I was asked recently what the Large Hadron Collider, the giant particle accelerator outside Geneva, is good for. After $10 billion and 15 years, the machine is ready to begin operations early next year, banging together protons in an effort to recreate the conditions of the Big Bang. Sure, there are new particles and abstract symmetries in the offing for those few who speak the language of quantum field theory. But what about the rest of us?

The classic answer was allegedly given long ago by Michael Faraday, who, when asked what good was electricity, told a government minister that he didn’t know but that “one day you will tax it.”

Not being fast enough on my feet, I rattled off the usual suspects. Among the spinoffs from particle physics, besides a robust academic research community, are the Web, which was invented as a tool for physicists to better communicate at CERN  the European Organization for Nuclear Research, builders of the new collider  and many modern medical imaging methods like M.R.I.’s and PET scans.

These tests sound innocuous and even miraculous: noninvasive and mostly painless explorations of personal inner space, but their use does involve an encounter with forces that sound like they came from the twilight zone. When my wife, Nancy, had a scan known as a Spect last fall, for what seems to have been a false alarm, she had to be injected with a radioactive tracer. That meant she had to sleep in another room for a couple of days and was forbidden to hug our daughter.