Big Bang

[[Image:Universe_expansion.png|thumb|240px|According to the Big Bang theory, the universe originated in an extremely dense and hot state (bottom). Since then, space itself has expanded with the passage of time, carrying the galaxies with it.]] In physical cosmology, the Big Bang is the science theory of the origin of the universe as an explosion of space and matter, starting from an enormously density and temperature state at some finite time in the past. The central idea is that the observed redshift of the galaxy (Hubble's law) shows that the galaxies are receding from each other, which implies that they were much closer together in the past. Extrapolation to the extreme, this line of reasoning leads to the conclusion that all the constituents of the universe began at very high density and temperature (perhaps even a gravitational singularity). Since then, space itself has expanded with the passage of time, carrying the galaxies with it. The term "Big Bang" is used both in a narrow sense to refer to a point in time when the observed expansion of the universe (Hubble's law) began—measured to be 13.7 billion (1 E17 s) years ago—and in a more general sense to refer to the prevailing cosmological paradigm explaining the origin and evolution of the universe. One consequence of the Big Bang is that the conditions of today's universe are different from the conditions in the past or in the future. From this Model (abstract), George Gamow in 1948 was able to predict the cosmic microwave background radiation (CMB). The CMB was discovered in the 1960s and served as a confirmation of the Big Bang theory over its chief rival, the steady state theory. ==History== The Big Bang theory developed from observations and theoretical considerations. Observationally, in the 1910s, Vesto Melvin Slipher and later Carl Wilhelm Wirtz determined that most spiral nebulae were receding from Earth, but they weren't aware of the cosmological implications, nor that the supposed nebulae were actually galaxies outside our own Milky Way. Also in the 1910s, Albert Einstein's theory of general relativity was found to admit no static cosmological solutions given the basic assumptions of cosmology described in [http://en.wikipedia.org/wiki/Big_Bang#Theoretical_underpinnings this section]. The universe was described by a metric tensor that was either expanding or shrinking, a result that Einstein himself considered wrong and he tried to fix by adding a cosmological constant. The first person to seriously apply general relativity to cosmology without the stabilizing cosmological constant was Alexander Friedmann, whose equations describe the Friedmann-Lema�tre-Robertson-Walker universe. In 1927, the Belgium Jesuit priest Georges Lema�tre independently derived the Friedmann-Lema�tre-Robertson-Walker equations and proposed, on the basis of the recession of spiral nebulae, that the universe began with the "explosion" of a "primeval atom"—what was later called the Big Bang. In 1929, Edwin Hubble provided an observational basis for Lema�tre's theory. Hubble proved that the spiral nebulae were galaxies and measured their distances by observing Cepheid variable stars. He discovered that the galaxies are receding in every direction at speeds (relative to the Earth) directly proportional to their distance. This fact is now known as Hubble's law (see ''Edwin Hubble: Mariner of the Nebulae'' by Edward Christianson). Given the cosmological principle, Hubble's law suggested that the universe was expanding. This idea allowed for two opposing possibilities. One was Lema�tre's Big Bang theory, advocated and developed by George Gamow. The other possibility was Fred Hoyle's steady state model in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time. It was actually Hoyle who coined the name of Lema�tre's theory, referring to it sarcastically as "this 'big bang' idea" during a 1949 BBC radio program, ''The Nature of Things'', the text of which was published in 1950. For a number of years the support for these theories was evenly divided. However, the observational evidence began to support the idea that the universe evolved from a hot dense state. Since the discovery of the cosmic microwave background radiation in 1965 it has been regarded as the best theory of the origin and evolution of the cosmos. Before the late 1960s, many cosmologists thought the infinitely dense and physical paradox singularity at the starting time of Friedmann's cosmological model could be avoided by allowing for a universe which was contracting before entering the hot dense state and starting to expand again. This was formalized as Richard Tolman's oscillating universe. In the sixties, Stephen Hawking and others demonstrated that this idea was unworkable, and the singularity is an essential feature of the physics described by Einstein's gravity. This led the majority of cosmologists to accept the notion that the universe as currently described by the physics of general relativity has a finite age. However, due to a lack of a theory of quantum gravity, there is no way to say whether the singularity is an actual origin point for the universe or whether the physical processes that govern the regime cause the universe to be effectively eternal in character. Virtually all theoretical work in cosmology now involves extensions and refinements to the basic Big Bang theory. Much of the current work in cosmology includes understanding how galaxies form in the context of the Big Bang, understanding what happened at the Big Bang, and reconciling observations with the basic theory. Huge advances in Big Bang cosmology were made in the late 1990s and the early 21st century as a result of major advances in telescope technology in combination with large amounts of satellite data such as that from COBE, the Hubble space telescope and WMAP. These data have allowed cosmologists to calculate many of the parameters of the Big Bang to a new level of precision and led to the unexpected discovery that the expansion of the universe appears to be accelerating. (See dark energy.) See also: Timeline of cosmology == Overview == Based on measurements of the expansion of the universe using Type I supernovae, measurements of the lumpiness of the cosmic microwave background radiation, and measurements of the correlation function of galaxies, the universe has a measured Age of the universe of 1 E17 s. The agreement of these three independent measurements is considered strong evidence for the so-called Lambda-CDM model that describes the detailed nature of the contents of the universe. The early universe was filled homogeneously and isotropically with a incredibly high energy density and concomitantly huge temperatures and pressures. It expanded and cooled, going through phase transitions analogous to the condensation of steam or freezing of water as it cools, but related to elementary particles. Approximately 10^-35 seconds after the Planck epoch, a phase transition caused the universe to experience exponential growth during a period called cosmic inflation. After inflation stopped, the material components of the universe were in the form of a quark-gluon plasma (also including all other particles—and perhaps experimentally produced recently as a quark-gluon liquid^{[http://www.aip.org/pnu/2005/split/728-1.html]}) in which the constituent particles were all moving relativity. As the universe continued growing in size, the temperature dropped. At a certain temperature, by an as-yet-unknown transition called baryogenesis, the quarks and gluons combined into baryons such as protons and neutrons, somehow producing the observed asymmetry between matter and antimatter. Still lower temperatures led to further symmetry breaking phase transitions that put the fundamental force and particle physics into their present form. Later, some protons and neutrons combined to form the universe's deuterium and helium atomic nucleus in a process called Big Bang nucleosynthesis. As the universe cooled, matter gradually stopped moving relativistically and its rest mass energy density came to gravity dominate that of radiation. After about 300,000 years the electrons and nuclei combined into atoms (mostly hydrogen); hence the radiation decoupling from matter and continued through space largely unimpeded. This relic radiation is the cosmic microwave background. Over time, the slightly denser regions of the nearly uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures observable today. The details of this process depend on the amount and type of matter in the universe. The three possible types are known as cold dark matter, hot dark matter, and baryonic matter. The best measurements available (from WMAP) show that the dominant form of matter in the universe is cold dark matter. The other two types of matter make up less than 20% of the matter in the universe. The universe today appears to be dominated by a mysterious form of energy known as dark energy. Approximately 70% of the total energy density of today's universe is in this form. This component of the universe's composition is revealed by its property of causing the Hubble Law to deviate from a linear velocity-distance relationship by causing spacetime to expand faster than expected at very large distances. Dark energy in its simplest formation takes the form of a cosmological constant term in Einstein's field equations of general relativity, but its composition is unknown and, more generally, the details of its equation of state and relationship with the standard model of particle physics continue to be investigated both observationally and theoretically. All these observations are encapsulated in the Lambda-CDM model of cosmology, which is a mathematical model of the big bang with six free parameters. Mysteries appear as one looks closer to the beginning, when particle energies were higher than can yet be studied by experiment. There is no compelling physical model for the first 10^-33 seconds of the universe, before the phase transition called for by grand unification theory. At the "first instant", Einstein's theory of gravity predicts a gravitational singularity where densities become infinite. To resolve this physical paradox, a theory of quantum gravity is needed. Understanding this period of the history of the universe is one of the greatest unsolved problems in physics. See also: Timeline of the Big Bang == Theoretical underpinnings == As it stands today, the Big Bang is dependent on three assumptions: # The universality of physical laws # The cosmological principle # The Copernican principle When first developed, these ideas were simply taken as postulates, but today there are efforts underway to test each of them. Tests of the universality of physical laws have found that the largest possible deviation of the fine structure constant over the age of the universe is of order 10^-5. The isotropy of the universe that defines the Cosmological Principle has been tested to a level of 10^-5 and the universe has been measured to be homogenous on the largest scales to the 10% level. There are efforts underway to test the Copernican Principle by means of looking at the interaction of galaxy clusters with the CMB through the Sunyaev-Zeldovich effect to a level of 1% accuracy. The Big Bang theory uses Weyl's postulate to unambiguously measure time at any point as the "time since the Planck epoch". Measurements in this system rely on conformal coordinates in which so-called comoving distances and conformal times remove the expansion of the universe from consideration of spacetime measurements. The comoving distances and conformal times are defined so that objects moving with the cosmological flow are always the same comoving distance apart and the particle horizon or observational limit of the local universe is set by the conformal time. As the universe can be described by such coordinates, the Big Bang is