Someday before i read about a article which explained about a phenomenon called BIG CRUNCH, according to it the way Big Bang happened because of which the remains moved away from one another forming universe planets and all other celestial bodies. In the same way some day the gravitational pull caused by each of these celestial bodies will drag each other celestial bodies towards it ending the universe by making it one, is this true can this happen?
The 3 major theories are Big Crunch, Big Freeze, and Big Rip. Each of them have reasons why they work and don't work. The future will shed some light on this, but for now it's just fun to talk about!
Big Crunch: Poetry of sort, the universe started with a big bang and will end collapsing into the same "infinitely" small point.
Big Freeze: Everything is moving away from everything else. Eventually things will be so far away that as stars blow up, reform, and the sources of hydrogen and other things that provide stars their fuel become more rare, things will eventually become colder and colder until there's nothing but ice cubes with no scotch to put them in.
Big Rip: I don't know much about this one, mostly because it doesn't seem to be likely from what I've heard others say. I'd suggest reading up on it on the wiki article (http://en.wikipedia.org/wiki/Big_Rip) or googling it.
You can see an episode from National Geographic that talks about these 3 theories here: https://www.youtube.com/watch?v=eYc8iRyL7YU
A short article on the Big Crunch: http://www.universetoday.com/37018/big-crunch/ A short article about Big Rip (includes some talk of the math that Godzy referenced): http://www.universetoday.com/22382/no-big-rip-in-our-future-chandra-provides-insights-into-dark-energy/
To answer your question: yes it can happen.
Three major theories exist: big crunch, big freeze (or heat death), big rip.
Big crunch means everything is eventually crushed into a single point. Big freeze is that things get so far appart that "nothing" can happen anymore (except quantum stuff but that's another story), the universe becomes the most boring place in the ...hmm universe... Big rip means that eventually the fabric of time and space stretches so much that everything is torn appart (absolutely everything) in a rather short instant.
To simplify, they really depends on a ratio being smaller than 1, equal to 1 or greater than 1. Right now, the measurement of this ratio is that it's very close to 1... + or - a small quantity. But this small quantity makes all the difference. So until we can refine this measurement, we don't know. It's like keeping a pencil on its end: whether it falls left or right can depend on a very subtle initial imbalance. Right now, we say "it's sort of in the middle" which is not very useful!
It is one of the three theory's they have on this moment about possible ends for the universe. So we can't be sure, they can't really test it yet and there is not enough evidence to mark it as true. It is just a logical answer to a question, but still only a possibility.