sooncf replied:
This is what I know from Discovery channel.
At this time, all the galacies are moving apart at high speed.
And the speed isn't constant,
It actually speeding up (moving faster and faster)
The Discovery Channel does not say why it speeding up.

Well, the farther away a galaxy is, the faster it moves away
from us.

This is what I thought.
Consider the momentum of a galaxy MV, (mass X velociy)
M=total mass of a galaxy, V=speed of that galaxy.
If M is reducing (mass loss in all Star in the fusion reaction,
where mass are converted into energy)
That is why V have to increase to keep the momentum constant.

An interesting observation. For most moving objects, momentum is
constant because mass is constant. If mass decreases, momentum will
decrease, but the speed won't. If this were the case, galaxies
would eventually fly apart (if the stars lost speed) or collapse
(if the stars gained speed). This is not observed to happen.

But there is a giant black hole in the centre of each galaxy.

Maybe for spirals, not sure about ellipticals.

Soon or later all the Star will fall into that black hole.

Don't think so. It's like saying that the planets will fall into
the sun, but that would take a lot of energy. And it's not been
observed to happen.

It is at the centre of the black hole where energy are
converted back to mass.

Where did this come from? Although outside of a BH matter can
be converted to energy with very high efficiency, once inside
a BH I'm not aware of any mechanisms which will convert
matter to energy or vice versa.

Soon or later the reverse process will take place.

It will? How is this?

That is the Mass of the galaxy will increase and the speed of
the galaxy will start to slow down.

Where will the additional mass come from?

And the universe will start to compress toward a single point.
When all the galacies are compressed into that single point,
perhaps another Big Bang will happen again.

You've got me confused.

Rich