Historical Models of the Universe ------------------------------- The Friedmann model, which we examined in some detail, is only one of the many possible interpretations of Einstein's descriptions of the universe. We look at some of the others, now only of historical interest. We start with the genralized equations of the cosmos, where no presumption is made about LAMBDA and k. These equations were developed by LeMaitre in 1931. LeMaitre was unaware of Friedmann's work of 1922. To honor the two for arriving at virtually the same equations, these generalized equations are called the Friedmann- LeMaitre equations. LeMaitre championed the Friedmann model because it had a definite beginning for the universe, the moment for R = 0. He could not stomach the deSitter and Einstein models with their infinite prior existence for the universe. The universe to LeMaitre had to have a real and definitive origin. He called the state of R = 0 the 'primoidal atom'. +---------------------------------------------------+ | FRIEDMANN-LEMAITRE EQUATIONS OF THE UNIVERSE | | | | 2der(R,t) = -4 * pi * gamma * rho0 / (3 * R^2)) | +| + LAMBDA * R / 3 | | | | | 1der(R,t)^2 / 2 = 4 * pi * gamma * rho0 / (3 * R) | | + LAMBDA * R^2 / 6 - k * c^2 | +---------------------------------------------------+ We also have the definitions of H and q +----------------------------------+ | FRIEDMANN-LEMAITRE DEFINITIONS | | OF H AND q | | | | H = 1der(R,t) / R | | | | q = -R * 2der(R,t) / 1der(R,t)^2 | | = -2der(R,t) / (R * H^2) | +----------------------------------+ The Friedmann-LeMaitre equations can be thrown into a form involving LAMBDA, k, H and q. First for LAMBDA 2der(R,t) = -4 * pi * gamma * rho0 / (3 * R^2) + LAMBDA * R / 3 2der(R,t) / (R * H^2) * (R * H^2) = -4 * pi * gamma * rho0 / (3 * R2) LAMBDA * R / 3 -q * R * H^2 = -4 * pi * gamma * rho0 / (3 * R^2) + LAMBDA * R / 3 q * R * H^2 = 4 * pi * gamma * rho0 / (3 * R^2) + LAMBDA * R / 3 LAMBDA * R / 3 = 4 * pi * gamma * rho0 / (3 * R^2) - q * R * H^2 LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 Then for k 1der(R,t)^2 / 2 = 4 * pi * gamma * rho0 / (3 * R) + LAMBDA * R^2 / 6 - k * c^2 = 4 * pi * gamma * rho0 / (3 * R) + (4 * pi * gamma * rho0 / R^3 - 3 * q * H^2) * R^2 / 6 - k * c^2 = 4 * pi * gamma * rho0 / (3 * R) + 2 * pi * gamma * rho0 / (3 * R) - q * H^2 * R^2 / 2 - k *c^2 = 6 * pi * gamma * rho0 / (3 * R) - q * H^2 * R^2 / 2 - k * c^2 1der(R,t)^2 = 12 * pi * gamma * rho0 / (3 * R) - q * H^2 * R^2 - 2 * k * c^2 = 4 * pi * gamma * rho0 / R - q * H^2 * R^2 - 2 * k * c^2 1der(R,t)^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - q * H^2 - 2 * k * c^2 / R^2 H^2 = 4 * pi * gamma * rho0 / R^3 - q * H^2 - 2 * k * c^2 / R^2 2 * k * c^2 / R^2 + H^2 = 4 * pi * gamma * rho0 / R^3 - q * H^2 2 * k * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - q * H^2 - H^2 = 4 * pi * gamma * rho0 / R^3 + (-q -1) * H^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 +------------------------------------------------------------------+ | EQUATIONS RELATING LAMBDA, k, H, AND q | | | | LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 | | | | 2 * k * c*2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 | +------------------------------------------------------------------+ In principle all the quantities on the right of these two equations are directly observable and mensurable, thereby firmly fixing the values for k and LAMBDA. Diversity of Cosmological Models ------------------------------ The Einstein relativity theory can make rather specific predictions about so many aspects of the world around us and then turn uncertain in describing uniquely the world itself! This shortcoming comes from the uncertainty in the parameters needed to apply Einstein physics to the cosmos as a whole. On this cause there derived from it not merely several knids of universe but very different ones. Universes with no mass, with no gravity, with diffuse matter evenly spread thruout, with Euclid geometry, with momEuclid geometry, with the lambda force, with no lambda force, &c, &c. How can this be when in so many other situations the Einstein system is pretty much right on the money? No one knows. There are hundreds of distinct models of the universe but most are mathematical manipulations having little to do with the observable world. Others probably deserve renewed study. The models described here include the famous ones and a bunch of lesser fame. We give a few paragraphs for each because the models are highly evolved in their maths and physics. However for those in the Friedmann-LeMaitre family we do give some of details. The models are laid out in alpha order over the next several sections. The models are named for their inventors or