not an explosion of matter moving outward to fill an empty universe; what is expanding is spacetime itself. It is this expansion that causes the physical distance between any two fixed points in our universe to increase. Objects that are bound together (for example, by gravity) do not expand with spacetime's expansion because the physical laws that govern them are assumed to be uniform and independent of the Metric space. Moreover, the expansion of the universe on today's local scales is so small that any dependence of physical laws on the expansion is unmeasurable by current techniques. ==Observational evidence== It is generally stated that there are three observational pillars that support the Big Bang theory of cosmology. These are the Hubble Law seen in the redshifts of galaxies, the detailed measurements of the cosmic microwave background, and the abundance of light elements. (See Big Bang nucleosynthesis.) Additionally, the observed correlation function (astronomy) of Large-scale structure of the cosmos fits well with standard Big Bang theory. ===Hubble law expansion=== Observations of distant galaxies and quasars show that these objects are redshifted, meaning that the light emitted from them has been proportionately shifted to longer wavelengths. This is seen by taking a frequency spectrum of the objects and then matching the spectroscopy pattern of emission lines or absorption lines corresponding to atoms of the elements interacting with the radiation. From this analysis, a measured redshift can be determined which is explained by a recessional velocity corresponding to a Doppler shift for the radiation. When the recessional velocities are plotted against the distances to the objects, a linear relationship, known as the Hubble Law, is observed: ''v'' = ''H''₀ ''D'' where ''v'' is the recessional velocity, ''D'' is the distance to the object and ''H''₀ is the Hubble constant measured to be 71 � 4 kilometers/second/Megaparsec by the WMAP probe. ===Cosmic microwave background radiation === [[Image:WMAP.jpg|thumb|240px|WMAP image of the cosmic microwave background radiation]] The Big Bang theory predicted the existence of the cosmic microwave background radiation or CMB which is composed of photons emitted during baryogenesis. Because the early universe was in thermal equilibrium, the temperature of the radiation and the plasma were equal until the plasma recombination. Before atoms formed, radiation was constantly adsorbed and reemitted in a process called Compton scattering: the early universe was opaque to light. However, cooling due to the expansion of the universe allowed the temperature to eventually fall below 3000 K at which point electrons and nuclei combined to form atoms and the primordial plasma turned into a neutral gas. This is known as photon decoupling. A universe with only neutral atoms allows radiation to travel largely unimpeded. Because the early universe was in thermal equilibrium, the radiation from this time had a blackbody spectrum and freely streamed through space until today, becoming redshifted because of the Hubble expansion. This reduces the high temperature of the blackbody spectrum. The radiation should be observable at every point in the universe to come from all directions of space. In 1964, Arno Penzias and Robert Woodrow Wilson, while conducting a series of diagnostic observations using a new microwave receiver owned by Bell Laboratories, discovered the cosmic background radiation. Their discovery provided substantial confirmation of the general CMB predictions—the radiation was found to be isotropic and consistent with a blackbody spectrum of about 3 K —and it pitched the balance of opinion in favor of the Big Bang hypothesis. Penzias and Wilson were awarded the Nobel Prize for their discovery. In 1989, NASA launched the Cosmic Background Explorer satellite (COBE), and the initial findings, released in 1990, were consistent with the Big Bang's predictions regarding the CMB. COBE found a residual temperature of 2.726 K and determined that the CMB was isotropic to about one part in 10⁵. During the 1990s, CMB anisotropies were further investigated by a large number of ground-based experiments and the universe was shown to be geometrically flat by measuring the typical angular size (the size on the sky) of the anisotropies. (See shape of the universe.) In early 2003 the results of the WMAP (WMAP) were released, yielding what were at the time the most accurate values for some of the cosmological parameters. (see Cosmic_microwave_background_radiation#Experiments). This satellite also disproved several specific cosmic inflation models, but the results were consistent with the inflation theory in general. ===Abundance of primordial elements=== Using the Big Bang model it is possible to calculate the concentration of helium-4, helium-3, deuterium and lithium-7 in the universe as ratios to the amount of ordinary hydrogen, H. All the abundances depend on a single parameter, the ratio of photons to baryons. The ratios predicted are about 0.25 for ⁴He/H, about 10^-3 for ²H/H, about 10^-4 for ³He/H and about 10^-9 for ⁷Li/H. The measured abundances all agree with those predicted from a single value of the baryon-to-photon ratio. This is considered strong evidence for the Big Bang, as the theory is the only known explanation for the relative abundances of light elements. Indeed there is no obvious reason outside of the Big Bang that, for example, the universe should have more helium than deuterium or more deuterium than ³He. ===Galactic evolution and distribution=== Detail observations of the Hubble sequence and Large-scale structure of the cosmos of galaxies and quasars provide strong evidence for the Big Bang. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the big bang, and since then larger structures have been forming, such as groups and clusters of galaxies and superclusters. Populations of stars have been aging and evolving, so that distant galaxies (which are observed as they were in the early universe) appear very different from nearby galaxies (observed in a more recent state). Moreover, galaxies that formed relatively recently appear markedly different from galaxies formed at similar distances but shortly after the Big Bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions, and larger structures agree well with Big Bang simulations of the formation of structure in the universe and are helping to complete details of the theory. ==Features, issues and problems== Historically, a number of problems have arisen within the Big Bang theory. Some of them are today mainly of historical interest, and have been avoided either through modifications to the theory or as the result of better observations. Other issues, such as the cuspy halo problem and the dwarf galaxy problem of cold dark matter, are not considered to be fatal as they can be addressed through refinements of the theory. There are a small number of proponents of non-standard cosmology who believe that there was no Big Bang at all. They claim that solutions to standard problems in the Big Bang involve ad hoc modifications and addenda to the theory. Most often attacked are the parts of standard cosmology that include dark matter, dark energy, and cosmic inflation. However, while explanations for these features remain at the frontiers of inquiry in Unsolved problems in physics, each one is strongly suggested to exist in some form by observations of the cosmic microwave background, Large-scale structure of the cosmos and type IA supernovae. The gravity effects of these features are understood observationally and theoretically even as models for them have not yet been fully incorporated into the standard model of particle physics in an accepted way. Though such aspects of standard cosmology remain inadequately explained, the vast majority of astronomers and physicists accept that the close agreement between Big Bang theory and observation have firmly established all the basic parts of the theory. What follows is a short list of standard Big Bang "problems" and puzzles: ===The horizon problem=== The horizon problem results from the premise that information cannot travel faster than light, and hence two regions of space which are separated by a greater distance than the speed of light multiplied by the age of the universe cannot be in causality (physics) contact. The observed isotropy of the cosmic microwave background (CMB) is problematic in this regard, because the particle horizon size at that time corresponds to a size that is about 2 degrees on the sky. If the universe has had the same expansion history since the Planck units, there is no mechanism to cause these regions to have the same temperature. This apparent inconsistency is resolved by inflationary theory in which a homogeneous and isotropic scalar energy field dominates the universe at a time 10^-35 seconds after the Planck epoch. During inflation, the universe undergoes exponential expansion, and regions in causal contact expand so as to be beyond each other's horizons. Heisenberg's uncertainty principle predicts that during the inflationary phase there would be primordial fluctuations, which would be magnified to cosmic scale. These fluctuations serve as the seeds of all current structure in the universe. After inflation, the universe expands according to a Hubble Law, and regions that were out of causal contact come back into the horizon. This explains the observed isotropy of the CMB. Inflation predicts that the primordial fluctuations are nearly Scale invariance and Normal distribution which has been accurately confirmed by measurements of the CMB. ===Flatness=== The flatness problem is an observational problem that results from considerations of the shape of the universe associated with Friedmann-Lema�tre-Robertson-Walker metric. In general, the universe can have three different kinds of geometries: hyperbolic geometry, Euclidean geometry, or elliptic geometry. The geometry is determined by the total energy density of the universe (as measured by means of the stress-energy tensor): the hyperbolic results from a density less than the critical density, elliptic from a density greater than the critical density, and Euclidean from exactly the critical density. The universe is measured to be required to be within one part in 10¹⁵ of the critical density in its earliest stages. Any greater deviation would have caused either a heat death or a Big Crunch, and the universe would not exist as it does today. The resolution to this problem is again offered by inflationary theory. During the inflationary period, spacetime expanded to such an extent that any residual curvature associated with it would have been smoothed out to a high degree of precision. Thus, inflation drove the universe to be flat. ===Magnetic monopoles=== The magnetic monopole objection was raised in the late 1970s. Grand unification theory predicted Topological defect in space that would manifest as magnetic monopoles with a density much higher than was consistent with observations, given that searches have never found any monopoles. This problem is also resolvable by cosmic inflation, which removes all point defects from the observable universe in the same way that it drives the geometry to flatness. ===Baryon asymmetry=== It is not yet understood why the universe has more matter than antimatter. It is generally assumed that when the universe was young and very hot, it was in statistical equilibrium and contained equal numbers of baryons and anti-baryons. However, observations suggest that the universe, including its most distant parts, is made almost entirely of matter. An unknown process called baryogenesis created the asymmetry. For baryogenesis to occur, the Sakharov conditions, which were laid out by Andrei Sakharov, must be satisfied. They require that baryon number not be conserved, that C-symmetry and CP-symmetry