Present era, 10-20 x 109 y after big bang
Present
Density 1 H-atom/m3; 1080 particles in observable universe
109 photons and neutrinos for each proton or neutron
Galaxies exist in billions; stars forming everywhere
CBR has redshift of 1000 and temperature of 3o K
Universe 109 y old
Density 100 H-atoms/m3
Galaxies coming into existence
Universe 106 y old
Density 1 H-atom/cm3
No galaxies existed prior to 106 y
Matter era, >106 y
Quasars and clusters of galaxies condensing
Density 10-22 g/m3, temperature > 3000o K
Universe flooded with brilliant yellow light
Radiation era, 1s - 106 y
1 s after big bang, radiation era began
Radiation more dense than matter, 105 g/cm3 compared to 0.1 g/cm3
"Matter was like a faint precipitate suspended in a world of dense light." Edward Harrison
Temperature 1010 K
Expanding space filled mostly with protons and neutrinos
Protons and neutrons combined to produce deuterium
Helium synthesized when Universe some 200 s old
Later, when Universe between 105 and 106 years old
Temperature 3000o K, electrons captured by protons to form hydrogen atoms
Electrons no longer scatter photons
Universe becomes transparent to radiation; decoupling epoch when radiation decouples from matter
Fireball that flooded expanding Universe for first 106 y appears as CBR
Lepton era, 10-4 to 1 s
Leptons - light subatomic particles
Interact through electromagnetic and weak forces
Examples: electrons, positrons, and neutrinos
Begins with temperature of 1012 K and ends with 1010 K
Approximately equal numbers of photons, electrons, and neutrinos; these constituents continually interacting
For every 109 photons, electrons, or neutrinos, approximately 1 proton or neutron
Era ended when neutrinos broke away to form ghost world of their own, moving about eternally and independently of other constituents
Present neutrino temperature 2 K, number 103 neutrinos/cm3
Cannot be detected with present technology
If neutrinos have mass, they dominate all else in determining mass of Universe
Hadron era, < 10-4 s
Hadrons - heavy subatomic particles
Interact through electromagnetic and weak forces
Also interact through strong force
Examples: protons, neutrons, and pions
Universe is dominated by dense sea of hadrons; 109 nucleons for every photon or neutrino
Events are unclear; poor understanding of interactions among strongly interacting heavy nuclear particles
Matter and antimatter about evenly divided and continually being created and annihilated
Matter must be somewhat more plentiful than antimatter by 1 in 109
If matter-antimatter equal, should completely annihilated each other; consequently Universe would consist of radiation and very little matter
Nothing prohibits Universe from being fragmented into islands of matter and antimatter, but there are no compelling arguments for this arrangement either
End of era marked by annihilation of matter and antimatter dominating creation; hence almost all matter and antimatter vanishes
Quark era, <10-23 s
Subatomic particles divided into leptons and hadrons
Leptons relatively few in kind and have apparently no internal structure
Hadrons numerous in kind and have apparently complex internal structure
1964, Murry Gell-Mann (b. 1929) and George Zwieg (b. 1937) independently proposed quark model for hadrons
Hadrons composed of more elementary particles called quarks
3 quarks and 3 antiquarks with 4 basics characteristics for total of 24 different quarks/antiquarks
Quarks have no internal structure
No quark in an isolated state in nature has been discovered
Quark theory basically accepted by physics community
10-23 s defines quark era
No structured particles, hadrons, exist
Density 1055 g/cm3, temperature 1022 K
Radius of observable universe 10-13 cm or about size of present-day proton
Planck Era, <10-43 s
Planck time equals 10-43 s; time prior to which Einstein's theory of gravity breaks down (becomes inconsistent)
Planck length equals 10-33 cm; length smaller than which expect quantum fluctuations
Initial state immediately after big bang
Chaotic, superdense > 1094 g/cm3, superthermal > 1032 K
Quantum cosmology era, about which we know almost nothing
Quantum fluctuations of spacetime, of scale equal to Planck length, are of cosmic magnitude
Space and time scrambled together discontinuously and non sequentially in chaotic fashion
John Wheeler visualizes spacetime under these conditions as a chaotic foam
Space and time no longer exist in sense that we normally understand; no "now" and "then," and no "here" and "there;" everywhere is torn into discontinuities
Birth of Universe - Big Bang
Standard big bang cosmological models, such as Friedmann's models, assume that
Universe's matter-radiation content began expansion some 10-20 x 109 years ago
Expansion continues today
Universe is homogeneous and isotropic with no irregularities sufficient distinguish one location from another
At instant when time (expansion) began, primeval fireball erupted from conversion of elementary particles into gamma-ray photons
Period from big bang to approximately 10-4 s is not well understood
Although this period may seem to short to be of any importance, it is, in fact, all important
Laws of physics that have been operating in Universe and, consequently, the nature of Universe today came into existence during this period
