The Universe: What is it; Big Bang Theory; Future

The Universe is the entirety of what we would call 'space'. It includes the Earth, the Sun, the planets and all of the stars you can see at night, plus many more you can't see.

The universe is made up of galaxies. These are clumps of stars, planets, gas and dust that are held together by gravity. The Galaxy that we are in is called the 'Milky Way'; most scientists believe it is held together by the gravity of a black hole. A black hole, often caused by a dying star, has a gravitational pull so intense; light cannot escape from inside it. Galaxies come in various shapes and sizes. Our Galaxy is a spiral shape.

To get an idea of the size of the universe, the Milky Way is 180,000 light years across, meaning it would take 180,000 years for light to travel from one side of the Milky Way to the other. If you think that's impressive – consider there are billions of galaxies in the observable universe, possibly billions more outside of the area we can see.

This is probably one of the most famous scientific discoveries, and yet it's a phrase people use ever day, without really knowing what it means.

This theory – more or less the one we still use today, was proposed by someone whose name you probably don't know. He never gets attention in the press. He was a Catholic Priest from Belgium called Georges Lemaître and put forward this theory in 1931. The theory suggests the universe began as one very small particle consisting of the entire universe squashed into it. This particle then 'exploded', and as happens with an explosion, it pushes outwards (think of movies). This caused the universe to expand and it is believed that the universe continues to expand. This expansion means all the galaxies in our universe are moving away from each other. This has been observed by astronomers; providing evidence for this theory.

Further evidence for the Big Bang is background radiation. Background radiation is the low levels of radiation that exist all around us. This radiation is picked up by an analogue television to produce 'snow' when it is not tuned in properly. Background radiation in the universe is said to be leftover heat energy from the initial explosion of the universe.

If the universe is expanding, it means it has been possible for scientists to project what might be the fate of the universe in the future, although it depends upon the mass of the universe.

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   Big Crunch

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   A common theory is that the big crunch this will happen if the universe is above a critical mass. It says the universe will eventually stop expanding and then compact again. As it compacts, things will begin to heat up. In theory, the universe will eventually compact into a single particle - just like at the beginning of the Big Bang. Many say that the universe will then be 'reborn' with another big bang and continue expanding and contracting forever.

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2. 2
   Continued Expansion

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   Another possibility is if the mass is too low, in which case, the universe will continue to expand forever, getting colder and colder as it does so; until it eventually becomes a virtual empty and frozen universe.

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