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Monday, 29 April, 2002, 15:34 GMT 16:34 UK
Q&A2: 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 of your questions on cosmology.

Dale Nichols, from England, asks: "What is at the end of the Universe?"

Does it have to have an end? Remember that we are dealing with the Universe here and fundamental concepts of space and time. It does not have to be like the Earth. It may be that space across the Universe is curved. So, just as you can travel in one direction across the face of the Earth without ever reaching the end, it may be the same with space and the Universe.

Steven, from England, asks: "Nothing comes from nothing, does it?", and Craig Withers, from England, asks: "I was always told at school that you cannot create energy from nothing, so where did the Universe come from?"

It is a strange, and probably profound, fact that the entire Universe adds up to nothing. To explain: there are two types of energy. One is the positive energy bound up in matter and the other is the negative energy bound up in gravity. Taken together, they cancel each other out. So, you could say the Universe is nothing, or, rather, a very special arrangement of nothing!

Michael, from the US, asks: "Would physics and its laws be created at the same instant of the Big Bang?"

That's a really profound question. Some astronomers speculate that if there are repeated big bangs then the laws of nature could be rewritten in each one. This would mean that only in certain universes would there be stars and planets. In other universes, there would be something different - if anything at all. Certainly, if there were repeated big bangs and the laws of nature were the same then something would have been remembered from the past universe, implying that there was something bigger. Confused yet?

Nuno Cardoso da Silva, from Lisbon, Portugal, asks: "Why?"

Why not?

Phil Welch, from England, asks: "Just because I can write an equation for something, does it make it real?"

It is a fact, a true law of nature, that mathematics does accurately describe the physical Universe. The behavior of stars and planets as well as atoms and sub-atomic particles follows mathematical principles. But how does an electron for instance know it has to do certain things according to a grand plan? Nobody really knows.

Jeremy Pethick, from Norway, asks: "If dark matter is a sort of antigravity, could we use it to make antigravity rockets?"

Dark matter is an unknown form of matter that is scattered throughout the Universe but it has an ordinary pull of gravity. It is the recently discovered "dark energy" that seems to push space apart causing the Universe to expand ever faster. If there really is a dark energy in the Universe then it is in every part of the Universe, including the space around us. If we could but tap this energy.

See also:

26 Apr 02 | Sci/Tech
Q&A: The 'cyclic' Universe
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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