be violated, and that the universe depart from thermodynamic equilibrium. All these conditions occur in the big bang, but the effect is not strong enough to explain the present baryon asymmetry. New developments in high energy particle physics are necessary to explain the baryon asymmetry. ===Globular cluster age=== In the mid-1990s, observations of globular clusters appeared to be inconsistent with the Big Bang. Computer simulations that matched the observations of the stellar populations of globular clusters suggested that they were about 15 billion years old, which conflicted with the 13.7-billion-year age of the universe. This issue was generally resolved in the late 1990s when new computer simulations, which included the effects of mass loss due to stellar winds, indicated a much younger age for globular clusters. There still remain some questions as to how accurately the ages of the clusters are measured, but it is clear that these objects are some of the oldest in the universe. ===Dark matter=== During the 1970s and 1980s various observations (notably of galaxy rotation problem) showed that there was not sufficient visible matter in the universe to account for the apparent strength of gravitational forces within and between galaxies. This led to the idea that up to 90% of the matter in the universe is not normal or baryonic matter but rather dark matter. In addition, assuming that the universe was mostly normal matter led to predictions that were strongly inconsistent with observations. In particular, the universe is far less lumpy and contains far less deuterium than can be accounted for without dark matter. While dark matter was initially controversial, it is now a widely accepted part of standard cosmology due to observations of the anisotropies in the CMB, galaxy cluster velocity dispersions, large-scale structure distributions, gravitational lensing studies, and x-ray measurements from galaxy clusters. Dark matter has only been detected through its gravitational signature; no particles that might make it up have yet been observed in laboratories. However, there are many particle physics candidates for dark matter, and several projects to detect them are underway. ===Dark energy=== In the 1990s, detailed measurements of the density of the universe revealed a value that was 30% that of the critical density. Since the universe is flat, as is indicated by measurements of the cosmic microwave background, fully 70% of the energy density of the universe was left unaccounted for. This mystery now appears to be connected to another one: Independent measurements of Type I supernova have revealed that the expansion of the universe is undergoing a non-linear accelerating universe rather than following a strict Hubble Law. To explain this acceleration, general relativity requires that much of the universe consist of an energy component with large equation of state (cosmology). This dark energy is now thought to make up the missing 70%. Its nature remains one of the great mysteries of the Big Bang. Possible candidates include a scalar cosmological constant and quintessence (physics). Observations to help understand this are ongoing. ==The future according to the Big Bang theory== Before observations of dark energy, cosmologists considered two scenarios for the future of the universe. If the mass density of the universe is above the critical density, then the universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state that was similar to that in which it started—a Big Crunch. Alternatively, if the density in the universe is equal to or below the critical density, the expansion would slow down, but never stop. Star formation would cease as the universe grows less dense. The average temperature of the universe would asymptotically approach absolute zero. Black holes would evaporate. The entropy of the universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as ''heat death''. Moreover, if proton decay exists, then hydrogen, the predominant form of baryonic matter in the universe today, would disappear, leaving only radiation. Modern observations of accelerating universe imply that more and more of the currently visible universe will pass beyond our event horizon and out of contact with us. The eventual result is not known. The Lambda-CDM model of the universe contains dark energy in the form of a cosmological constant. This theory suggests that only gravitationally bound systems, such as galaxies, would remain together, and they too would be subject to heat death, as the universe cools and expands. Other explanations of dark energy—so-called phantom energy theories—suggest that ultimately galaxy clusters and eventually galaxies themselves will be torn apart by the ever-increasing expansion in a so-called Big Rip. ''See also Ultimate fate of the universe.'' ==Speculative physics beyond the Big Bang== While the Big Bang model is well established in cosmology, it is likely to be refined in the future. Little is known about the earliest universe, when cosmic inflation is hypothesized to have occurred. There may also be parts of the universe well beyond what can be observed in principle. In the case of inflation this is required: exponential expansion has pushed large regions of space beyond our observable horizon. It may be possible to deduce what happened when we better understand physics at very high energy scales. Speculations about this often involve theories of quantum gravity. Some proposals are: * cosmic inflation * brane cosmology models, including the ekpyrotic model in which the Big Bang is the result of a collision between branes * an oscillatory universe in which the early universe's hot, dense state resulted from the Big Crunch of a universe similar to ours. The universe could have gone through an infinite number of big bangs and big crunches. The cyclic model extension of the ekpyrotic model is a modern version of such a scenario. * models including the Hartle-Hawking state in which the whole of space-time is finite. Some of these scenarios are qualitatively compatible with one another. Each involves untested hypotheses. ==Philosophical and religious interpretations== There are a number of interpretations of the Big Bang theory that are entirely speculative or extra-scientific. Some of these ideas purport to explain the cause of the Big Bang itself (first cause), and have been criticized by some philosophical naturalism philosophers as being modern creation myths. Some people believe that the Big Bang theory lends support to traditional views of creation, for example as given in Genesis, while others believe that all Big Bang theories are inconsistent with such views. The Big Bang as a scientific theory is not associated with any religion. While certain fundamentalism interpretations of religions conflict with the Big Bang history of the universe, there are more liberal interpretations that do not. The following is a list of various religious interpretations of the Big Bang theory: * A number of Christianity apologetics, the Roman Catholic Church in particular, have accepted the Big Bang as a description of the origin of the universe, interpreting it to allow for a philosophical first cause. Pope Pius XII was an enthusiastic proponent of the Big Bang even before the theory was scientifically well established. * Some students of Kabbalah, deism and other non-anthropomorphic faiths concord with the Big Bang theory, for example connecting it with the theory of "divine retraction" (tzimtzum) as explained by the Jewish scholar Maimonides. * Some modern Islamic scholars believe that the Qur'an parallels the Big Bang in its account of creation, described as follows: "Do not the unbelievers see that the heavens and the earth were joined together as one unit of creation, before We clove them asunder? We have made every living thing out of the water." (Ch:21,Ver:30). The Qur'an also appears to describe an expanding universe: "The heaven, We have built it with power. And verily, We are expanding it." (Ch:51,Ver:47). * Certain theism branches of Hinduism, such as the Vaishnava-traditions, conceive of a theory of creation with similarities to the theory of the Big Bang. The Hindu mythos, narrated for example in the third book of the Bhagavata Purana (primarily, chapters 10 and 26), describes a primordial state which bursts forth as the Great Vishnu glances over it, transforming into the active state of the sum-total of matter ("prakriti"). *Buddhism has a concept of a universe that has no creation event. The Big Bang, however, is not seen to be in conflict with this since there are ways to get an eternal universe within the paradigm. A number of popular Zen philosophers were intrigued, in particular, by the concept of the oscillating universe. ==External links and references== ===Big Bang overviews=== *Open Directory Project: [http://www.dmoz.org/Science/Astronomy/Cosmology/ Cosmology] *PBS.org, [http://www.pbs.org/deepspace/timeline/ "From the Big Bang to the End of the Universe. The Mysteries of Deep Space Timeline"] *[http://www.historyoftheuniverse.com/ "Welcome to the History of the Universe"]. Penny Press Ltd. *Cambridge University Cosmology, "[http://www.damtp.cam.ac.uk/user/gr/public/bb_home.html The Hot Big Bang Model]". Includes a discussion of the problems with the big bang. *Smithsonian Institution, "[http://cfa-www.harvard.edu/seuforum/bigbanglanding.htm UNIVERSE! - The Big Bang and what came before]". *D'Agnese, Joseph, "[http://www.findarticles.com/p/articles/mi_m1511/is_7_20/ai_55030837 The last Big Bang man left standing, physicist Ralph Alpher devised Big Bang Theory of universe]". ''Discover'', July 1999. *Felder, Gary, "[http://www.ncsu.edu/felder-public/kenny/papers/cosmo.html The Expanding Universe]". *LaRocco, Chris and Blair Rothstein, [http://www.umich.edu/~gs265/bigbang.htm "THE BIG BANG: It sure was BIG!!"]. *Mather, John C., and John Boslough 1996, ''The very first light: the true inside story of the scientific journey back to the dawn of the universe''. ISBN 0-465-01575-1 p.300 *Shestople, Paul, "[http://cosmology.berkeley.edu/Education/IUP/Big_Bang_Primer.html "Big Bang Primer"]. *Singh, Simon, ''Big Bang: the origin of the universe'', Fourth Estate (2005). A historical review of the big bang. Sample text and reviews can be found at [http://www.321books.co.uk/reviews/big-bang-simon-singh.htm]. *Wright, Edward L., [http://www.astro.ucla.edu/~wright/BBhistory.html "Brief History of the Universe"]. ===Technical introductions=== *S. Dodelson, ''Modern Cosmology'', Academic Press (2003). Released slightly before the WMAP results, this is the most modern introductory textbook. *E. W. Kolb and M. S. Turner, ''The Early Universe'', Addison-Wesley (1990). This is the classic reference for cosmologists. *P. J. E. Peebles, ''Principles of Physical Cosmology'', Princeton University Press (1993). Peebles' book has a strong historical focus. ===Some primary sources=== *G. Lema�tre, "''Un Univers homog�ne de masse constante et de rayon croissant rendant compte de la vitesse radiale des n�buleuses extragalactiques''" (A homogeneous Universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae), ''Annals of the Scientific Society of Brussels'' 47A (1927):41—GRT implies the universe has to be expanding. Einstein brushed him off in the same year. Lema�tre's note was translated in ''Monthly Notices of the Royal Astronomical Society'' 91 (1931): 483–490. *G. Lema�tre, ''Nature'' 128 (1931) suppl.: 704, with a reference to the primeval atom. *R. A. Alpher, H. A. Bethe, G. Gamow, "The Origin of Chemical Elements,"''Physical Review'' 73 (1948), 803. The so-called αβγ paper, in which Alpher and Gamow suggested that the light elements were created by protons capturing neutrons in the hot, dense early universe. Bethe's name was added for symmetry. *G. Gamow, "The Origin of Elements and the Separation of Galaxies," ''Physical Review'' 74 (1948), 505. These two 1948 papers of Gamow laid the foundation for our present understanding of big-bang nucleosynthesis. *G. Gamow, ''Nature'' 162 (1948), 680. *R. A. Alpher, "A Neutron-Capture Theory of the Formation and Relative Abundance of the Elements," ''Physical Review'' 74 (1948), 1737. *R. A. Alpher and R. Herman, "On the Relative Abundance of the Elements," ''Physical Review'' 74 (1948), 1577. This paper contains the first estimate of the present temperature of the universe. *R. A. Alpher, R. Herman, and G. Gamow ''Nature'' 162 (1948), 774. *A. A. Penzias and R. W. Wilson, "A Measurement of Excess Antenna Temperature at 4080 Mc/s," ''Astrophysical Journal'' 142 (1965), 419. The paper describing the discovery of the cosmic microwave background. *R. H. Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson, "Cosmic Black-Body Radiation," ''Astrophysical Journal'' 142 (1965), 414. The theoretical interpretation of Penzias and Wilson's discovery. *A. D. Sakharov, "Violation of CP invariance, C asymmetry and baryon asymmetry of the universe," ''Pisma Zh. Eksp. Teor. Fiz.'' 5, 32 (1967), translated in ''JETP Lett.'' 5, 24 (1967). *R. A. Alpher and R. Herman, "Reflections on early work on 'big bang' cosmology" ''Physics Today'' Aug 1988 24–34. A review article. ===Religion and philosophy=== * Leeming, David Adams, and Margaret Adams Leeming, ''A Dictionary of Creation Myths''. Oxford University Press (1995), ISBN 0195102754. * Pius XII (1952), "Modern Science and the Existence of God," ''The Catholic Mind'' 49:182–192. === Research articles === Most scientific papers about cosmology are initially released as preprints on [http://arxiv.org arxiv.org]. They are generally technical, but sometimes have introductions in plain English. The most relevant archives, which cover experiment and theory, are the [http://arxiv.org/archive/astro-ph astrophysics] archive, where papers closely grounded in observations are released, and the [http://arxiv.org/archive/gr-qc general relativity and quantum cosmology] archive, which covers more speculative ground. Papers of interest to cosmologists also frequently appear on the [http://arxiv.org/archive/hep-th high energy phenomenology] and [http://arxiv.org/archive/hep-th high energy theory] archives. Astrophysics Cosmology simple:Big Bang th:บิกแบง vi:Big Bang

Big Bang

Talk:Big Bang/Archive1 == Finite universe == Maybe something should be added about the misconception that the Big Bang theory implies a finite-size universe? - User:Fredrik | User talk:Fredrik 13:56, 30 Jan 2005 (UTC) :I hadn't heard about that misconception. Whether the universe is finite size or not is a question that cannot be answered from the context of the Big Bang. User:Joshuaschroeder 15:07, 30 Jan 2005 (UTC) ::My experience (I did a brief presentation about the shape of the universe in high school, and the possibility of infiniteness surprised most listeners) is that people commonly visualize an expanding universe as a finite, three-dimensional ball of space that grows from an initially infinitesimal three-dimensional ball of space. User:Fredrik | User talk:Fredrik 15:28, 30 Jan 2005 (UTC) :::In fact, given a positive cosmological constant, not only the ''observable'' universe's size, but also its entropy, is bounded. --User:Pjacobi 18:25, 2005 Jan 30 (UTC) ::::Well, the misconceptions about the size and shape of the universe notwithstanding, I think that the section on the future of the universe gives a pretty good guideline for saying the true answer to the boundaries of the universe: we just don't know -- if they are there, they're outside our observable horizon. User:Joshuaschroeder 19:50, 30 Jan 2005 (UTC) == Standard Problems (old) == I hope I'm not reopening old wounds, but I felt the introduction to the Standard Problems sections was inaccurate so I rewrote it to make the following clear and make it, if anything, more neutral: 1 - most physicists accept the basic picture of the big bang 2 - dark matter, dark energy and inflation have not yet been detected in a way that would make a particle physicist happy, so they remain somewhat controversial (dark matter less so) :The most convincing argument seems to be Occams razor: A rather simple theory with not that much free parameters gives a good fit to current observations of the microwave background and large scale structure surveys. :In fact some recent reviews, have focused on the information theoretic aspect of this. Standard, flat, Lambda-CDM model plus plain vanilla inflation gives such a good fit, that adding more parameters doesn't make the fit better, compared to the amount of input to the formalus. :User:Pjacobi 00:01, 2005 Feb 5 (UTC) ''dark matter, dark energy and inflation have not yet been detected in a way that would make a particle physicist happy'' -- the cross-sections and energy regimens for probing these phenomena are not touched by particle physics yet. I'm sorry if they are unhappy, but the burden is on them to show and observation that will shed light on the phenonmena, not on the cosmologists. User:67.172.158.8 04:05, 7 Feb 2005 (UTC) Hi, I made the above modifications, and I stand by them. The statement I added: "However, dark energy and dark matter are only known through their gravity, whereas cosmic inflation is only known for setting the boundary condition for the big bang. There is not yet a consensus on their particle physics origin." is a fair representation of the views of almost all workers in the physics community, particle physicists and cosmologists included. ::Cosmic inflation has evidence through the anisotropies of the CMB. This isn't simply a boundary condition (which is different from an initial condition, by the way). This is actually demanded of from the parameter fitting. Without inflation, the CMB data doesn't match with other observations. User:Joshuaschroeder 16:45, 7 Feb 2005 (UTC) ::: The boundary condition article discusses initial conditions. The initial conditions that inflation sets are: a flat, empty universe which is homogeneous on vastly superhorizon scales, and a nearly-scale invariant spectrum of scalar curvature perturbations with amplitude

\delta\rho/\rho=10^{-5}

. ::::Correct, but not the entire story. Inflationary scenarios drive the universe toward this (as we observe the universe now to be). It's not really an initial condition at all. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) :::::I meant from the point of view of the hot big bang, it is an initial condition. For example, when you integrate the Boltzmann equation to get the CMB spectrum, the initial conditions are a nearly scale invariant spectrum. --User:Joke137 05:14, 8 Feb 2005 (UTC) :::The simplest, most robust models of inflation include a spectral index around .95 and a specific amplitude for the tensor modes. This says nothing about where the particle physics of inflation should come from. Just because inflation is the best-established theory to acheive these initial conditions doesn't mean it should be accepted into the canon of the big bang along with such well-tested and understood theories as big-bang nucleosynthesis and structure formation. ::::Well, the problem is if infation didn't happen, the thing that did happen looks so much like it, it's like arguing over whether Newtonian gravity or GR describe the orbits of the planets. Nobody is seriously proposing any alternatives to inflation that don't let the universe expand exponentially. In fact, there's a mathemtical proof by Linde that given any of a series of universes (even without the scalar field assumption) inflation has to happen. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) :::Jim Peebles -- I doubt one could find a more trusted authority -- says in [http://lanl.arXiv.org/abs/astro-ph/0410284]: "The accompanying evidence for flat space sections was welcomed as a prediction of inflation, but you can count that welcome as an effect of social pressure because inflation is a social construction, which is to say that it is a promising working hypothesis that awaits searching scientific tests." --User:Joke137 23:36, 7 Feb 2005 (UTC) ::::I don't disagree with Peebles, his experience with the CMB discovery is illustrative for to what the above quote refers. The predictions of inflation are for the most part "post-hoc", but the fact is that there are inflationary tests (including gravitational waves and polarization of the CMB) that may very well provide the tested predictions to which Peebles is refering. If inflation happened in a non-vanilla way, this criticism will be satisfied. The danger is if we fall into a parameter space where the kind of inflation that happened is not well constrained. Then there's not much left that people have thought to test. Still, this is a highly nuanced issue and can't really captured well for a general audience. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) :::::The nearly-scale invariant spectrum is an extremely important prediction of inflation. Gravity waves and B-modes in the CMB haven't yet be measured, and when they are they will constrain inflation. That still leaves a number of problems: nobody has yet found a natural way to fit inflation into the standard model. Moreover, it looks that the slow-roll conditions of inflation are incredibly hard to satisfy, because inflationary potentials in quantum field theory get renormalized to be much too steep. String theory also seems to have trouble producing inflation. In the face of this, alternatives need to be investigated: things like infrared modifications of gravity, ekpyrotic models, holographic cosmologies like Banks-Fischler. --User:Joke137 05:14, 8 Feb 2005 (UTC) ::::::Slow-roll inflation as it is normally taught is almost certainly incorrect. However, that's not the only kind of inflation available (though it's the easiest to understand conceptually). Infrared gravity has real problems reproducing large-scale structure observations. The ekpyrotic and holographic cosmologies have their own versions of inflationary scenarios. In short, I don't see what you think is so risky about claiming inflation occurred. ::In terms of only gravitational effects, this isn't quite true either. CDM is known to work through detail considerations of the time of decoupling which isn't a gravitational effect at all. Dark energy is known to work through structure formation which is more detailed than simply a "gravitational effect". User:Joshuaschroeder 16:45, 7 Feb 2005 (UTC) :::No, these are both absolutely gravitational effects. They do not involve CDM or dark energy coupling through any force other than gravity. In the same paragraph, Peebles continues: ::::No, decoupling is purely a particle physics effect. Structure formation is tied to gravity, but includes other terms in the Vlasov equation. It isn't purely gravitational. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) :::"It is important that there are independent lines of evidence for the detection of Lambda, mainly from measures of the angular size distance as a function of redshift, and from the WMAP measurement of the CBR anisotropy. The latter is somewhat beclouded by its dependence on a structure formation model with anomalies that, if real, will drive adjustments of the model and maybe of the constraint on Lambda, and it is beclouded also by the puzzle of the quantum vacuum energy density, which might drive adjustments of the world picture or of the gravity theory and the interpretation of the cosmological tests. One can make a similar list of hazards for each estimate of Omega_m, of course; the big difference is in the lengths of the lists of independent evidence. The issue of Einstein�s cosmological constant has been under discussion since 1917. I suggest we wait a few more years to see how the evidence develops ... before making a definite decision about the reality of this curious term." ::::I think Peeble's conservatism in this regard is admirable. There is, however, no question that he is stating that the thoroughly independent measurements of lambda, for example, are not dependent on single parts of physics as you have claimed. