The future of the universe is a continuous and intriguent question, sofar without any definitive answer. But there many models giving more or less acceptable solutions.
The "collapsing model": which requires a strong density, much higher than the critical density, leading to a "big crunch", but that is in contradiction with all the data.
The "pure matter model" : requiring sufficient real matter in the universe, what certainly is not the case, it should lead to a rather constant expansion of the universe.
The "cosmological constant model": Einsteins' idea, based on the famous"vacuümenergy", it leads to a constant accelerated expansion of the universe. It means a more and more empty universe expanding for ever, an anathema for astronomers.
The "quintessence model":
The essential feature of this theory is the supposed dynamic of the quintessence field, in fact a quantumfield (scalarfield), what gives an acceptable explanation both for the inflation and the evolution of the universe, particularly for the fast expansion over the last billions years, including a solution for the difference in measured and calculated density. Anyhow, the theory requires the questionable Dark Energy (= vacuüm energy).
Another consequence of the theory is that there will be an ending to the condensation of matter, that is the creation of new stars and starsystems, the density of matter will continuously decrease and maybe the acceleration of the expansion will increase. But it is also possible be that with a declining quintessencefield new forms of radiation and dustforming evolve in creating and expanding “bubbles” of “empty space”, of which the envelopes absorb still more energy, what then can be the cause of the formation of new forms of protons and neutrons and perhaps, finally, stars and starsystems and perhaps life.
A nice predictive theory, but yet with many suppositions still to be proved.




All authors have as an established pattern always the Big Bang model assimilated in their theories. That model also comprises the Inflation theorie, the theory supposing a very fast expansion of the universe (within 10^-35 sec). In principle every cosmologist accepts that model.
It is worthwhile to underline that the idea many people have about the Big Bang, namely an explosion of dust in space from a specific point or something like that, is absolutely wrong:
What was before the Big Bang is unknown, but it is clear that the notion of time in the Planck - period (10^-44 sec) does not have any meaning, it is leading to a singularity at t = 0, where all quantities get infinite values, which is a horror for scientists.
To explain the situation in that first period there is a search for a theory coupling or integrating quantummechanics and relativity theory for which indeed stringtheory is the most promising at the moment.
In the model of the Big Bang after the creation of the universe, space and the distribution of matter therein is stricly bound: because of the tremendous high energy with very high temperatures there is no difference between fundamental particles, they have no mass and are converted in each other without problems. Just after a “phase transition”, to compare with condensation of vapour by decreasing temperature, massive particles are created with mass clotting together by gravitation forces. The inflationary expansion of the system with stars and galaxies means an expansion of space itself. The average density in space decreases and the distribution of matter forms no limitation to that space. In an “explosion” the fastest particles are moving to an empty space, in the Big Bang model particles fill space in an uniform way and expansion takes place from each point of that space. The expansion had little influence on the dimensions of galaxies and clusters, which were bound by gravitation, the space between the matter-objects has simply increased, to compare with plumcake: during baking the raisin dough will rise, there is no movement of the raisins with respect to the dough, yet distances between raisins increase because of the movement of the dough, the speed of the raisins with respect to each other is directly related to the quantity of dough between them.
Space expands “in the nothingness”, in the mean time material conglomerates are created, moving compulsary.
But as said before the Big Bang model involves also the "INFLATION" process: on the expected expansion a superfast expansion is superimposed.
The inflation theory implies that scalarfields cause the expansion in a very early phase of space evolution after the start of the Big Bang, in such a way that it may be considered to be an “explosion” (but is is not!) in a fraction of a second, that is within 10^-34 sec., resulting in an increase in size of 10^30!
Within the Planck-time: 10^-44 s, there was a situation that we still do not know or understand, A time t = 0 cannot physically exist because the infinite values physical quantities will get. An dark time so, of which the stringtheory states on the basis of mathematical considerations that you cannot even enter there, you simply will be sent back at the border, to say it that way, the sign of various quantities simply switches.
But let us assume a start with a very dense plasma at a very high temperature and a homogeneous radiation-dominated universe of unimaginable small size, which indicates that there is high, temperature-dependent potential-energy density, that large that it suggests a negative pressure, leading in a more or less natural way to a fast expansion.
During that expansion the potential energy decreases, transferring energy to the system.
Later on when matter is formed, temperature variations cause gravitational variations in matter density, from which in the long run objects are created nowadays observed by us on the firmament.
After the inflationperiod, that is after ~ 10^-35 s, there is the period of primordial nucleosynthesis, when from the original soup of elementary particles (quarks, gluons, electrons, etc.) protons and neutrons are formed, followed by the formation of the nucleï of light elements (He, Li, H), but then we are already a 100.000 year further in time, it is the time of “decoupling” or “recombination”. Radiation is yet hardly scattered and the photons get free way that is: maximum kinetic energy, the universe is “optically thin”. After this “last scattering” the CMB-RADIATION starts, the cosmic microwave backgound radiation.

