Institute of Astronomy

The expansion of the universe

Published on 08/02/2012 
Question: 

I'm a 13 year old, and i have been thinking about the big bang and how it happened. I came up with the theory that dark matter is the force that is making the universe expand and dark energy is trying to send it backwards, as far as i know. And if dark energy wins and pulls everything back and smashes everything into atoms. Like the suns made of hydrogen, carbon, and other materials. And that the whole universe just is engulfed and destoryed. then when it gets to the smallest it gets to, everything just explodes backwards and starts the whole universe all over again. Its like a recycling system for the universe.

It's great that you are thinking about these big questions! The accelerated expansion of the universe is a very difficult concept to grasp.

First off, I think it's important we distinguish between Dark Matter and Dark Energy.  While astronomers don't know exactly what either of these two things are, we do know that they behave in very different ways.  Dark Matter feels an attractive force of gravity, just like the normal matter that we can see.  In other words, Dark Matter gets pulled in. On the other hand, Dark Energy expands space out and is responsible for the expansion of the universe.

So with that in mind, if we think of a universe that has a lot of matter in it (both Dark Matter and normal matter) and no Dark Energy, then the Universe would eventually collapse due to the force of gravity pulling all the matter inwards.  This scenario is appropriately named the "Big Crunch," and as you say, everything would be destroyed in a kind of backwards explosion.

However, we believe our universe does have Dark Energy in it, in addition to Dark Matter and normal matter. This being the case, we can think of two other scenarios for the fate of the Universe:  Either Dark Energy fills more and more space, and the expansion of the universe gets faster and faster, until everything is essentially torn apart (called the "Big Rip"). Or the matter and the Dark Energy find a point of equilibrium, and space just keeps coasting outwards (called the "Big Chill").  As of right now, we don't have enough observational evidence to say which scenario is correct.

There are many questions that we cannot yet answer about the expansion of the universe.  There is lots of room for new ideas and new theories, so keep thinking about it! Hope this background information helps!
 

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Page last updated: 8 February 2012 at 14:24