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) :::::I don't think you're understanding what I say. Decoupling, surely, is not purely gravitational. Most of the formation of large-scale structure, which is governed by CDM, is, but baryonic processes can be non-gravitational. However, these do not involve postulating any non-gravitation interaction for CDM or dark energy. In these models, CDM is a pressureless, non-dissipative non-interacting gas, and dark energy is either a cosmological constant or a very light scalar field with equation of state less than < -1/3. It both cases, in the model, they do not couple to the visible sector we observe other than through the curvature of space. --User:Joke137 05:14, 8 Feb 2005 (UTC) ::::::Neither couples today. However, the times when coupling is important are probed in ways other than direct astronomical or particle physics observations. User:Joshuaschroeder 05:26, 8 Feb 2005 (UTC) :::Lambda and inflation are promising working hypotheses, and standard parts of the most accurate working model of the big bang, but most people would reserve judgment on the extent to which, and certainly the way in which they are a part of our universe. I have trouble understanding what is objectionable about my original quote. --User:Joke137 23:36, 7 Feb 2005 (UTC) ::::There are, unfortunately, a few things incorrect about your original quote (for example claiming that evidence for CDM only comes from gravitational effects). I have tried to include the correct and valid arguments you made in the article. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) There are many candidates for non-baryonic dark matter, although none have been confirmed, and thus it seems like the theory is well ground, but nobody has yet come up with a fundamental theory of dark energy or cosmic inflation, and I think it is important to point this out, to separate what has been established in the big bang from what is still speculative. --User:Joke137 06:05, 7 Feb 2005 (UTC) ::The observational evidence for dark matter and dark energy are well-established. The details of them are not, but that is already mentioned in the article. User:Joshuaschroeder 16:45, 7 Feb 2005 (UTC) :::Again, I suggest you look at the text I recommend adding. It does not contradict what you're saying. I think it is important to maintain a distinction in the article between the canonical features of the big bang, and what is still likely to change substantially. --User:Joke137 23:36, 7 Feb 2005 (UTC) ::::This may be a bit of missing the forest for the trees. That the global properties of the effects of inflation, CDM and Lambda will be around in the final draft of the Big Bang is not up for debate. As to what form they will have, we aren't exactly sure. While science is cautious, we cannot simply make the claim that these areas are going to change "substantially". When I think of "substantially" I think of a change in substance. Brane cosmology, for example, doesn't claim to change the substance of dark matter, but only recast it in terms of higher physics. ::::To put it another way, imagine writing an article in the late 19th century about gravity. Nobody yet knew about relativity, but the predictive power of Newton's Laws were unmistakable. GR didn't change the major face of non-relativistic gravity, but it was still a major paradigm shift. I wouldn't call the change, however, "substantial" since Newtonian gravity still worked for the regime in which it was considering. Classical physics was, however, a "substantial" change over Aristotlean physics. They actually predicted substantively different things for all regimes. ::::Maybe this is the old argument about linear theory. Is the first order-approximation a substantial difference from the second order? I say no. User:Joshuaschroeder 00:51, 8 Feb 2005 (UTC) :::::I agree that we are missing the forest for the trees, and I agree that in the final draft of the big bang we will see something with the same effects as CDM, inflation and Lambda. Perhaps we disagree about what substantial means. I am suggesting that it should be made clear in the article that the community, as yet, does not put inflation and dark energy on quite the same footing as, say, the prediction of acoustic peaks in the CMB, structure formation, BBN, the quark-gluon plasma, decoupling, reionization, etc. Baryongenesis and dark matter are perhaps somewhere in between, the ideas are in place but the details have yet to be revealed. --User:Joke137 05:14, 8 Feb 2005 (UTC) ::::::Since WMAP, the concordance model astrophysics is really quite intertwined with each other. Denying Dark energy and inflation would require the skeptic to explain WMAP, something I have yet to see done. Right now, the only thing that is fishy in the big picture is the high-optical-depth to reionization. I suppose the "house of cards" could fall completely, but our probes of this era are not the best and Tegmark claims that we can patch it up anyway. User:Joshuaschroeder 05:26, 8 Feb 2005 (UTC) I'm going to be a curmudgeon and just write my comments at the end. I don't think slow-roll inflation, as it is usually taught, is almost certainly wrong. Sure, it seems incompatible with QFT but I don't see anything better supplanting it, and it has a great advantage over every other model of inflation: it makes robust predictions. It is true that the holographic cosmology needs inflation to push perturbations outside the horizon, but ekpyrotic cosmologies do not (although the cyclic model has dark energy, the perturbations are generated in a slowly contracting phase). But this is beside the point, I think. Regarding dark matter and dark energy, you say: "Neither couples today. However, the times when coupling is important are probed in ways other than direct astronomical or particle physics observations." I disagree, Lambda+CDM or DE+CDM models used to do simulations of structure formation generally do not include any coupling at any epoch. I encourage you to look in the literature. This in important -- as far as we know, CDM could be anything from WIMPs, to 10⁶ solar mass black holes, to some non-dissapative matter on a hidden brane, to superpartners, to an IR modification of gravity, each of which would have very different properties. Some components of dark matter, like neutrinos, do, of course, interact, but they don't make up the non-baryonic ~25%. Even less is known about dark energy, other than some constraints on its homogeneity, energy density and equation of state. I said it above: "in the final draft of the big bang we will see something with the same effects as CDM, inflation and Lambda." I don't pretend they will go away (incidentally, I think the large value of tau will), but given that we only have a very limited window on them, it is crucial to keep an open mind. --User:Joke137 14:52, 8 Feb 2005 (UTC) ::Other models make robust predictions too. Tegmark's paper on the subject was particularly elucidating on the matter. It seems that traditional slow-roll is almost entirely excluded form WMAP parameterspace consideration (to something like the 4 or 5 sigma level). ::Strucuture formation simulations are not the only theoretical work being done in cosmology. Of course, there is no reason to include dark energy or dark matter coupling in them. By the way, we know that the blackhole model doesn't work because the hierarchical clustering model fails with dark matter chunks that big. Brane-dark matter would still see a decoupling event that would make it non-baryonic CDM just as predicted from current observations. ::The open mind is, of course, always important. I think the article as it is makes that point. User:Joshuaschroeder 00:53, 9 Feb 2005 (UTC) :::I am a bit confused by what you are suggesting Tegmark said. Can you give me the astro-ph phone number of this paper? WMAP does claim to rule out the simplest phi^4 models of inflation, but as with anything in the CMB, I think you can bring them back into the contours by adding more parameters to your MCMC. In any case, the charm of vanilla slow roll inflation, as far as I am concerned, is that there isn't much room to muck with the spectrum. A lot of other theories seem designed to account for any possible observation in the future: isocurvature, non-gaussianity, running spectral index etc... These theories are not easily falsifiable, which makes them less useful as models than simple things like lambda and slow-roll. Ordinary slow roll inflation is falsifiable, and has the additional benefit that it hasn't been falsified yet but could be in the near future (e.g. by finding n_s=1.00 to good accuracy, or not finding B-modes). ::::I miswrote. It's not a Tegmark paper, but rather a talk he gave at two AAS conferences ago. [http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003PhRvD..68l3508L&link_type=EJOURNAL&db_key=AST here] is a paper which constrains slow-roll to WMAP results. Simplest slow-roll is ruled out. We're on the same page here. phi^4 models are what I usually call slow-roll, but obviously second and third order corrections might be (and indeed are) claimed to be slow roll as well. User:Joshuaschroeder 00:47, 13 Feb 2005 (UTC) :::I think inserting a sentence or two in the Standard Problems section that indicates some of the problems with dark matter, dark energy and inflation have not yet been resolved is important. My original sentences are fair and correct: "However, dark energy and dark matter are only known through their gravity, whereas cosmic inflation is only known for setting the boundary condition for the big bang. There is not yet a consensus on their particle physics origin." Here is a more modest version: "There is not yet a consensus on the particle physics origin of dark matter, dark energy and cosmic inflation. While their gravity are understood observationally and theoretically, they have not yet been incorporated into the standard model of particle physics in an accepted way." This is important, because these are three of the biggest problems in particle physics today. An earlier writer put: "the cross-sections and energy regimens for probing these phenomena are not touched by particle physics yet." That is not true, particularly in the case of dark matter there have been plenty of opportunities to detect such a particle, and we have not, ruling out swathes of parameter space. Nobody knows how to detect dark energy or the inflaton yet, since their interactions are not known, so it is not yet even a problem of energies and cross sections. --User:Joke137 18:56, 11 Feb 2005 (UTC) ::::''dark energy and dark matter are only known through their gravity'' -- again, I disagree with this statement. They are also known through other effects that are not gravitational. Since the parameter space is dependent on a variety of details, it's not quite correct to claim they are only known by gravitational effects. User:Joshuaschroeder 00:47, 13 Feb 2005 (UTC) :::::I still disagree with this, but I think we are probably arguing about semantics. ::::''"There is not yet a consensus on the particle physics origin of dark matter, dark energy and cosmic inflation. While their gravity are understood observationally and theoretically, they have not yet been incorporated into the standard model of particle physics in an accepted way."'' This I like much better. Please put this into the article. User:Joshuaschroeder :::::Sure! ::::''particularly in the case of dark matter there have been plenty of opportunities to detect such a particle, and we have not, ruling out swathes of parameter space.'' --> True before WMAP, I think now, though, that the CDM has to be so collisionless as to be