A long-debated theory of physics designed to join Einstein's theory of general relativity with quantum mechanics could be put to the test later this year, according to a team of U.S. researchers.

String theory — a theory of the universe that reduces the forces and matter of the universe to tiny vibrating one-dimensional filaments called strings —  has been hailed by its proponents as the best theory for unifying all of nature's fundamental forces.

However, its critics say the theory has little value, because there is no way to test the movement of something in ten dimensions, so none of its predictions can be tested.

While the U.S. researchers behind a paper to be published in the January 26 issue of Physical Review Letters don't have a proof of string theory, they said they have developed a test that could help disprove it.

Scientists at the University of California, San Diego, Carnegie Mellon University, and the University of Texas at Austin believe testing how high-energy particles scatter during particle collisions could help put the theory to the test.

The scientists said these particle collisions would be testable at the Large Hadron Collider, a subatomic particle collider scheduled to begin operating later this year at the European Laboratory for Particle Physics, or CERN.

"Our work shows that, in principle, string theory can be tested in a non-trivial way," said Ira Rothstein, co-author of the paper and professor of physics at Carnegie Mellon.

Rothstein said their test will track the scatter pattern of W bosons, quantum particles that carry the property of the weak nuclear force that makes its presence felt in the radioactive decay of neutrons in an atom.

W bosons are too small to be seen with current particle accelerators, but researchers hope the Large Hadron Collider will be able to detect them.

The group of researchers said they hope to compare the scatter pattern of the particles to a set of limits based on the assumptions of string theory.

"If the bounds are satisfied, we would still not know that string theory is correct," said Jacques Distler, a professor of physics at the University of Texas at Austin. "But, if the bounds are violated, we would know that string theory, as it is currently understood, could not be correct."

The physics world has been at a loss to reconcile the world of black holes and galaxies in Einstein's theory of general relativity with the tiny universe of quantum mechanics. Both theories were postulated more than a century ago.

It has been difficult in particular to join gravity with the three other known forces of nature — electromagnetism and the strong and weak nuclear forces.

The Large Hadron Collider, expected to begin operating in November 2007, is eagerly anticipated in the physics world for its potential to experimentally test for particles that currently exist only in theories.