promotors. cosmology was -- and is -- a close-knit disciline. A model promoted by a one nat have features contributed by others. Yhe models are discussed roughly in time dequence. Some decades had several current models. Einstein (Original) Universe -------------------------- Einstein -- and most scientists -- believed in the mid 1910s that the universe was static and enduring. Those who suggested that the spiral nebulae were whole other Milky Ways assumed that these other systems were sitting at rest quietly beyond the Milky Way. Others questioned the Milky Way as merely one of the galaxies, an 'island universe'. They asserted that all of space is filled with stars like within the Milky Way. In this millieu Einstein in 1917 set H = 0, R = 1. This made the model conform to the believed real world. For simplicity's sake Einstein allowed a uniform distribution of mass thruout the universe. Thus LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 = 4 * pi * gamma * rho0 / 1 - 3 * q *H^2 = 4 * pi * gamma * rho0 - 0 = 4 * pi * gamma * rho0 2 * k * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 = 4 * pi * gamma * rho0 / 1 - (q + 1) * H^2 = 4 * pi * gamma * rho0 - (q + 1) * 0 = 4 * pi * gamma * rho0 - 0 = 4 * pi * gamma * rho0 = LAMBDA LAMBDA is equal to 4*pi*gamma*rho0, which is essentialy the collapsive force due to the universe's self-gravitation. LAMBDA is itself a 'force', exactly equal in magnitude, but opposite in direction, to the gravity force. LAMBDA exactly counteracts the collapse and maintains a static cosmos. Moreover, Einstein believed strongly that the universe must have spherical geometry with k = +1. Einstein invented a cosmos of matter with no motion, matching the prevalent notions of the cosmos. This universe is dynamicly unstable. If rho0 changes by even the slightest amount, the equation unbalances and the left or right side dominates. The universe will begin either a runaway collapse or runaway expansion. A peculiar feature of the Einstein model is its frame of absolute reference! The matter all at rest within this universe constitutes a coordinate system against which absolutr -- not just relative -- motion can be assessed. This feature gave Einstein all levels of fits. +--------------------------------+ | EINSTEIN ORIGINAL UNIVERSE | | | | LAMBDA = 4 * pi * gamma * rho0 | | | | k = +1 | | | | q = not applicable | +--------------------------------+ deSitter Universe --------------- deSitter in 1917 held that the universe is actually empty. Only the Milky Way -- with the spiral nebulae within it -- occupried the whole of infinite space. He also believed in a flat cosmic geometry. These premises make k = 0 and rho = 0. deSitter objected to the innate instability of the Einstein model. It could not prevail today, butt already would have collapsed or dissipated. According to deSitter LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 = 4 * pi * gamma * 0 / R^3 - 3 * q * H^2 = 0 - 3 * q * H^2 = -3 * q * H^2 2 * k * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) *H^2 = 4 * pi * gamma * 0 / R^3 - (q + 1) * H^2 = 0 - (q + 1) * H^2 = -(q + 1) * H^2 2 * 0 * c^2 / R^2 = -(q + 1) * H^2 0 = -(q + 1) * H^2 which is satisfied only by q+1 = 0 q + 1 = 0 q = -1 Then LAMBDA = -3 * q * H^2 = -3 * (-1) * H^2 = 3 * H^2 Here we have a situation where there is motion with no matter! Raw empty space just continuously outswells and dissipates and expands on its own! The LAMBDA repulsion force has no gravity force to check it and the universe simply grows without limit. At all times the geometry is flat, like a Euclid plane. deSitter postulated that this continuous expansion could be monitored if there were visible specks, cosmic confetti, sprinkled in space. He, thus, is the first person to actually formulate the notion of the expanding universe. He could not then appreciate that the universe IS filled with cosmic confetti! The luminous specks are the galaxies! In the early 1920s some astronomers argued for the extragalactic nature of the spiral nebulae BECAUSE they exhibited redshifts indicative of the deSitter expansion! +-------------------+ | deSITTER UNIVERSE | | | | LAMBDA = 3 * H^2 | | | | k = 0 | | | | q = -1 | +-------------------+ Einstein-deSitter Universe ------------------------ This model has LAMBDA = 0 and k = 0 and was developed by Einstein & deSitter in 1932. It is a sort of compromise between their earlier individual schemes. In this, now the 'standard' model, Einstein did away with his cosmological constant or lambda force, being that the universe was now observed to expand. later cosmologists and astronomers noted that Einstein's invention of lambda force in his first model was the biggest mistake he ever made in science. 2 * k * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 2 * 0 * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 0 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 (q + 1) * H^2 = 4 * pi * gamma * rho0 / R^3 q + 1 = 4 * pi * gamma * rho0 / (R^3 * H^2) LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 0 = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 3 * q * H^2 = 4 * pi * gamma * rho0 / R^3 3 * q = 4 * pi * gamma * rho0 / (R^3 * H^2) = q + 1 2 * q = 1 q = 1/2 Which is exactly the result we obtained from the detailed analysis; this is the deceleration parameter. Note that in the Einstein-deSitter universe rho is a derived quantity to satisfy k = 0 and q = 1/2. Thus 4 * pi * gamma * rho0 / (R^3 * H^2) = q + 1 4 * pi * gamma * rho0 / (3 * H^2) = 3/2 rho0 / R^3 = rho = (3/2) * H^2 / (4 * pi * gamma) = 3 * H^2 / (8 * pi * gamma) Which is exactly what we obtained from the detailed analysis. This is the closure or critical density. +----------------------------+ | EINSTEIN-deSITTER UNIVERSE | | | | LAMBDA = 0 | | | | k = 0 | | | | q = 1/2 | +----------------------------+ Eddington Universe ---------------- From the one relativity theory come simultaneously and independently two completely different models of universe! Both enjoy infinite past life. One, by Einstein, has a uniform distridution of matter and the other, by deSitter, has no matter at all. One stays static (in the absence of disturbances) and the other continually swells ever outward. Both had strong adhaerents in the late 1910s and early 1920s. In fact, both satisfied a very prevalent assumption. The universe had no specific beginning but lived for all past time. Furthermore, the Einstein and the deSitter models were for a decade merely mathematical exercises with no appeal to astronomy. Largely this was due to the unawareness of the galaxies and of the Hubble expansion. These were not announced until the mid 1920s. Eddington was the first regular astronomer to apply realtivity to astronomy and to elaborate a cosmological model. Previous workers were mathematicians or physicists. He in 1927 favored the infinite life in the past for the universe and believed in the expansion feature of deSitter. However, he felt that the universe had a indefinite prior life as an Einstein system and then suffered a disturbance. This may have been the condensation of gas clouds into galaxies. This triggered runaway expansion, which persists to the present era. leMaitre Universe --------------- leMaitre in 1931 cooked up a universe that began as a Friedmann universe with a closed and spherical geometry. When the universe reached the maximum scalefactor under this expansion mode it switched to a deSitter expansion, which we are in at the present epoch. He took this route becuase he knew only of the closed solution, k = +1, of the Friedmann model and could not stomach the ultimate destiny of it in a colossal collapse. leMaitre was the first to assert an actual bigbang origin for the universe. Altho Friedmann postulated a zero volume origin, he never applied it to the realities of astronomy. leMaitre, on the other hand, insisted that the universe must have a definite creation, mainly from his profession as an abbe. leMaitre held that the universe really did begin as a 'primaeval atom' about the diameter of the Earth's orbit and as dense as the atomic nucleus. It by some superfission exploded into the universe we live in. Later in 1950 leMatire added a 'dwell' phase, when R remains constant for some long while, between the initial Friedmann expansion and the later deSitter expansion. This accommodated new finds from geology and astrophysics which greatly lengthened the known age of the universe. The original model now had too short a lifespan and had to be somehow stretched out. The dwell phase at constant R was to leMaitre the period of galaxy formation, a process requiring a billion years or so. Once fully developed, the galaxies could begin their present expansion along the deSitter part of his model. Tolman (Oscillating) Universe --------------------------- In 1934 Tolman believed in a closed universe that will in time undergo a colossal collapse. Moew over he noted that the collapse is followed by the birth of a new universe, separate and distinct from the old. That is, the universe oscillates or cycles between bigbang and colossal collapse over and over again. In the collapse all identity from the previous world is lost and the new one starts off with all-new physics. The values of the physical constants are in general unrelated to their old values. However, the one thing that does percolate across the collapse is the entropy of the old universe. The new universe sets off with a base