outside the range of our particle accelerators. User:Joshuaschroeder :::::I didn't realize WMAP constrained dark matter interactions -- is it something to do with free-streaming and structure formation? ::::::Yes. In order for the hierarchical model to be correct, CDM had to decouple from the field way too soon for us to observe it in the lab -- though we're getting close to reaching it. In some sense, it was really COBE (or technically BOOMERanG) that nailed it since they were the ones that actually determined how small the anisotropies were. User:Joshuaschroeder 06:26, 13 Feb 2005 (UTC) ::::''Nobody knows how to detect dark energy or the inflaton yet, since their interactions are not known, so it is not yet even a problem of energies and cross sections. '' --> Inflation not being dependent on cross-sections I agree with. However, the energy density of dark energy is well known, and it's tiny. We cannot probe changes in energy density on such scales at this time. User:Joshuaschroeder 00:47, 13 Feb 2005 (UTC) :::::Yes, I agree absolutely. --User:Joke137 01:08, 13 Feb 2005 (UTC) :::::Don't wanting to disturb your conversation, but wouldn't it be a good option to give a more elaborate discussion of cosmological parameters, including which observations implies what, and subsequent consequences for inflation models in another article. It seems best to me, to let Big Bang be the overview articles, including history and all that, and the details should go elsewhere. Perhaps to Lambda-CDM model? --User:Pjacobi 00:59, 2005 Feb 12 (UTC) ::::::I think this is a great idea to expand the Lambda-CDM article in this way. I don't have time to write this now, but maybe in the summer. --User:Joke137 01:08, 13 Feb 2005 (UTC) == Problems with the introduction == First, let me say that this is a fine article and my comments may well be nitpickish, but - I think the introduction is too technical in style. Cosmology is difficult to understand. However, the fundamental concept of the theory of a non-static universe, specifically, an expansion of space itself, should be described explicitly, because that is one of the aspects that many might understand more easily than the rest of he theory. I have tried to rewrite the introduction, but upon some more consideration it looks like my command of the English language is insufficient to improve the style. Please could somebody give it a try? User:Kosebamse 10:12, 23 Feb 2005 (UTC) == Historical material == The Medieval Jewish scholar Nachmanides (1194-1270, in his commentary on Genesis 1:4) states that the universe started "the size of a mustard seed" (i.e. something tiny) and increased in size afterwards. While I concede that this is not a scientific observation, he ''did'' argue against the then-prevalent Aristotleian steady-state approach and may be notable. What are the other authors' feelings on this matter? User:Jfdwolff | User_talk:Jfdwolff 14:33, 23 Feb 2005 (UTC) :In principle, this can be mentioned in the Deistic/Jewish section of Philosophical and Religious implications section. Something along the lines of what is written in the Islam section might suffice. User:Joshuaschroeder ==Removed material== I am not at my computer right now, and cannot login, but I removed some edits: *''evolution'' is not a dirty word and will be used in the article as that is the word used by scientists. *Gap creationism may be interesting, but says nothing about the Big Bang per se. We aren't just talking about what people do to accomodate the Big Bang in their religious traditions but what the implications of the Big Bang ARE on said traditions. *Space is not "created" in the Big Bang. It's just rulers streching. User:161.97.202.103 20:32, 23 Feb 2005 (UTC) (User:Joshuaschroeder Evolution is a biological concept. The Universe, and galaxies, are not biological. It is a misapplication of the word to use it outside of a biological context. To apply it outside of biology is just a secular humanistic POV jab at creationists. The encyclopedia should not be used to enforce your POV on others. To promote the idea that evoution happens outside of biology is just propoganda. My edit is going back. The word "development" is perfectly appropriate in place of the word "evolvolution". User:KeyStroke 16:34, 2005 Feb 24 (UTC) The first usage of the word "evolution" in English is recorded in the mid-17th century. Clearly it can be used in a way that has nothing to do with biology, which is the way that astrophysicists use it when talking about "galactic evolution." This is a standard usage and should be restored. It is not propoganda: using the word evolution does not imply that selection happens. --User:Joke137 17:22, 24 Feb 2005 (UTC) The only thing you gain by using "evolution" over the word "developement" is to further your POV agenda against creationists. Using the word "development" takes nothing away from the meaning of the article. But using "development" does clean up the article by removing the humanistic secualarist idea that we are all on some grand evolution to a higher state of being. Which is a religion made out of quasi-science. User:KeyStroke 12:31, 2005 Feb 25 (UTC) It seems like the only agenda here is yours. Re-read my previous comments. The word evolution, in physics, means change over time. Look in the OED or Google "galactic evolution" and "galactic development:" evolution gets more than one hundred times more hits. It is absurd to avoid such a standard usage in wikipedia because of prejudice against the word. --User:Joke137 15:03, 25 Feb 2005 (UTC) Using "development" in place of "evoution" does not detract from the meaning of the article in the slightest. The fact that there is at least one person (me) that sees the use of the word "evolution" as confusing the concepts being discussed should be enough to justify replacing "evolution" with "development". You don't have any need to keep "evolution" except to promote a secular humanist agenda. And you can't even demonstrate the honesty to admit that. User:KeyStroke 21:42, 2005 Feb 25 (UTC) Evolution is the term most often used in scientific papers on this subject. --User:Pjacobi 22:03, 2005 Feb 25 (UTC) == Oscillating universe == I added something to the history section about the oscillating universe, which was removed by User:Joshuaschroeder. The truth is, that before the mid sixties and Hawking's work on the singularity theorems, the big bang was not generally understood as it is today: many physicists were convinced it did not mark the start of time, as we now understand it, and Lifshitz and Khalatnikov were occupied with trying to prove that singularities were not a generic feature of general relativity, Misner was trying to show that Mixmaster behavior set the initial conditions for the big bang, etc. At the beginning of their classic 1965 paper, Dicke, Peebles, Roll and Wilkinson wrote: "One of the basic problems of cosmology is the singularity characteristic of the familiar cosmological solutions of Einstein's field equations. Also puzzling is the presence of matter in excess of antimatter in the universe [...] We can distinguish three main attempts to deal with these problems: "1. [The steady-state model] "2. The assumption [due to Wheeler] that the creation of new matter is intimately related to the existence of the singularity, and the resolution of both paradoxes may be found in the quantum mechanical treatment of Einstein's field equations. "3. The assumption that the singularity results from a mathematical over-idealization, the requirement of strict isotropy or uniformity, and that it would not occur in the real world. [Wheeler, Lifshitz and Khalatnikov]" Option two corresponds very roughly to our understanding of the big bang today, and option three corresponds to Richard Tolman's oscillating universe scenario. It wasn't until Hawking's work on singularities that cosmologists were forced to accept option two. It is pseudo-historical (similar to how quantum mechanics is often taught) to put things so simply. --User:Joke137 22:25, 21 Mar 2005 (UTC) :It's not true that Hawking eliminated option 3. We can, in fact, still match a DeSitter Waist onto a universe before the Planck Time because the GR-solutions allow us to do so. Thus, claiming that the oscillating universe is no longer viable is incorrect. User:Joshuaschroeder 16:04, 23 Mar 2005 (UTC) ::Yes, it is true that if you start violating energy conditions, you can have a bouncing universe, and that there is no a priori reason to assume the energy conditions are satisfied, except that we have always known them to be. Tolman's oscillating universe picture didn't postulate any extraordinary physics to cause the reversal from contraction to expansion, however: it was assumed general relativity would do it with ordinary matter. (It was also ruled out because entropy would build up in the horizon.) ::Incidentally, the de Sitter waist is unstable to small perturbations: it will form a singularity instead of a waist if slightly perturbed. That's the reason that past-eternal inflation doesn't work. --User:Joke137 17:43, 23 Mar 2005 (UTC) :::Although Tolman's first try at the oscillating universe didn't require "Speculative physics beyond the Big Bang" we should be careful to keep the article NPOV with respect to the option that we might still live in a different kind of oscillating universe that would look superficially similar. While I understand there are "fine-tuning" arguments against the simplest patch allowing for an oscillating universe, the whole point of speculation pre-inflation is we don't know all the conditional arrangements of the universe. This is due primarily to the fact that no one has a consistent theory of quantum gravity. To be perfectly honest, we should keep the osciallting universe in the Speculative physics section. I also think the mention of it in the history section is a bit too great, but that's an editorial opinion. ::::Good point. I've added it back in. I think the speculative physics section is the weakest link right now, and could stand some expansion and revision. As for the mention in this history section, it is a matter of taste. I think it is important to keep it in because I think it affected how we see the universe in nearly as profound a way as discarding the static and steady state models. --User:Joke137 00:40, 24 Mar 2005 (UTC) == Confused about nucleosynthesis == I'm having trouble with the following paragraph: "Measurements of primordial abundances for all four isotopes are consistent with a unique value of that parameter, and the fact that the measured abundances are in the same range as the predicted ones is considered strong evidence for the Big Bang. There is no obvious reason outside of the Big Bang that, for example, the universe should have more helium than deuterium or more deuterium than ³He." Since a previous guess I made was wrong, here's my suggested rewrite: "The measured abundances are in the same ranges as the predicted ones. This in itself is considered strong evidence for the Big Bang, as without it the Big Bang there is no obvious reason that, for example, the universe should have more helium than deuterium or more deuterium than ³He. As further evidence, measured primordial abundances of all four isotopes are consistent with a unique value of the baryon-to-photon ratio." :I agree, it is kind of obtuse as written. I like your revision, but I can't understand what the last sentence adds. How about: ::''The measured abundances all agree with those predicted from a single value of the baryon-to-photon ratio. This is considered strong evidence for the Big Bang, as the theory is the only known method that explains the relative abundances of light elements.'' :::Okay, I'm about to use that, a little more concise ("the only known explanation for"), and I'm going to try to keep the point that other methods don't even get the orders of magnitude right, which