Summary of History of Universe
Epoch, Time, Density (g/cm3), Temperature (K), Event
Big Bang, Begins at zero, Almost infinitely high, Extremely high, Birth of the Universe
Planck era, <10-43, >1094, >1032, Quantum cosmology era with Universe occupying volume of nucleon
Quark era, <10-23 s, >1055, >1022, Densely populated with free quarks
Hadron era, <10-4 s, >1014, >1012, Annihilation of matter and antimatter
Lepton era, 10-4 s to 1 s, 1014-105, 1012 - 1010, Rapid expansion and cooling; thermal equilibrium of electrons, positrons, neutrinos, and photons
Radiation era, 1 s to 106 y, 105a-10-22, 1010 - 3000, Formation of helium and deuterium; radiation uncouples from matter at end of era
Matter era, >106 y, <10-22, <3000b, Quasars and clusters of galaxies condense
Present era, 15-20 x 109 y, 5x10-30-5x10-31, 3b, Galaxies and stars have formed; stars still forming
a At beginning of radiation era, when Universe was 1 s old and T = 1010 K, radiation density equivalent to about
105 g/cm3, while matter density only about 0.1-1.0 g/cm3
b Temperature of cosmic background radiation, which is no longer coupled to matter and its temperature
22.2. Inflationary Epoch
Flatness problem: among Friedmann universes
Infinite number are open
Infinite number of values exist for mean density that are less than critical value
Each value corresponds to one member of family of open universe models
Infinite number are closed
Infinite number of values exist for mean density that are greater than critical value
Each value corresponds to one member of family of closed universe models
Only one marginally open
Only one critical value exists for mean density for matter
Observational tests suggest that cosmological model astonishingly close to least probable one, flat marginally-open Friedmann universe
Consequently, value for mean density immediately after big bang was to very high degree the critical value in order for it to be only slightly different, if at all, after 10-20 x 109 y
This enigmatic result is known as flatness problem
Homogeneity problem
Strange that CBR coming from 15 x 109 ly in one direction being incredibly like that coming from 15 billion ly in any other direction
Observed isotropy of Universe and, consequently, its implication that Universe is homogeneous on its largest scale sizes as contained in the cosmological principle is an improbable result
This is because an infinite number of degrees of in homogeneity exist, but there is only one state of homogeneity
Problem: Universe has expanded from those chaotic conditions following big bang for some 15 x 109 y, and has yet managed to remain homogeneous and to contain just the right amount of matter to make its geometry a flat Euclidean one
Inflationary epoch
Early 1980s, Alan Guth suggested new epoch should be added, known as inflationary epoch, lasting between 10-35 and 10-24 s
Characteristics of inflationary epoch
Extremely small portion of Universe ballooned outward in all directions at speeds much greater than speed of light
Becomes many billions of times its original size to become visible Universe of today
Inflated portion pushed much of material that was originally near our location far beyond its boundaries
Because inflated portion so small, its properties, such as temperature, extremely homogeneous accounting for homogeneity of observable Universe
Because observable Universe is tiny fraction of entire Universe, it appears very flat, just as a baseball field can appear quite flat while actually being part of curved surface of Earth
Grand Unified Theory (GUT)
During very early period in Universe, another series of events possibly took place which were predicted in early 1970s
Suspected that all four forces in nature - gravity, electromagnetic, and strong and weak forces - were unified into a single force at time of big bang
Gravity became separate force at 10-43 s after big bang, when temperature 1032 K
Strong force became separate force at 10-35 s, or beginning of inflationary epoch, when temperature 1027 K
Electromagnetic and weak force broke apart at 10-12 s, when temperature was 1015 K
22.3. Hydrogen, Deuterium, and Helium
During first 200 seconds of radiation era, at fireball temperature of 109 K
Most hydrogen, deuterium, and helium nuclei synthesized, when expanding Universe had cooled enough
Calculated percentage of deuterium and helium created depends critically on values for early matter density and present temperature of CBR
Results reasonably consistent with present observed cosmic ratios of deuterium and helium to hydrogen
Measured density of deuterium leads to estimates of present average matter density that are less than critical density needed to close Universe
Calculated abundance ratio of helium to hydrogen is about 25% by weight, or 1 helium atom to 12 hydrogen atoms - about same as observed ratios in stars
Predicted abundance for heavier elements, however, very low in comparison with observed values
Heavier elements created primarily long after big bang inside stars and in supernova outbursts
22.4. Matter Era, Formation of Clumps of Matter
Era of galaxies began when matter was more plentiful than radiation
Universe 106 y old and 106 times more dense than at present
How was primordial matter, density <10-22 g/cm3, 100 atom/cm3, relatively low temperature, distributed?
