Discovering the Quantum Universe

Albert Einstein, Edwin Hubble, and Walter Adams (l-r) in 1931 at the Mount Wilson Observatory 100" telescope, in the San Gabriel Mountains of southern California. It was here in 1929 that Hubble discovered the cosmic expansion of the universe. Courtesy of the Archives, California Institute of Technology

On his death bed, Einstein asked for a pen and paper, to work on his calculations of a unified field theory. “I am optimistic,” he told a friend, “I think that I am getting close.”

The dream of today’s particle physicists, like that of Einstein, is to find a theory that describes a single unified force of nature. A century after Einstein, the combined capabilities of the LHC and the ILC promise to lead the way toward that ultimate theory.

The precision of its electron-positron collisions would give a linear collider the potential to act as a telescope to see into energies far beyond those that any particle accelerator could ever directly achieve. As a telescope to the beyond, a linear collider could explore energies a trillion times that of the accelerator itself, in the ultrahighenergy realm where physicists believe all of nature’s forces become one.

A linear collider’s capability as a telescope to ultrahigh energies rests on the quantum properties of matter discovered in the past few decades. This hardwon understanding gives physicists a means to measure the effects of phenomena occurring at energies beyond those that accelerators can reach.

For now, though, the telescopic view to the beyond is obscured by lack of knowledge of Terascale physics. Data from the LHC and the ILC would part the clouds of physicists’ ignorance of the Terascale and allow a linear collider to act as a telescope to the unknown.

In the current understanding of the universe, the laws of the large and the laws of the small do not agree. Is it possible to reconcile gravity (the laws of the large) with quantum theory (the laws of the small) and thereby address this central question of modern physics?

Physicists believe that just one force existed after the Big Bang. As the universe cooled, that single force split into the four forces we know today: gravity, electromagnetism, and the strong and weak nuclear forces. Physicists have already discovered that remarkably similar mathematical laws and principles describe three of the four forces. However, at the final step of bringing gravity into the fold, ideas fail; some key element is missing.

String theory is the most promising candidate to unify the laws of the large and the small. The theory holds that all particles and forces are tiny vibrating strings. One vibration of the string makes it a quark, while another makes it a photon. String theory brings with it a number of dramatic concepts including supersymmetry and extra dimensions of space. Among the most exciting possibilities for the LHC is its very real potential to discover the superpartners of the known particles.

Theorists cannot yet predict at what energy the evidence for extra dimensions – if they exist – will emerge. A linear collider’s sensitivity would make it the best window on quantum gravity, extra dimensions and the physics of strings that physicists are likely to have for a long time – perhaps ever.

Physicists could use a linear collider to focus on the point where both forces and masses may unify, linked by supersymmetry into one theory that encompasses the laws of the large and the laws of the small.

Overview: Discovering the Quantum Universe

Einstein's Telescope