I think is what the original author was saying. —User:JerryFriedman 15:33, 27 Apr 2005 (UTC) And are we really talking about measurements of primordial abundances, or are the measurements made now and assumed to be the same as the primordial amounts, or extrapolated backwards somehow? —User:JerryFriedman 19:17, 26 Apr 2005 (UTC) :Yes. All that. --User:Joke137 21:09, 26 Apr 2005 (UTC) ::Got it. —User:JerryFriedman 15:33, 27 Apr 2005 (UTC) == Confused about galaxy formation == I'm taking another guess. Current version (without links, sorry): "The details of the distribution of galaxies and quasars both constrain and confirm current theory. The finite age of the universe at earlier times means that galaxy evolution is closely tied to cosmology. The types and distribution of galaxies appear to change markedly over time, evolving by means of the Boltzmann Equation. Observations reveal a time-dependent relationship of the galaxy and quasar distributions, star formation histories, and the type and size of the largest-scale structures in the universe (superclusters). These observations are in statistical agreement with simulations. They are well explained by the Big Bang theory and help constrain model parameters." My suggestion: "The details of the distribution of galaxies and quasars both constrain and confirm current theory. The changing conditions in the Big Bang universe mean that galaxy evolution is different at different epochs. (In contrast, the growth and death of organisms in a stable ecology are overall the same in different years.) In fact, the types and the distribution of galaxies appear to change markedly over time, evolving by means of the Boltzmann Equation. Observations reveal a time-dependent relationship among the galaxy and quasar distributions, star formation histories, and the type and size of the largest-scale structures in the universe (superclusters). These observations are in statistical agreement with Big Bang simulations and help constrain model parameters." —User:JerryFriedman 16:08, 27 Apr 2005 (UTC) ---- I'm not entirely happy with this, because it talks about galaxy ''evolution.'' It makes it sound like a population of galaxies was around in the primordial universe, and has merely changed in character since then, when in fact the galaxies formed from an extraordinarily homogeneous background. Also, I'd take out the reference to the Boltzmann equation, which doesn't add anything. How about: :The details of the distribution of galaxies and quasars provides strong evidence for the Big Bang. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the big bang, and larger structures have been forming since then, such as groups and clusters of galaxies and superclusters. Galaxy populations have been aging and evolving, so that distant galaxies observed in the early universe appear very different from nearby galaxies. Moreover, galaxies that formed relatively recently apear markedly different from galaxies formed shortly after the big bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions, and larger structures are helping to complete details of the big bang theory, and are in good agreement with simulations of the formation of structure in the universe. --User:Joke137 19:12, 27 Apr 2005 (UTC) ::I understand it and I'm about to add it, with a minor change or two. —User:JerryFriedman 16:28, 29 Apr 2005 (UTC) == Confused about 10^-33 s. == While I'm at it, does anyone understand the time mentioned in this sentence? "There is no compelling physical model for the first 10^-33 seconds of the universe." What happened at 10^-33 seconds? Is there any chance that's a typo for 10^-43 seconds, roughly the Planck time? —User:JerryFriedman 16:11, 27 Apr 2005 (UTC) :It's the GUT time, which corresponds to an energy scale of around 10¹⁴ GeV (actually, the GUT scale is more like 10¹⁶ GeV, but who's counting?), roughly the scale of inflation and perhaps baryogenesis, when our understanding of the particle physics gets hazy. You could probably push things back to 10^-37 seconds, but I think it would be wrong to choose the Planck time. --User:Joke137 18:45, 27 Apr 2005 (UTC) == Vesto Slipher == Why is Vesto Slipher not mentioned in this article? --User:Mmcarvalho 18:18, 28 Apr 2005 (UTC) :He should be -- in the history section. Why don't you try to work him in? User:Joshuaschroeder 16:04, 29 Apr 2005 (UTC) ::Okay, I did instead. From what I found on the Web, I'm assuming that the statement that ''Hubble'' found the recession speeds of "spiral nebulae" in 1913 was simply wrong. —User:JerryFriedman 19:27, 4 May 2005 (UTC) == Slightly confused about dark energy (but who isn't?) == Current version: "In the 1990s, detailed measurements of the density of the universe revealed a value that was 30% that of the critical density. For the universe to be flat, as is indicated by measurements of the cosmic microwave background, this would have meant that fully 70% of the energy density of the universe was left unaccounted for. Measurements of supernova reveal that the universe is undergoing a non-linear accelerating universe of the Hubble Law expansion of the universe. General relativity requires that this additional 70% be made up by an energy component with large equation of state." My suggestion: In the 1990s, detailed measurements of the density of the universe revealed a value that was 30% that of the critical density. Since the universe is flat, as is indicated by measurements of the cosmic microwave background, fully 70% of the energy density of the universe was left unaccounted for. The mystery was parametrized further by independent measurements of supernova which revealed that the universe is undergoing a non-linear accelerating universe of the Hubble Law expansion of the universe. To explain this acceleration, general relativity requires that much of the universe consist of an energy component with large equation of state. This "dark energy" is now thought to make up the missing 70%." —User:JerryFriedman 18:15, 2 May 2005 (UTC) :Not bad. I tweaked it slightly to avoid the "From another quarter" awkward wording. User:Joshuaschroeder 19:42, 2 May 2005 (UTC) ::Hm, I can't understand "The mystery was parametrized further". Since I gather my version didn't introduce any mistakes, I'm going to put it into the article with yet another beginning of that sentence, and you (or anyone) can improve that if necessary. —User:JerryFriedman 22:01, 2 May 2005 (UTC) == Philosophical and religious references == It would be totally cool to have some more, within reason. Just a thought. —User:JerryFriedman 17:05, 4 May 2005 (UTC) **The word "anthropomorphic" (meaning formed like man) in "Some students of Kabbalah, deism and other non-anthropomorphic faiths..." is not appropriate here. Does the writer mean anthropocentric?** Look in the dictionary. An anthropomorphic faith is one that ascribes "a human form and attributes to the Deity." --User:Joke137 21:36, 22 May 2005 (UTC) =="See also" section is redundant...== ...and should thus be removed. Topics already covered in text clearly need not be repeated, and related topics are handled by the category system. User:Fredrik | User talk:Fredrik 01:51, 18 Jan 2005 (UTC) :I copied the above statement out of the talk page archive as I fully agree and would like to start action. Does anybody see any link, which is nit in the prose, but so central, that it should be preserved. --User:Pjacobi 15:11, 2005 Feb 6 (UTC) ::I agree with this, so I took it out since nobody bothered to disagree. The links in the see also section were seemingly chosen at random, and most of them were already in the text somewhere. --User:Joke137 17:50, 4 May 2005 (UTC) == Dark matter and energy == I moved the "Dark Energy" subsection after "Globular Cluster Age" because it led so nicely into the next section, but now I see that it also followed "Dark Matter" nicely. So I'll let others decide whether to move it back. Also, each "standard problem" is bolded (horizon problem, flatness problem, etc. I don't think this adds anything to most of the subsections—but it would make me smile to see dark matter and dark energy in dark type. Too frivolous? —User:JerryFriedman 19:37, 4 May 2005 (UTC) == CMB == I really don't understand the reference to symmetry breaking in the CMB section. The radiation was in equilibrium from the end of baryogenesis to photon decoupling, wasn't it? --User:Joke137 01:58, 16 May 2005 (UTC) :It is in the sense of symmetry breaking being a feature of traveling out of thermal equilibrium... but I can see that it isn't the most standard use of the term. Rewording it is fine. User:Joshuaschroeder 04:02, 16 May 2005 (UTC) =='A' or 'The' Theory?== User:Joshuaschroeder: While the big bang is the ''best'' theory at explaining the beginning of the universe, shouldn't we represent it as "a" theory, not "the" theory? As is noted in Wikipedia:Scientific point of view, Wikipedia should include all scientific views. However, we can still characterize the theory as the most widely accepted. —User:Joe Jarvis 02:56, May 30, 2005 (UTC) :If you read the opening sentence it clearly states that the "Big Bang is the scientific theory that describes the early development and shape of the universe". No other idea from inside or outside the scientific establishment that has been put forward does that. The now discredited steady state model doesn't do it, and neither do the protestations of Halton Arp, et al. or the plasma cosmology folks. The Big Bang is a paradigmatic formalism in cosmology, similar to the way in which Maxwell's Equations as "the set of four equations, attributed to James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter". Even though there are those people who think some parts of Maxwell's Equations are wrong (magnetic monopoles for example, may exist), we still use the definitive article because that is the way science works. You can peruse the science pages here on wikipedia for myriad more examples. True scientific theories, by definition, don't lend themselves to concessions of plurality because there can be only one theory available that describes the observations. In the case of the Big Bang, it (and nothing else) is the one theory available that describes the observations. This has nothing to do with being "neutral", it has to do with reporting the facts about a scientific theory and its applicability to the natural universe. User:Joshuaschroeder 14:00, 30 May 2005 (UTC) ::Sorry, you are mistaken. There are plenty of theories that purport to describe the "early development and shape of the universe" (see Roman, Hindu, or Maori creation myths for example), and even if there were none, that doesn't mean there can't be any more in the future, so this is definitely ''a'' theory. ::The Big Bang is not comparable to Maxwell's equations in this regard. The latter deal with these so-called "electric and magnetic fields", which are a convenient mathematical construct that explains observed phenomena. The Big Bang deals with the universe itself. --User:P3d0 19:18, May 31, 2005 (UTC) :::I've clarified to ''In physical cosmology'', so the first objection is void. The second objection is a mis-interpretation, how physics is done. The Big Band Theory, as well as Maxwell's equations, is concerned about observable phenomena. --User:Pjacobi 19:24, 2005 May 31 (UTC) ::::Ok, but, it's still a simple matter: the Big Bang theory claims the universe started with a large explosion at some finite time in the past. There are alternative explanations for the "early development and shape of the universe". Ergo, the Big Bang is not ''the'' theory, regardless of how much evidence that we have, just like "round earth" theory is ''a'' theory of the shape of the Earth, no matter how convinced you are personally that it is the correct theory. ::::Joshuaschroeder said "No other idea from inside or outside the scientific establishment that has been put