Bouncing universe

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SCIENCE by Alex Simpson and Les Hearn THE Big Bang brought into existence a universe which has been expanding for the 15 billion years since. Will this expansion continue for ever (an open universe) or will it • stop, to be followed by contraction (a closed universe?

There is no force to slow down the flight of the galaxies except the force of gravity between them and there has to be a certain amount of matter in the universe to provide enough gravity to stop the expansion. However, up to now it has seemed that there is only about 10% of the matter needed to "close" the universe, and astronomers have generally agreed that the cosmos will expand infinitely.

But recently evidence has come to light of vast amounts of invisible, dark matter. What is the evidence and where is the matter?

From the appearance of galaxies, stars near the centres should be orbiting faster than those further out, as each galaxy spins. Now it has been found that the outer stars are orbiting faster than expected, implying that galaxies are surrounded by vast dark haloes of matter.

Some astronomers believe that up to 90% of the matter in galaxies could be in the dark haloes, making the total amount of matter close to the critical amount for a closed universe. So what is this dark matter made of? There are two suggestions:

Two pamphlets summing up the ideas of Socialist Where We Stand - 20p plus 16p postage. 'How to fight the Tories' - 10p plus 16p postage. Or the two together for 45p including postage. From Socialist Organiser, 28 Middle Lane, London N8 11 Super-massive black holes Black holes are made matter that has collapsed in itself under its own gravity. Th collapsed matter exerts. such concentrated gravitational for that not even light can escap Though they can't be seen, the should be detectable. Matti being sucked into these blar holes should give out radiatic which would seem to be comin from all parts of the sky. So fa attempts to detect this har heen inconclusive.

2] Neutrinos.

These odd particles can trav through the Earth as though wasn't there. They are affecte by gravity and might be exper ted to orbit around galaxies. Bi to plage ah ey need to have mat gall closing t and hitherto have been thougl to have none. Recent contre versial experiments sugger they have a small mass - les than one-ten thousandth of a electron. This is not much, but large enough number of neu trinos could weigh an awfi lot!

What, then, are the conse quences of living in a close universe? None, immediately you will be relieved to hear, bu there will come a time (i perhaps 70 billion years) whe the expansion stops and is rever sed. The galaxies will fal towards each other, the sky wil become brighter and brighter and the temperature will rise Eventually, everything will enc in a "Big Crunch" : followec perhaps by another Big Bang.

Hence the theory of the "Bouncing" or "Pulsating' universe.

This fits in with the theories of some physicists about the nature of space.

According to David Bohm of Birkbeck College, London, what we think of as empty space actually contains an immense background of energy while the universe consists of a series of ripples on this sea of energy, radiating qut from a "Big Splash"

But why was there a Big Bang in the first place? Edward Tryon of City University, New York, suggests that our universe is the result of a chance fluctuation in this vast sea of energy. If the universe is closed, Tryon calculates that the amount of positive energy that exists is equal to the amount of negative energy stored as gravity. In other words, the total amount of energy is zero and the universe has been created out of nothing.

This is rather like a bubble of steam forming in superheated water and then collapsing again into water.

This doesn't match up with "common sense" ideas of the universe, but it does provide some sort of answer to the question of where the universe came from and where it is going.

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