ORIGIN AND EVOLUTION OF THE UNIVERSE • Solar System – Sun with 9 (or10?) planets and 34 moons • mass = 2 x 1033 grams age = 5 x 109 years • diameter = 2 x 1015 cm temperature = 5700 K • 73% H, 25% He, 1% carbon and oxygen • Galaxy – consists of 2 x 1011 stars • Local Group – a cluster of 30 galaxies • Super Cluster – several clusters so that the density is • at most 10-31 g/cm3 • Quasars – interstellar objects at much greater distance
*Homogeneity and isotropy of the universe * Based on cosmological principle – on a large enough scale the universe looks very much the same no matter where the observer is located. The universe has no unique center and therefore no unique boundary. galaxies are distributed evenly across the sky stars – size ~ 1 light year 1 light year = 9.461 x 1015 m galaxies – size ~ 106 light years clusters – size ~ 3 x 107 light years
evidence: 1) distribution of galaxies in the sky and in the distribution of their apparent magnitudes and red-shifts 2)isotropy of the distribution of radio sources in the sky 3)isotropy of the cosmic microwave radiation (discovery in 1965)
Standard Hot Big Bang Model Evolution governed by laws of thermodynamics, hydrodynamics, atomic physics, nuclear physics, high-energy physics and gravitation dominates the over-all expansion. Assumption of the model: The universe “began” in a state of rapid expansion from a very nearly homogeneous, isotropic condition of infinite (or near infinite) density and temperature ( a singularity – incomplete physical understanding).
Time after beginning initial state, decoupling, free propagation of gravitons & neutrinos 1 s , temperature of the universe was so high that there was complete thermodynamic equilibrium between photons, neutrinos, electrons, positrons, neutrons, protons, various hyperons, and mesons, and perhaps even gravitons (gravitational waves). thermal equilibrium, decay of particles, recombination few s, temperature dropped to about 1010 K and its density was down to ~105 g/cm3; so all nucleon-antinucleon pairs had recombined, all hyperons and mesons had decayed, and all neutrinos and gravitons had decoupled from matter. Universe consisted of freely propagating neutrinos, perhaps gravitons, with black-body spectra at temperature T ~ 1010 K, plus electron-positron pairs in the process of recombining, plus electrons, neutrons, protons and photons all in thermal equilibrium at T ~ 1010 K.
The gravitons (if present) and neutrinos have continued to propagate freely, maintaining black-body spectra, but their temperature have been red-shifted by the expansion of the universe in accordance with the law T a-1 , a = radius of universe Their temperatures today should be roughly 3K and should fill the universe. “Sea” of neutrinos and gravitons still undetected with today’s technology.
Primordial element formation 2s t 103 s, temperature is ~1010 to ~109 K, ~ 10+5 10-1g/cm3, during which primordial element formation occurred. Calculations reveal that about 25% of the baryons in the universe should have been converted into He4 during this period, and about 75% should have been left as protons (H1). Traces of deuterium, He3, and Li should have been also created, but essentially no heavy elements. Heavy elements observed today must have been made later, in stars. Current astronomical studies of the abundances of the elements give some support for these predictions, but the observational data are not yet very conclusive.
thermal interaction of matter and radiation 103s t 105 years Matter and radiation continue to interact thermally through frequent ionization and recombination of atoms keeping each other at same temperature, if not, radiation will cool more slowly than matter. For adiabatic expansion, Tr a-1, but Tm a-2 ,Tris the radiation temperature. Thus thermal equilibrium was maintained only by a constant transfer of energy from radiation to matter. Energy transfer held up the temperature of matter (Tm = Tr) without significantly lowering the temperature of the radiation. The total mass-energy of matter was and is dominated by rest mass. So energy transfer had negligible influence on m (density of matter).