forward does that." Even if true, this doesn't make it ''the'' theory; it only makes it ''the first'' such theory. If I claims that the diamond crystals in Pluto's core are arranged in a happy face shape, I don't get to claim that the Diamond Happy Face theory is ''the'' theory of the arrangement of diamonds in Pluto's core, just because nobody else has come up with a competing theory yet. ::::Besides which, even if you believe that it is ''the'' theory, then saying ''a'' theory is still correct, and I think it's reasonable for an encyclopedia to take the less contentions route. --User:P3d0 19:15, Jun 1, 2005 (UTC) :::::Accepted: The Big Bang theory is not the only theory describing the history of the universe. Many others have been proposed, believed, discredited, or left open to debate. Perhaps there are more to come. That does not matter. As this article is written today, it does not claim to be the only theory. It says (abbreviated) that the Big Bang is the theory that the universe started as an "explosion" of space. That is correct. It is the only theory that postulates that origin. (Or rather, it subsumes all such theories.) User:Chris Mid 00:43, 15 Jun 2005 (UTC) == Correction == The big bang was not an explosion as we are used to think of it. It was not a normal explosion in space, it was an explosion of space. When the universe inflated, new space was created (see image. http://www.nasa.gov/images/content/56200main_dark_expansion-lg.jpg. That's the way it was according to general relativity. See also the balloon analogy and dark energy. Take note that the big-bang model is based on two assumptions. The first is that Albert Einstein's general theory of relativity correctly describes the gravitational interaction of all matter. The second assumption, called the cosmological principle, states that an observer's view of the universe depends neither on the direction in which he looks nor on his location. This principle applies only to the large-scale properties of the universe, but it does imply that the universe has no edge, so that the big-bang origin occurred not at a particular point in space but rather throughout space at the same time. These two assumptions make it possible to calculate the history of the cosmos after a certain epoch called the Planck time. Scientists have yet to determine what prevailed before Planck time. User:Joshuaschroeder 16:02, 23 Mar 2005 (UTC) And those who think this is philosophy, what do you think the big bang is other than philosophy? What is general relativity if not philosophy? -- User:Orionix 14:14, 18 Mar 2005 (UTC) The Big Bang need not be described as an "explosion" at all. That's a holdover and a misnomer. User:Joshuaschroeder 16:02, 23 Mar 2005 (UTC) I think the problem with the "explosion" concept is that the less sophisticated reader tends to assume that an explosion exists in a small space within a larger (perhaps low density) one. The balloon analogy more or less handles that one, but suggests too strongly a positively curved space-section, and also implies, even when one is careful, that there are more dimensions in which the space being discussed is imbedded. Seems to me that there must be some good elementary/novice level discussions one could borrow from. I think Abell once used an expanding, leavened cake with raisins in it. Finally, I think one has to be open about open questions, such as what could have come before the big bang, and what was its "cause". We are all used to cause and effect in a limited context, and it may or may not be meaningful to treat these issues, but I doubt that they will be settled or very much clarified on these pages. Best to sum up in a very few pithy sentences that we are approaching the limits of present theories so it is a research area. User:Pdn 04:06, 2 Jun 2005 (UTC) I agree. I am very uncomfortable with the new introduction, because it leads to exactly the sorts of confusion User:Pdn mentioned. –User:Joke137 13:51, 2 Jun 2005 (UTC) Ok, I made a rather lame attempt to fix this by calling it an "explosion of space itself", but please feel free to re-edit it if this is still not good enough. I was just trying to achieve the following things: # Indicate that the universe used to be much smaller (not just denser) # Give some explanation as to why it's called a "bang" # Give the lay person an initial gut feel for what is involved in such a colossal bang Of course, accuracy is the paramount consideration. --User:P3d0 14:43, Jun 2, 2005 (UTC) Incidentally, if anyone objects to the idea that the Big Bang necessarily implies a singularity, we had better change the caption on the first image. --User:P3d0 15:28, Jun 2, 2005 (UTC) == Standard Problems == I would like to change the name of this section. Does anyone have any ideas? It's confusing: why are the problems "standard"? I have a suspicion that it refers to the standard problems resolved by cosmic inflation, but that only applies to the first three. –User:Joke137 15:56, 2 Jun 2005 (UTC) == Reversion == Someone changed the page to say it was about a "geometric" theory and other nonsense - of course there's a lot of physics in the CBR, synthesis of He (and traces of Be, Li) so it was just an attempt to downgrade the theory and I reverted it. User:Pdn 03:32, 9 Jun 2005 (UTC) :What about the addition in the Overview section reading: "It appears that the redshift research performed by Halton Arp in the 1960's is now more respected within the scientific community (not to mention the theological community). In 2005 and many scientists now prefer the steady-state theory over the Big Bang theory based up recent findings that support Arp's theories."? I don't think this is accurate and might be lost in the recent reverts. User:JHG 08:03, 9 Jun 2005 (UTC) ::Removed. --User:P3d0 12:33, Jun 9, 2005 (UTC) == Singularity or not singularity? == Is there some reason we're being so careful not to commit ourselves to the concept of a gravitational singularity? Does anyone have a reference that indicates that some scientists consider the singularity to be in doubt? --User:P3d0 12:48, Jun 9, 2005 (UTC) Yes. I think most theories of quantum gravity attempt to eliminate the singularity. As it exists in general relativity, the singularity is a bad thing because it is not predictive. In no particular order, a list of attempts to resolve the singularity: * Loop quantum gravity uses some technology to show that the superspace volume operator is bounded below (so that there is a minimum volume of space that can exist). *String theory has some other ideas, some of which have to do with making singularities more fuzzy and some of which have to do with "resolving" the singularity by various mathematical tricks. *The Hartle-Hawking state try to show that there is a unique, non-singular initial condition for the universe determined by some criteria or other. *Brane cosmology may resolve the singularity by saying that, while it looks catastrophic in four dimensions, in a higher dimensional theory it is a less singular event, like the collision of two membranes. *People used to think cosmic inflation resolved the singularity problem, but it turns out that inflation cannot go on eternally to the past, because de Sitter space is unstable. *People used to believe that the singularity predicted by general relativity was a mere accident due to the high degree of symmetry of the Friedmann-Lema�tre-Robertson-Walker universe, and that the universe would actually contract to a very dense state and start expanding again: the oscillatory universe. This idea was disproved by Steven Hawking in 1967, and it was shown that you would need to resort to quantum mechanics or exotic forms of matter to make the universe bounce in that way. I could dig up references for any of these things, but it is hard to see where to start.–User:Joke137 18:40, 9 Jun 2005 (UTC) == What About before the primeval atom? == I was looking for information on the origin of the universe and studied the big bang theory for a few years but i kept coming back to what came before the primeval atom? what caused or "created it?" how did it come into exsistence? :those questions are referenced in the second-to-last question in the article. User:Joshuaschroeder 12:56, 19 Jun 2005 (UTC) == Apparent Expansion == Does anyone have any additional information regarding apparent expansion? It seems plausible, but would require some more details. :The "apparent expansion" that was included in the article did not belong here and was removed. User:Joshuaschroeder 13:42, 22 Jun 2005 (UTC) == Milne Model? == I think you may be referring ("Apparent Expansion") to the Milne model. It is no longer acceptable but is dealt with in [http://arxiv.org/PS_cache/astro-ph/pdf/0503/0503690.pdf] as well as Rindler's and John D. North's books, I believe. If you mean something else, plz so state.User:Pdn 12:03, 22 Jun 2005 (UTC) Actually, the Milne model still defines a universal edge. Apparent Expansion says there is no edge. Like in the illustration of a sphere whose side continues in all directions with no edge, or the premise that the universe leads to an infinite number of multiple universes, so if you traveled in one direction for long enough, you would apparently return to the same place (and the same time) you left from. The premise behind apparent expansion is the fact that there appears to be no center of expansion, but rather everything is expanding uniformly. Picture a galaxy at 5 million light years away. Now assume that beyond it there are five galaxies, say around 7-8 mln. light years away. And beyond that, at 10-12, twenty-five, and so on, to infinity. Let's assume the gravity of the more distant galaxies (and remember, we're assuming their amount is infinite) is always pulling the galaxy at 5 light years away farther away from us, we being the centre of the universe from our perspective (although threre can be no centre except relatively). We can follow the same example for those galaxies 7-8 million light years away, and so on. The farther the galaxy the fast it seems to be moving, but only relatively. It is obvious that in the galaxy 5 mln light years away, the further galaxies would seem to move at a slower rate than is apparent on earth. The whole model draws from the fact that according to quantum physics there is no universal edge or universal centre, things imperative for the big bang to make sense.--User:ChadThomson 03:36, 23 Jun 2005 (UTC) : Several of these statements are puzzling. In particular, as the universe's distribution is approximately uniform on large scales, the galaxy 5 million LY away wouldn't be pulled away from us by gravity, but would stay in the same position relative to us, if space itself were not expanding (it sees equal amounts of matter on all sides of it). If space _is_ uniformly expanding, per the big bang model, then there is nothing magical needed in order to explain that more distant galaxies are moving faster, relative to you, than nearby ones no matter where you stand, so I'm not seeing what you're trying to add. Secondly, I am reasonably familiar with "quantum physics", and I don't see how the claims you ascribe to it are drawn from it (it can deal with bounded systems just fine, and the idea that our place in the universe should _not_ be assumed to be special predates it by centuries). If you could cite a few papers that take the position you are trying to illustrate, that would perhaps be a better source to draw material from. --User:Christopher Thomas 04:42, 23 Jun 2005 (UTC) :: I guess my question would be this: to what degree is space expanding? Is the space between atoms' nuclei and electrons also expanding? We could never find out, because we, the observers, would be expanding at the same rate as everything else. Even so, the idea is ridiculous, as the atomic force keeps the atoms the way they are. And why are the galaxies moving away from each othe