Today, Einstein’s goal of combining the physical laws of the universe in one theory that explains it all is the Holy Grail of modern physics.

Although Newton discovered the law of gravity nearly 300 years ago, until Einstein came along, scientists had no idea how gravity actually worked.

Einstein’s success in explaining gravity as warps and curves in the fabric of space and time set him on a quest to unify gravity with electricity and magnetism.

As Einstein struggled to unite the weak force of gravity with the much stronger force of electromagnetism, physics moved on, examining the bizarre way tiny bits of matter interact with one another inside the atom.

According to quantum mechanics, at the tiny scale of atoms and particles, the world is a game of chance.

For decades, no one could figure out how gravity operates when you get down to the quantum world of atoms and subatomic particles.

Now string theory—the idea that everything is made of tiny, vibrating strands of energy—holds out the hope of unifying the world of the very large and the world of the very small.

String theorists have a problem: strings, if they exist, are so small that there’s little hope of ever seeing one, so how can the theory be tested?

taken from: http://www.pbs.org/wgbh/nova/elegant/program.html