entropy equal to that of the old at collapse. Because entropy continuously increases during the life of the universe, each successive universe has greater and greater entropy. The oscillating universe was abandoned when the standard bigbang model was generally accepted, which has but a single world expanding into infinite future time. Never the less the Tolman model is resurrected from time to time, as by Landsberg and by Wheeler in 1975. leMaitre-Tolman Universe ---------------------- leMaitre in 1933 came up with the first nonhomogenous solution for the description of the universe. Previous models and most current ones assume the universe to be smooth and uniform thruout. Tolman continued leMaitre's work in 1934, but did not actually collaborate with him. In this model there are cells of uniformity and smoothness in the universe within which the Friedmann scenarios operate. Each cell is isolated from the others and behaves like a miniuniverse with its own bigbang and Hubble expansion regime. The geometries of the cells depend on their individual densities and may be hyperbolic. planar, or spherical. Some cells are in expansion while others are contracting. With this model leMaitre & Tolman were first to sugget a multiverse scehem for the cosmos. That we may live in one cell within a many-cellled world is revived from time to time, often in ignorance of leMaitre & Tolman. Milne Universe ------------ Milne in 1935 developed a cosmology based on the absence of gravity! The universe is entirely kinematic with no forces at all! In this scheme LAMBDA = 0 and gamma = 0. 2 * k * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) * H^2 = 4 * pi * 0 * rho0 / R^3 - (q + 1) * H^2 = 0 - (q + 1) * H^2 = -(q + 1) * H^2 = -(0 + 1) * H^2 = -H^2 which only k = -1 can satisfy k = -1 LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 = 4 * pi * 0 * rho0 / R^3 - 3 * q * H^2 = 0 - 3 * q * H^2) = -3 * q * H^2 0 = -3 * q * H^2 which only q = 0 can satisfy q = 0 This universe, with mass but no gracity forcess, expands from a bigbang to infinite scalefactor at a constant H and no deceleration. +----------------+ | MILNE UNIVERSE | | | | LAMBDA = 0 | | | | k = 0 | | | | q = 0 | +----------------+ Dirac Universe ------------ Dirac in 1937 hit on the concept that the basic parameters of nature are somehow interrelated. He claimed that the ratio of the Couloumb and Newton force in an atom and that of the size of an atom and the universe were so similar that they must actually be equal. This, he concluded, meant that there was some inner connection between the cosmic and atomic worlds. One result of this reasoning was that the Newton constant varies with time. Fc = qe * qp / (4 * pi * epsilon0 * r^2) Fn = gamma * me * mp / r^2 where Fc is the Coulomb force; Fn, Newton force; qe, me, electric charge and mass of electron; qp, mp, charge and mass of proton. Fc / Fn = (qe * qp / (4 * pi * epsilon0 * r^2)) / (gamma * me * mp / r^2) = qe * qp / (4 * pi * epsilon0 * gamma * me * mp) = (1.602E-19c) * (1.602E-19c) * (8.988E9n.m^2/c^2) / (6.673E-11n.m^2/kg^2) * (9.109E-31kg) * (1.673E-28kg) = 2.268E39 ru = c * T0 re = qe^2 / (4 * pi * epsilon0 * me * c^2) where ru is the raddius of the universe; re, radius of electron. ru / re = (c * T0 / (qe^2 / (4 * pi * epsilon0 * me * c^2)) = me * c^3 * T0 * 4 * pi * epsilon0 / qe^2 = (9.109E-31kg) * (2.998E8m/s)^3 * (5.870E16s) / ((8.988E9n.m^2/c^2) * (1.602E-19c)^2) = 6.246E39 Altho the two ratios are off by about 3:1, Dirac laid the discrepancy to inaccurate values for the ingredients. The peculiar slug 1/(4*pi*epsilon0) comes up over and over again in electromagnetics and has the consolidated value 8.988E9n.m^2/c^2. It is the Couloumb constant, parallel to the Newton constant. epsilon0 is the permittivity of space, 8.854E-12c^2/n.m^2. Right away we see that T0 is far too low by today's estimation; it's based on Hubble's far too large H0. It was the best availabe at the time. There is also the issue of the 'radius' of an electron. Dirac treated the electron as a particle having a definible size. At any rate by forcing the equality Dirac found that some physical factor had to vary with time. Fc / Fn = ru / re qe * qp / ( 4 * pi * epsilon0 * gamma * me * mp) = me * c^3 * T0 * 4 * pi * epsilon0 / qe^2 The left side has all 'constants' while the right contains the variable T0. Clearly to Dirac certain of the 'constants' are actually functions of time. He chose gamma for he believed that all the others, coming from relativity and atomics, were somehow more basic and were truly constants. So gamma = qe^2 * qe * qp / (16 * pi^2 * epsilon0^2 * c^3 * me^2 * mp * T0)) = func(1/T0) The Newton constant decreases with time! This has all sorts of consequences