The Big Bang
About 14 billion year ago,the universe materialized out of nothing for unknown reason. Infinitely smaller than an atom to begin with,the universe expanded to a trillion kilometres across in under a a second -an event the Big Bang.
Time came into existence when the universe began,so the question "What happened before?" has no meaning Space also came into existence.The Big Bang was not an explosion of matter through space - it was an expansion of space itself.
At first the universe consisted of pure energy.but within a trillionth of a second some of this energy turned into matter.Forming a vast soup of subatomic particles ( particles smaller than atoms).It took nearly 400.000 years for the particles to cool dwon enough to fron atoms.and than another 300 million years before the atoms formed planets,stars and galaxies. The expansion that began in the Big Bang continues to this day. and most scientists think it will carry on forever.
The expanding Universe
The illustration below does not show how the universe has expanded and changed since the Big Bang. We know the Universe is expanding because the most distance galaxies are rushing apart ans fantastic speeds. By running the clock backwards,astronomers figured out that the expansion began 13.8 billion years ago at a single point: The Big Bang.
1.The Universe appears out of nowhere. At the start, the universe consists purely of energy and is infinitely dense and unimaginably hot-10 billion trillion trillion C (18 billion trillion trillion F)
2. Within a tiny fraction of a second the Universe balloons in size from trillion of times smaller than a atom to the size of a city.The rate of expansion then slows.
3.The intense energy of the newborn Universe creates matter.At first, the matter is a soup of particles and antiparticles There crash into at cancel each other out, turning back into energy. But some of the matter is left over this will eventually turn into atoms and later stars and galaxies.
4.The Universe is now about 1 microsecond old and 100 billion km (60 billion miles)wide.The leftover particles begin to from protons and neutrons-the particles that today make up the nuclei of atoms to form yet.Light cannot pass through the sea of particles,so the young Universe resembles a dense fog.
5.After 379.000 years, the Universe cools enough for atoms to form.The Universe is now a vast cloud of hydrogen and helium. Light can pass through space mare easily, and the Universe becomes transparent.
6.Half a million years after the Big Bang,matter is spread out almost evenly in the Universe, but tiny ripples exist. Working on these denser patches,gravity begins pulling the matter into clumps.
7.At 300 million years, stars appears. Stars form when great clouds of gas are pulled into tight knots by gravity. The pressure and become so intense in the dense pockets of gas that nuclear reactions begin,igniting the star.
8. At 500 million years, the first galaxies are forming. Galaxies are enormous clouds of stars,held together by gravity.
9. Now 5 billion years old, the Universe consists vast clusters of galaxies arranged in threads.with gigantic voids between them.The voids get ever bigger as space continues to expand.At 8 billion years, the expansion of the Universe begins to accelerate.
10.Our Solar System forms at 9 billion years. When the Universe is 20 billion years old,the Sun will expand in size and destroy Earth
11. The Universe will carry on expanding forever, becoming cold and dark everywhere.
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