one location but instead, it This is the Cosmic Microwave came from all directions at Background which has been accurately measured by once. It became obvious that orbiting detectors, Holmdel what they heard was radiation Horn Antenna and is very good evidence that the Big Bang from the farthest reaches of the theory is correct. universe which had been left over from the Big Bang. This cosmic microwave background radiation was later mapped in greater detail by NASA's COSMIC BACKGROUND EXPLORER (COBE) mission in the early 1990s and the Wilkinson Microwave Anisotropy Probe (WMAP), launched in 2001. 3. Abundance of light elements The observed abundance of light elements supports the big bang theory. The theory predicts that the universe is composed of 75% Hydrogen and 25% Helium by mass. The prediction correlated to the measured abundances of primordial material in unprocessed gas in some parts of the universe with no stars.  According to the theory, the density of the early universe shortly after the Big Bang generated enough heat to trigger a process of nuclear fusion that combined single protons together creating lighter elements: hydrogen, helium, lithium, and beryllium. It also merged them with neutrons, allowing for isotopes such as deuterium, which is a variation of hydrogen that contains a proton and a neutron in its atomic nucleus.  Stellar nucleosynthesis is the process by which elements are created within stars by combining the protons and neutrons together from the nuclei of lighter elements. Elements heavier than beryllium are formed through stellar nucleosynthesis.  A star begins its life as a cloud of gas, which is mostly hydrogen and helium. The particles experience a very weak attraction towards each other due to gravity. As the gas cloud becomes denser, the effect of gravity is to increase the pressure and temperature. As more gas is drawn in by the increasing gravity, the mass of the cloud increases and therefore so does its gravity. The increasing gravity compresses the gas further so that it becomes hotter and denser. It eventually becomes a PROTOSTAR.  When the temperature and pressure become high enough, the hydrogen nuclei fuse into helium nuclei, releasing large amounts of energy. The star is now a stable MAIN SEQUENCE STAR. In the core of the main sequence stars, helium is formed from hydrogen nuclei fused together. When most of the hydrogen in the core is fused into helium, fusion stops, and the pressure in the core decreases. Gravity squeezes the star to a point that helium and hydrogen burning occur. Helium is converted to carbon in the core while hydrogen is converted to helium in the shell surrounding the core. The star has become a RED GIANT.  When the majority of the helium has been converted to carbon, the rate of fusion decreases. Gravity again squeezes the star. In a low-mass star there is not enough mass for a carbon fusion to occur. The star’s fuel is depleted, and over time, the outer material of the star is blown off into space. The only thing that remains is the hot and inert carbon core. The star becomes a WHITE DWARF.  However, the fate of a massive star is different. A massive star has enough mass such that temperature and pressure increase to a point where carbon fusion can occur. The star goes through a series of stages where heavier elements are fused in the core and in the shells around the core. The element oxygen is formed from carbon fusion; neon from oxygen fusion; magnesium from neon fusion: silicon from magnesium fusion; and iron from silicon fusion. The star becomes a RED SUPER GIANT.  The fusion of elements continues until iron is formed by silicon fusion. Elements lighter than iron can be fused because when two of these elements combine, they produce a nucleus with a mass lower than the sum of their masses. The missing mass is released as energy. Therefore, elements lighter than and including iron can be produced in a massive star, but no elements heavier than iron are produced. When the core can no longer produce energy to resist gravity, the star is doomed. Gravity squeezes the core until the star explodes and releases a large amount of energy. The star explosion is called a SUPERNOVA.  INSIDE A RED GIANT STAR INSIDE A RED SUPERGIANT STAR 1. PROTON-PROTON CHAIN REACTION 2. CARBON-NITROGEN-OXYGEN CYCLE 3. TRIPLE ALPHA PROCESS 4. THE ALPHA LADDER 5. S- PROCESS  The PROTON-PROTON CHAIN is a series of thermonuclear reactions in the stars. It is the main source of energy radiated by the sun and other stars. It happens due to the large kinetic energies of the protons. If the kinetic energies of the protons are high enough to overcome their electrostatic repulsion, then proton-proton chain proceeds. * This occurs in MAIN SEQUENCE STARS.  The CARBON-NITROGEN-OXYGEN CYCLE is a sequence of thermonuclear reactions that provides most of the energy radiated by the hotter stars. It is only a minor source of energy for the Sun and does not operate at all in very cool stars. For more massive and hotter stars, the carbon- nitrogen-oxygen cycle is the more favorable route in converting hydrogen to helium. The cycle proceeds as follows: 1. Carbon-12 nucleus captures a proton and emits a gamma ray, producing nitrogen-13. 2. Nitrogen-13 is unstable and emits a beta particle, decaying to carbon-13. 3. Carbon-13 captures a proton and becomes nitrogen-14 via emission of a gamma-ray. 4. Nitrogen-14 captures another proton and becomes oxygen- 15 by emitting a gamma-ray. 5. Oxygen-15 becomes nitrogen-15 via beta decay. 6. Nitrogen-15 captures a proton and produces a helium nucleus (alpha particle) and carbon-12, which is where the cycle started. Thus, the carbon-12 nucleus used in the initial reaction is regenerated in the final one and hence acts as a catalyst for the whole cycle. The cycle commences once the stellar core temperature reaches 14 × 106 K and is the primary source of energy in stars.  The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. Helium accumulates in the core of stars as a result of the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle. Further nuclear fusion reactions of helium with hydrogen or another alpha particle produce lithium-5 and beryllium-8 respectively. Both products are highly unstable and decay, almost instantly, back into smaller nuclei, unless a third alpha particle fuses with a beryllium before that time to produce a stable carbon-12 nucleus. * This occurs in RED GIANT STARS   At sufficiently high If a star has sufficient mass, the temperatures and densities, a 3- temperatures and densities be body reaction called the triple enough to overcome the Coulomb alpha process can occur: barrier for combining heavy elements. Two helium nuclei (alpha particles) fuse to form unstable beryllium. If another helium nucleus can fuse with the beryllium nucleus before it decays, stable carbon is formed along with a gamma ray.  The alpha process, also known as the, ALPHA LADDER is one of two classes of nuclear fusion reactions by which stars convert helium into heavier elements, the other being the triple-alpha process  SUPERNOVAS are often seen in other galaxies. But supernovas are difficult to see in our own Milky Way galaxy because dust blocks our view. In 1604, JOHANNES KEPLER discovered the last observed supernova in the Milky Way. JOHANNES KEPLER (1571-1630)  A SUPERNOVA is a massive explosion of a star that occurs under two principal scenarios. The first is that a white dwarf star undergoes a nuclear-based explosion after it reaches its limit after absorbing mass from a neighboring star (usually a red giant). The second, and more common, cause is when a massive star, usually a supergiant, reaches nickel-56 in its nuclear fusion processes.