As scientists struggled to understand the physics behind the big bang that led to the creation of the universe, they also pondered whether the universe would ever end. It has always been thought that the universe was constantly expanding; however, recent astronomical observations have led scientists, including Andrei Linde of Standford University to rethink their ideas about this end.
In 1998 astronomers concluded that the expansion of the universe was speeding up, rather than slowing down as previously assumed. The gravitational pull of matter that controlled the expansion of the universe was now being overruled by an anti-gravity force that was pushing the universe apart. As matter in the universe thinned out as the universe itself expanded, a repulsive force gained influence in its place. This suspect force, or dark energy, is an unknown, invisible substance distributed evenly throghout space and accounting for around 73 percentage of the universe. Untill this discovery, it was assumed that the universe would expand so much that it eventually fell apart in some big rip. Linde's insight, announced in 2002, is that this dark energy will not just drop to zero as the universe expands, but become negative. When it does, it will slow and then reverse the universe's expansion and couse space and time to collapse in a "big crunch".
Since the universe is already 14 billion years old and if the collapse is dated to about 10 to 20 billions years time, than we are currently living in its middle age. Whether Linde is right will never be known for earth will have collapsed into the Sun ling before that.
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