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Stars and the Universe

The Universe - The End.

There are two possible endings for the expanding Universe.

1. If the forces (gravity) which pull matter together
are stronger than the the forces (dark energy)
which push matter apart, then the Universe
may stop expanding and collapse back in on itself again.
The Universe would contract at an ever increasing rate
until all the matter collided at the tiny point which started it all.
This is the reverse of the big bang and is called the "big crunch".

2. If the forces (gravity) which pull matter together are weaker
than the the forces (dark energy) which push matter apart, then
the Universe may continue to expand at an ever increasing rate
and eventually all the galaxies become so far apart that you
wouldn't be able to detect that other galaxies existed. The whole
thing would just fade out like the glowing remains of a firework.

Whether we have the big crunch or the big fade depends
on the amount of mass (gravity) compared to the
repulsive forces of dark energy. These are difficult to
estimate since a large amount of mass may exist
as dark matter which can't be seen. Current calculations
suggest that the Universe is expanding at an
ever increasing rate which would favour the big fade.

What is Dark Matter?

It is not known what dark matter is. Some may be in
the form of a black dwarf or a black hole but the
majority of the substance that exists as dark matter
may be made from a substance that is different
from anything else that has yet been discovered.

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