Saul Perlmutter, of the University of California, Berkeley, another of the dark energy Nobel winners, said, “The danger, of course, is that we will watch the science (and scientists — and good students) move on to other countries and continents, where projects are being begun and completed.”

With them, scientists say, could go the cultural excitement and innovative spark that invigorates the economy. The World Wide Web, for example, was invented at CERN, the European Organization for Nuclear Research (home to the world’s most powerful particle accelerator, the Large Hadron Collider), to help particle physicists communicate.

By contrast, the United States’ flagship lab for high-energy physics, the Fermi National Accelerator Laboratory, known as Fermilab, had to close down its accelerator. the Tevatron, last fall, and learned from the Energy Department in March that the agency could not afford to follow through for now on a $1.3 billion underground experiment to study the spooky shape-shifting properties of particles known as neutrinos in an effort to investigate why the universe is made of matter and not antimatter.

At the same time, the department also canceled money for studies for the world’s next big physics machine, the International Linear Collider, which would be the successor to CERN’s giant collider. American scientists are resigned to the likelihood that it will not be built in the United States.

American physicists are now rethinking how to carry out the neutrino experiment, which was to have been the centerpiece of a plan to convert the old 8,000-foot-deep Homestake gold mine in Lead, S.D., into a national laboratory for underground science.

Similar facilities in Italy, Canada and Japan have become centers in the search for dark matter, neutrino experiments and other delicate work that requires shelter from cosmic rays. But in 2010, the National Science Foundation walked away from the $875 million project, citing unease about safety and “stewardship” of the old mine, which is half full of water. Meanwhile with support from a philanthropist, T. Denny Sanford, the State of South Dakota has reopened parts of the mine for a pair of physics experiments.

Of course, there is no achievement of modern American science — from the Manhattan Project to the Hubble Space Telescope to the decoding of the human genome — that does not owe a debt to hard and even heroic bargaining in the formerly smoke-filled rooms of Congress and the White House. Complaints and grim prognostications about the federal research budget are part of the background music of science. The situation is always fluid.