We should realize that albeit that the original universe was very strong curved (three-dimensionally, the time-coordinate is usually not involved, but is certainly also curved!), we just see today a very, very small part of its “horizon”, such a small piece is suggesting a very flat spacetime compared with the related part of the original universe. (imagine the inflation of a balloon!).



The first stars may have 
lighted up the cosmos 
within 200 to 400 million 
years after the Big Bang, 
and then clustered together 
into what later became 
galaxies .

On November 2, 2005, a team of astronomers (including Alexander Kashlinsky, Richard G. Arendt, John Mather, and S. Harvey Moseley) using NASA's Spitzer Space Telescope announced the detection of near-infrared light that may radiated from the the very first stars and/or from hot gas falling into the first black holes more than 13 billion years ago . Based at NASA's Goddard Space Flight Center, the team captured a diffuse glow of infrared light six-months apart in Constellation Draco after the removal of light attributed to stars, galaxies, and artifacts of telescopic observation. The resulting near-infrared image shows a field of merging blobs of light that may have beem radiated by extremely massive Population III stars and/or superheated gas near black hole horizons within 200 to 400 million years after the Big Bang. Such a strong signal was detected that the first stars are deduced to be very massive stars, much bigger than those seen today. They may have been hundreds of times as massive as Sol, burning out in just a few million years but emitting vast amounts of ultraviolet radiation which was stretched out as the Universe expanded, leaving an infrared signature.



The Microwave Sky
WMAP has produced a new, more detailed picture of the infant universe. Colors indicate "warmer" (red) and "cooler" (blue) spots. This new information helps to pinpoint when the first stars formed and provides new clues about events that transpired in the first trillionth of a second of the universe.

The CMB Angular Spectrum

The "angular spectrum" of the fluctuations in the WMAP full-sky map. This shows the relative brightness of the "spots" in the map vs. the size of the spots. The shape of this curve contain a wealth of information about the history the universe.

There is a "black" period between the inflation process and the start of CMB - radiation (see article 46). We call that period "DARK AGES", the period where stars and systems were born. Fortunately there is a very poor radiation: "spin-radiation" , in the radio-frequency region with some cm's wavelength, which is stretched by the expansion up to some hundreds of meters. That radiation can yet be used to investigate that period, albeit that we need antenna's of kilometers length!.
The expansion goes on and on, even in an accelerated way since the last ~ 7 billion years!
For stopping the expansion of the universe dark matter is not the answer, (if dark matter should consist of normally matter formed from elements it can only exist in very short supply, otherwise the limit of the critical mass will be severely exceeded). If we take all observed resp. calculated stardust and dark matter (as defined in article 37) together, then it is still only a fraction of the critical mass necessary, less than 30%.
Therefore there must be another source of density compensating for the great deficiency in required density. That is the reason for the introduction of the notion “DARK ENERGY”, an energy being “invisible” but contributing to the density of the universe in order to reach the critical density (energy = mass!) . That energy is not just fantasy, it comes out that when it is added as extra mass to the universe to explain the now observed ever increasing expansion it fills up exactly the 70% deficiency in density.

The universe has been created from a very hot and dense “prehistoric soup”, a plasma of electrons and positrons, of various sorts neutrino’s with their antiparticles and of protons and neutrons. Photons were strongly bound, escaping was not possible, but fluctuations in density occur, that is “quantum noise”. When the temperature decreased by super-fast expansion of the universe, those fluctuations were isolated and blown up into inhomogeneous areas of various densities, where gravitational forces had the final word at last.
The masses in the inhomogenities were enormous, equal to stars or even galaxies. So 300.000 - 400.000 year after the inflationperiod, when the temperature has dropped to about 3000 K, the original fluctuations became all “frozen" in as anisotropies, that is: photons therein had no longer any pressure effect, they are no more bound, moving more or less free through space after their last scattering.
Those free photons give a radiation phenomenon: the CMB : COSMIC MICROWAVE BACKGROUND - radiation, which presents the temperature differences between small areas on the firmament against a continuous background. The temperature differences are “frozen” acoustic oscillations, mathematically expressed in a “powerspectrum”, (see figure).
The first large-scale measurements of CMB by the Cobe-satellite show a very homogeneous universe, with many small spots of just a bit higher or lower temperature (1 on 100.000!) from which finally the larger structures in the present day cosmos were formed, such as galaxies.
The intensity of light emitted as CMB-radiation shows an frequency distribution analogous to the spectrum of light, that is emitted by a black box with T = 2.7 Kelvin. That spectrum has a wavelength distribution with a peak at ~ 2 mm.
Be aware of the fact that the CMB - radiation has shifted from the highfrequency area (gamma-rays) to the microwave area today by the expansion of the universe during 13 billion years.