plasma recombination and transition to matter dominance T ~ 105 years. The falling temperature reached a few thousand degrees (a/a0 ~ 10-3; a = radius at time of emission; a0 – initial radius; ~ 10-20 g/cm3), two things of interest happened: universe ceased to be radiation – dominated and became matter dominated; photons ceased to be energetic enough to keep hydrogen atoms ionized; so electrons and protons quickly recombined. That these two events were roughly coincident is a result of the specific, nearly conserved value that the entropy per baryon has in our universe. S entropy per baryons ~ (number of photons in universe)/ (number of baryons in universe) ~ 108
Recombination of the plasma at t ~ 105 years was crucial, because it brought an end to the interaction and thermal equilibrium between radiation and matter. With very few electrons off which to scatter, and with Rayleigh scattering of atoms and molecules unimportant, the photons propagated almost freely through space. The expansion of the universe has red-shifted the temperature of the freely propagating photons in accordance with T a-1. As a consequence, today they have a blackbody spectrum with a temperature of 2.7 K. They identified with the cosmic microwave radiation are discovered in 1965 and they give one direct information about the nature of the universe at the time they last interacted with matter (a/ao ~ 10-3, t ~ 105 years if reionization did not occur; a/ao ~ 0.1, t ~ 108 years if reionization did occur).
condensation of stars, galaxies and clusters 103y t 109 years Before plasma recombination, the photon pressure prevented uniform matter (25% He4, 75% H1) from condensing into stars, galaxies, or clusters of galaxies. After recombination, the photon pressure was gone, and condensation could begin. Small perturbations in the matter density, perhaps dating back to the beginning of expansion, then began to grow larger and larger. Somewhere between a/a0 ~ 1/30 and a/a0 ~ 1/10, these perturbations began developing into stars, galaxies and clusters of galaxies. Slightly later, at a/a0 ~ 1/4 , quasars probably “turned on”, emitting light which astronomers now receive on Earth.
Other cosmological theories 1.Steady-state theory (Hoyle, Bondi and Gold, 1948) – has not succeeded in accounting for the cosmic microwave radiation or in explaining observed evolutionary effects in radio sources and quasars. 2.Hierarchic cosmology of matter in an asymptotically flat space time (Alfven-Klein, Moritz, de Vaucauleurs) – disagrees with cosmic ray and gamma-ray observation. The standard big-bang model of the universe predicted by general relativity accords remarkably well with observation.
Fate of the Universe: Parameters Central problem of cosmology – will the universe continue to expand forever; or will it slow to a halt, reverse into contraction, and implode back to a state of infinite (or near infinite) density, pressure, temperature and curvature? *universe after big bang expands to maximum dimension, then recontracts and collapses Reprocessing the universe reprocesses also the physical constants.
parameters hc/2e2 = 137.036 = fine structure constant ~ 1080 particles in the universe ~ 1040 = e2/GmM = electric force/gravitational force ~ 1020 = [e2/mc2]/[hG/2c3] = ‘size’ of elementary particle/Planck length Planck length = 1.616 x 10-33 cm ~ 1010 = number of photons in universe/number of baryons in universe
These are part of the initial value data. Such #s are freshly given for each fresh cycle of expansion of the universe. A % change one way will cause all stars to be red stars; and a comparable change the other way will make all stars blue stars. In neither case will any star like the Sun be possible. So life as we know it may not exist. Could life have developed if the determinants of the physical constants had differed substantially from those that characterize this cycle of the universe? 1.What good is that universe without awareness of that universe? 2.But awareness demands life. 3.Life demands the presence of elements, heavier than hydrogen. 4.The production of heavy elements demands thermonuclear combustion. 5.Thermonuclear combustion normally requires several 109 years of cooking time in a star. 6.Several 109 years of time will not and cannot be available in a closed universe, according to general relativity, unless the radius-at-maximum expansion of that universe is several 109 light years or more.
Hubble’s Work 1.isotropic universe 2.all galaxies except our nearest neighbors show a red shift in their spectral features (an expanding universe) Hubble’s law v = Hr, H = 17 x 10-3 m/(s ly) velocity of recession indicated by the red shift is distance of galaxy from us. 1 ly =3.0856 x 10exp18 cm
Arno Pensias and Robert Wilson -Discovered the cosmic microwave background – the echo of the Big Bang itself = 7 cm -equivalent to the radiation from a blackbody with a temperature between 2.5 K (actually 2.7 K) and 4.5 K, left-over radiation from the hot phase still permeating today. The basic parameter that governs the physical processes is the temperature of the gas of interacting quantum particles that fills the whole space of the universe. Temperature because it is proportional to the average energy of the colliding particles, establishes which new quantum particles can be created from the energy of the collisions.
