The Ending of the Universe

Most astronomers agree about how the Universe began with a Big Bang and how it has evolved since then. They are not sure what will happen in the future. Certainly for many billions of years the Universe will continue to expand. But will it expand forever?

Most astronomers think that it will. Thye say we have an open Universe. The only thing that could prevent the galaxies flying apart forever would be gravity. For gravity to be powerful enough to do this, the Universe must have a certain mass. But there appears to be nowhere near enough mass in the stars and galaxies to halt the expansion.

Dark Matter

However, astronomers know that stars and galaxies are not the only matter in the Universe. There is also dark matter which we are largely unable to detect. There is dark matter in the dust-clouds in space and in dead burned-out stars. There is also matter hidden in the abyssal depths of the black holes.

Other possible sources of dark matter are the atomic particles called neutrinos. Recent experiments have indicated that they might have a slight mass. If they have, they would greatly increase the density of the Universe because there are so many of them.

Crunch, bang, crunch...

If there is sufficient dark matter to halt the expansion of the Universe, then we have a closed Universe. Eventually the Universe will collapse in on itself and end in a Big Crunch. But things may not end here. Another Big Bang may be triggered off
that will set the Universe expanding once again. In turn will come another Big Crunch, yet another Big Bang and so on. We will have an oscillating Universe.

Development of the Universe
1.The Universe is created, and time and space begin.
2 A dense opaque cloud of particles and radiation fills the cooling, expanding Universe
3 The particles condense into galaxies and stars begin to shine.
4 After 15,000 million years, the Universe reaches the stage it is today. It is filled with spiral, elliptical and irregular galaxies rushing headlong through space, bringing about further expansion. What happens next will depend on whether the Universe is open or closed.

Closed Universe Open Universe

In a closed universe the gravitaional attraction of all the the visible and invisible matter will one day cause the galaxies to slow down and eventually stop. They will start to move closer together again. The Universe will shrink more and more until it disappears in a Big Crunch. In an open Universe there is not enough matter present to hold back the outward-rushing galaxies. They will continue to move apart. Eventually they will run out of nuclear fuel and will start to fade. Maybe they will in time break down into particles and radiation.

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Closed Universe	Open Universe
In a closed universe the gravitaional attraction of all the the visible and invisible matter will one day cause the galaxies to slow down and eventually stop. They will start to move closer together again. The Universe will shrink more and more until it disappears in a Big Crunch.	In an open Universe there is not enough matter present to hold back the outward-rushing galaxies. They will continue to move apart. Eventually they will run out of nuclear fuel and will start to fade. Maybe they will in time break down into particles and radiation.