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A closed or finite universe is one in which, after having traveled in one direction on it, you can find yourself back to where you started.
Barring any new discoveries that may refute the WMAP’s findings, it’s official – the Universe is flat. That also means it should be infinite in extent. Still, that doesn’t mean we can altogether throw other models, like that of a finite one, into the trash bin. After all, the colorful history of science has oftentimes been dotted by discoveries that have sea-sawed contradicting models.
Take the particle and wave theory of light for example. These two opposing theories strived to define the true nature of light. Eventually, it was found that both theories were correct after all. Of course, that doesn’t happen all the time. But what if beyond the horizon the Universe is found to be in fact a finite one?
What then are the characteristics of a finite universe?
If our universe is finite in extent, that would only mean that it is closed or, for purposes of visualization, shaped like a sphere. That’s the reason why we said earlier that if we traveled in one direction on it, we can find ourselves back at our point of origin.
A closed and finite universe may also mean that the average density of matter inside it is greater than what is known as the critical density. Combining what they know about the geometry and density of matter inside it, scientists can predict the possible ending our universe may have.
For one, when all matter has an average density greater than the pre-determined critical density, they (matter) would have enough gravitational force to pull the entire universe back into a singularity.
You see, ever since the Big Bang, the Universe’s expansion has been influenced by a tug-of-war between its outward momentum and the gravitational force of all its constituents. If the gravitational force is large enough, the expansion will eventually reach a maximum and then a collapse will ensue.
Scientists who believe that a collapse is unavoidable are further divided into two groups: those who believe that the Universe will end in a Big Crunch and those who are more inclined towards a more peculiar end: a Big Bounce. Both of these endings can only be realized if one condition is also satisfied – that we have a finite universe.
We have some articles in Universe Today that are related to the finite universe. Here are two of them:
Infinite universe articles brought to you by Physics World, here are the links:
Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste: