For decades, the big guns of American science have been the U.S. Department of Energy's particle colliders, which investigate the nature of matter by accelerating subatomic particles and smashing them together. Colliders at the Fermi National Accelerator Laboratory (Fermilab), Stanford Linear Accelerator Center (SLAC) and Brookhaven National Laboratory have discovered exotic particles such as the top quark and revealed phenomena that hint at new laws of physics. But this great American enterprise, like so many others, is now moving overseas. While the Europeans and Japanese build new particle accelerators, the U.S. is poised to shut down its premier colliders at Fermilab and SLAC over the next few years. And funding for Brookhaven's Relativistic Heavy Ion Collider (RHIC) is so tight that the lab could not have run its full slate of experiments this year without $13 million raised by a New York billionaire.

The sad story began in 1993, when Congress canceled the $11-billion Superconducting Super Collider, the intended successor to Fermilab's Tevatron. CERN, the European laboratory for particle physics near Geneva, then started work on the Large Hadron Collider (LHC), which would produce impacts with energies seven times higher than the Tevatron's. Because the greater energies could enable researchers to discover hypothesized particles such as the Higgs boson, American physicists flocked to the LHC, which is expected to begin operating next year.

Some scientists realized, however, that they could continue to do experiments at American colliders that would complement the research at the LHC. One group designed a device called BTev that would study the decay of B mesons emanating from collisions in the Tevatron. BTev employed such sophisticated technology that it could have outperformed a similar detector at the LHC. But last year the Department of Energy canceled BTev. Without that experiment, most physicists see no compelling reason to keep the Tevatron running after the LHC comes online. SLAC plans to shut down its linear collider when that lab concludes its own B-meson study by 2008. And the National Science Foundation recently killed an experiment called RSVP that would have used Brookhaven's accelerator to investigate rare particle decays that could not be observed at the LHC.

Besides depriving researchers of potential discoveries, these cuts threaten to make the U.S. less economically competitive. The development of high-energy accelerators has led to advances in medicine and electronics, and American expertise in this field will wither if the U.S. ceases to build and operate colliders. Moreover, although American scientists will participate in the research at the LHC, the Europeans will get most of the educational benefits of the facility, which will inspire and train the next generation of physicists. To stem the damage, the DOE has proposed a budget for 2007 that would restore funding for RHIC and bolster neutrino research at Fermilab.

But America's physicists yearn to work on the high-energy frontier, and their last great hope is the International Linear Collider, which would probe the new particles revealed by the LHC. The design, expense and location of this facility have not yet been determined, but the U.S. should do everything in its power to ensure that it is built, preferably on American soil. Although the project's price tag might ultimately rival that of the Super Collider, the cost of not doing the science would be even higher.