Einstein's general theory of relativity predicted that time-space started at the Big Bang singularity and it would reach at the end at the Big Crunch (if the whole universe would indeed suffer again a collapse ) or a singularity in the interior of a black hole (if a local region, like a star, would suffer a collapse ).
It is needed to explain briefly the general accepted history of the universe, which is according with what is known as "the hot Big Bang model". This involves that the universe is described back until the Big Bang using a Friedmann model. According to this model, when the universe is expanding ,matter or the radiation from in it cools down. Because temperature is a measure of the average energy(or speed)of particles, this cooling of the universe should have an important effect upon the matter in it.
At the Big Bang, it is believed that the universe had 0 size and so it was infinitely hot. As the universe was expanding, the radiation temperature would have diminish .A second after Big bang, it would have diminished to 10 10degrees At approximately 100 seconds from Big Bang, the temperature would have dropped to 1 billion degrees. In a few hours before Big Bang, the production of helium and other elements stopped .And after that, in the next million years the universe would have keep expanding, nothing much happening. Finally, once the temperature dropped at a few thousand degrees, the electrons and the nucleuses would have started combining themselves forming atoms. The universe continued to expand and to cool, but in regions that were less dens than the media, the expansion would have been slowed down by the extra gravitational attraction. It would eventually stop the expansion in some regions and would determine them to produce again the collapse. During this, the gravitational attraction of matter outside this region can make them spin easily .As the region was getting smaller, it would spin faster. In the end, as the region becomes smalls enough, it would spin fast enough to balance the gravitational attraction and thus the rotating galaxies were born, disc shaped. Other regions that didn't started to spin became oval shaped objects, called elliptical galaxies.
As time was flowing, hydrogen and helium from the galaxies would brake in smaller clouds that would suffer a collapse under there own gravity. When they contract and the atoms inside collide between them, the gas temperature would become high enough to start the nuclear fusion reactions. These reactions convert hydrogen into more helium and the heat resulted from this process determines pressure to increase and so the ending of the clouds contraction. The reactions stay stable enough like stars similar to our sun, which transforms hydrogen into helium and radiates the resulting energy as heat and light.
Will the galaxies continue to fly apart forever, their glow fading until the cosmos is cold and dark? Or will the expansion slow to a halt, reverse direction and send 10 octillion (10 trillion billion) stars crashing back together in a final, apocalyptic Big Crunch, the mirror image of the universe's explosive birth? Despite decades of observations with the most powerful telescopes at their disposal, astronomers simply haven't been able to decide.
The latest news from space would be profoundly significant; understanding where we came from and where we are headed have been obsessions of thinking humans, probably for as long as we've walked the earth. But the particulars of these discoveries shed light on even deeper mysteries of the cosmos, lending powerful support to radical ideas once considered speculative at best. For one thing, the new observations bolster the theory of inflation: the notion that the universe went through a period of turbocharged expansion before it was a trillionth of a second old, flying apart (in apparent, but not actual, contradiction of Albert Einstein's theories of relativity) faster than the speed of light.
An equally bizarre implication is that the universe is pervaded with a strange sort of "antigravity," a concept originally proposed by and later abandoned by Einstein as the greatest blunder of his life. This force, which has lately been dubbed "dark energy," isn't just keeping the expansion from slowing down, it's making the universe fly apart faster and faster all the time, like a rocket ship with the throttle wide open.
It gets stranger still. Not only does dark energy swamp ordinary gravity but an invisible substance known to scientists as "dark matter" also seems to outweigh the ordinary stuff of stars, planets and people by a factor of 10 to 1. These mind-bending discoveries raise more questions than they answer. For example, just because scientists know dark matter is there doesn't mean they understand what it really is. Same goes for dark energy. "If you thought the universe was hard to comprehend before," says University of Chicago astrophysicist Michael Turner, "then you'd better take some smart pills, because it's only going to get worse."
Tens of billions of years from now, the Milky Way will be the only galaxy we're directly aware of (other nearby galaxies, including the Large Magellanic Cloud and the Andromeda galaxy, will have drifted into, and merged with, the Milky Way).
By then the sun will have shrunk to a white dwarf, giving little light and even less heat to whatever is left of Earth, and entered a long, lingering death that could last 100 trillion years-or a thousand times longer than the cosmos has existed to date. The same will happen to most other stars, although a few will end their lives as blazing supernovas. Finally, though, all that will be left in the cosmos will be black holes, the burnt-out cinders of stars and the dead husks of planets. The universe will be cold and black.
But that's not the end, according to University of Michigan astrophysicist Fred Adams. An expert on the fate of the cosmos and co-author with Greg Laughlin of The Five Ages of the Universe (Touchstone Books; 2000), Adams predicts that all this dead matter will eventually collapse into black holes. By the time the universe is 1 trillion trillion trillion trillion trillion trillion years old, the black holes themselves will disintegrate into stray particles, which will bind loosely to form individual "atoms" larger than the size of today's universe.
If the latest results do hold up, some of the most important questions in cosmology-how old the universe is, what it's made of and how it will end-will have been answered, only about 70 years after they were first posed..