in the evolution of the universe. But most cosmologists dismiss Dirac's number playing as so much mumbo-jumbo. The results are mere coincidence with no deeper meaning. And gamma really is invariant over time. Never the less some astronomers today are intrigued by the close approximation of these (and other) ratios of constants. Alpher-Bethe-Gamow Universe ------------------------- Until World War II cosmology was mostly geometric, with a crude attempt at phyiscal explanation by leMaitre. Following the war atomics emerged as a major division of physics. By accepting the Einstein- deSitter or Friedmann-leMaitre model, physicists tried to work out the early mix of nuclides under the high densities and temperatures near the bigbang moment. Alpher, Bethe, & Gamow in 1948 were the first to apply atomic physics to cosmology. They derived the observed mix of hydrogen, helium, and heavies from the initial bigbang state. This replication of the observed elemental alloy from the bigbang added strong support for the bigbang theory as a real historical origin for the universe. One result of their work was Gamow's 1948 prediction that there was a moment when the energy-dominated bigbang photosphere would dissolve into the present matter-dominated cosmos. We should be immersed in the residual photospheric radiation from that moment, whose temperature now should be about 5K. There was no way for about 15 years to hunt for this radiation, given that electronics were still too weak and radioastronomy was too new in 1948. A search for this relic background was started in 1964 by Dicke & Peebles but Penzias & Wilson found it first in 1965. Cosmologists generally regard this cosmic background radiation as almost a conclusinve proof of the bigbang theory. Even Hoyle threw up his hands and abdicated his competing steady-state theory. He quickly picked it up again with a steasy-state explanation of this radiation. 'Bigbang' ------- A-B-G, sometimes called the 'alpha-beta-gamma' team, did not coin the origin moment 'bigbang'. They merely descrined their model without a specific name. The name 'big bang', as two words, was coined by Hoyle, who with others proposed a rival cosmology, the steady state theory. Hoyle, contrary to legend, did not mean to ridicule Gamow's theory. He just wanted a short quick way to describe Gamow's scheme. Yes, the name stands today, often as one word. In the early 1990s Sky and Telescope magazine put up a contest to rename the bigbang model. It asked astronomers for replacement terms. S&T posted a judging panel that featured Carl Sagan, who just presented his 'Cosmos' TV series with 'big bang' freely cited thruout it. The project closed with no winner picked, S&T found that most entries were silly, spiteful, hostile. And just about all astronomers realized that Sagan will never adopt any new name for 'big bang'. Bondi-Gold (Steady State) Universe -------------------------------- This, the steady-state system, is included here for completeness in the summary of other cosmological models. Bondi & Gold in 1948 found a model extending the cosmological principle. In the other models the universe is the same at all positions at the same moment. But not at all moments. The universe evolves over time and R, rho, and H, for instance, are functions of time. Bondi & Gold asserted that the universe is the same in every place AND IN EVERY TIME. There is NO evolution. In this model LAMBDA = 0, H = H0, rho0/R^3 = rho = rho0. This makes R^3 = 1. The motivation for the steady-state model was to accommodate the observed Hubble expansion within a universe of infinite past life. Bondi & Gold had an abhorrence for the bigbang concept. 2 * k * c^2 / R^2 = 4 * pi * gamma * rho0 / R^3 - (q + 1) *H^2 2 * k0 * c^2 / R^2 = 4 * pi * gamma * rho0 / 1 -(q0 + 1) * H0^2 Because the right side is a constant, being made of all fixed quantities, the left side must also be a constant. It can not have a variable 1/R^2. To make the left side a constant, k0 = 0. k0 = 0 2 * 0 * c^2 / R^2 = -(q0 + 1) * H0^2 0 = -(q0 + 1) * H0^2 Because H0 is nonzero, only (q0+1) = 0 satisfies this equation q0 + 1 - 0 q0 = -1 LAMBDA = 4 * pi * gamma * rho0 / R^3 - 3 * q * H^2 = 4 * pi * gamma * rho0 / 1 - 3 * (-1) * H0^2 = 4 * pi * gamma * rho0 / 1 - 3 * (-1) * H0^2 = 4 * pi * gamma * rho0 + 3 * H0^2 = 0 4 * pi * gamma * rho0 = -3 * H0^2 Recall that rho0 and H0 DO NOT vary over time; these are NOT merely the instant values of rho and H. The universe does expand at a constant rate H0 yet the density of matter within it remains the same rho0. How can rho0 remain constant when the space containing it outswells, tending to decrease rho0? Bondi & Gold postulate that new matter is spontaneously created to