I read this story a long time ago, and have been trying to find it now to re-read it and see if it is still as good as I remembered.
Synopsis: Begins inside a highly technologically advanced society where everthing is provided inside a large dome and everyone is cloned and lives long time. Everyones wishes can be met inside their room, and they meet each other by holographic projections. "Town hall" meetings of millions of them are also done holographically. No one wants to go outside nor had any wish to leave dome. Of course, except one person who has an compulsion to find out whats outside. After some time he finds a unused trainline underneath city, which leads to a sister city long way away.
This second city is rural paradise with few thousand people all of who have strong psychic powers.
The person finds out that he is one of many "glitches" that has been programmed into cloning machine, to shake things up and find a way to get two societies back together. He is only one to succeed.
They figure out they must take a hidden space craft with a star drive to a far away solar system to release a Creature that has been "growing" for many millions of years. Seems the advanced society created some evil creature that cannot be destroyed, so they imprisioned it. Then created this new creature that is supposed to grow for a few millions of years and then do battle with the evil creature at some epoch in the future.
Not sure if I am getting the right important points of the book, but it was a hard sci fi novel.
If anyone can help me with a name, I would be very grateful!!