CMB - radiation is everywhere present in the universe, so also around ourself: about 1% of the noise on T.V. - screens is determined by that.
Those areas with different temperatures form also the basis of the matter in the present day universe: stars and galaxies, because it is supposed that the resulting density-anisotropies grew by gravitation forces to the objects now observed by us.
This proces of gravitational attraction, causing the accretion of matter around the original small fluctuations, forming still larger structures, is called: the “gravitational instability model” for the formation of the structure of the universe.




A supernova is a stellar explosion which produces an extremely bright object that fades to invisibility over weeks or months. A supernova may briefly overshine its entire galaxy, It would take bilions of years for the sun to produce the energy output of an ordinary Type II supernova. There are at least two possible routes to their formation. A massive star may cease to generate "fusion energy" from fusing the nuclei of atoms in its core and collapse under the force of its own gravity to form a neutron star or black hole. It is the Type II supernova.
Alternatively a white dwarf star may accumulate material from a companion star until it nears its "Chandrasekhar limit" ( 1.2 - 1.4 sunmasses), then it undergoes runaway nuclear fusion in its interior, completely disrupting it. This the Type I supernova.

TYPE I Supernova:
This type is the brightest kind of supernovae. The companion star is often a red giant. The process is sometimes called: "stellar cannibalism": the white dwarf soak up the outer layers of the red giant, increasing its mass, raising the temperature near the center. At some point carbon fusion is born causing within a period of only a few seconds the integral temperature to raise to billions of degrees. Then the star explodes violently, releasing a shockwave while matter is ejected at speeds of 5 - 20.000 km/sec (3 % of the light speed). The energy released in the explosion increases the luminosity up to
~ 5 x 10^9 times brighter than the sun, that's what we observe then.

TYPE II sueprnova:
Stars much more massive, typically more then eight solar masses, evolve in more complex fashions. First hydrogen is fused into helium, releasing energy which heats the core providing pressure against gravitation forces. The very high core mass stimulates further contraction as hydrogen is exhausted, inducing helium fusion, carbon fusion and fusing to progessively heavier elements. In between the core collapses further until iron is produced, the most stable atoms in nature, resulting in no more temperature raising, no more counterpressure and a density in the core of more than one million kg per cm3! This happens within seconds. Because of the enormous mass the star core collapses by gravitation, an unstoppable implosion, and a neutron star remains. Once the collapse stops, the infalling matter from the surrounding layers rebounds, producing a shockwave that propagates outwards causing the outer layers to explode.



August 30, 2006
X-Ray Burst Leads Scientists to See Supernova in Action
By David Biello
A star in a galaxy about 440 million light-years away released in a few seconds more energy than the sun will over the course of its entire lifetime, according to observations made on February 18. A high-energy jet of x-rays shot out from the doomed star's core and was captured by the Burst Alert Telescope on NASA's Swift satellite. The satellite relayed the information to astronomers on the ground, and within days a wide array of telescopes turned to the exploding object.
Meanwhile the other telescopes on Swift continued to observe the unusually long-lived burst; it lasted more than 30 minutes compared with other examples that flared up for only milliseconds. As the x-rays faded away, the star itself exploded in a spectacular supernova -- shown in the before (l) and after (r) images above -- the first such supernova to be observed from start to finish.
This supernova was half as bright as those typically preceded by such a burst, despite its emanating from a star 20 times as massive as the sun
Usually these events are not detected until after the supernova has brightened substantially. On this occasion, they were able to study the remarkable event in all its glory from the very beginning.



Astronomers using the NASA Hubble Space Telescope's Advanced Camera
for Surveys (ACS) have found two supernovae that exploded so long
ago they provide new clues about the accelerating universe and its
mysterious "dark energy." The supernovae are approximately 5 and
8 billion light-years from Earth. The farther one exploded so long ago the universe may still have been decelerating under its own gravity.

Type Ia supernovae are believed to be white dwarf stars that pull in
gas from an orbiting companion star. The white dwarf siphons off
mass until it hits a critical point where a thermonuclear "burning"
wave of oxygen, carbon, and heavier elements immolates the star in
a few seconds. The physics of the explosions is so similar from star
to star that all Type Ia supernovae glow at a predictable peak
brightness. This makes them reliable objects for calibrating vast
intergalactic distances

Information from studies of Type Ia supernovae confronted
astronomers about five years ago with the stunning, unexpected
revelation that galaxies appeared to be moving away from each other
at an ever-increasing speed. They have attributed this accelerating
expansion to a mysterious factor known as dark energy that is
believed to permeate the universe

Continued studies of supernovae will allow us to uncover the full
history of the universal expansion