maintain the fixed rho0. Any patch of the universe has a mix of 'old' matter carried apart by the expansion and 'new' matter formed to fill the regions vacated by the old. In this way the universe presents the same demeanor and guise not only everywhere but also everywhen. The rate of this continuous creation, according to Bondi & Gold, is essentially the rate of increase of volume as it is filled with new matter of density rho0 V = R^3 1der(V,t) = 3 * R^2 * 1der(R,t) = 3 * R^3 * (1der(R,t) / R) * R = 3 * R^3 * H0 rho0 * 1der(V,t) / V = 1der(m,t) / V = 3 * R^3 * H0 * rho0 / V = 3 * H0 * rho0 which with typical values for H0 and rho0 is 1der(m,t) / V = 3 * H0 * rho0 = 3 * (1.6E-18/s) * (4E-28kg/m^3) = 19.2E-46kg/s.m^3 This is an incomprehensibly tiny rate beyond all hope of detection. It is equivalent to about two Suns per cubic megalightyear per century! In practical terms it amounts to finding the two new stars created anywhere within the Milky Way and environs every 100 years! +---------------------+ | BONDI-GOLD UNIVERSE | | | | LAMBDA = 0 | | | | k = 0 | | | | q = -1 | +---------------------+ Godel Universe ------------ In the usual cosmological model there is a clear segregation between the past and the future. The light from other parts of the univerwe came from long ago times in the past while that leaving us will reach pther places some long time in the future. This is the separation of past and future lightcones. A 'lightcone' is the locus of lightrays (all EMR) converging onto or diverging outof a given point. The converging cone is the past lightcone; diverging, future. The cone analog comes from the representation of two dimensions of space and one of time in the x-y-ct system. In the real wolrd the 'cone' is the three-dimensional locus in x-y-z-ct spacetime. On a cylindrical surface, to cite a familiar geometry, two rays, forward and backward in time, at a point eventually intersect again elsewhere on the surface. A message on the forward ray could be passed to the backward ray at the intersection and modify its character. Godel first worked the details out in 1949: Events in the future can modulate events in the past! A ray of light from us is sent into spacetime with a message. Normally only a future observer can receive this message and act on it. In Godel's model that ray could be captured by a 'future' observer who transfers the message to a new ray directed at us. We ourselves can ultimately get that message -- from our own past -- and therby be influenced by it. From the eye of the lightray, it goes into the future to reach the past! This sounds so bizarre, like some kind of time travel, that the Godel universe today is not widely supported. Alfven-Klein Universe ------------------- Alfven & Klein in 1965 were the first to invoke plasma physics into cosmology. Their model postulates that the world was from infinite past time filled with a rarified fluid of plasma. This consisted of protons, electrons, positrons (antielectrons), and negatrons (antiprotons). The fluid was so sparse that the particles were too far apart to interact. At some moment a casual enhacement of local density collected the plasma into a contracting sphere under sel-fgravitation. As the material densified the particles began a violent reign of self annihilation. The resulting radiation was so intense that it heaved out the sphere to become the expanding univrse we now observe. This radiation is also the 2.7K relic radiation we see today. The expansion carried away the remaining matter so that the world today is half particles and half antis. They are separated by distance in segregated sections of the universe. Only at the boundaries between the sections do they touch to produce violent explosive events, which were discovered in the early 1960s. Arp Universe ---------- SInce the discovery of quasars in the early 1960s Arp has questioned their redshifts as caused by Hubble expansion. He claims that quasars are associated with regular, tho active, galaxies and are at the same distance away as them. The redshifts are produced by an as-yet incomprehensible process within the quasars. His evidence are alignments of quasars with galaxies, attachemnt of quasars to adjacent galaxies by bridges or threads, and foreground superposition of quasars on the image of a remoter galaxy. By Arp, the quasars are mixed in with galaxies and are not standing at the fartherst realms of the universe. In 1990 he turned off to the bigbang models and started to develop a steady-state scheme, based on the Bondi-Gold model. In the mid 1990s it is still unfinished. The crux of the Arp system, as gleaned from partial publications of it, is that the quasars are the seats of continuous creation