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Friday, 26 April, 2002, 14:10 GMT 15:10 UK
Q&A: The 'cyclic' Universe
Graphic, BBC
Two researchers have proposed an alternative model to explain the Universe - one which has no "beginning" and no "end". BBC News Online Science Editor, Dr David Whitehouse, answers some basic questions on cosmology.

If the Universe never began, how come it exists?

It is not a flippant answer to say that just because the Universe exists (as it obviously does because you are reading this), it had to have a beginning. It might have always existed.

Right, so if it had no beginning, how come I've read another story on your site saying the universe is 14 billion years old?

The best explanation for the history of the Universe is the Big Bang idea. Because we can see the galaxies receding from each other, most astronomers believe that these star groupings were closer together in the past.

If you "run the film backwards" then all matter, space and time would have erupted from a point in a Big Bang about 14 billion years ago .

Questions about what happened "before" the Big Bang are difficult because there may have been "no" before - because there was no time.

Those astronomers unhappy with the Big Bang theory because it suggests a beginning have put forward the idea that our Big Bang was just one of an endless cycle.

The problem is that science can never prove anything about a previous Big Bang or subsequent Big Crunch (in which all matter comes back together) or can they?

In recent years, so-called M-theory has suggested that our Big Bang may be the result of the collision of two "proto-universes" floating in an abyss of such universes. Some researchers have even suggested that we may be able to obtain evidence for the existence of these proto-universes by studying gravity.

What's this "dark energy" about?

A few years ago astronomers realised that not only were the galaxies receding from each other, the recession was actually speeding up. It was quite a surprise as most researchers believed that either the Universe would expand forever at the same rate or else slow down and contract.

To explain this acceleration, astronomers invoked the idea that space contains a so-called dark energy that is pushing the galaxies apart.

What's the cosmos?

Cosmos is a Greek word that means whole and order, the opposite of chaos. It is used to describe everything that has been, is and ever will be. The term Universe refers to everything that is, atoms, stars, galaxies, space and time.

OK, so if there are Big Bangs, and they are part of an endless cycle, when is the next one?

If the Universe is indeed accelerating, there won't be another one, unless Steinhardt and Turok are correct. Then eventually the dark energy will change its nature, cause the Universe to become empty and then allow another Big Bang to take place.

So, if everything in the Universe is moving apart at an accelerating rate, will we get further away from the Sun and freeze to death?

In the Universe everything is moving apart due to the cosmic expansion, but the effect is only detectable over very large distances. It is insignificant to us and our Solar System because the Universe is so vast.

Astronomers say the Universe looks the same in all directions? That can't be right - if I look up in the sky, I can only see Orion in one place.

The exact arrangement of nearby stars that comprise the constellation of Orion is a matter of chance and of no importance. Whatever direction in space you look (once you remove local things such as our galaxy and the cluster of galaxies of which it is a member), the Universe is the same in all directions.

And are we in the only universe? If not, where are the others?

Some researchers believe that there are other dimensions that we cannot experience because these dimensions are "folded". Some theorists believe that our Universe was spawned from a proto-Universe that exists inside the very fabric of space.

If so, then the Universe next door is closer to you than the clothes you are wearing.

Why do any of these findings matter, and when will scientists know they have the definitive answer?

It matters that we understand the Universe from which we spring. These are deep and fundamental questions at the heart of the most profound of mysteries: why are things the way they are?

Mankind is what he is because we ask questions and they don't come any bigger than this. We should take pride that with just the view from planet Earth to help us we have discovered so much.

See also:

25 Apr 02 | Sci/Tech
Universe in 'endless cycle'
25 Apr 02 | Sci/Tech
Age of Universe confirmed
26 Apr 00 | Sci/Tech
Universe 'proven flat'
27 Feb 98 | Sci/Tech
Universe's expansion speeds up
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