2.A big bang (794198)
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A Big Bang
It all started with a Big Bang but there's no Big Finish in sight.
HOW DID the universe become the way it looks today, and what is its eventual fate? Astronomy Christopher Impey of the University of Arizona in Tucson, whose research specialty is observational cosmology tried to shed light on the subject.
How did the universe begin?
We think the universe started about 12 billion years ago, from a fantastically hot and dense point, and then expanded outward-colloquially called Big Bang. There are problems with the name, because “the birth of the universe” didn't make a sound and it was not an explosion, which are major misconceptions. Instead, all of space unfolded. The Big Bang has an origin in time but not at any particular point in space.
The Big Bang theory is the story of what happened afterward. The story can only be told, with the physics we know, starting about 1 microsecond after the start of the Big Bang. Before that is speculative. After that first microsecond, radiation dominated everything that happened for the first 10000 years or so. The universe was a dense sea of radiation. In the first couple of minutes, the universe had the temperature of the core of the star. In time, expansion cooled the universe, and fusion couldn't occur any more.
After that, gravity started to become significant, and things began to form from the seething froth of material. At 300000 years, the universe became "transparent". That's the point where regular parts of matter go their separate ways and interact rarely.
It took maybe half a billion years for the first galaxies to form. The galaxies are made of luminous material but there is also a sea of invisible dark matter, whose existence we infer. The history of the universe now is one of star formation, where space between galaxies is mostly empty. Today, the universe is enormous, and it's cold and it's dark. The expansion rate, which was once fast, has decelerated.
What happens after this? How and when will the universe end?
The consensus is that the universe is "open" and will expand forever. Eventually, the stars in the galaxies will exhaust their nuclear fuel and go out. The really speculative stuff is the ultimate and infinite future of the universe. As Stephen Hawking suggested in the 1970s, even black holes can evaporate, losing material. And eventually, normal matter like protons and neutrons (the building blocks of atoms) will decay. Theoretically, that could occur after 10^35 years. The collapsed objects will evaporate into a particle fizz that is the final, bleak fate of the universe.
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