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Stars and the Universe

The Universe - Big Bang - Origin and Age of the Universe.

If the Universe is now expanding, then it must
have been smaller in the past. The further back
into the past you go, the smaller the Universe was.

If you go back far enough in time
the entire Universe seems to have existed at one tiny point.
This point was the origin (beginning) of the Universe.
The big bang was an explosion at this point and the
Universe has been expanding away from this point ever since.

If you look at how fast the Universe is expanding today
then you can make an estimate (guess)
of the length of time the Universe has been expanding
in order to occupy the size it has today.
This length of time is the age of the Universe.

It is not easy to estimate the age of the Universe.
Gravity is an attraction between all the matter in the Universe.
This attraction tends to slow the rate of expansion down.
There is another force (called dark energy) which tends
to push matter apart and speed the rate of expansion up.

It is believed that the Universe is expanding
more quickly today than it has done in the past.
Taking this into account, scientists estimate
the age of the Universe to be about 14 billion years
(1 billion = 1,000,000,000 or 1 thousand million).

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