Birth, Life & Death of Stars What is the source of stellar energy? 1926 -subatomic nuclear processes according to Arthur Eddington were responsible for the star’s energy. -center is about 40 million K (today ~ 14 million K) 1928Quantum Theory of Gamow, Gurney and Condon (tunnel effect) particles did not have to surmount the repulsive energy barrier but could tunnel under it 1929Robert d’Atkinson and Fritz Houtermans -energy production of stars by nuclear fusion explained through the “tunneling effect” 1938 Hans Bethe and Carl Friedrich von Weizsacker suggested the “carbon cycle” – where hydrogen nuclei and carbon nucleus as a catalytic agent, burned hydrogen
Some scientific advances. A. Observational facilities in understanding features of stars 1. sensitive electronic detector 2. artificial satellites 3. X-ray astronomy 4. new optical, infrared and radio telescopes 5. sophisticated electronic system. B.Emergence of quantum theory of atoms, the theoretical and experimental understanding of nuclear physics and plasma physics (charged particles) . C.Advent of powerful computers.
·A star is a sphere of a hot gas, (H2 & He) held together by gravity. Gravitational force increases with mass, so the larger the star, the greater The force tending to collapse the star. But there is an opposing pressure to prevent this collapse. The rapidly moving gas particles collide with each other. The frequent collisions means greater pressure, thus, making the gas expands more thereby preventing the collapse. At the core of the star, the nuclei are squeezed closely together. The enormous weight due to the entire mass - equivalent to about 2 million tons resting on a peso coin. The extreme pressure high burning temperature at the core ignites the thermonuclear burning process of hydrogen fusing into helium, generating heat energy. If temperature is small in the core, nucleus fusion will not last and the star lives for about 20 million years. When a star contracts, ½ of gravitational energy released becomes heat energy, which in turn supports the star.
·The stability of a star is due to the dynamic balance • of gravity and the heat that this collapse generates. • ·Stars continue to shrink as fuel is burned and due to • relentless crush of gravity – so they are not really • that stable. Some sources of energy to prevent • utter collapse are: • chemical sources to last 20 million years. • nuclear burning of Hydrogen to keep a solar-mass star • going for billions of years. • 3. burning of He extends this period.
The Interior of Stars. Core inner connective layer – connective currents of hot matter -cooking pot for heavy elements essential for building planets and life layer of gas – transfers radiant energy from core to stars outer connective layer Jupiter has 0.1% of sun’s mass – about 1/20 the mass of the lowest-mass star. Planets form out of flattened disk of gas and cosmic debris surrounding a newly born star. Stars are opaque – light cannot get out right away from the core. This radiation heats up the gas in the star’s outer layers stirring them up the way the sun heats the air on a hot day. This interior movement creates sound waves, which bounce around inside the star.
This acoustic energy is dumped in the solar corona – upper very hot atmosphere of the sun. These groans, screams, drum-rolls can be detected. The sun also vibrates like a shaking bowl of gelatin, which gives clues on the internal motion of the core relative to its outer layer. A picture of the universe can be gleaned from distant sources of electromagnetic radiation: visible, radiowave, infrared and microwave, X-rays and -rays. A star has color and luminosity – its total energy output. red to blue cold to hot surface related to These are plotted as luminosity vs. temperature surface temperatur called Hetzspring – Russell diagram
Spectra stars from modern spectroscopy developed by Fraunhoffer, Kirchoff and Bunsen – stars differ in chemical composition. A.Population I – 1 to 2% of chemical elements heavier than H or He. B.Population II – those relatively lacking in heavy elements.
How is a star made? -formation of stars in giant molecular – cloud complexes – clouds consisting mostly of hydrogen and whose mass >> individual star. -cloud fragments into smaller clump and results in mutual gravitational attraction of gas particles and dust. -Sun was probably formed by a disk of leftover matter swishing around it like the white (scalar nebula) of a fried egg surrounding the yolk and from it the solar system of planets subsequently formed. Stars lead uneventful, middle-class lives, lasting for billions of years.
