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| Present Expansion and the Future |
We have already explained that the universe is expanding at this moment. What
will happen in the future? Will it keep expanding endlessly? Or perhaps someday,
will the expansion will stop and contract to one point because of universal
gravitation?
In current cosmology, it is said that there is nothing outside the universe, and the universe itself is not affected by any external force. Also, we can apply the current rule of physics to the universe today, and if we can acknowledge the way of current expansion, we can expect that it will continue expanding in the future.
Our observational technology has developed so far as to recognize the bubble-like structure and the massive structure such as the Great Wall. Now, we are able to look at the universe in the level of several billion light years. But we still have not observed the whole universe. The universe is full of mysteries, such as the amount of existing dark matter. The amount of dark matters is one of the keys to the universe.
| Key to the Universe: Dark Matter |
Gravity in the universe works towards collapsing, depending on how much mass is contained in the universe. In the pages explaining about the varieties of galaxies, we said that the galaxy settles as it is because of the balance between the force that tries to expand and the universal gravitation that tries to pull everything into the middle. We can say the same thing about the universe itself. The future of the universe depends on the balance between the gravitational pull of the mass of all substances existing in the universe, and the force of expansion.
If gravity is stronger, then the universe will stop expanding eventually, and will collapse according to gravity. If the force to expand is greater, the universe will continue expanding forever.
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Size of the universe in the future
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So how much total mass is contained in the universe? That depends on how much
dark matter there is, the distribution of which is not yet known. If there was
a great amount of dark matter and the gravitation overpowered the force to expand,
the expansion of the universe will soon stop and get pulled by the gravitation
and eventually crush. If there wasn't much dark matter and gravitation had less
power than the force to expand, the universe will continue expanding as it is
and will never stop.
Incidentally, the density of universe when the two forces are in balance with each other, is called the critical density. Critical means boundary or borderline. If the density of the universe is below the critical density, then the universe will continue expanding, and if it is higher, then it will collapse.
So in these three cases, we will look in a deeper way at how the universe will turn out and what will happen to the life of living organisms as the result.
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Future Expansion
Future Expantion