and that they disperse and turn into galaxies. In this way the mean density of the universe is held stable. Hoyle-Narlikar Universe --------------------- Hoyle & Narlikar in 1964 developed a steady-state universe of the smae geometry as Bondi & Gold, but derived from electromagnetics as well as gravity. They were the first to incorporate electromagnetics into cosmology, it being only newly discovered thru radioastronomy. Prior models ignored electromagnetics as insignificant or unknown. In this model the cosmological redshift arises from the varying mass of the atoms causing the spectral lines. Mass increasess since the time the atom was created. The light is really enitted at the longer wavelength in remote past time and reamins fixed during the light's travel to us. There is no expansion redshift! When in 1965 the cosmic background radiation was found by Penzias & Wilson, Hoyle and other steasy-state promotors offered a novel expalantion for it. The radiation is merely stellar and other regular radiation which has been thermalized over vast travel distances into a low grade 2.7K heatflux. The thermalizing agent is alleged to be thin long 'whiskers' of iron supposedly a copious product of supernovae. Brans-Dicke Universe ------------------ Brans & Dicke in 1961 looked to replace Einstein physics with an all-new system and to base a cosmology on it. In the Brans-Dicke world gravity is a derived function of the scalefactor and it does not enter into the equations of the universe. Under this scheme the motions of bodies in space should be quite different from that predicted by Einstein. They tested the model on Mercury's perihelion, one of the crown tests used to prove relativity. They could make their model satisfy the observed perihelion excess by claiming a oblate Sun. But in solar eclispes of the 70s careful attention to the profile of the Sun turned up no oblateness. When the model was tested on other solar system phaenomenoa and tweeked into agreement, it became indistinguishable from Einstein relativity. With the necessity and convenience of the Brans-Dicke univere eroded, It was abandoned by 1980. EdeWitt (Many-Worlds) Universe --------------------------- By the 1970s cosmology had fused with quantum and atomic physics such that papers in the one field often appeared in journals of the others. The tools of quantum physics were applied to cosmology in many ways. One was that of deWitt in 1975. Quantum physics predicts the probablility of an event's many possible occurrences, like the spot on a screen where an electron will strike from a cathode ray tube. It can not tell which occurrence will take place for a given instance. Yet the electron somehow chooses a one and only one spot to hit on each instance. How? deWitt and his school interpret this behavior as the coexistence simultaneously of many worlds intertwined in the one space and time. Each world allows for each occurrence of a event. When the electron leaves the tube it 'jumps onto' one of the many universes, one that controls one of the spots on the screen. It 'rides' in that universe to the spot. On a second shot it may pick an other one of the universes and hit some other point. Thus we live in a multitude of worlds swopping in and out of our lifes at each occasion of a quantum event. The mechanism by which these worlds coexist is the subject of rather byzantine quantum physics far beyond this paper. Since the 1970s the many-worlds idea developed into that of multiverses nd is a large theme in a newer discipline of string cosmology. Guth (Inflationary) Universe -------------------------- One of the problems unexplained by the standard bigbang model is the horizon problem. If the universe expanded according to the Einstein-deSitter plan even the minutest deviation from pure uniformity and smoothness would have unraveled everything into a clumpy blotchy universe. But the cosmos is, under the standard model, uniform and smooth. In order to keep it so there must have been no chance for blotches and clumps to develop. Guth in 1981 theorized that the instant after the genesis the universe swelled instantly from the singularity to a certain finite size with all uniformity preserved. From this moment the Einstein-deSitter (or other Friedmann) expansion commenced. With nothing now to introduce the clumps and blotches these never formed and the universe remains uniform and smooth. This model is also called the inflationary universe from this initial vast inflation before the expansion phase. The Guth model is the first to be built from quantum physics. The earlier efforts at using quantum physics, as in the deWitt universe, were not thoroly worked out into free-standing cosmological models.