If this so-called antimatter comes into contact with actual matter—even for a fraction of an instant—it will be annihilated in a quick flash of energy. So experts at the European Organization for Nuclear Research, known as CERN, will, over the course of four hours Tuesday, gingerly wheel out from its lab about 100 antiprotons. They are suspended in a vacuum inside a specially designed box and held in place by supercooled magnets.

Then, they'll ease it into a truck, and take about a half-hour drive to test how—if at all—the infinitesimal particles can be transported by road without seeping out. If all goes well, the antiprotons will be returned back to the lab.

The hard part: Manipulating antimatter, like antiprotons, can be tricky business. As scientists understand the universe today, for every type particle that exists, there is a corresponding antiparticle, exactly matching the particle but with an opposite charge.

If those opposites come into contact, they "annihilate" each other, setting off lots of energy, depending on the masses involved. Any bumps in the road on the test journey that aren't compensated for by the specially-designed box could spoil the whole exercise.

Tuesday's practice is a first step toward making good on hopes, one day, to deliver CERN antiprotons to researchers at Heinrich Heine University in Düsseldorf, Germany, which is about eight hours away in normal driving conditions.