Stars lead uneventful, middle-class lives, lasting for billions of years. A.T - Tauri stars – about 100 K to 106 years; they exhibit unconventional behavior – rich, complex, often anomalous emission spectra. Surrounded by hot gas and luminous sets of matter. B.Cepheid variables – brightness oscillates with period ranging from 3 days to weeks. Blinking beacons in the sky, e.g. polaris, the Ninth star. They release energy by pulsating their intrinsic brightness. Discovered by Henrietta Leavitt in 1912, period – luminosity relation. Death of Stars:when burning stops, star resumes collapsing. Three possible fates white dwarfs – tiny stars made of solid carbon matter thousands of times denser than ordinary matter. Stars with mass < 1.4 times the sun’s mass. 2.Neutron – star – recurrent of a supernova explosion when more cursive stars collapse. The recurrence is a gigantic atomic nucleus the size of a city. (discovered in 1967) pulsars – spring neutron star. 3.Black hole – stars with masses > 2 solar masses collapse to objects in which space itself gets turned “inside out”
Puzzles from particle physics Standard model says • There are four fundamental forces • There are three families of matter -- 1st: electron and its neutrino; up and down quarks -- 2nd: muon and its neutrino; charm and strange quarks -- 3rd: tau and its neutrino; top and bottom quarks • 1st family makes up all of ordinary matter (elements, molecules, compounds, proteins, DNA, cells, etc.)
Puzzles from particle physics • Unification of fundamental forces is an attractive idea • So far unification of weak and e.m. forces verified • Models of grand unified theories unify weak, e.m. and strong forces These models are characterized by: -- unstable proton with lifetime 1032 years -- observed particles with integral charges -- existence of magnetic monopoles not verified
Puzzles from particle physics • Unification idea anchored on notion of spontaneous breaking symmetry (Higgs mechanism) to differentiate forces at low energies • 3 major puzzles -- “rareness” of magnetic monopoles -- smallness of contribution of symmetry breaking to cosmological constant -- masses of particles affect the value of ῼ of the universe • Theories of elementary particles describe the universe at very early stages • Study of elementary particles, the subatomic domain or inner space is linked to study of the universe
Puzzles from cosmology • The Big Bang Theory is the most popular cosmological theory. It accounts for: -- the relative abundance of elements in the universe -- the background microwave radiation with characteristic temperature of 2.7K
Puzzles from cosmology • The smoothness problem – the background radiation is fairly uniform. Opposite regions in the universe, which are not casually connected (the time it takes for light to traverse the distance is more than the age of the universe) have the same background radiation
Puzzles from cosmology • The age problem – present estimates from Hubble expansion suggest that the universe is between 15 to 20 billion years old. This means that the universe started with a value of ῼ = 1 because otherwise it would have reached its final state of the Big Chill (infinite, very cold universe) or the Big Crunch (recollapsed universe). Present value of ῼ ~ 1 but the matter distribution to support this value is still not found yet (the missing mass problem)
Puzzles from cosmology • The lumpiness problem – the universe contains lumps of matter: clusters of galaxies, stars, etc. What is the origin of these lumps? The 1990 experiment COBE (Cosmic Background Explorer) took a picture of the universe at 300,000 years old showing “hot” and “cold” spots representing the evolution of the “wrinkles” in space-time at 10-43 s after creation. Large galactic clusters formed at the “cold” spots. • The rotation problem – why is it that the universe has zero rotation? This follows from the fact that the Hubble expansion has no center.
The Inflationary Universe • In 1980, Alan Guth, was applying the physics of unification to the problem of the evolution the universe. In particular, he was trying to solve the monopole problem. His solution is revolutionary and he gave it a catchy name, the Inflationary Universe Model (IUM)
The IUM did not only solve the monopole problem, it also solved the other 4 problems that the BBT failed to solve. The BBT was amended that the universe expanded very fast (inflated) during the brief period 10-35 to 10-32 s after creation. This period saw the separation of strong force from others. After this period, the usual expansion of the universe under the BBT resumed.
How does the inflationary phase during the brief period after creation solved the problems of Big Bang Cosmology? • First, IU assumes that the universe came from a single bubble of space-time out of the zillions that came to be after the Big Bang. Each bubble contained only a single monopole, explaining why monopoles are hard to come by • Coming from a single point, all points are causally connected, explaining the smoothness problem
As the universe expanded fast, its rotation will be quickly damped to zero, solving the rotation problem • The large structures come from the small fluctuations in energy density inside the bubble, a way out of the lumpiness problem • Inflation will make any curved region in space-time flat making ῼ = 1 explaining the age problem
The Higgs mechanism of particle physics sustained the inflationary universe.