How did it formed into superclusters, clusters, and individual galaxies?
Georges Lemaitre noted that
If homogeneous and isotropic cosmological model expanding from big bang is reasonable place to begin Universe, critical step is to account for small, local departures from homogeneity in order to form galaxies, clusters, and superclusters
If matter evenly distributed in expanding Universe, every piece of matter feels an equal pull by other pieces of matter in all directions
Consequently, trajectory of each piece of matter remains unchanged, and no disturbance occurs to increase density anywhere
Thus, no gravitational field created to attract matter and make superclusters, clusters and individual galaxies, and Universe just continues expanding smoothly never forming any lumps of matter
Suppose in beginning a tiny excess of matter occurs in a number of locations
Such excesses could exert unequal attractions on their surroundings
By accumulating more matter excesses would grow into extremely dense regions today
Much denser than any part of visible Universe that we see
Such regions would, in fact, grow so dense that they would turn into supermassive black holes eventually swallowing up all matter in Universe
For Universe to be no more lumpy than it is today after 15 x 109 y of expansion, distribution of matter in Universe just after big bang would have had to be extremely smooth, but not quite perfect
An extremely tight balancing act, or a very unlikely situation, for Universe to have actually followed
Assuming Universe actually did accomplish balancing act, one approach to formation of galaxies is to have matter accumulate out of churning primordial eddies
Favorable period when very large turbulent eddies could have formed occurred at beginning of matter era, when temperature was 3000 K
Summary of spectrum of ideas concerning formation of galaxies in big-bang cosmology
At one end of spectrum, it is supposed that superclusters formed first and then later fragmented into clusters and eventually into individual galaxies
At other end of spectrum, it is assumed that small clumps formed first and accreted into galaxies, which in turn accreted into clusters and eventually into superclusters in overdense regions
In both, Universe grew more irregular under dominion of gravity
22.5. Primordial Black Holes
Quantum gravity
1970s Stephen Hawking combined gravity with quantum mechanics to developed quantum theory to analyze properties of black hole
Density fluctuations during big bang could create enormous numbers of small black holes - primordial black holes
Black holes capable of emitting particles and photons in thermal fashion
Temperature is measure of rate of emission; the larger the mass of black holes, the lower is its temperature
As particles escape from black hole, its mass decreases and, consequently, its temperature goes up
Eventually, process becomes a runaway one that ends in complete evaporation of black hole
Length of time before evaporation occurs is proportional to third power of mass
During final seconds of evaporation, vast quantities of particles and photons pour out making black hole a source of matter and energy rather than a sink
Approaching point of evaporation, gamma-ray emission from evaporating black hole might be detectable with today's instruments
Different mass black holes
For 1Mo black hole, its temperature is a tiny fraction above absolute zero, and black hole's calculated lifetime is 1066 y, trillions of trillions of times the accepted age of Universe (10-20 x 109 y)
For asteroid-size (109 tons) black hole, its Schwarzschild radius is comparable to proton (10-13 cm)
Has temperature of 1011 K
Life expectancy equal to age of Universe
Flash of gamma radiation arising at time of its rapid demise down to zero mass might now be observable
Another means of verifying big-bang cosmology, is finding powerful gamma-ray radiation pouring out of primordial mini black holes that were created during early Universe
22.6. Possible Fates of Universe
If Universe is closed
Space will cease to expand at some point in the future and begin slow contraction that accelerates over time towards "big crunch."
As this occurs, temperature will rise awaiting that instant when all matter and energy are forced back together as a cosmic singularity
If Universe is open, marginally or not
Galaxies will recede from each other forever
Furnaces in interiors of stars will process most of hydrogen and helium into heavier elements
Some time beyond 1012 y, new star formation will cease so that only white dwarfs, neutron stars, black holes or cold clumps of matter (planets, asteroids, etc.) populate galaxies
Beyond 1027 y, these dead stars and cold clumps in galaxies will merge into one galactic-sized black hole
Beyond 1031 y, even galaxies-turned-black-holes in clusters and superclusters will merge to form supergalactic black holes
Stellar black holes will evaporate in 1067 y, galactic black holes will evaporate in 1097 y, and supergalactic black holes evaporate in 10106 y
Each of these evaporation's results in burst of particles and radiation
What will Universe be then? We can only vaguely imagine!